CORROSION AND PROTECTION

Corrosion Science and Corrosion Engineering

2011-10-08T13:52:00.001+01:00

Since corrosion involves chemical change, the student must be familiar with principles of chemistry in order to understand corrosion reactions. Because corrosion processes are mostly electrochemical, an understanding of electrochemistry is also important. Furthermore, since structure and composition of a metal often determine corrosion behavior, the student should be familiar with the fundamentals of physical metallurgy as well.

The corrosion scientist studies corrosion mechanisms to improve (a) the understanding of the causes of corrosion and (b) the ways to prevent or at least minimize damage caused by corrosion. The corrosion engineer , on the other hand, applies scientific knowledge to control corrosion. For example, the corrosion engineer uses cathodic protection on a large scale to prevent corrosion of buried pipelines, tests and develops new and better paints, prescribes proper dosage of corrosion inhibitors, or recommends the correct coating. The corrosion scientist, in turn, develops better criteria of cathodic protection, outlines the molecular structure of chemical compounds that behave best as inhibitors, synthesizes corrosion - resistant alloys, and recommends heat treatment and compositional variations of alloys that will improve their performance. Both the scientific and engineering viewpoints supplement each other in the diagnosis of corrosion damage and in the prescription of remedies.

(Reference: "Corrosion and Corrosion Control", Revie and Uhlig, 2008)

Metal Cladding

2011-10-08T08:39:00.000+01:00

The corrosion resistance of a substrate can be improved by metallurgically bonding to the susceptible core alloy a surface layer of a metal or an alloy with good corrosion resistance. The cladding is selected not only to have good corrosion resistance but also to be anodic to the core alloy by about 80 to 100 mV. Thus if the cladding becomes damaged by scratches, or if the core alloy is exposed at drilled fastener holes, the cladding will provide cathodic protection by corroding sacrificially.

Cladding is prevalently applied at the mill stage by the manufacturers of sheet, plate or tubing. Cladding by pressing, rolling or extrusion can produce a coating in which the thickness and distribution can be controlled over wide ranges and the coatings produced free of porosity. Although there is almost no practical limits to the thickness of coatings that can be produced by cladding, the application of the process is limited to simple shaped articles that do not require much subsequent mechanical deformation.

Aluminum Cladding

Among the principal uses are aluminum cladding in the aircraft industry, lead and cadmium sheathing for cables, lead-sheathed sheets for architectural applications and composite extruded tubes for heat exchangers. The thickness of the cladding is usually between 2% and 5% of the total sheet or plate thickness, and since the cladding is usually a softer and lower strength alloy, the presence of the cladding can lower the fatigue strength and abrasion resistance of the product. In the case of thick plate where substantial amounts of material may be removed from one side by machining so that the cladding becomes a larger fraction of the total thickness, the decrease in strength of the product may be substantial.

A clad finish being soft in nature is subject to damage during manufacturing and while in service. Caution must be exercised while polishing or cleaning, since it is sensitive to harsh chemicals and abrasive materials.

Cladding and Weld Overlaying

Compared to carbon and alloy steels, all corrosion resistant alloys are expensive. In many cases, corrosion resistance is required only on the surface of the material and carbon or alloy steel can be clad with a more corrosion resistant alloy. Cladding can save up to 80% of the cost of using solid alloy. Cladding of carbon or low alloy steel can be accomplished in several ways including roll bonding, explosive bonding, weld overlaying and “wallpapering”. Clad materials are widely used in the chemical process, offshore oil production, oil refining and electric power generation industries. The use of clad steel is not new. Corrosion resistant alloy clad steel has been available for over 40 years. Almost any corrosion resistant stainless steel or nickel alloy can be bonded to steel. The steel can be clad on both sides or on one side only. The hot roll bonding process is used to produce over 90% of clad plate products.

Approximately 60,000 tons of hot roll bonded corrosion resistant alloy clad steel plate is produced annually. In this process, specially cleaned plates of steel and the corrosion resistant alloy are placed together and hot rolled. A metallurgical bond is formed between the steel and the corrosion resistant alloy through the combination of heating and deformation during rolling. In most cases, multiple “sandwiches” of alternating steel and corrosion resistant alloy plates are hot rolled in one operation for economy. The thickness of the cladding is normally in the 1.5 to 5 mm range although thicker cladding is possible. Total hot roll bonded plate thicknesses of from 6 mm to 20 cm are available in widths of up to 4 meters and lengths of up to 20 meters.

Clad plate can be formed and fabricated using conventional techniques. The steel is welded using ordinary welding materials and practices. The clad material is welded using high alloy filler metal. The techniques for welding clad steel are well developed. The explosive bonding process utilizes the high-energy impulse from an explosive charge to drive together the surfaces of the metals to be bonded. The plastic deformation of the metals during the high -energy collision forms a metallurgical bond between them. Explosive bonding can join almost any two (or more) metals. Explosive bonding can be used to fabricate plate, pipe, fittings, and other shapes. Cladding thicknesses for explosive bonding usually range from 1.5 mm to 2.5 cm.

Cladding with corrosion resistant alloys thinner than 1.5 mm is difficult. In some cases, explosive bonding is followed by hot rolling to improve the bond between the steel and corrosion resistant alloy. Weld overlaying is commonly used to clad the surfaces of fabricated steel structures. The actual weld overlay process used depends on many factors including access, welding position, the alloy applied, and economics. In some alloy combinations, dilution of the weld overlay material by the steel requires that more than one weld pass is required. Post weld heat treating to temper the backing steel may be required in some cases. Wallpapering, also known as sheet lining, was originally developed in the 1920’s to fabricate stainless steel clad steel vessels for the chemical process industry. In wallpapering, thin sheets of corrosion resistant alloy are edge welded to the carbon steel structure.

In some cases where larger wallpapering sheets are used, plug welds at intervals on the wallpapering sheet are also required. Wallpapering can be a very economical way to provide excellent corrosion resistance for steel structures. Both stainless steels and the more corrosion resistant nickel alloys can be economically applied to steel by wallpapering. Wallpapering has also been widely used to line interiors of stacks and ducting for flue gas desulfurization units in fossil fuel power plants. One major benefit of wallpapering and weld overlaying is that they can be used to repair or modify existing steel structures.

Source: http://corrosion-doctors.org/MetalCoatings/Cladding.htm

Reinforced Concrete: CP

2011-10-07T08:40:00.000+01:00

The pH of environment in concrete usually is greater than 12.5, which causes a passive film on the surface of embedded steel reinforcement. However, this protective film breaks down when concrete reacts with atmospheric carbon dioxide or chloride ions (present in aggressive environments such as seawater or de-icing salt) penetrate into the hardened concrete and reach the surface of reinforcing steel.
Corrosion products cause expansive stresses in the concrete which leads to cracking and spalling.

Cathodic protection (C.P.) is a well-accepted technology for the corrosion prevention of the reinforcing steel in concrete.

Figure:
-Deteriorated structure
-CP Installation
-Rehabilitated structure after CP Installation

Source: http://www.corrosionservice.com/reinforced_concrete.asp

The chloride threshold

2011-10-07T08:38:00.002+01:00

The chloride threshold for the initiation of pitting corrosion for a given structure depends on numerous factors. Major factors have been identified in the pH of concrete, i. e. the concentration of hydroxyl ions in the pore solution, the potential of the steel and the presence of voids at the steel/concrete interface.

The hydroxyl ion concentration in the pore solution mainly depends on the type of cement and additions . It was suggested that pitting corrosion could take place only above a critical ratio of chloride and hydroxyl ions . For instance, the Figure shows that the risk of significant corrosion increases as the [Cl–]/[OH–] ratio in the pore solution rises above a certain value. Although several authors confirmed the dependence of corrosion initiation on the [Cl–]/[OH–] ratio, a great variability was found for the threshold value. The great variability of the [Cl–]/[OH–] threshold is, first of all, a consequence of the stochastic nature of the initiation of pitting corrosion; it appears that the chloride threshold can only be defined on a statistical basis.

Source: Bertolini, L. et. al, Corrosion of Steel in Concrete, Wiley-VCH, 2004

Corrosion of Steel in Concrete: Prevention, Diagnosis, Repair

2011-10-07T08:38:00.000+01:00

by: Pietro Pedeferri Rob B. Polder
Link:
http://rapidshare.com/files/17988933/Corrosion_of_Steel_in_Concrete.rar.html
or
http://ifile.it/mrsf2x

Chloride Attack

2011-10-07T08:36:00.001+01:00

By Dr. J. P. Broomfield

Chlorides can be present in concrete for a number of reasons:

1. Contamination

-Deliberate addition of calcium chloride set accelerators
-Deliberate use of sea water in the mix
-Accidental use of inadequately washed marine sourced aggregates
2. Ingress
-De icing salt ingress
-Sea salt ingress
-Chlorides from chemical processing etc.

Until the later 1970s it was widely held that chlorides cast into concrete were largely bound as chloroaluminates and would not cause corrosion. It was then found that large numbers of structures with chloride cast into the mix did suffer from corrosion and that binding was not as effective as initially believed. ACI Report 222R-96 reviews the national standards and laboratory data. The consensus is that a chloride level of 0.4% chloride by weight of cement is a necessary but not sufficient condition for corrosion and that in variable chloride and aggressive conditions corrosion can occur at lower chloride levels, down to about 0.2% chloride by weight of cement.

