As its name suggests, scc takes the form of a network of cracks that eventually will lead to sudden, catastrophic failure in your tanks. Residual stresses and stress corrosion cracking in pipe fittings ronald j. Abstractstress corrosion cracking scc in steel gas pipelines has been experienced in many regions of the world and have been known to cause ruptures. The great majority of those failures have involved intergranular cracking, but more recently instances of transgranular cracking have been observed. This type of failure is known as stress corrosion cracking, often abbreviated to scc. A high chlorine peak was observed in both locations indicating high chloride levels.
Pdf stress corrosion cracking of pipelines alexander. Science and engineering of pipeline stress corrosion cracking. Structural failure due to scc can be very unpredictablefailure could occur after as little as a few hours of exposure, or the equipment could continue to function normally for. Stakeholder communications stress corrosion fact sheet.
Stress corrosion cracking of highstrength pipeline steels. Abstract a comparison is made of the characteristics of the two forms of stress corrosion cracking in pipelines, i. Stress corrosion cracking scc is the cracking induced from the combined influence of tensile stress and a corrosive environment. Definition of stress corrosion cracking form of corrosion susceptible material specific corrosive medium tensile stress. Stress corrosion cracking of pipelines researchgate. Scc occurs when the tensile stress and a specific environment are able to cause failure by their combined action, but are insufficient to cause failure by either one acting alone. Corrosion is related to the susceptibility of the material to the environment, while stresses may be residual, external or. Stress corrosion cracking in pipelines begins when small cracks develop on the external surface of buried pipelines. Corrosionpedia what is stress corrosion cracking scc. Stress corrosion cracking scc of pipelines, from the soil side, was first recognised over three decades ago j and has now been experienced in several countries throughout the world. Stress corrosion cracking scc is a fracture process that involves the combined and simultaneous action of a tensile stress and a corrosive environment. We have completed the public inquiry into stress corrosion cracking on canadian oil and gas pipelines in accordance with the boards terms of reference of 6 september 1995. The impact of scc on a material usually falls between dry cracking and the fatigue threshold of that material.
A closeup of the surface of a steel pipeline showing indications of stress corrosion cracking two clusters of small black lines revealed by magnetic. Explains why pipeline stress corrosion cracking happens and how it can be prevented. The inlaboratory degraded 17 1s and 60 pipeline steels tested in the s4 solution saturated ith 2 under open circuit potential revealed the susceptibility to stress corrosion cracking, reflected in the degradation of echanical properties, and at the sa e ti e the degraded 60 steel sho ed higher resistance to stress corrosion cracking than the. Mar 15, 20 stress corrosion cracking at pipeline welds. 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. Clusters of fine stress corrosion cracks on the external surface of buried steel natural gas pipelines in contact with groundwater have been examined and studied. Jul 16, 2011 there is a free corrosion condition below the coating that results in an environment with a ph around 5 to 7. Stress corrosion cracking by anodic dissolution and. Stress corrosion cracking by anodic dissolution and hydrogen.
Aluminum alloys that contain appreciable amounts of soluble alloying elements, primarily copper, magnesium, silicon, and zinc, are susceptible to stresscorrosion cracking scc. Stress corrosion cracking scc of pipeline steels has been studied extensively for 30 years. Throughout the book, the author develops a number of theoretical models and concepts based on advanced microscopic electrochemical. The sensitized structure is an indication of the materials susceptibility to intergranular corrosion andor cracking. There are field data that indicate that with a decreasing stress ratio there is an increased propensity for cracking. At the same time stress corrosion cracking has been identified as one of the predominant failures in pipeline steels in humid environments, which causes rupture of highpressure gas transmission. Our awareness of scc on the canadian pipelines we regulate began in 1985. Pipeline stress corrosion cracking scc over 98% of pipelines are buried.
The steel samples were immersed in an anaerobic dilute. Sections of pipe ejected from the crater as a result of. Stress corrosion cracking scc is cracking induced by the combined influence of tensile stress and corrosive environments. Stress corrosion cracking in a brewery paul mueller company. The required tensile stresses may be in the form of directly applied stresses or in the form of residual. Stress corrosion cracking scc is the growth of crack formation in a corrosive environment. Causes of stress corrosion cracking in pipelines stress corrosion cracking scc is a type of environmentallyassisted cracking eac, or the formation of cracks caused by various factors combined with the environment surrounding the pipeline. The final chapter is dedicated to effective management and mitigation of pipeline stress corrosion cracking. Tensile stresses may be directly applied residual, and the problem is often very complex.
