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GENERAL INTEREST
STRAY CURRENT CORROSION
AC CORROSION
CATHODIC PROTECTION (CP) |
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GENERAL INTEREST |
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| (10102) Can we Afford to Ignore Corrosion? |
In a recent editorial in the British Corrosion Journal, they referred to the objection of a councilor on Surrey County Council who objected to the provision of a £20,000 sterling laboratory to be associated with a new sewage disposal plant. He objected because he could not understand why anyone would want to play around with “it” and analyze “it’ when all they wanted to do was to get rid of “it”. For those who specialize in corrosion, it is difficult to realize that most industries are not as interested in understanding and analyzing their corrosion problems as they are in getting rid of them.
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| (10104) Corrosion: Costs, Causes, and Cures (February 1978) |
Corrosion is best defined as “the process by which a material, usually a metal, combines with certain elements within its environment to produce a product that does not retain the useful properties of the original material”. Unfortunately, this seemingly innocuous textbook definition does not convey the economic losses that result from corrosion damage. The minimum financial losses due to this “process” are well in excess of the combined annual costs of fires, floods hurricanes, tornadoes, and earthquakes in North America.
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| (10209) Remote Monitoring of Electrochemical Protection Systems in North America (November 1987) |
Use of electrochemical protection systems (Cathodic, Papritection, and Anodic) has significantly increased during the last decade. CP has been routinely installed on underground structures such as pipelines and storage tanks. However, the use of electrochemical protection system has now gained acceptance to protect the internal surfaces of expensive process vessels. These systems are extremely cost effective but have a common drawback in that periodic monitoring and minor maintenance is required.
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STRAY CURRENT CORROSION
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| (11403) Comparison and Optimization of Reverse Current Switches (March 1980) |
Reverse current electrolysis switches have been used for many years to minimize stray current corrosion damage to underground metallic structures. Various types of systems have been utilized with varying degrees of success. During the past 30 years, the power electronics industry has come of age resulting in new, more reliable, higher power devices for the corrosion engineer to utilize in the fabrication of reverse current switches. This paper will examine the need for such untis as well as compare and optimize their usage.
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| (11405) Evaluation of Telluric Current Effects on the Maritimes and Northeast Pipeline (October 1999) |
The Maritimes and Northeast Pipeline on the east coast of north America is being constructed through an area where large geomagnetic disturbances can be expected and where the electric fields produced will be amplified by the coast effect. In addition, the water movement associated with the rise and fall of tides in the Bay of Fundy (the highest tides in the world) will produce significant tidal electric fields. Because of these factors, it was decided to include consideration of telluric current effects in the design of the CP system for the new pipeline.
An evaluation was made of the electric fields expected to be produced by geomagnetic disturbances and the tidal dynamo. A computer model was also set up to examine the pipeline response to these electric fields. This allowed calculations of the pipe-to-soil potentials produced with different coating resistances and placement of insulating flanges and ground beds. The modeling capability allowed various cathodic protection schemes to be evaluated before construction and has resulted in a more cost effective CP design for the pipeline.
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| (11401) Electrical Interference on Underground Structures (November 2000) |
Interference can be defined as any electrical disturbance on a structure caused by a stray current. In this context, ‘stray’ refers to a current in an unintended path, although it is recognized that current will take all available paths in inverse proportion to the relative resistance of each available path.
Corrosion as a result of interference from a DC transit system was first reported by Stone & Forbes in 1894, just six years after the transit system began operation. Their paper was entitled ‘Electrolysis of Water Pipes’ and then term ‘electrolysis’ has persisted ever since to denote the corrosion attack on an underground structure caused by a stray current. Regional committees of underground utility representatives that were formed to discuss mutual electrical interference problems are called Electrolysis Committees.
Sources of stray current are any AC or DC systems that are grounded to the earth or use the earth as a current path. This includes both AC and DC power systems, cathodic protection systems, electrified transit systems, and telluric currents caused by the interaction of solar particles in the earth’s magnetic field.