A recent literature review suggested that the whether chlorides are bound or not, the chloroaluminates break down releasing chloride ions for participation in the passivation break down process. They suggested that the discussion about the amount of chloride bound in the cement paste is therefore less important than previously thought. They also pointed out that the amount of calcium hydroxide available to maintain the pH has a profound effect on initiation of corrosion. This has implications for cement replacement materials.

Source: http://www.jpbroomfield.co.uk/html/corrosion_topics-chloride-attack.htm

Cathodic Protection of Steel in Concrete

2011-10-07T08:31:00.001+01:00

by: Paul M. Chess
Link:
http://ifile.it/2blduc7
or
http://www.filefactory.com/file/d8607e/n/0419230106_zip
or
http://rapidshare.com/files/148336319/0419230106.zip

ASTM C867 Criteria for Corrosion of Steel in Concrete

2011-10-07T08:30:00.001+01:00

Corrosion of Steel In Concrete 2nd Edition

2011-10-07T08:29:00.000+01:00

by: Broomfield
Link:
http://ifile.it/g90yjkz

Degradation of Concrete

2011-10-07T08:28:00.001+01:00

Degradation processes of concrete can be classified (Figure below) as: physical (caused by natural thermal variations such as freeze-thaw cycles, or artificial ones, such as those produced by fires), mechanical (abrasion, erosion, impact, explosion), chemical (attack by acids, sulfates, ammonium and magnesium ions, pure water, or alkali aggregate reactions), biological (fouling, biogenic attack) and structural (overloading, settlement, cyclic loading). In practice these processes may occur simultaneously, frequently giving rise to synergistic action.

Alterations that occur in concrete before the structure has been completed, that is within the first hours to months after casting (among these are cracking due to plastic settlement, plastic or drying shrinkage, creep, thermal shrinkage), are traditionally not considered among the phenomena of deterioration, although they are important to the durability of the structure.

The processes of deterioration of concrete and corrosion of reinforcement are closely connected (Figure beside). The former provoke destruction of the concrete cover or cause microcracking that compromises its protective haracteristics. On the other hand, corrosion attack, because of the expansive action of corrosion products, produces cracking or delamination of the concrete and reduces its adhesion to the reinforcement.

Source: Bertolini, L. et. al, Corrosion of Steel in Concrete, Wiley-VCH, 2004

Repair of concrete damaged by reinforcement corrosion: report of a working party

2011-10-07T08:27:00.001+01:00

by: Concrete Society
Link:
http://ifile.it/hv5sykm

Corrosion of Steel in Concrete

2011-10-07T08:26:00.001+01:00

By Dr. J. P. Broomfield

Reinforced concrete is one of the most durable, versatile and widely used construction materials. However, occasionally it does not give the low maintenance life expected of it. Sometimes this is due to incorrect expectations, sometimes to inadequate specification or construction and sometimes due to more adverse conditions than initially expected. Consequently, there are many structures in the built environment suffering from corrosion induced damage.

The one estimate from the USA is that the cost of damage due to de icing salts alone is between $325 and $1000 million per year to reinforced concrete bridges and car parks. In the UK the Department of Transport estimates a total repair cost of £616.5 million (approximately one billion US dollars) due to corrosion damage to motorway bridges. These bridges represent about 10% of the total bridge inventory in the UK. The total problem may therefore be ten times the DoT estimate. There are similar statistics for Australia, Europe and particularly the Middle East where the warm marine climate with saline ground conditions increase all corrosion problems. Corrosion control is made more difficult by the problems of curing concrete in hot, drying environments and has led to very short lifetimes for reinforced concrete structures. Deterioration occurs on buildings and other structures as well as bridges.

As concrete is porous and both moisture and oxygen can move through the pores and microcracks in concrete, the basic requirements for corrosion of mild or high strength ferritic reinforcing steels are present. The reason that corrosion does not occur in most cases is that the pores contain high levels of calcium, sodium and potassium hydroxide, which maintain a pH of between 12 and 13. This high level of alkalinity passivates the steel, forming a dense gamma ferric oxide that is self maintaining and prevents rapid corrosion.

In many cases any attack on reinforced concrete will be on the concrete. However, there are two chemicals that penetrate the concrete and attack the steel without breaking down the concrete first. The culprits are chlorides and carbon dioxide as these are the main common atmospherically borne species that penetrate concrete without causing significant damage and then promote the corrosion of steel by removing the protective passive oxide layer on the steel, created and sustained by the alkalinity of the concrete pore water.

Source: http://www.jpbroomfield.co.uk/html/corrosion_topics-corrosion-of-steel-in-concrete.htm

Corrosion Restoration Technologies: Lifejacket

2011-10-07T08:25:00.000+01:00

The Lifejacket system has a specially designed anode that gets encapsulated within a cavity between the existing piling and a two-piece fiberglass form

Corrosion is caused by chemical or electrochemical attack

Wooden forms are used to retain grout while pouring and curing. They are later removed to allow saltwater to wet the anode interface within the jacket

The finished product encases the piers

By Douglas L. Leng

Source: http://www.djc.com/news/ae/11194205.html

Uncoated vs Galvanized Rebar

2009-12-08T11:19:00.000Z

Zinc coatings have a higher chloride (Cl -) corrosion threshold (2-4 times) than that of uncoated steel, significantly extending the time until corrosion initiation.
Once corrosion of the zinc coating does occur, the properties of the corrosion products and their ability to migrate into the concrete matrix reduces stress generation in the surrounding concrete, further extending the life of the reinforced concrete structure. Black and galvanized rebar corrosion performance in concrete can be shown graphically as :

Source: http://www.galvanizedrebar.com/corrosion_model.htm

How Do We Know When We Have Enough Cathodic Protection?

2009-12-04T10:10:00.000Z

We know whether or not we have enough current by measuring the potential of the steel against a standard reference electrode, usually silver silver/chloride (Ag/AgCl sw.), but sometimes zinc (sw.).

Current flow onto any metal shifts its normal potential in the negative direction. History has shown that if steel receives enough current to shift the potential to (-) 0.800 V vs. silver / silver chloride (Ag / AgCl), the corrosion is essentially stopped.

Due to the nature of the films which form, the minimum (-0.800 V) potential is rarely the optimum potential, and designers try to achieve a potential between (-) 0.950 V and (-) 1.000 V vs. Ag/AgCl sw.

Figure 3: Protected vs Unprotected structures as verified by cathodic protection potential

by: Richard Baxter, Jim Britton
Source: http://www.cathodicprotection101.com/

Impressed Current Cathodic Protection Systems

2009-12-04T10:07:00.000Z

Due to the high currents involved in many seawater systems it is not uncommon to use impressed current systems. Impressed current systems use anodes of a type that are not easily dissolved into metallic ions, but rather sustain an alternative reaction,
oxidization of the dissolved chloride ions.
2Cl^- => Cl₂ + 2e^- Power is supplied by an external DC power unit..

Figure 2: Impressed current cathodic protection system in seawater

by: Richard Baxter, Jim Britton
Source: http://www.cathodicprotection101.com/

Basic Considerations When Designing Sacrificial Anode Systems

2009-12-04T10:03:00.000Z

The electrical current which an anode discharges is controlled by Ohm's law; that is:

I=E/R

I= Current flow in amps
E= Difference in potential between the anode and cathode in volts
R= Total circuit resistance in ohms

Initially current will be high because the difference in potential between the anode and cathode are high, but as the potential difference decreases due to the effect of the current flow onto the cathode, current gradually decreases due to the polarization of the cathode. The circuit resistance includes both the water path and the metal path, including any cable in the circuit. The dominant value here is the resistance of the anode to the seawater.

For most applications the metal resistance is so small compared to the water resistance that it can be ignored. (Not true for sleds, or long pipelines protected from both ends). In general, long thin anodes have lower resistance than short fat anodes. They will discharge more current, but will not last as long.

Therefore a cathodic protection designer must size the anodes so that they have the right shape and surface area to discharge enough current to protect the structure and enough weight to last the desired lifetime when discharging this current. As a general rule of thumb:

Length of the anode determines how much current the anode can produce, and consequently how many square feet of steel can be protected.

Cross Section (Weight) determines how long the anode can sustain this level of protection.

by: Richard Baxter, Jim Britton
Source: http://www.cathodicprotection101.com/

How Does Cathodic Protection Stop Corrosion?

2009-12-04T07:37:00.001Z

Cathodic protection prevents corrosion by converting all of the anodic (active) sites on the metal surface to cathodic (passive) sites by supplying electrical current (or free electrons) from an alternate source.

Usually this takes the form of galvanic anodes, which are more active than steel. This practice is also referred to as a sacrificial system, since the galvanic anodes sacrifice themselves to protect the structural steel or pipeline from corrosion.

In the case of aluminum anodes, the reaction at the aluminum surface is: (four aluminum ions plus twelve free electrons)
4Al => 4AL⁺⁺⁺ + 12 e^-

and at the steel surface, (oxygen gas converted to oxygen ions which combine with water to form hydroxyl ions)

3O₂ + 12e^- + 6H₂0 => 12OH^-

As long as the current (free electrons) is arriving at the cathode (steel) faster than oxygen is arriving, no corrosion will occur.

