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. The exposure conditions involved hydrocarbon fluids following an initial hydrotest. Stress corrosion cracking behavior of pipeline steels in. Effect of co2 on nearneutral ph stress corrosion cracking. Environmentally induced cracking of api grade steel in near. Cyclic tests of stresscorrosion cracks in steel gas pipelines with. Fatigue crack growth modelling for pipeline carbon steels under gaseous. Influence of strain rate on the stress corrosion cracking of x70 pipeline steel in dilute nearneutral ph solutions b. This information is then used to support proposed mechanisms for. The source of the co2 is typically the decay of organic matter and geochemical reactions in the soil. Near neutral ph stress corrosion cracking nonclassic type a near neutral ph scc environment appears to be a dilute groundwater containing dissolved co 2. Characteristics and historical information on both forms of cracking are discussed. Stress corrosion cracking of x70 pipeline steel in near neutral ph.
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. Abstract nearneutralph scc has been one of the major remaining concerns to pipeline safe operation. Experimental and theoretical approaches towards the study on mechanism of stress corrosion cracking scc of pipeline steels in nearneutral ph environment have been performed. 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. Ke assessment of stress corrosion cracking and hydrogen embrittlement susceptibility of buried pipeline steels a. Electrochemical noise for detection of stress corrosion. Influence of inclusions on initiation of pitting corrosion. The pitting occurred in the absence of chlorides at a near neutral ph where aluminum would be expected to exhibit good resistance to corrosion. It has been found that low ph scc occurs in environments with a low concentration of.
These recommended practices represent an overview of the methods used by cepa member companies to. These recommended practices represent an overview of the methods used by cepa member companies to manage near. 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. Nearneutral ph stress corrosion cracking nonclassic type a nearneutral ph scc environment appears to be a dilute groundwater containing dissolved co 2.
Effect of potential on scc initiation for pipeline steel. Mechanistic aspect of nearneutral ph stress corrosion. Causes of stress corrosion cracking in pipelines ducorr. High ph scc of carbon steel pipelines can occur in a highly concentrated bicarbonatecarbonate hco 3 co 3 2 solution with high ph. Nearneutral ph stress corrosion cracking of pipelines. In order to improve our understanding of its initiation mechanism a comprehensive testing setup was used in this study. Corrosionpedia what causes stress corrosion cracking in.
The environmental factors that increase the cracking susceptibility include higher temperatures, increased chloride content, lower ph, and higher levels of tensile stress. Stresscorrosion cracking of steels in ammonia with. In the case of near neutral ph scc, the cracking environment. 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. Rogge, the role of residual stress in neutral ph stress corrosion cracking of pipeline steels. 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. A mechanistic study on nearneutral ph stress corrosion cracking of pipeline steel. 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. 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.
While there is general agreement on a role for hydrogen in th. When cyclic loading was applied in the stress corrosion cracking initiation. 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. 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. As has been proved by our previous work 77,78, x70 steel displays scc susceptibility in the nearneutral ph solution. 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. In the case of nearneutral ph scc, the undercoating water can contain dissolved carbon dioxide that.
The relationship between inclusions and stress corrosion cracking is investigated by ssrt test and sem observation of the side surface morphologies. Characteristics of nearneutralph stress corrosion cracks in an x. As has been proved by our previous work 77,78, x70 steel displays scc susceptibility in the near neutral ph solution. Investigating the mechanism of stress corrosion cracking.
Hydrogen in stress corrosion cracking of x70 pipeline. 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. An overview of nearneutral ph stress corrosion cracking. Lowph scc occurs in the presence of dilute ground waters containing free carbon dioxide co 2 having a. Nearneutral ph stress corrosion cracking nonclassic type a nearneutral ph scc environment appears to be a dilute groundwater containing dissolved co2. 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. Deterioration by clscc can lead to failures that have the potential to release stored energy andor hazardous substances. This paper investigates mechanistically stress corrosion cracking scc of an x70 pipeline steel that is under cathodic protection cp in a nearneutral ph solution. It can lead to unexpected sudden failure of normally ductile metal alloys subjected to a tensile stress, especially at elevated temperature. 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. Environmentinduced cracking of materials 1st edition. In the case of near neutralph scc, the cracking environment.
Stress corrosion cracking scc tests were conducted on american petroleum institute api grade x70 line pipe steel using smooth. The mhanisms of scc m the nearneutral ph solutions were proposed based on the andysis of the results from ssrt. Mechanistic studies on stress corrosion cracking of. Scc in pipelines is a type of environmentally assisted cracking eac. The results showed that scc intensity increased at high cathodic protection potential. King f 2010 stress corrosion cracking of carbon steel used fuel. Nearneutral ph stress corrosion crack initiaion under simulated coating disbondment. Abstract near neutral ph scc has been one of the major remaining concerns to pipeline safe operation.