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| (1406) Telluric Current Effects on Corrosion & Corrosion Control Systems on Pipelines in Cold Climates (February 2001) |
The impact of telluric current activity on the corrosion control systems on pipelines in northern regions and cold climates is examined. Three specific areas of concern are identified. These factors are corrosion of the pipe during positive cycles of the telluric disturbances, accurate measurement of cathodic protection performance parameters, and coating damage during negative cycles of the telluric activity. Corrosion rates are calculated versus the magnitude of the pipe potential change caused by discharging telluric current for different values of the Kp geomagnetic index. Methods of compensating and mitigating telluric current effects are discussed in the context of the cathodic protection design and monitoring procedures. The benefits of using potential controlled rectifiers and integrated reference/coupons in mitigating current effects are illustrated.
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| (1408) Telluric Compensation for Pipeline Test Station Survey (February 2003) |
Transient phenomena can significantly affect the accuracy of pipe-to-soil potential (PSP) measurements. This paper discusses two methods of improving the accuracy of CP test station survey measurements that have been affected by geomagnetically induced currents (GIC’s). The effectiveness of these techniques is explored in the context of two pipeline surveys totaling more than 1200km in length.
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| AC CORROSION
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| (10207) AC Corrosion – A New Challenge to Pipeline Integrity (March 1998) |
Corrosion of steel by alternating current was investigated as far back as the early 1900’s. These early studies and others in the 150-60’s indicated that AC corrosion of steel was only a fraction of an equivalent amount of direct current (i.e. less than 1% of a like amount of DC) and in addition was controlled to negligible levels when CP was applied to industry standards. In 1986, however, an investigation into a corrosion failure on a high pressure gas pipeline in Germany indicated that the sole cause of the failure was AC corrosion. This corrosion failure on an otherwise well protected pipeline resulted in the initiation of several laboratory and field studies which indicated, that above a certain minimum AC current density, normal levels of CP will not control AC corrosion to acceptable levels and that AC mitigation is often required to prevent serious corrosion. Several other AC corrosion sites were discovered at coating holidays during the follow-up investigations in Germany. A graph, relating AC voltage to holiday size at the minimum AC current density for corrosion, is presented to assist the pipeline operator in determining whether or not a pipeline is susceptible to AC corrosion activity.
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| (10208) AC Corrosion – Case Histories, Test Procedures, and Mitigation (March 1998) |
Literature dating back to the early 1960’s has shown that AC current can cause corrosion of cathodically protected steel under laboratory conditions. Until recently, however, there has been little evidence to suggest that AC corrosion of cathodically protected structures may be of practical concern.
In Ontario over the past six years, the authors have investigated several corrosion anomalies occurring on pipelines exposed to induced AC interference. This paper discusses a number of such cases where AC corrosion was suspected. The test procedures used to identify AC corrosion are discussed, as are some of the methods of minimizing the risks of AC corrosion.
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| CATHODIC PROTECTION (CP) |
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General
Watermains
Concrete Structures
Storage Tanks
Pipelines
Marine Structures
Transmssion Lines |
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| (11141) Comparison and Optimization of Alternative Energy Sources for Cathodic Protection (March 1979) |
To date, the majority of CP systems utilize either sacrificial anode or impressed current systems relying upon AC to DC rectifiers powered from the conventional electric power grid. In remote locations, however, many alternative energy sources have been used with varying degree of success. As the cost of conventionally derived electric power increases as a result of increasing fuel costs and as we move further from inhabited areas in the search for petrochemical reserves, the use of alternative energy sources becomes more viable as CP energy sources. Unfortunately, as everybody realizes, the equipment necessary to convert this energy to electricity is not necessarily inexpensive.
This paper is intended to establish an approximate cost per watt to convert the various alternative energy sources to electrical energy as compared to the powering of conventional CP systems from the electrical grid. This cost per watt should only be used as a guide in seeking the viability of a particular source. The main objective of this paper is to describe how to optimize the use of these relatively inexpensive systems to ensure all available power is used efficiently.