Figure 1: Sacrificial anode system in seawater

by: Richard Baxter, Jim Britton

Source: http://www.cathodicprotection101.com/

How Does Steel Corrode in Water?

2009-12-04T07:20:00.001Z

To understand cathodic protection one must first understand the corrosion mechanism. For corrosion to occur, three conditions must be present.

1. Two dissimilar metals
2. An electrolyte (water with any type of salt or salts dissolved in it)
3. A metal (conducting) path between the dissimilar metals

The two dissimilar metals may be totally different alloys, such as steel and aluminum, but are more usually microscopic or macroscopic metallurgical differences on the surface of a single piece of steel.

If the above conditions exist, at the more active metal surface (in this case we will consider freely corroding steel which is non uniform), the following reaction takes place at the more active sites: (two iron ions plus four free electrons)
2Fe => 2Fe⁺⁺ + 4e^-

The free electrons travel through the metal path to the less active sites where the following reaction takes place: (oxygen gas converted to oxygen ion - by combining with the four free electrons - which combines with water to form hydroxyl ions)

O₂ + 4e^- + 2H₂0 => 4 OH^-

Recombinations of these ions at the active surface produce the following reaction, which yields the iron corrosion product ferrous hydroxide: (iron combining with oxygen and water to form ferrous hydroxide)

2Fe + O₂ + 2H₂O => 2Fe (OH)₂

This reaction is more commonly described as 'current flow through the water from the anode (more active site) to the cathode (less active site).

by: Richard Baxter, Jim Britton

Source: http://www.cathodicprotection101.com/

Coating Defect Survey - DC Voltage Gradient

2009-12-04T04:22:00.000Z

Today, DC voltage gradient surveys have evolved as the most accurate and economic means of locating coating defects.

When a DC current is applied to a pipeline in a similar manner to cathodic protection, ground voltage gradients are created due to passage of current through resistive soil. Well coated pipelines have a high resistance to earth. However, at locations where there are coating defects the resistance to earth is of such way that current can flow through the soil to be picked-up by the pipe. In the vicinity of these defects measurable voltage gradients can be detected at ground level. The larger the defect, the greater the current flow. Increasing the current flow also results in an increased voltage gradient for a given soil resistivity.

The application of DC current to a pipeline at a regular pulsed frequency using special developed interrupters enables coating defects to be distinguished by stray traction and telluric currents. Existing cathodic protection systems may be utilized to inject the required signal, or temporary earths may be established at convenient connection points along the line.
The defects found during a DCVG survey can size and be mapped by GPS coordinates and will fully documented on special developed defect sheets.

Principle of survey

This survey technique utilises a dc current (either the impressed current CP system or a temporary system) which is pulsed by means of a current interrupter.

Current flow through the soil causes voltage gradient at coating defects that are detected using two earth contact probes and measured using a voltmeter.

The voltmeter incorporated in the survey equipment is a sensitive, centre zero instrument allowing location of defect to be determined by relative location of the probes and polarity of the reading.

Defects can be 'pin point' by obtaining a null reading when the two probes are located such that no voltage difference exists between them i.e. they are on an equipotential line.

Comparing the volt drop in the soil with the applied potential shift can assess severity of defects.

Site equipment

High sensitivity centre zero voltmeter.

Current Interrupter (suitable for current to be interrupted and with a switching speed compatible with the survey meter).

Reference (Ski) probes compatible with the survey meter.

Temporary dc current source and groundbed equipment (required if pipeline not protected by impressed current or system cannot be interrupted).

Survey procedure

Prior to commencement of any survey section a current interrupter is installed in the nearest existing cathodic protection station or temporary current source which may be established as necessary.

Typically, a minimum potential swing of 500-600 mV is sought and the current source output is adjusted accordingly. The application of a pulsed current enables coating defects to be distinguished from stray traction and telluric currents.

The difference between 'on' and 'off' potentials is recorded at the test point nearest the survey start point, and all other test points encountered, and the survey commenced.

The operator traverses the pipeline route using the probes as walking sticks. One probe is in contact with the ground at all times and for a short duration between strides both probes must be in ground contact. One probe can be on the centreline of the pipeline and the other maintained at a lateral separation of 1-2 m or probes can leap-frog along the centre line. If no defects are present the needle on the voltmeter registers no movement.

As a defect is approached a noticeable fluctuation is observed on the voltmeter at a rate similar to the interruption cycle. The amplitude of the fluctuation increases as the defect is approached and adjustment of voltmeter sensitivity is made as necessary. The swing on the voltmeter is directional, providing the probes are maintained in similar orientation parallel to the pipeline.

Thus, the defect is centred by detailed manoeuvre around the epicentre and the size of the defect estimated by considering signal strength at the defect, difference between 'on' and 'off' potential at adjacent test point and the distance from those points.

Data obtained

The DCVG survey provides an evaluation of each defect located. The defect can be sized by relating the signal voltage (or potential swing) to remote earth (mV1) to the signal voltage (potential swing) recorded at the nearest two test post (mV2,, mV3). The distances of defect to these two test posts (m1, m2) are also brought in account. In addition, it is also possible to determine whether active corrosion is taking place at the defect.

Processing and presentation of data

Coating defects are recorded defect sheets with reference to a fixed point marked on route alignment sheets and/or a stake placed in the ground.

Comments on signal strength should be recorded and the defect graded, where

mV1
%IR = ------------------------------------------------
mV2 - (m1/(m1+m2)*(mV2-mV3))

Values greater than 35% IR require immediate attention, values between 16 and 35% IR require attention under general maintenance and less than 15% IR need not be repaired.

Manpower and Vehicles

One man who needs to be experienced in the survey technique to evaluate results in the field can undertake the DCVG survey. An assistant may be required in difficult terrain but only one vehicle would be necessary.

Advantages of the DCVG survey

• Survey technique can provide an assessment of coating condition over areas of difficult access i.e. road, rail and water crossing etc.

• Estimates defect sizes in order to prioritise excavation and repair
• Minor defect: from 0% IR => 15% IR
• Medium defect: from 16% IR => 35% IR
• Large defect: from 36% IR => 100% IR

• Has already proven in use and accuracy

• One person can conduct survey, although 2 persons are recommended (progress, & safety).

• Provide data for cathodic protection adjusment/upgrading.

• Survey can be conducted in areas affected by stray currents and telluric effects in most soil conditions.
• Involves no trailing wires
• High accuracy in locating and pin-pointing defects
• Can be used in combination with other techniques
• CIP
• GPS Mapping
• Right-of-way-inspection
• Suitable to complex piping arrangements
• The technique is rapid and low in cost
• Has been proven successful in detecting disbanded coating

Source: http://www.the-sniffers.be/pipeline/dcvg.htm

Installation of Impressed Current Cathodic Protection System

2009-12-04T03:45:00.000Z

The Division provides maintenance to 108 numbers of suspended marine structures all over Hong Kong. Suspended deck structures are normally built of reinforced concrete (RC) and are subject to reinforcement corrosion in the aggressive marine environment.

The durability of RC structures is largely depended on the conditions of the embedded reinforcement. In the tidal zone and the splash zone, water and oxygen contents are optimal for reinforcement corrosion to occur.

The volume of corrosion products (i.e. rusts) occupies some four times the original volume of the embedded steel and the forces due to such increase in volume lead to concrete spalling and cracking. Our experience shows that reinforcement corrosion starts, normally accompany with signs of rust stains,concrete spalling and cracking of the under-deck structural elements at about 15 years after completion of a new pier.

The conventional concrete repair method (i.e. removal of defective concrete for reinstatement by patch repair, sprayed concrete or partial recasting) is short term in nature and can only restore the structural integrity temporarily and hence the next repair of such elements would be repaired in short periods of less than seven years. It is envisaged that repeated cycles of such repairs, if carried out, would inevitably impair the structural integrity of the pier-deck beam elements.

As a long-term solution to stop the reinforcement corrosion in the pier deck, we design and install impressed current cathodic protection (ICCP) systems at some selected piers. This method would significantly minimize the frequency of repair and hence, in long term, achieve cost-effectiveness in the maintenance of piers.

What is ICCP system?
Steel in concrete is protected against corrosion by a passivating gamma ferric oxide film, which forms on the steel surface because of the highly alkaline environment produced by cement hydration. In the presence of chloride ions, oxygen and water in concrete, the passive film on steel is destroyed and rusting due to anodic and cathodic reactions occurs. The theory of cathodic protection is to apply sufficient current to the steel reinforcements so that the rate of metal dissolution into the surrounding electrolyte or simply the anodic current is either stopped or reduced to an acceptable level. Thus, making the potential of reinforcement more negative and resulting in the acceleration of cathodic reaction and the reduction of anodic reaction.

A simple ICCP system includes an anode intended to distribute the cathodic protection current to the embedded reinforcement, through the concrete. The system also incorporates cables connecting the positive and negative terminals of a rectifier carrying DC current to the anode and to the reinforcement respectively.