Corrosion of underground natural gas and liquid petroleum pipelines occurs in a variety of forms and requires specialized mitigation methods to detect and control. Part one covers the mechanisms of scc and hydrogen embrittlement, while the focus of part two is on methods of testing for scc in metals. Explains why pipeline stress corrosion cracking happens and how it can be prevented pipelines sit at the heart of the global economy. The board says the rupture was due to stress corrosion cracks on the outside surface of the pipe. Stakeholder communications stress corrosion fact sheet phmsa. Recent gas pipeline rupture due to stress corrosion cracking. Scott freddie torres kapl4798 june 1994 prepared for the united states department of energy prepared by knolls atomic power laboratory p. There are several types of stress corrosion cracking scc, for example, chlorideinduced scc and h 2 sinduced scc. Also, scc is a major issue for steam generator tube integrity in many us pwrs. A corrosive medium especially chloridebearing or hydrogensulphide h 2 s media. Stress corrosion cracking led to canadian pipeline rupture, fire. The similarities, the differences and the influencing factors are considered for the high ph stress corrosion cracking caused by a concentrated bicarbonatecarbonate solution, and for the low ph stress corrosion cracking due to a diluter solution.
External stress corrosion cracking on pipelines shuler cox materials engineering unit. Stress corrosion cracking scc is the progressive cracking of metals and alloys caused by the combined effect of. Sep 15, 2014 stress corrosion cracking of gas pipelines 3 minute 2014 thesis finalist university of adelaide. Stress corrosion cracking of pipelines in acidic soil environments.
The combined effects of stress and corrosion can cause a special type of failure known as stress corrosion cracking scc. Pipeline stress corrosion cracking scc corrosion doctors. Scc results from the formation of cracks due to various factors in combination with the environment surrounding the pipeline that together reduces the pressurecarrying capability of the pipe. First, the part must be stressed, either from an applied force or due to residual stress usually from forming. The phenomenon of transgranular stress corrosion cracking is observed in buried pipelines operating in contact with diluted solutions under disbonded coatings. Stress corrosion cracking is a major issue for rcs system pipes particularly in the weld regions where it is connected to rpv nozzles through safe ends. Failures due to stresscorrosion cracking scc generally involve several adjacent, parallel, deep cracks that because of their proximity coalesce to form long flaws, which can cause ruptures. This has been demonstrated qualitatively for alloy 600 fittings by testing in high purity 400c steam and for stainless steel fittings by testing in boiling magnesium chloride. For any given environment, stresscorrosion cracking is possible only within a certain limited range of potentials. Stress corrosion cracking scc is characterized by cracks propagating either transgranularly or intergranularly along grain boundaries. Scc can affect materials in a number of ways, from dry cracking to catastrophic failure. An extensive failure analysis shows how many service failures occurred in the industry and what kind of alloys and stresses led to initiation and propagation of stress corrosion cracks which caused these service failures.
When they are in good working order, they deliver fuel to meet the evergrowing demand for energy around the world. Scc results from the formation of cracks due to various factors in combination with the environment surrounding the pipeline that together. Aug 28, 2015 stress corrosion cracking scc is the progressive cracking of metals and alloys caused by the combined effect of. Scc in pipelines is a type of environmentally assisted cracking. External corrosion of oil and natural gas pipelines. Stress corrosion cracking scc is a progressive fracturing that occurs in metals as a result of the combined influence of tensile stress and a corrosive environment. External corrosion of oil and natural gas pipelines john a. Ctlstress corrosion cracking of a stainless steel pipeline. Inhibition of stresscorrosion cracking of steel pipeline. Stress corrosion cracking of pipelines book chemistryviews. Scc is a form of corrosion that occurs in nearly all alloys, including the grades of stainless steel commonly used in brewery equipment types 304, 304l, 316, and 316l. We are now pleased to make our report to the board pursuant to section 15 of the. The primary cause of scc is the residual stress created in the component during manufacturing or fabrication. The general public is not aware of the number of pipelines.
Stress corrosion cracking industrial metallurgists. These cracks are not visible initially, but as time passes, these individual cracks may grow and forms colonies, and many of them join together to form longer cracks. The author explains how and why pipelines fall prey to stress corrosion cracking and then offers tested and proven strategies for preventing, detecting, and monitoring it in order to prevent pipeline failure. The growth rates of transgranular stress corrosion cracks have been modeled and determined by conducting laboratory tests under similar conditions to those recorded in practice. Lynch,defencescienceandtechnology organisation dsto,australia 1. Stress corrosion cracking of gas pipelines 3 minute 2014.
