Luo department of chemical and materials engineering, university of alberta, edmonton, alberta t6g 2g6, canada abstract the roles of dissolved hydrogen in material and anodic dissolution in the nearneutral ph stress corrosion cracking scc process of a pipeline steel was investigated. Lowph scc or near neutral ph on the outer surface of pipelines is associated with specific soil conditions at free corrosion potential, where cathodic protection is ineffective. Abstract near neutral also termed low ph transgranular cracking of line pipe steels has been recognized as distinct from socalled high ph or classical pipeline scc since the mid1980s. That is to say, scc of pipeline steels is mixcontrolled by anodic dissolution ad and hydrogen embrittlement he. Weixing chen, an overview of nearneutral ph stress corrosion cracking in pipelines and mitigation strategies for its initiation and growth, corrosion. Transgranular stress corrosion cracking of highpressure. Near neutral ph stress corrosion cracking nonclassic type a near neutral ph scc environment appears to be a dilute groundwater containing dissolved co 2. Near neutral ph stress corrosion crack initiaion under simulated coating disbondment. As such, the newly discovered form of scc is equally referred to as transgranular scc or nearneutral ph scc. Instances of tgscc have been associated with dilute solutions with ph values in the region of 6. The effect of hydrogen on the stress corrosion cracking scc for x70a and x70b pipeline steels in near neutral ph environments was studied by monotonic tensile tests on slow strain rate tests ssrt machine and cyclic tests on ssrt machine and fatigue machine.
Combined effect of alternating current interference and. It was found from the ssrt results that the initiation stress decreased with the decrease in the potential from 790mvsce to 950mvsce. Nearneutral ph stress corrosion cracking nonclassic type a nearneutral ph scc environment appears to be a dilute groundwater containing dissolved co2. The exposure conditions involved hydrocarbon fluids following an initial hydrotest.
Stress corrosion cracking of x70 pipeline steel in near neutral ph. Scc in pipelines is a type of environmentally assisted cracking eac. Influence of strain rate on the stress corrosion cracking of x70 pipeline steel in dilute nearneutral ph solutions b. Jul 17, 2017 near neutral ph stress corrosion cracking nonclassic type a near neutral ph scc environment appears to be a dilute groundwater containing dissolved co 2. In the case of near neutralph scc, the cracking environment. Corrosion susceptibility of peened friction stir welded 7075 aluminum alloy joints.
Investigating a mechanism for transgranular stress. Investigating the mechanism of stress corrosion cracking. A method for predicting the location of stress corrosion cracking in a steel gas pipeline in which in line stress corrosion cracking smart tool data, external low level metal loss data and soil characterization data are compiled to predict the location of stress corrosion cracking in a steel gas pipeline segment. The crack that caused the release was determined to have propagated due to corrosion fatigue that progressed from an area of nearneutral ph stress corrosion cracks. No matter how well these pipelines are designed, constructed and protected, once in place they are subjected to environmental abuse, external damage, coating disbondments, inherent mill. Corrosion fatigue and nearneutral ph stress corrosion. This paper provides an overview of mechanisms for highph and nearneutral ph stress corrosion cracking of underground pipelines.
Cracking rates were studied at a range of frequencies and rvalues. Cepa recommended practices for managaing nearneutral ph scc 1 of 158 3rd edition, may 2015 executive summary this 3rd stedition of the cepa recommended practices for stress corrosion cracking builds on the 1 and 2nd editions published in 1999 and 2007, respectively. Rogge, the role of residual stress in neutral ph stress corrosion cracking of pipeline steels. Review of stress corrosion cracking of pipeline steels in.
Different electrochemical techniques have been used to estimate the risk of the scc. Lowph scc occurs in the presence of dilute ground waters containing free carbon dioxide co 2 having a. Nearneutral ph stress corrosion cracking of pipelines. In the nearneutral ph solution, both dissolution of the steel and hydrogen ingress into the steel are acknowledged to be involved in the scc process of pipeline steels 38,39,40. The earliest cracks to appear initiated at corrosion pits that formed around nonmetallic inclusions, and later cracks grew from corrosion p its that formed randomly on the surface. Mechanisms of highph and nearneutralph scc of underground. Influence of strain rate on the stress corrosion cracking of x70 pipeline steel in dilute near neutral ph solutions b. High ph scc of carbon steel pipelines can occur in a highly concentrated bicarbonatecarbonate hco 3 co 3 2 solution with high ph.