Source: http://www.cedd.gov.hk/eng/about/organisation/org_ceo_pm.htm

Crevice Corrosion

2009-09-30T05:39:00.000+01:00

This form of attack is generally associated with the presence of small volumes of stagnant solution in occluded interstices, beneath deposits and seals, or in crevices, e.g. at nuts and rivet heads. Deposits of sand, dust, scale and corrosion products can all create zones where the liquid can only be renewed with great difficulty. This is also the case for flexible, porous or fibrous seals (wood, plastic, rubber, cements, asbestos, cloth, etc.).

Crevice corrosion is encountered particularly in metals and alloys which owe their resistance to the stability of a passive film, since these films are unstable in the presence of high concentrations of Cl^- and H⁺ ions.
The basic mechanism underlying crevice corrosion in passivatable alloys exposed to aerated chloride-rich media is gradual acidification of the solution inside the crevice, leading to the appearance of highly aggressive local conditions that destroy the passivity.
in an interstice, convection in the liquid is strongly impeded and the dissolved oxygen is locally rapidly exhausted. A few seconds are sufficient to create a "differential aeration cell" between the small deaerated interstice and the aerated remainder of the surface. However, "galvanic" corrosion between these two zones remains inactive.
As dissolution of the metal M continues, an excess of Mn⁺ ions is created in the crevice, which can only be compensated by electromigrationof the Cl^- ions (more numerous in a chloride-rich medium and more mobile than OH^- ions). Most metallic chlorides hydrolyse, and this is particularly true for the elements in stainless steels and aluminium alloys. The acidity in the crevice increases (pH 1-3) as well as the Cl^- ion concentration (up to several times the mean value in the solution). The dissolution reaction in the crevice is then promoted and the oxygen reduction reaction becomes localized on the external surfaces close to the crevice. This "autocatalytic" process accelerates rapidly, even if several days or weeks were necessary to get it under way.
Means of preventing or limiting crevice corrosion : Use welds rather than bolted or riveted joints, design installations to enable complete draining (no corners or stagnant zones), hydrofuge any interstices that cannot be eliminated, and in particular, grease all seals and seal planes, use only solid, non-porous seals, etc.

source: http://www.cdcorrosion.com/mode_corrosion/corrosion_crevice.htm

Atmospheric test-sites

2009-09-06T16:37:00.000+01:00

Atmospheric corrosion tests consist in the exposure of samples to atmospheric conditions at test-sites and in their periodic evaluation. To expose materials and their surface coatings to all factors of atmospheric environment is only possible by their exposure to a realistic environment whilst studying all parameters of that environment. The performance of corrosion testing is experimentally and time demanding.
Continual measurements of environmental parameters - temperature, humidity, sun radiation, amount of rainfall, Pollution by SO2, NOx and O3, pH and conductivity of rainfall, content of chlorides, sulfates and nitrates in rainfall are carried out. Due to a slow rate of atmospheric corrosion it is recommended for the exposure to last for 1 year, 2 years, 5 years, 10 years or 20 years according to the corrosion stability of a tested material.
Picture: Test-site in Czech Republic

Source: http://www.svuom.cz/index.php?zobraz=atmzkusebst&lang=en

Zinc Ribbon Anode for Cathodic Protection

2009-08-29T07:48:00.000+01:00

Source: http://www.farwestcorrosion.com/fwst/anodgalv/platt01.htm

Cathodic Protection

2009-08-28T05:26:00.000+01:00

Cathodic protection is the most widely applied electrochemical corrosion control technique. This is accomplished by applying a direct current to the structure which causes the structure potential to change from the corrosion potential (E_corr) to a protective potential in the immunity region.

The required cathodic protection current is supplied by sacrificial anode materials or by an impressed current system. Most metals in contact with an aqueous environment having a near neutral pH can be cathodically protected.

Figure: Typical cathodic polarization curve for steel

Source: http://www.westcoastcorrosion.com/Service%20cathodic%20protection.htm

Hydrogen Embrittlement (HE)

2009-08-28T04:59:00.000+01:00

Hydrogen embrittlement (HE) is a process resulting in a decrease of the toughness or ductility of a metal due to the presence of atomic hydrogen. Hydrogen embrittlement has been recognized classically as being of two types. The first, known as internal hydrogen embrittlement, occurs when the hydrogen enters molten metal which becomes supersaturated with hydrogen immediately after solidification. The second type, environmental hydrogen embrittlement, results from hydrogen being absorbed by solid metals. This can occur during elevated-temperature thermal treatments and in service during electroplating, contact with maintenance chemicals, corrosion reactions, cathodic protection, and operating in high-pressure hydrogen.

Mechanism
In the absence of residual stress or external loading, environmental hydrogen embrittlement is manifested in various forms, such as blistering, internal cracking, hydride formation, and reduced ductility. With a tensile stress or stress-intensity factor exceeding a specific threshold, the atomic hydrogen interacts with the metal to induce subcritical crack growth leading to fracture. In the absence of a corrosion reaction (polarized cathodically), the usual term used is hydrogen-assisted cracking (HAC) or hydrogen stress cracking (HSC). In the presence of active corrosion, usually as pits or crevices (polarized anodically), the cracking is generally called stress-corrosion cracking (SCC), but should more properly be called hydrogen-assisted stress-corrosion cracking (HSCC). Thus, HSC and electrochemically anodic SCC can operate separately or in combination (HSCC). In some metals, such as highs-strength steels, the mechanism is believed to be all, or nearly all, HSC. The participating mechanism of HSC is not always recognized and may be evaluated under the generic heading of SCC.

Prevention
Hydrogen embrittlement can be prevented through:

Control of stress level (residual or load) and hardness.
Avoid the hydrogen source.
Baking to remove hydrogen.

Source: http://www.corrosionclinic.com/types_of_corrosion/hydrogen_embrittlement_HE.htm

Potential Adjustment Protection

2009-08-27T05:46:00.000+01:00

Normally passive metals when exposed to oxidizing halide environments can suffer from pitting and crevice corrosion. By the application of a direct current the structure potential can be shifted back to the passive region from the transpassive region. This method is used extensively on stainless steel bleach washer facilities in the pulp and paper industry. Stainless steel flue gas scrubbers and brine evaporators have also been protected using this method. In effect this technique up-grades the corrosion resistance of passive metals making their corrosion resistance comparable to higher grade alloys.
Figure: Typical polarization behaviour for stainless steel in an oxidizing chlorine environment.

source: http://www.westcoastcorrosion.com/service%20pap%20protection.htm

Stainless Steel - Corrosion Resistance: Stress Corrosion Cracking (SCC)

2009-08-25T06:07:00.000+01:00

Under the combined effects of stress and certain corrosive environments stainless steels can be subject to this very rapid and severe form of corrosion. The stresses must be tensile and can result from loads applied in service, or stresses set up by the type of assembly e.g. interference fits of pins in holes, or from residual stresses resulting from the method of fabrication such as cold working. The most damaging environment is a solution of chlorides in water such as sea water, particularly at elevated temperatures.

As a consequence stainless steels are limited in their application for holding hot waters (above about 50°C) containing even trace amounts of chlorides (more than a few parts per million). This form of corrosion is only applicable to the austenitic group of steels and is related to the nickel content. Grade 316 is not significantly more resistant to SCC than is 304. The duplex stainless steels are much more resistant to SCC than are the austenitic grades, with grade 2205 being virtually immune at temperatures up to about 150°C, and the super duplex grades are more resistant again. The ferritic grades do not generally suffer from this problem at all.

In some instances it has been found possible to improve resistance to SCC by applying a compressive stress to the component at risk; this can be done by shot peening the surface for instance. Another alternative is to ensure the product is free of tensile stresses by annealing as a final operation. These solutions to the problem have been successful in some cases, but need to be very carefully evaluated, as it may be very difficult to guarantee the absence of residual or applied tensile stresses.

From a practical standpoint, Grade 304 may be adequate under certain conditions. For instance, Grade 304 is being used in water containing 100 - 300 parts per million (ppm) chlorides at moderate temperatures. Trying to establish limits can be risky because wet/dry conditions can concentrate chlorides and increase the probability of stress corrosion cracking. The chloride content of seawater is about 2% (20,000 ppm). Seawater above 50°C is encountered in applications such as heat exchangers for coastal power stations.

Recently there have been a small number of instances of chloride stress corrosion failures at lower temperatures than previously thought possible. These have occurred in the warm, moist atmosphere above indoor chlorinated swimming pools where stainless steel (generally Grade 316) fixtures are often used to suspend items such as ventilation ducting. Temperatures as low as 30 to 40°C have been involved. There have also been failures due to stress corrosion at higher temperatures with chloride levels as low as 10 ppm. This very serious problem is not yet fully understood.