Stress corrosion cracking of gas pipeline steels of. Review of stress corrosion cracking of pipeline steels in. Cheng has provided an important service by writing this book, delivering a valuable source of knowledge and information on technologies for managing stress corrosion cracking and enhancing pipeline integrity. According to the electrochemical theory, this requires a condition along grain boundaries that makes them anodic to the rest of the microstructure so that corrosion propagates selectively along them. Feb 22, 2001 stress corrosion cracking scc defined. It was proposed that this kind of cracking is explained by the evolution and permeation of hydrogen at the crack tip, as observed in nuclear pressurevessel steels and other lowalloy steels. Quantitative residual stress measurements were performed on alloy 600. Stress corrosion cracking in pipelines sciencedirect. The observed crack propaga tion is the result of the combined and synergistic interaction of mechanical stress and corrosion re actions. Inclined stress corrosion cracks in steel pipelines.
Scc is highly chemically specific in that certain alloys are likely to undergo scc only when exposed to a small number of chemical environments. A pim program supports monitoring, inspection, and maintenance programs to reduce greatly the risk of failures that could cause disastrous consequences to human life, the environment, and business operations. Throughout the book, the author develops a number of theoretical. Causes of stress corrosion cracking in pipelines ducorr. Scc is a form of corrosion that produces a marked loss of pipeline strength with little metal loss. When they fail due to stress corrosion cracking, they can wreak environmental havoc. Stress corrosion cracking in aluminum alloys is characteristically intergranular. Mechanisms of stresscorrosion cracking asm international. This type of failure is referred to as stress corrosion cracking scc. Stress corrosion cracking in pipeline steels scientific.
Failures due to stress corrosion cracking scc generally involve several adjacent, parallel, deep cracks that because of their proximity coalesce to form long flaws, which can cause ruptures. I a factor used to describe the stress intensification of applied stress at the tip of a crack of known size and shape. What is stress corrosion cracking and why does it occur. 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. L51803 failure criterion for stresscorrosion cracking in. The original 1997 cepa stress corrosion cracking recommended practices hereafter referred to as the practices were prepared and made public by cepa in response to a the national energy board of canadas public inquiry mh295 into the problem of stress corrosion cracking scc in oil and gas pipelines.
This arises under specific circumstances for a given alloy. Thompson, cc technologies pipelines play an extremely important role throughout the world as a means of transporting gases and liquids over long distances from their sources to the ultimate consumers. Pdf stress corrosion cracking of gas pipeline steels of. Stress corrosion cracking of gas pipeline steels of different. What causes stress corrosion cracking in pipelines. Inhibition of stresscorrosion cracking can occur through more than one mechanism. Stress corrosion cracking can be defined as the interaction of a tensile stress and an aqueous environment acting on a susceptible metallic surface to initiate and propagate cracks. Stress corrosion cracking of gas pipelines 3 minute 2014 thesis finalist university of adelaide. Stress corrosion cracking facts and how to reduce the risk. Pipeline ruptures, though a rare event, generally stimulate much regulatory and public interest. 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. A cyclical load is critical for crack initiation and growth.
Stress corrosion cracking scc is a type of environmentallyassisted cracking eac, or the formation of cracks caused by various factors combined with the environment surrounding the pipeline. Potentialph diagram which demonstrates the regimes for intergranular and transgranular scc at 24 c in solutions containing different amounts of co2. First identified in the 1960s, stress corrosion cracking scc is a form of corrosion that results in clusters or colonies of cracks on the external surface of the affected pipeline. The combined influence of pipeline stress due to its pressurized contents and a corrosive medium can occasionally result in the formation of interlinking crack clusters that can grow until the affected pipe fails. Recent studies indicate that such multiple flaws cause a local increase in compliance as compared to a single crack that represents the largest of the cracks involved. Stress corrosion cracking cause of 2018 enbridge pipeline blast. Since the first discovery of stress corrosion cracking scc on the exterior surface of a buried high. Our recent studies have shown that an important factor of main pipelines serviceability loss under their longterm service is the inbulk metal degradation of the pipe.
1134 1506 460 882 141 118 320 1403 886 736 1084 13 539 1576 234 130 626 1172 625 1442 1312 1164 361 104 12 1036 378 108 187 804 562 598 2 822 1285 1324 538