Environmentally induced cracking of api grade steel in. Cepa recommended practices for managing near neutral ph. In air, the macro fracture shows apparent necking deformation and the. 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 nearneutralph scc has been one of the major remaining concerns. 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. As such, the newly discovered form of scc is equally referred to as transgranular scc or nearneutral ph scc. Near neutral ph stress corrosion crack initiaion under simulated coating disbondment. For high ph stress corrosion cracking, it is well accepted that the. The buried pipelines experienced two forms of stress corrosion cracking scc, i. 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.
Proceedings of the 2018 12th international pipeline conference. The effect of the ph of ammonum nitrate solution on the. 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. 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.
When stainless steels are fully immersed, it is rare to see chloride stress corrosion cracking at temperatures below 60 c 150 f. Marathon ashland pipe line llc mapl experienced a pipeline release on january 27, 2000 from cracking in a bottomside shallow deformation. It was found that there is a critical potential range, i. Influence of strain rate on the stress corrosion cracking of x70 pipeline steel in dilute near neutral ph solutions b. Stress corrosion cracking of pipeline steels in nearneutral ph. 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. Stress corrosion cracking of pipelines begins with a brief introduction and then explores general principals of stress corrosion cracking, including two detailed case studies of pipeline failure.
Research on stress corrosion cracking scc of welded line pipe steel can contribute knowledge that is important in establishing pipeline integrity. 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. 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. Chapters 3 and 5 were also submitted for publication. 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. Weixing chen, an overview of nearneutral ph stress corrosion cracking in pipelines and mitigation strategies for its initiation and growth, corrosion. Stress corrosion cracking scc is the growth of crack formation in a corrosive environment. At the present time in china, there are plans to build.
Cracking rates were studied at a range of frequencies and rvalues. Investigating a mechanism for transgranular stress. 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. The pitting occurred in the absence of chlorides at a near neutral ph where aluminum would be expected to. It was found from the ssrt results that the initiation stress decreased with the decrease in the potential from 790mvsce to 950mvsce. 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. Ke assessment of stress corrosion cracking and hydrogen embrittlement susceptibility of buried pipeline. This paper provides an overview of mechanisms for highph and nearneutral ph stress corrosion cracking of underground pipelines. The localized pitting corrosion was produced in aluminum floats on a storage tank roof.
Combined effect of alternating current interference and. 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. Stress corrosion cracking of pipeline steels in near neutral ph solutions. Fatigue crack initiation on lowcarbon steel pipes in a. Characteristics of nearneutralph stress corrosion cracks. 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. This paper provides an overview of mechanisms for high ph and near neutral ph stress corrosion cracking of underground pipelines. 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. 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. The source of the co 2 is typically the decay of organic matter and geochemical reactions in the soil. Role of stress in transgranular stress corrosion cracking of transmission pipelines in nearneutral ph environments. The dashed line represents the test result on the same test. Chloride stress corrosion cracking in austenitic stainless.
Corrosion fatigue and nearneutral ph stress corrosion. Transgranular stress corrosion cracking of highpressure. The electrolyte was very dilute brine bubbled with 10% carbon dioxide. A mechanistic study on nearneutral ph stress corrosion. Overview of a carbon steel container corrosion model for a deep. Stress corrosion life and corrosion potential the entire stress corrosion test carried out under a constant load of 90% of the yield stress 206. In laboratory tests, nearneutral ph scc cannot in general be reproduced unless.
Corrosion susceptibility of peened friction stir welded 7075 aluminum alloy joints. Mechanisms of highph and nearneutralph scc of underground. Instances of tgscc have been associated with dilute solutions with ph values in the region of 6. 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. 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. Understanding the effects of hydrogen, hydrostatic testing. Role of stress in transgranular stress corrosion cracking. Stress corrosion cracking of pipeline steels in nearneutral ph solutions. Some factors affecting initiation of stress corrosion cracking of an x80 pipe steel in nearneutral ph environment.
With the superimposition of ac current 110 macm2, the direct current dc potential shifts. What causes stress corrosion cracking in pipelines. This information is then used to support proposed mechanisms for crack initiation and growth. That is to say, scc of pipeline steels is mixcontrolled by anodic dissolution ad and hydrogen embrittlement he. Some factors affecting initiation of stress corrosion. Scc is highly chemically specific in that certain alloys are likely to undergo scc only when exposed to a small number of chemical environments. 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. Different electrochemical techniques have been used to estimate the risk of the scc.
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