Source: http://www.azom.com/details.asp?articleID=1177

Stainless Steel - Corrosion Resistance: Crevice Corrosion

2009-08-25T05:57:00.000+01:00

The corrosion resistance of a stainless steel is dependent on the presence of a protective oxide layer on its surface, but it is possible under certain conditions for this oxide layer to break down, for example in reducing acids, or in some types of combustion where the atmosphere is reducing. Areas where the oxide layer can break down can also sometimes be the result of the way components are designed, for example under gaskets, in sharp re-entrant corners or associated with incomplete weld penetration or overlapping surfaces.
These can all form crevices which can promote corrosion. To function as a corrosion site, a crevice has to be of sufficient width to permit entry of the corrodent, but sufficiently narrow to ensure that the corrodent remains stagnant. Accordingly crevice corrosion usually occurs in gaps a few micrometres wide, and is not found in grooves or slots in which circulation of the corrodent is possible. This problem can often be overcome by paying attention to the design of the component, in particular to avoiding formation of crevices or at least keeping them as open as possible. Crevice corrosion is a very similar mechanism to pitting corrosion; alloys resistant to one are generally resistant to both. Crevice corrosion can be viewed as a more severe form of pitting corrosion as it will occur at significantly lower temperatures than does pitting.

Source: http://www.azom.com/details.asp?articleID=1177

Stainless Steel - Corrosion Resistance: Pitting Corrosion

2009-08-24T06:04:00.000+01:00

Pitting Corrosion

Under certain conditions, particularly involving high concentrations of chlorides (such as sodium chloride in sea water), moderately high temperatures and exacerbated by low pH (ie acidic conditions), very localised corrosion can occur leading to perforation of pipes and fittings etc. This is not related to published corrosion data as it is an extremely localised and severe corrosion which can penetrate right through the cross section of the component. Grades high in chromium, and particularly molybdenum and nitrogen, are more resistant to pitting corrosion.

Pitting Resistance Equivalent number (PRE)

The Pitting Resistance Equivalent number (PRE) has been found to give a good indication of the pitting resistance of stainless steels. The PRE can be calculated as:

PRE = %Cr + 3.3 x %Mo + 16 x %N

One reason why pitting corrosion is so serious is that once a pit is initiated there is a strong tendency for it to continue to grow, even although the majority of the surrounding steel is still untouched.

The tendency for a particular steel to be attacked by pitting corrosion can be evaluated in the laboratory. A number of standard tests have been devised, the most common of which is that given in ASTM G48. A graph can be drawn giving the temperature at which pitting corrosion is likely to occur, as shown in Figure beside.

This is based on a standard ferric chloride laboratory test, but does predict outcomes in many service conditions.

Source: http://www.azom.com/details.asp?articleID=1177

The Galvanic Corrosion Trap

2009-08-23T07:01:00.000+01:00

Abstract:

The Galvanic Corrosion Trap. The wrong combination of metals can produce a corrosion cell of unequal voltage where one metal gives up its electrons and corrodes away. If the corrosion is not detected it will result in eventual failure of the equipment. Galvanic corrosion prevention is a design selection issue that one must always be aware of, as it can arise with the simplest of decisions. This article highlights a galvanic corrosion problem often seen in industry and sometimes missed by the person selecting equipment.

Keywords: rusting, corrosion scale, galvanic corrosion cell

source: http://lifetime-reliability.com/tip_016_pipe_galvanic_corrosion.html

Stainless Steel - Corrosion Resistance: Background

2009-08-23T06:57:00.000+01:00

Although one of the main reasons why stainless steels are used is corr osion resistance, they do in fact suffer from certain types of corrosion in some environments and care must be taken to select a grade which will be suitable for the application. Corrosion can cause a variety of problems, depending on the applications:

· Perforation such as of tanks and pipes, which allows leakage of fluids or gases,

· Loss of strength where the cross section of structural members is reduced by corrosion, leading to a loss of strength of the structure and subsequent failure,

· Degradation of appearance, where corrosion products or pitting can detract from a decorative surface finish,

· Finally, corrosion can produce scale or rust which can contaminate the material being handled; this particularly applies in the case of food processing equipment.

Corrosion of stainless steels can be categorised as one of:

-General Corrosion

-Pitting Corrosion

-Crevice Corrosion

-Stress Corrosion Cracking

-Sulphide Stress Corrosion Cracking

-Intergranular Corrosion

-Galvanic Corrosion

-Contact Corrosion

Source: http://www.azom.com/details.asp?articleID=1177

Galvanic Corrosion

2009-08-23T06:48:00.000+01:00

Metals themselves can also set up corrosion cells. When a pipe consists of only one type of metal, impurities in the pipe wall can develop into anodes and cathodes. Alternatively, when two dissimilar metals come into contact, galvanic corrosion will occur. Galvanic corrosion is often set up in the distribution system in meter installations and at service connections and couplings.
The galvanic series, shown below, arranges metals according to their tendency to corrode. This series can be used to determine whether galvanic corrosion is likely to occur and how strong the corrosion reaction will be.

As you can see on the series, some metals (such as gold and silver) are very inactive and unlikely to corrode. Many of these metals have been traditionally used as jewelry because of their low tendency to corrode even when in the presence of salts (in sweat) and oils found on the human body. Although these inactive metals would make non-corrosive pipes, they are usually too expensive to use in the distribution system.

At the other end of the galvanic series are metals which are very active and have a high tendency to corrode. These metals can be used as sacrificial anodes, which we will discuss later. They should not be used for distribution system pipes.

Most of the metals used in piping - iron, steel, and copper - are found in the middle of the galvanic series. These metals have some tendency to corrode, with those higher on the galvanic series (such as iron and steel) tending more toward corrosion.

The distance on the galvanic series between two metals will also influence the likelihood of galvanic corrosion when the two metals are placed in conjunction with each other. For example, if aluminum is brought in contact with a steel pipe, the likelihood of corrosion is low since aluminum and steel are close together on the galvanic series. However, if a stainless steel fitting is used on an iron pipe, the likelihood of corrosion is much higher.

When galvanic corrosion occurs, the more active metals always become the anodes. This means that they are corroded, and in extreme cases can begin to leak. The less active metal becomes the cathode and is not damaged.

Source: http://water.me.vccs.edu/concepts/corrosiontypes.html

Pitting corrosion mechanism of crude oil tanker's cargo tank bottom plate

2009-08-23T06:42:00.000+01:00

Source: http://www.jfe-steel.co.jp/en/release/2008/080129.html

Corrosion environment with crude oil tanker's cargo tank

2009-08-23T06:38:00.000+01:00

Source: http://www.jfe-steel.co.jp/en/release/2008/080129.html

Pitting Corrosion: Mechanism

2009-08-15T06:08:00.000+01:00

For a defect-free "perfect" material, pitting corrosion is caused by the ENVIRONMENT (chemistry) that may contain aggressive chemical species such as chloride. Chloride is particularly damaging to the passive film (oxide) so pitting can initiate at oxide breaks.

The environment may also set up a differential aeration cell (a water droplet on the surface of a steel, for example) and pitting can initiate at the anodic site (centre of the water droplet).

For a homogeneous environment, pitting is caused by the MATERIAL that may contain inclusions (MnS is the major culprit for the initiation of pitting in steels) or defects. In most cases, both the environment and the material contribute to pit initiation.

The ENVIRONMENT (chemistry) and the MATERIAL (metallurgy) factors determine whether an existing pit can be repassivated or not. Sufficient aeration (supply of oxygen to the reaction site) may enhance the formation of oxide at the pitting site and thus repassivate or heal the damaged passive film (oxide) - the pit is repassivated and no pitting occurs. An existing pit can also be repassivated if the material contains sufficient amount of alloying elements such as Cr, Mo, Ti, W, N, etc.. These elements, particularly Mo, can significantly enhance the enrichment of Cr in the oxide and thus heals or repassivates the pit.

Source: http://www.corrosionclinic.com/types_of_corrosion/pitting_corrosion.htm

Metallic Materials: Physical, Mechanical, and Corrosion Properties (Corrosion Technology)

2009-08-15T03:48:00.001+01:00

P.E., Philip A. Schweitzer
code:
http://rapidshare.com/files/112470275/0824747410.zip.html
or
http://www.filefactory.com/file/ac45d7/n/0824747410_zip

Encyclopedia of Corrosion Technology, Second Edition

2009-08-15T03:47:00.000+01:00

P.E., Philip A. Schweitzer
code:
http://ifile.it/942qo8
or
http://www.mediafire.com/?ckx0ckxegoe

Pitting Corrosion (2)

2009-08-14T17:01:00.001+01:00

ASTM-G46 has a standard visual chart for rating of pitting corrosion

The shape of pitting corrosion can only be identified through metallography where a pitted sample is cross-sectioned and the shape the size and the depth of penetration can be determined.

Source: http://www.corrosionclinic.com/types_of_corrosion/pitting_corrosion.htm

Pitting Corrosion (1)

2009-08-14T16:55:00.000+01:00

Pitting Corrosion is the localized corrosion of a metal surface confined to a point or small area, that takes the form of cavities. Pitting is one of the most damaging forms of corrosion. Pitting factor is the ratio of the depth of the deepest pit resulting from corrosion divided by the average penetration as calculated from weight loss. This following photo show pitting corrosion of SAF2304 duplex stainless steel exposed to 3.5% NaCl solution.

Pitting corrosion forms on passive metals and alloys like stainless steel when the ultra-thin passive film (oxide film) is chemically or mechanically damaged and does not immediately re-passivate. The resulting pits can become wide and shallow or narrow and deep which can rapidly perforate the wall thickness of a metal.