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| (11112) Cathodic Protection Criteria – A critical review of NACE standard RP-01-69 (March 1986) |
NACE recommended practice RP-01-69 contains criteria for the cathodic protection of steel structures in natural soil and water environments and these criteria have been widely accepted both by the owners of cathodically protected structures and by cathodic protection practitioners. Despite this, it has become increasingly apparent that many of the criteria as stated in the standard are in serious error with the fundamental science and in conflict with other standards and the interpretation of some regulatory agencies. Recent studies, which have appeared in the literatures, further confirm that the criteria require revision to ensure that only polarized potentials are used in the criteria and, furthermore, that potential measurements are corrected for IR drop error.
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| (11123) Economics of Cathodic Protection (June 1989) |
Cathodic protection is discussed in relation to the likelihood that its application will rest on economic considerations. Various methods are presented from the literature and a case is made for the use of the Equivalent Annual Cost Method together with several illustrations of its use.
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| (11139) Corrosion Control of Municipal Infrastructure Using Cathodic Protection (February 2000) |
Since its introduction in 1824, CP technology has developed to become a fundamental tool for preventing corrosion on municipal infrastructure. Potable water storage tanks and piping, pre-stressed concrete cylinder pipe, reinforced concrete structures, bridges, parking structures, underground fuel tanks, and effluent treatment clarifiers now benefit from this technology.
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| (11143) Quality Control and Data Auditing During Cathodic Protection Surveys (February 2003) |
Regulatory agencies in Canada’s oil and gas industry provide instructions for the monitoring frequency and criteria to be used for evaluating the performance of CP systems. Frequently, the actual monitoring of these systems is contracted out to third party service providers who may have divergent opinions of what constitutes an effective survey procedure. Incomplete current interruption, loss of rectifier synchronization, auto-rectification of induced AC voltages on pipelines, and lack of considering foreign current sources are only four survey difficulties than can make the difference between a valid and n erroneous CP survey. Modern equipment allows for effective consideration and evaluation of these potential difficulties, and also provides concrete documentation that allows the end user to audit the performance of their service provider. This paper provides information to end users with which to avoid the more common pitfalls that can invalidate CP protection pipe-to-soil potential survey data.
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| (11151) Technical considerations on the use of the 100mV cathodic polarization criterion (March 2007) |
The 100mV CP criterion is being using more extensively on piping in the soil and gas industry which has prompted a discussion on the limits of its use. This paper summarizes the technical literature on the validity of this criterion with respect to elevated temperature, sulfate reducing bacteria, mill-scale, type of metal, mixed metal structures, stress corrosion cracking, soil moisture, and AC corrosion.
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| (11125) Watermain Corrosion Control: Cost-benefit and Program Implementation (September 1988) |
This paper presents an economic model of a watermain, in terms of corrosion costs, as a tool for the waterworks engineer to assess the benefit of upgrading alternatives. The general effects of various upgrading alternatives are indicated using the model, and the steps for implementing a corrosion control program are outlined.
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| (11126) Watermain Corrosion Control: Cathodic Protection System Design (September 1989) |
This paper outlines the procedures used in designing a cathodic protection system for new or existing iron water piping. Both sacrificial and impressed current systems are discussed, and design examples for various applications of these systems are also given.
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| (11131) The Effect of Copper on the Corrosion of Iron Watermains (1990) |
The data obtained from several municipal watermain corrosion studies in the province of Ontario is presented. This data corroborates the findings of a previous study indicating that the galvanic couple formed by the connection of copper service piping to iron watermains is a principal factor controlling the watermain corrosion rates. Soil electrical resistivity is found to be of major importance only where this galvanic couple exists. A simple means of estimating the integrity of a watermain based on solid resistivity and service type is also presented.