The crack that caused the release was determined to have propagated due to corrosion fatigue that progressed from an area of near neutral ph stress corrosion cracks. Abstract near neutral ph scc has been one of the major remaining concerns to pipeline safe operation. Ke assessment of stress corrosion cracking and hydrogen embrittlement susceptibility of buried pipeline steels a. Abstract nearneutralph scc has been one of the major remaining concerns to pipeline safe operation. King f 2010 stress corrosion cracking of carbon steel used fuel. Scc crack propagation nearneutral ph solution does not occur under constant. Although intergranular stress corrosion cracking igscc of highpressure gas pipelines has been known for more than 20 years, a transgranular form tgscc was detected more recently. In the case of near neutral ph scc, the undercoating water can contain dissolved carbon dioxide that. Abstract nearneutral also termed low ph transgranular cracking of line pipe steels has been recognized as distinct from socalled highph or classical pipeline scc since the mid1980s. The electrolyte was very dilute brine bubbled with 10% carbon dioxide. Effect of potential on scc initiation for pipeline steel. The pitting occurred in the absence of chlorides at a near neutral ph where aluminum would be expected to. May, 2018 near neutral ph stress corrosion cracking nonclassic type a near neutral ph scc environment appears to be a dilute groundwater containing dissolved co2.
Research on stress corrosion cracking scc of welded line pipe steel can contribute knowledge that is important in establishing pipeline integrity. Nearneutral ph stress corrosion cracking nonclassic type a nearneutral ph scc environment appears to be a dilute groundwater containing dissolved co 2. Environmentally induced cracking of api grade steel in near. These recommended practices represent an overview of the methods used by cepa member companies to. Characteristics and historical information on both forms of cracking are discussed. Scc is highly chemically specific in that certain alloys are likely to undergo scc only when exposed to a small number of chemical environments. At the present time in china, there are plans to build. The severity of four different soil environments toward the development of nearneutral ph stress corrosion cracking scc of pipeline steel was evaluated using slow strainrate testing ssrt. Stress corrosion cracking scc is the growth of crack formation in a corrosive environment.
Marathon ashland pipe line llc mapl experienced a pipeline release on january 27, 2000 from cracking in a bottomside shallow deformation. This paper investigates mechanistically stress corrosion cracking scc of an x70 pipeline steel that is under cathodic protection cp in a nearneutral ph solution. In the case of near neutral ph scc, the cracking environment. These recommended practices represent an overview of the methods used by cepa member companies to manage near. A mechanistic study on nearneutral ph stress corrosion. With the superimposition of ac current 110 macm2, the direct current dc potential shifts. Characteristics of nearneutralph stress corrosion cracks. Abstract nearneutralph scc has been one of the major remaining concerns. It has been found that low ph scc occurs in environments with a low concentration of. A method for predicting the location of stress corrosion cracking in a steel gas pipeline in which inline stress corrosion cracking smart tool data, external low level metal loss data and soil characterization data are compiled to predict the location of stress corrosion cracking in a steel gas pipeline segment. Mechanistic aspect of nearneutral ph stress corrosion.
When stainless steels are fully immersed, it is rare to see chloride stress corrosion cracking at temperatures below 60 c 150 f. The buried pipelines experienced two forms of stress corrosion cracking scc, i. Experimental and theoretical approaches towards the study on mechanism of stress corrosion cracking scc of pipeline steels in nearneutral ph environment have been performed. Some factors affecting initiation of stress corrosion.
Cyclic tests of stresscorrosion cracks in steel gas pipelines with. The relationship between inclusions and stress corrosion cracking is investigated by ssrt test and sem observation of the side surface morphologies. Corrosionpedia what causes stress corrosion cracking in. Causes of stress corrosion cracking in pipelines ducorr. Effect of co2 on nearneutral ph stress corrosion cracking. As such, the newly discovered form of scc is equally referred to as transgranular scc or near neutral ph scc. Mechanical and environmental effects on stress corrosion cracking scc susceptibility of x52 pipeline steel were investigated using slow strain rate tests ssrt performed in a glass autoclave. It was found that there is a critical potential range, i.
Electrochemical noise for detection of stress corrosion. Characteristics of nearneutralph stress corrosion cracks in an x. Deterioration by clscc can lead to failures that have the potential to release stored energy andor hazardous substances. In air, the macro fracture shows apparent necking deformation and the. Stress corrosion cracking of pipeline steels in nearneutral ph. What causes stress corrosion cracking in pipelines. The source of the co2 is typically the decay of organic matter and geochemical reactions in the soil. The results showed that scc intensity increased at high cathodic protection potential. It can lead to unexpected sudden failure of normally ductile metal alloys subjected to a tensile stress, especially at elevated temperature.
In order to improve our understanding of its initiation mechanism a comprehensive testing setup was used in this study. Hydrogen in stress corrosion cracking of x70 pipeline. Fatigue crack growth modelling for pipeline carbon steels under gaseous. The effect of applied potential on the stress corrosion cracking scc initiation of x70 pipeline steel in near neutral ph solution has been investigated by using a slow strain rate testing ssrt apparatus and electric potential drop epd method. Influence of alternating current ac on pitting corrosion and stress corrosion cracking scc behavior of x70 pipeline steel in the nearneutral ph environment under cathodic protection cp was investigated.