Source: http://www.corrosionclinic.com/types_of_corrosion/pitting_corrosion.htm

Oxygen concentration, temperature and corrosion of steel pipes

2009-08-14T16:18:00.000+01:00

Effects of oxygen concentration and temperature on the corrosion of low-carbon steel pipes

Source: http://www.engineeringtoolbox.com/oxygen-steel-pipe-corrosion-d_1170.html

Corrosion in refineries (European Federation of Corrosion Publications)

2009-08-13T16:41:00.000+01:00

J.D. Harston and F. Ropital
code:
http://ifile.it/5ozgw67

Cathodic Protection: Underground Bare Structures

2009-08-13T16:39:00.000+01:00

The problems presented in attempting to provide cathodic protection for existing bare structures are much more difficult than those on coated structures. The major difficulty arises because of the much greater magnitude of current required. On a well-coated underground storage tank, it is not unusual to be able to provide protection with one or two galvanic anodes while it is not uncommon to have several rectifier units in a large complex tank farm.

Because of the much greater current requirement, interference problems can be created on other nearby underground utility systems. On systems using sacrificial anodes, the number of anodes required is similarly much greater on bare structures than on coated.

We have seen one example where one anode was sufficient to provide protection for a coated 10,000 gallon tank. On the other hand, a poorly coated or bare 10,000 gallon tank can require in excess of 1.5 amps to achieve effective corrosion control. For one bare UST piping system in Ohio consisting of 1,200 feet of 3" diameter pipe, 2 amperes of current was required for full corrosion control. If magnesium anodes were selected for use, over 60 anodes would be required.

Source:www.bushman.cc/pdf/corrosion_theory.pdf

Corrosion induced by low-energy radionuclides: Modeling of Tritium and Its Radiolytic and Decay Products Formed in Nuclear Installations

2009-08-13T16:38:00.000+01:00

Gilbert Bellanger
code:
http://ifile.it/u4onbhy
or
http://rapidshare.com/files/133025997/0080445101.rar

Pitting Corrosion

2009-08-13T16:36:00.001+01:00

Pitting corrosion on outside surface of cast iron bathtub

Source: http://metallurgist.com/html/corrosion.htm

Techniques for Corrosion Monitoring

2009-08-13T16:35:00.001+01:00

L. Yang
code:
http://rapidshare.com/files/144395382/1420070894.zip.html
or
http://ifile.it/beawvir

Cathodic Protection: Underground Coated Structures

2009-08-13T16:29:00.000+01:00

The economics favoring cathodic protection of cross country pipelines are so overwhelming, particularly on high pressure gas and oil lines, that practically every new line of consequence is provided with cathodic protection almost immediately after completion. The Department of Trans-portation has passed Federal legislation requiring that all oil, gas and gas products pipelines be cathodically protected and that the level of protection meets designated standards and regulations.

New structures are generally provided with a good, high resistivity coating that is applied with techniques that leave almost negligible amounts of the surface exposed to the soil. However, it is recognized that a coating, no matter how good or how well applied, is never perfect.

The corrosion protection afforded by the coating must be supplemented with cathodic protection in order to achieve complete mitigation of corrosion. It is important to understand that coated structures develop leaks within a shorter period of time than do uncoated structures. This is true even though the total metal loss on a coated structure is appreciably less than on a bare structure. All of the corrosion activity is concentrated at the holidays or breaks in the coating rather than evenly dispersed over the entire surface, thus accelerating the corrosion rate at the holiday locations.

Fortunately for the structure owner, coating and cathodic protection work very well together. When a tank or pipe is coated with one of the high quality materials and closely controlled application techniques that are available today, a relatively small magnitude of current can provide complete cathodic protection for tanks and their associated piping.

Although protection of cross country pipelines and existing rural tank farms is usually provided with the rectifier type systems, the use of such systems in congested areas is often very difficult because of the many interference problems created on nearby structures. Therefore, in congested areas, sacrificial anode type systems are more often used.

One example was of a well coated 10,000 gallon underground storage tank located in Detroit, Michigan. It was amply protected with one anode installed on one end of the tank with a total current output of less than 10 milli-amperes of current. The fact that sacrificial anodes have been installed on over 200,000 well-coated underground storage tanks without a single corrosion related product discharge is a testament to the effectiveness of this approach.

In many instances, spacing of anodes can be extended to 100 - 500 feet or more on small diameter buried piping depending on the quality of the coating and environmental conditions. As a consequence, many companies in recent years have established programs in which magnesium anodes are installed on pre-selected spacings as the well-coated piping is laid.

Source:www.bushman.cc/pdf/corrosion_theory.pdf

Microbiologically Influenced Corrosion: An Engineering Insight

2009-08-13T16:27:00.001+01:00

Reza Javaherdashti
code:
http://ifile.it/feywtno

Undewater Corrosion

2009-08-13T10:07:00.000+01:00

severe corrosion damage noted on marine structural pipe pile after 15 years of service

Source: http://www.westcoastcorrosion.com/services.htm

Corrosion Control Through Organic Coatings

2009-08-13T10:05:00.000+01:00

Amy Forsgren
code:
http://ifile.it/dm763k

Erosion Corrosion

2009-08-13T09:57:00.000+01:00

Rapidly flowing solutions can often disrupt adherent surface films and deposits that would otherwise offer protection against corrosion. Thinning or removal of surface films by erosion from the flowing stream results in accelerated corrosion, called erosion-corrosion. The attack is accelerated at elbows, tube constrictions, burrs, and other structural features that alter flow direction or velocity, and increase turbulence.

Erosion-corrosion takes the form of grooves, waves, gullies, teardrop-shaped pits, and horseshoe-shaped undercutting in the surface. The effects of the hydrodynamic are not well understood. Undercutting may occur in either upstream or the downstream direction. As described in the schematic below, turbulent eddies thin the protective film locally to produce undercutting, which is seen in the accompanying photograph.

Source: http://www.corrosionlab.com/papers/erosion-corrosion/erosion-corrosion.htm

Anodic Protection

2009-08-13T09:37:00.000+01:00

In circumstances where cathodic protection is not practical, such as in strongly alkaline or acidic environments, anodic protection is a useful corrosion control technique. Specifically, in metal-environment conditions where active-passive behaviour is demonstrated, anodic protection is usually effective. In practise, the metal-environment potential is held in the passive region by polarizing the structure in the electropositive direction. Historically, anodic protection has the widest application in the process industries and in particular on mild or stainless steel equipment use for concentrated sulphuric acid storage. Equipment, such as pulp and paper mill digesters and recausticizing (white, green & black) liquor clarifiers and storage tanks have also been effectively protected.
Here the metal potential is shifted to the passive zone from the active region by the application of a direct current.

Source: http://www.westcoastcorrosion.com/service%20anode%20Protection.htm

Impressed Current Anodes

2009-08-12T17:14:00.002+01:00

When a rectifier type system is used, the current is derived from an outside source and is not generated by the corrosion of a particular metal as is the case with galvanic anodes. However, materials used as energized anodes do corrode. Thus, junk pipe and steel rails that were at one time used extensively as anode materials in rectifier type systems, corrode at the rate of 20 lbs. per ampere year.
Even a relatively small rectifier system, with a capacity of only 10 amperes, would consume 2000 lbs. of steel in 10 years. Therefore, longer life anode materials were sought. The materials that are used almost universally today are graphite, high silicon cast iron and precious metal oxide coated titanium. In underground work, special coke breeze backfills are usually used for the purpose of providing a uniform environment around the anode and for lowering the anode-to-earth resistance.

Source:www.bushman.cc/pdf/corrosion_theory.pdf

Encyclopedia of Corrosion Technology

2009-08-12T17:14:00.001+01:00

Philip A. Schweitzer
code:
http://ifile.it/n0i3f16

Corrosion Inspection and Monitoring

2009-08-12T17:13:00.000+01:00

Pierre R. Roberge, R. Winston Revie
code:
http://rapidshare.com/files/118743284/bush_is_genocidal.7z
or
http://ifile.it/4t0bfd5

Sacrificial Anode on Water Pipe

2009-08-12T08:43:00.001+01:00

Sacrificial Anode on Water Main Pipe, Peterborough, Canada

Source: http://www.peterboroughutilities.ca/Water/Construction_Projects/Cathodic_Protection.htm

Principles of Corrosion Engineering and Corrosion

2009-08-12T08:42:00.002+01:00

Zaki Ahmad
code:
http://ifile.it/rpbcvq8

Analytical Methods In Corrosion Science and Engineering (Corrosion Technology)

2009-08-12T08:42:00.001+01:00

Philippe Marcus, Florian B. Mansfeld
code:
http://ifile.it/jx9duy3
or
http://www.filefactory.com/file/605ea9/n/Analytical_Methods_In_Corrosion_
Science_and_Engineering_0824759524_rar

Galvanic Anodes

2009-08-12T08:21:00.000+01:00

Protective current generated by galvanic anodes depends upon the inherent potential difference between the anodes and the structure to be protected. Thus, if the structure is made of iron or steel, any metal that is more active in the electromotive force series can theoretically be used as anode material. In practice, the materials generally used for galvanic anodes are zinc and magnesium.
Although aluminum is also a material which is more active than iron, it has not yet proved to be an effective galvanic anode material for underground use because of the polarization films which build up on the aluminum surface as it corrodes, thereby ceasing the generation of protective current. In recent years, some alloys of aluminum have been used successfully in seawater applications and work is progressing on alloys that may prove to be effective in other applications.