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| (11132) A Summary of the Findings of Recent Watermain Corrosion Studies in Ontario (1991) |
This paper provides a summary of the statistical findings of several recent watermain corrosion studies conducted for municipalities in southern Ontario. External corrosion rates are correlated with soil resistivity, chloride ion concentrations, pH, watermain material, and galvanic factors. Internal corrosion rates are correlated with watermain age and diameter, and are compared to external corrosion rates. Case studies of watermain failure histories are also presented for three municipalities.
The paper shows that where copper service piping is used, soil resistivity is the only soil characteristic which has a significant effect on the external corrosion rates. The corrosion rates of watermains connected to lead, galvanized iron, or ductile iron service piping, on the other hand, are found to be relatively independent of soil characteristics. Failure rates of iron watermains connected to lead or iron service piping are found to be consistently lower than those associated with copper service piping.
Internal corrosion rates are found to decrease exponentially with time, with large diameter mains generally exhibiting higher rates than small diameter mains, but the amount of internal surface area pitted is found to increase with time. Internal corrosion is found to result in a greater total loss of metal than external corrosion, but maximum internal pit penetration rates are limited to values much less than the maximum external rates.
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| (11210) Performance Efficiency of High Potential Mg Anodes for Cathodically Protecting Iron Watermains (2004) |
The service life of Mg anode CP systems installed on iron watermains has, in some instances, been significantly less than design calculations would predict. Testing of high-potential Mg alloys from various suppliers using the ASTM G97-89 test method indicates that efficiencies are widely variable and that the life of an Mg anode could be as much as 90% less than calculated, depending on the source of the Mg. The literature shows that various factors such as anode current density, anode oxidation reaction, anolyte chemistry, alloy chemical composition, and alloy microstructure can affect anode efficiency. Municipalities are advised to conduct tests for allow composition, microstructure, and backfill composition on anode from industry suppliers in order to ensure anode quality and maximum system life.
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| (11302) A New Approach to Cathodic Protection of Bridge Decks and Concrete Structures (October 1978) |
Up to the present time, the CP of bridge decks has been accomplished by installing anodes on the concrete surface or recessed into the concrete and covered with a conductive paving layer to achieve current spread over the entire surface of the structure to be protected.
This paper outlines the tests that have been undertaken using a wire anode consisting of platinized niobium. This wire anode is installed in bridge decks in a sawed slot with conductive backfill and the tests to date indicated that with careful spacing of the anode wire, protection of the bridge structure can be achieved without the use of conductive paving layer. This eliminates to a great extent the cost of the conductive paving and other wear courses to protect the conductive paving layer.
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| (10103) Rebar corrosion can be stopped (July 1985) |
Staggering replacement costs - that could total hundreds of billions of dollars – are facing the U.S. because of the corrosion attack on steel reinforced concrete structures. The Federal Highway Administration (FHWA) estimates that 300,000 reinforced bridge decks currently need applied Cp to stop the corrosion that will otherwise continues, necessitating the eventual replacement of the bridges.
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| (11312) Evaluating the Performance of Conductive Coating Cathodic Protection Systems Applied to Reinforced Concrete Parking Decks (November 1991) |
It is clear from the case histories reported in this paper that a cathodic protection system when installed and operated according to existing standards can maintain low delamination growth rates and therefore has a significant economic advantage over many other presently popular repair strategies. The delamination survey case histories also provide confidence that CP of reinforcing steel in parking garages using conductive coatings applied to the soffit can be as effective as the CP systems installed on bridges over the last 15 years. Furthermore, the durability of conductive coating systems is now less doubtful since many of these systems have been operating reliably for several years.
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| (11308) Cathodic Protection of Ice Shields on the Northumberland Strait Confederation Bridge (March 1998) |
Issues considered during the design of an impressed current type cathodic protection (ICCP) system for corrosion control on the submerged external surfaces of the steel ice shields on the bridge piers are presented. The challenges and CP system design solutions, associated with providing protection to the underwater CP components against ice damage, are discussed. The ICCP system is described including the different CP equipment arrangements utilized, based on the various pier configurations and construction methods. Results of the system effectiveness are also discussed.