The effect of applied potential on the stress corrosion cracking scc initiation of x70 pipeline steel in nearneutral ph solution has been investigated by using a slow strain rate testing ssrt apparatus and electric potential drop epd method. Colonies of stress corrosion cracks are often seen around weld heataffected zones hazs in pipelines that are operating in the field in contact with near neutral ph nnph environment. This information is then used to support proposed mechanisms for. Stress corrosion cracking behavior of pipeline steels in. Stress corrosion cracking of pipeline steels in near neutral ph solutions.
Environmentinduced cracking of materials 1st edition. Role of stress in transgranular stress corrosion cracking of transmission pipelines in nearneutral ph environments. Influence of inclusions on initiation of pitting corrosion. Colonies of stress corrosion cracks are often seen around weld heataffected zones hazs in pipelines that are operating in the field in contact with nearneutral ph nnph environment. Chapters 3 and 5 were also submitted for publication. Chloride stress corrosion cracking in austenitic stainless. Mechanistic studies on stress corrosion cracking of. This research is aimed at understanding nearneutral ph scc initiation under disbonded coatings of pipeline steels, and the effect of different environmental and operational factors on crack initiation. For high ph stress corrosion cracking, it is well accepted that the. The subject of the investigations included scc susceptibility at various testing conditions, hydrogen distribution around scc crack tip and the role of hydrogen in cracking process. Proceedings of the 2018 12th international pipeline conference.
This information is then used to support proposed mechanisms for crack initiation and growth. Stress corrosion cracking scc tests were conducted on american petroleum institute api grade x70 line pipe steel using smooth. A mechanistic study on nearneutral ph stress corrosion cracking of pipeline steel. Experimental and theoretical approaches towards the study on mechanism of stress corrosion cracking scc of pipeline steels in near neutral ph environment have been performed. The source of the co 2 is typically the decay of organic matter and geochemical reactions in the soil. Some factors affecting initiation of stress corrosion cracking of an x80 pipe steel in near neutral ph environment.
This research is aimed at understanding near neutral ph scc initiation under disbonded coatings of pipeline steels, and the effect of different environmental and operational factors on crack initiation. When cyclic loading was applied in the stress corrosion cracking initiation. Ke assessment of stress corrosion cracking and hydrogen embrittlement susceptibility of buried pipeline. In laboratory tests, nearneutral ph scc cannot in general be reproduced unless. Cepa recommended practices for managaing near neutral ph scc 1 of 158 3rd edition, may 2015 executive summary this 3rd stedition of the cepa recommended practices for stress corrosion cracking builds on the 1 and 2nd editions published in 1999 and 2007, respectively.
Stress corrosion cracking of pipeline steels in nearneutral ph solutions. Stress corrosion life and corrosion potential the entire stress corrosion test carried out under a constant load of 90% of the yield stress 206. The localized pitting corrosion was produced in aluminum floats on a storage tank roof. As has been proved by our previous work 77,78, x70 steel displays scc susceptibility in the near neutral ph solution. Overview of a carbon steel container corrosion model for a deep. The dashed line represents the test result on the same test. An overview of nearneutral ph stress corrosion cracking.
The environmental factors that increase the cracking susceptibility include higher temperatures, increased chloride content, lower ph, and higher levels of tensile stress. The mhanisms of scc m the nearneutral ph solutions were proposed based on the andysis of the results from ssrt. In the case of nearneutral ph scc, the undercoating water can contain dissolved carbon dioxide that. This paper provides an overview of mechanisms for high ph and near neutral ph stress corrosion cracking of underground pipelines. The severity of four different soil environments toward the development of near neutral ph stress corrosion cracking scc of pipeline steel was evaluated using slow strainrate testing ssrt. A mechanistic study on nearneutral ph stress corrosion cracking of pipeline steel b. As has been proved by our previous work 77,78, x70 steel displays scc susceptibility in the nearneutral ph solution. Fatigue crack initiation on lowcarbon steel pipes in a. Role of stress in transgranular stress corrosion cracking. The effect of hydrogen on the stress corrosion cracking scc for x70a and x70b pipeline steels in nearneutral ph environments was studied by monotonic tensile tests on slow strain rate tests ssrt machine and cyclic tests on ssrt machine and fatigue machine.
Stresscorrosion cracking of steels in ammonia with. Cepa recommended practices for managing near neutral ph. Nearneutral ph stress corrosion crack initiaion under simulated coating disbondment. No matter how well these pipelines are designed, constructed and protected, once in place they are subjected to environmental abuse, external damage, coating disbondments, inherent mill defects, soil movementsinstability and third party damage. Chloride stress corrosion cracking clscc is one the most common reasons why austenitic stainless steel pipework and vessels deteriorate in the chemical processing and petrochemical industries. The effect of the ph of ammonum nitrate solution on the. The pitting occurred in the absence of chlorides at a near neutral ph where aluminum would be expected to exhibit good resistance to corrosion. While there is general agreement on a role for hydrogen in th.
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