It should be noted that galvanic anodes consume themselves in the process of generating protective currents. The rate of consumption is dependent upon the magnitude of current generated as well as the material from which the anode is made. For example, the theoretical consumption rate of zinc is 23.5 lbs. per ampere year and that of magnesium is 8.7 lbs. per ampere year. In actual practice, not all of the metal is consumed in generating current that is useful for cathodic protection. Some of the metal is consumed in self-corrosion. Zinc is approximately 90% efficient and magnesium is approximately 50% efficient. Therefore, the actual pounds consumed per ampere year of protective current are 26 and 17 lbs. for zinc and magnesium respectively.

In underground applications, these anodes are normally surrounded with a special backfill. The backfill is usually a mixture of gypsum, Bentonite and sodium sulfate. This special backfill serves a number of purposes. First, it provides a uniform environment for the anode, thereby making the corrosion of the anode uniform; second, the backfill decreases the anode-to earth resistance; third, it retains moisture and thereby maintains a lower resistance; and fourth, it acts as a depolarizing agent.

Source:www.bushman.cc/pdf/corrosion_theory.pdf

Corrosion and Protection (Engineering Materials and Processes)

2009-08-12T07:59:00.000+01:00

Einar Bardal
code:
http://rapidshare.com/files/88771280/CP1852337583.rar.html
or
http://www.mediafire.com/?7gzzj9za19x

Corrosion of Linings and Coatings: Cathodic and Inhibitor Protection and Corrosion Monitoring (Corrosion Engineering Handbook, Second Edition)

2009-08-12T07:58:00.001+01:00

P.E., Philip A. Schweitzer
code:
http://www.filefactory.com/file/a63b69/n/0849382475_zip
or
http://ifile.it/xr4cv1d

Sacrificial Anode on the Hull of a Tug / Ship

2009-08-12T07:53:00.000+01:00

Steel hulls of ships, which come into contact with seawater (an electrolyte) and consequently corrode (rust) are directly connected with base metals (e.g. zinc) to provide protection against corrosion.
Through the transfer of electrons from the zinc to the iron atoms of the steel, corrosion is inhibited until the zinc has been completely dissolved by the electrochemical reaction. The sacrificed pieces of metal are known as "sacrificial anodes".

Source: http://www.tis-gdv.de/tis_e/misc/elektro.htm

Fundamentals of Metallic Corrosion: Atmospheric and Media Corrosion of Metals (Corrosion Engineering Handbook, Second Edition)

2009-08-12T07:49:00.001+01:00

P.E., Philip A. Schweitzer
download link:
http://rapidshare.com/files/67544180/Fundamentals_of_Metallic_Corrosion_0849382432.pdf
or
http://ifile.it/2j3vl4p

Handbook of Corrosion Engineering

2009-08-12T07:48:00.001+01:00

Pierre R. Roberge
code:
http://rapidshare.com/files/40761517/Handbook_of_Corrosion_Engineering.rar
or
http://ifile.it/ft5dpia

Application Method of Cathodic Protection (3)

2009-08-12T07:40:00.000+01:00

Regardless of the type of system used, current flows from the cathodic protection anode through the soil to the structure to be protected. Where this current flows onto a structure from the surrounding electrolyte (soil), the potential of the structure is made more negative. Cathodic protection is achieved when this change in potential is sufficient to arrest corrosion.

It would appear that cathodic protection can be achieved merely by the application of current of sufficient magnitude. Although this statement is true, it is deceptively simple because there are very large differences in the design of cathodic protection systems. These differences result from the infinite variety of structures that are to be protected and from the large assortment of environments in which those structures are located. Because of the large differences in the designs of systems necessary to achieve protection, it is often necessary for existing structures that each system be custom designed for a given location.

In order to prevent corrosion using cathodic protection, current must flow from the electrolyte onto the structure at all locations. If a portion of the structure does not receive current, the normal corrosion activity will continue at that point. If any of the cathodic protection current picked up by the structure leaves that structure to flow back into the electrolyte, corrosion will be accelerated at the location where the current is discharged. As an example, when mechanically coupled piping is used, this can be discontinuous from one pipe section to the next. If a galvanic anode type system is used for protection, it may be necessary to install an anode on each pipe length or to electrically bond across each joint. If one length of pipe is neglected, that length will receive no cathodic protection and the normal corrosion activity will continue. When a rectifier type system is installed on an underground storage tank system, it is even more important that the tank and lines be electrically continuous. If there are non-continuous joints, it is possible for the cathodic protection current to leave the pipe or tank to flow around the electrically discontinuous joint causing corrosion at each point where the current leaves the pipe surface. Similarly, if cathodic protection current is applied to one structure in an area, it is possible for other structures in the neighborhood to be exposed to damage unless proper steps are taken. Potential measurements are used to determine whether such damaging exposure exists. Just as protection is indicated when the potential of a structure is made more negative, stray current corrosion is indicated when the potential of a structure is made less negative as a result of the application of cathodic protection current.

Source:www.bushman.cc/pdf/corrosion_theory.pdf

Corrosion Engineering

2009-08-12T05:16:00.000+01:00

Pierre R. Roberge
code:
http://www.filefactory.com/file/4487e9/n/cepmzmdsdfasr0071482431_rar

Corrosion Prevention and Protection: Practical Solutions

2009-08-12T03:00:00.001+01:00

Edward Ghali, Vedula S. Sastri, M. Elboujdaini
code:
http://ifile.it/8dzwic9
or
http://rapidshare.com/files/159886139/047002402X.zip

Application Method of Cathodic Protection (2)

2009-08-12T02:56:00.000+01:00

In most cases, the rectifier type system is designed to deliver relatively large currents from a limited number of anodes, and the galvanic anode type system is designed to deliver relatively small currents from a large number of anodes.
Each method of applying cathodic protection has characteristics that make it more applicable to a particular problem than the other. A comparison of those characteristics is as follows:

Source:www.bushman.cc/pdf/corrosion_theory.pdf

Corrosion and Corrosion Control

2009-08-11T16:10:00.000+01:00

Winston Revie
code:
http://www.filefactory.com/file/f979ac/n/0471732796_rar
or
http://ifile.it/vkghem0

Application Method of Cathodic Protection (1)

2009-08-11T10:42:00.000+01:00

There are basically two methods of applying cathodic protection. One of these methods makes use of anodes which are energized by an external DC power source. In this type of cathodic protection system, anodes are installed in the electrolyte and are connected to the positive terminal of a DC power source and the structure which is to be protected is connected to the negative terminal of that source.
Because the power source is almost always a rectifier unit, this type of system is often referred to as a rectifier or impressed current type system.

The second method of protection makes use of galvanic anodes which have a higher energy level or potential with respect to the structure to be protected. These anodes are made of materials, such as magnesium or zinc, which are naturally anodic with respect to steel structures and are connected directly to these structures.

Source:www.bushman.cc/pdf/corrosion_theory.pdf

Corrosion behaviour and protection of copper and aluminum alloys in seawater

2009-08-11T09:16:00.001+01:00

Damien Féron
Code:
http://rapidshare.com/files/145427772/wcbpcaas.rar.html
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http://ifile.it/up9k17m

Corrosion of Aluminium

2009-08-11T09:01:00.000+01:00

Christian Vargel
code:
http://ifile.it/czj8mn4

Corrosion Control Mechanism

2009-08-11T03:28:00.001+01:00

Cathodic protection is an electrical method of preventing corrosion on metallic structures situated in electrolytes. In practical applications, the structures most commonly provided with protection are constructed of iron or steel (including stainless steel) and the electrolytes are most often soil and water. Other metals commonly provided with cathodic protection include, lead sheathed cables, copper and aluminum piping, galvanized steel, and cast iron.
Cathodic protection has also been used successfully in unusual electrolytes such as concrete, calcium chloride and caustic soda. However, the vast majority of cathodic protection systems are used to prevent corrosion on steel structures in soil and water. Cathodic protection has become a standard procedure for many structures such as underground storage tanks, pipelines, water storage tanks, ship hulls and interiors, lock gates and dams, water treatment facilities, well casings, trash racks and screens, bridge decks, and steel pilings.

As far back as the Bronze Age, it was observed that metals were not very stable when subjected to their natural environments such as soil and sea water. About 1780, a physiologist, Luigi Galvani, reported on his experiments with metallic arcs of dissimilar metals. He was studying the muscular structure of the frog. He noticed that when the frogs were suspended on an iron rack by copper hooks, there was a twitching in their leg muscles. One of the foremost physicists of the period, Alessandro Volta, was able to demonstrate that the phenomenon was caused by electricity produced by the dissimilarity of the metals in contact with the biological specimens.

In 1824, Sir Humphry Davy, on contract to the royal Navy, discovered the principle of cathodic protection for the mitigation of natural corrosion processes. He was searching for a method to prevent corrosion of the copper-clad wooden hulls of English ships. He attached billets of zinc to the copper and observed that the zinc would corrode to save the copper. Today, over one and one-half centuries later, corrosion engineers are still using this same method of preventing corrosion damage by applying this same zinc anode cathodic protection to steel ships around the world.