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| (11137) Corrosion Control for Underground and Surface Storage Tanks (May 1992) |
The corrosion causes and corrosion control options for surface storage tanks have been recently well documented. The installation of a cathodic protection system to arrest corrosion on the soil side surface of surface storage tanks can be accomplished at a fraction of the cost of a replacement tank bottom or the application of internal lining. Proper and comprehensive inspection by ultrasonic thickness testing is important in assessing the condition of the solid side surfaces. Even on severely corroded tank bottoms, the application of cathodic protection can extend the effective service life of that tank bottom indefinitely providing the cathodic protection system is properly designed, installed and maintained, The type of cathodic protection system which would be most effective depends on the number and size of tanks being protected, the nature of the soil conditions, and the operating temperature of the tank(s). New storage tanks having secondary containment liners which are also electrically insulating must have cathodic protection installed simultaneously with the tank because a retrofit installation would be economically prohibitive.
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| (11136) Cathodic Protection Potential Criterion for Underground Steel Structures (November 1993) |
This article traces the history and development of the -0.850 Vcse potential criterion used over the last 60 years with respect to thermodynamic considerations and empirical testing in both the laboratory and field. The significance of reference electrode position and IR-drop voltages for the protective potential measurement and the influences of soil resistivity, sulfate-reducing bacteria, and temperature on the effectiveness of the minimum potential value are reviewed. In addition, the hazards of overprotecting a steel structure with respect to hydrogen embrittlement and coating disbondment are considered.
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| (11138) Cathodic Protection of Surface Storage Tank Bottoms (June 1997) |
Soil side corrosion of surface storage tanks can be a serious problem. In many industries, the life of the tank is limited by external corrosion of the tank bottom. CP is a cost effective technique used to eliminate soil side corrosion and hence can indefinitely extend the life of the tank bottom and significantly increase the intervals between internal inspections as recommended in API653.
Many owners are now installing secondary containment when constructing new tankage. Most of the containment liners are fabricated from non-conductive materials that may prevent the application of cathodic protection unless specific components are installed concurrently with tank fabrication.
This paper will examine the corrosion mechanisms of tank bottoms as well as the various designs of CP systems with and without secondary containment.
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| (11140) Coating Quality Testing of Directionally Drilled Pipe Sections (February 2000) |
Methods of determining the coating quality on directionally drilled pipe sections were investigated in a research project sponsored by the Pipeline Research Committee of the American Gas Association. Tests were conducted on fusion bonded epoxy coated pipe samples which were buried in three different soil conditions and equipped with steel strip coupons to simulate coating damage. A field test procedure, which can be performed by a CP technician, was developed that estimates coating quality in terms of percentage bare.
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| (11142) Cathodic Protection Current Requirements for Electrical Grounding Materials (February 2003) |
Although cathodically protected pipelines are often connected directly to electrical ground in stations and plants, there is little information on the amount of current required to polarize various grounding materials such as copper, tinned copper, stainless steel, silicon iron, and galvanized steel. This paper presents results of short and long term CP tests on commercially available grounding materials buried in low resistivity clay and high resistivity sand. The results indicate that in the non-aerated clay all the grounding materials that would normally be cathodic to steel required the same or less current density than steel. In the more aerated sandy soil, the current requirements for all the cathodic materials as well as steel increased by at least 2 orders of magnitude with copper requiring an increase of 3 orders of magnitude. Packaged zinc and magnesium anodes were also included in the test since they are occasionally used as grounding electrodes for cathodically protected pipelines.
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| (11144) Advantages of Silicon Iron as an Alternative to Copper Grounding Electrodes – Impact on Cathodic Protection Systems (February 2004) |
Copper grounding has a detrimental effect on CP of interconnected underground carbon steel piping. The copper can consume large amounts of protection current as well as introducing significant measurement errors when verifying the protection level of the piping.