Source:www.bushman.cc/pdf/corrosion_theory.pdf

Electrocorrosion and Protection of Metals: General approach with particular consideration to electrochemical plants

2009-08-11T03:06:00.000+01:00

Joseph Riskin
link:
http://ifile.it/ksge78c

Corrosion Caused by Differences in the Electrolyte

2009-08-10T03:16:00.000+01:00

Corrosion can occur due to differences in the electrolyte. These differences may be in the soil resistivity, oxygen concentrations, moisture content and various ion concentrations. The variations produce current flow from one location, through the electrolyte, to another portion of the same metallic structure.

Electrolytic corrosion and galvanic corrosion are similar in that corrosion always occurs at the anodic areas. The essential difference between the two is that in the case of electrolytic corrosion, the external man-made current generates the corrosion; in galvanic corrosion, the natural process of corrosion generates the current. There is also a difference in polarity. In an electrolytic cell, the anode is the positive electrode; in a galvanic cell, the anode is the negative electrode.

It has been established that electric current can generate corrosion, corrosion, in turn can generate electric current. As indicated by these phenomena, it is then possible to prevent corrosion by use of electrical current. This, then, is the basis for cathodic protection. When direct current is applied with a polarity which opposes the natural corrosion mechanisms, and with sufficient magnitude to polarize all the cathodic areas up to the open circuit potential of the anodic areas, corrosion is arrested.

The theoretical considerations indicate that the basis for cathodic protection is relatively simple not difficult to understand. However, practical designs for various applications can vary considerably based on the type of structure to be protected and the conditions encountered.

Source:www.bushman.cc/pdf/corrosion_theory.pdf

GALVANIC CORROSION OF A SINGE METAL

2009-08-10T03:11:00.000+01:00

The same metallic structure, when placed in an electrolyte (e.g. soil) can develop dif-ferences in potential as a result of metal grain composition, milling imperfections, scratches, threads, etc., being exposed.
Those portions will usually be, anodic to the remainder of the surface and will corrode.

Source:www.bushman.cc/pdf/corrosion_theory.pdf

BI-METALLIC CORROSION

2009-08-10T03:04:00.000+01:00

Current will be generated when two dissimilar metals are electrically connected and immersed in an electrolyte. One of the metals will corrode.
The path of the current will be from the corroding metal, through the electrolyte (soil) to the non-corroding metal and then back through the connection (conductor) between the two metals. The corroding metal is the one where the current leaves to enter the electrolyte and is called an anode. The metal that receives the current is called the cathode.

Source:www.bushman.cc/pdf/corrosion_theory.pdf

Pipe-to-Soil Potential as a Criterion of Cathodic Protection

2009-08-09T15:26:00.000+01:00

It is almost universally accepted that a steel structure under cathodic protection is fully protected if the potential is at least 0.85-volt negative, referred to a standard copper-saturated copper sulfate electrode placed in the electrolyte immediately adjacent to the metal surface.
The entire structure is fully protected, of course, only if this criterion is met at every point on the surface. This is not a minimum requirement; it is a maximum. In other words, it is almost certainly true that protection is complete when this is achieved. It is also possible to have complete freedom from active corrosion at lower potentials.

Source: Parker, M.E, & Peattie. E.G., Pipe Line Corrosion and Cathodic Protection, Elsevier Science, 1999

Corrosion Mechanism

2009-08-08T07:36:00.000+01:00

There are two basic mechanisms by which metals in electrolytes corrode

• Electrolytic Corrosion
• Galvanic Corrosion

Electrolytic corrosion is a result of direct current from outside sources entering and then leaving a particular metallic structure by way of the electrolyte. Where current enters the structure, that part is usually unaffected or is provided with some degree of protection. Where current leaves the structure, corrosion occurs. In underground work, this type of corrosion is often referred to as stray current corrosion and results from currents entering the soil from sources of DC such as electric railway systems or DC machinery.

Galvanic corrosion is self-generated activity resulting from differences in energy levels or potentials which develop when metal is placed in an electrolyte. These differences can arise from the coupling of dissimilar metals, variations in the electrolyte, non-homogeneity of the metal, or a combination of the above.

Source:www.bushman.cc/pdf/corrosion_theory.pdf

Galvanic and CP

2009-08-08T03:35:00.000+01:00

Nature has endowed each metallic substance with a certain natural energy level or potential. When two metals having different energy levels or potentials are coupled together, current will flow. The direction of positive current flow will be from the metal with the more negative potential through the soil to that which is more positive. Corrosion will occur at the point where positive current leaves the metal surface. A dry cell battery is one example of a corrosion cell.

DC railways and other machinery often generate direct current. When this current flows through the soil indiscriminately, it is referred to as "stray" DC. The current may contact and follow a buried metallic structure such as a pipeline, but wherever it leaves that structure to return to it's origin, corrosion will occur.

Cathodic protection is an electrical method of preventing corrosion on metallic structures which are in electrolytes such as soil or water. It has had widespread application on underground pipelines, and ever increasing use as the most effective corrosion control method for numerous other underground and underwater structures such as lead cables, water storage tanks, lock gates and dams, steel pilings, underground storage tanks, well casings, ship hulls and interiors, water treatment equipment, trash racks and screens. It is a scientific method which combats corrosion by use of the same laws which cause the corrosion process.

Source: www.bushman.cc/pdf/corrosion_theory.pdf

Cathodic Protection of Steel in Concrete

2009-08-06T18:27:00.000+01:00

by: Paul M. Chess
Link:
http://ifile.it/2blduc7
or
http://www.filefactory.com/file/d8607e/n/0419230106_zip
or
http://rapidshare.com/files/148336319/0419230106.zip

Pipeline Corrosion and Cathodic Protection, Third Edition

2009-08-06T18:25:00.000+01:00

by: Marshall Parker Edward G. Peattie
Link:
http://rapidshare.com/files/8386457/Pipeline_Corrosion_and_Cathodic_Protection_3E.rar
or
http://ifile.it/cb0s2eg

Cathodic Protection: Historical

2009-08-05T08:46:00.000+01:00

The first application of cathodic protection (CP) can be traced back to 1824, when Sir Humphrey Davy, in a project financed by the British Navy, succeeded in protecting copper sheathing* against corrosion from seawater by the use of iron anodes. This limited use of CP on copper sheathing perdured and when wooden hulls were replaced by steel the fitting of zinc protector blocks on the sterns of naval vessels became traditional. These zinc slabs, although they offered some protection to steel hulls against local galvanic effects due to the presence of the bronze propellers, were generally not deemed to be effective.

This lack of efficiency was mainly due to the use of unsuitable zinc alloys and other factors such as insufficient appreciation of the technology of cathodic protection and the tendency to reduce the efficiency of the zinc material to zero by painting their surfaces. From that early beginning, CP has grown to have many uses in marine and underground structures, water storage tanks, gas pipelines, oil platform supports, and many other facilities exposed to corrosive environments. More recently, CP has been proved to be an effective method for protecting and reinforcing steel from chloride-induced corrosion.

The CP effectiveness at protecting steel in soils has been demonstrated in the early 1940s when CP was applied to an old natural-gas piping network that had been developing leaks at a rapidly increasing rate, enough so that abandonment was seriously considered. The observed reduction in the number of leaks immediately after the CP installation was impressive.

Modern specifications for the cathodic protection of active oceangoing ships were first described in 1950. Since that time progress has been rapid. Considerable advances in cathodic protection technology have been made, better sacrificial anode materials have been developed, and circuits for the use of controlled applied current systems, using inert anodes, have been perfected.

The first reinforced concrete-impressed current CP system was an experimental system installed on a bridge support beam in 1959. A more advanced system was subsequently installed on a bridge deck in 1972. The anode system used in both applications was based on a conventional-impressed current CP system for pipelines, but “spread out” over a bridge deck. CP has since then become one of the few techniques that can be applied to control corrosion on existing structures.

Source: Roberge, P.R., Corrosion Engineering: Principle and Practice, McGraw-Hill

Handbook of Cathodic Corrosion Protection, Third Edition

2009-08-05T08:22:00.000+01:00

by: Walter von Baeckmann Wilhelm Schwenk Werner Prinz
Link:
http://rapidshare.de/files/20920525/VON_BAECKMANN__W.__1997_._Handbook
_of_Cathodic_Corrosion_Protection__3rd_ed._.rar
or
http://www.filefactory.com/file/cccb04/n/0884150569_zip
or
http://ifile.it/hau9eow

Impress Current Layout for Pipe-line

2009-07-27T04:50:00.000+01:00

Cathodic protection by impressed current
Source: http://www.daviddarling.info/encyclopedia/C/AE_cathodic_protection.html

Presented in The 6th International Conference on Numerical Analysis in Engineering (NAE) 2009, May 15-16, Lombok Island, Mataram, Indonesia

2009-07-24T10:11:00.000+01:00

NAE 2009 Lombok - Safuadi and Syarizal Fonna

Presented in Indonesia’s Anti-Corrosion Days 2008, INDOCOR, 4 December 2008, Borobudur Hotel, Jakarta, Indonesia

2009-07-23T09:24:00.000+01:00

Safuadi and Syarizal Fonna- IACD 2008