This paper examines the interactions between copper grounding and pipeline systems as well as a cost effective solution to the problem. An actual case study is presented confirming that silicon iron can be used to replace copper electrodes resulting in effective electrical grounding with minimal impact on CP systems.
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| (11147) Results from an ECDA plan (April 2005) |
Under an Integrity Management Program (IMP) for natural gas transmission lines, the ECDA concept was analyzed and the process was validated from 2002 to 2004. A plan was developed and implemented in 2004 on one 17 km pipeline and segments of two other pipelines. This paper covers the Request for Proposal (RFP) methodology, the selection of a service provider, the execution plan and the results obtained.
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| (11149) Use of an Integrated CIPS/DCVG Survey in the ECDA process (March 2006) |
The paper describes the theoretical and practical aspects of merging two indirect inspection tools (ie. Close Interval Potential Survey and DC Voltage Gradient) in one integrated survey, as used in 2004 during an ECDA project covering more than 21 km of gas pipelines in southern Ontario.
A method was developed and verified in the field to calculate the %IR at coating defects using the recorded data, with no need to interrupt the survey or to return at the defect location in order to measure the total gradient to remote earth.
The data processing was improved by deriving the longitudinal gradient profile from the CIPS data. This enhancement will be used in future surveys to validate indications, in conjunction with the measured lateral gradient data.
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| (11150) New Concepts in the Prioritization of Multiple ECDA Indications (March 2007) |
This paper describes the challenge of integrating specific types of ECDA indications, such as AC enhanced corrosion (ACEC) and DC interference (DCI), under the prioritization criteria recommended by NACE RP-05-02.
Starting from the observation that the risk of corrosion does not always increase with the size of the holiday, the paper analyzes the interaction of up to four complementary ECDA indications (ie. CIPS, DCVG, ACEC and DCI), with and without prior history of corrosion, as a function of their severity.
New concepts, such as “distributed indication” and “relevant indication”, are introduced in order to establish the location of the direct examinations, where the indication affects entire sections of line (ie. 10 km of line subject to severe ACEC).
Simple rules are proposed for integrating these multiple ECDA indications in matrix type prioritization tables. The paper also includes an example of using these tables to prioritize a combination of three indications without prior history of corrosion (ie. Moderate DCVG in conjunction with a severe DCI and a severe CIPS indication).
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| (11114) Control of Corrosion on Marine Structures: Protective Coatings and Cathodic Protection may 1985) |
This paper reviews the fundamental concepts of corrosion and corrosion control utilizing protective coatings and cathodic protection for mild steel piping in marine environments. Cathodic protection techniques and two types of coatings: flake glass polyester and coal tar epoxy are discussed. Practical applications for new construction and rehabilitation are described.
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| (11309) Use of Internal Impressed Current Cathodic Protection Aystems for CO² Corrosion Control in Offshore Separators (March 2000) |
Due to failure of internal coatings in the high pressure and test separators on offshore production facilities, the option to install an internal cathodic protection system was considered. The background to the system selection (covering literature review, discussions with operators, laboratory study and computer modeling) are described.
The initial concept was to install a sacrificial anode system based on high-temperature zinc alloys. However, the prolonged shutdown required to install nearly 3000kg of anodes in a high-pressure separator was not economically viable (due to deferred production costs). Hence, an impressed current system was designed. This required considerable engineering work to overcome objections on electrical safety grounds in the hazardous environment of an oil production facility. Detailed HAZOP studies were carried out and special protection systems incorporated to ensure safe operation.
The final system installed is described together with preliminary data from commissioning program.
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| (11208) Cathodic Protection of Transmission Line Towers (November 1993) |
This paper discusses some of the corrosion problems typically experienced by the underground portions of electrical transmission line towers, and examines cathodic protection as a method by which tower footing corrosion can be prevented. A case history of one power company’s cathodic protection experiences is also presented.
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