Jul 16, 2011 continue monitoring for scc while managing integrity for other issues such as corrosion. 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. Stress corrosion cracking of pipeline steels in nearneutral ph solutions. Characteristics of nearneutralph stress corrosion cracks in an x.
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. Stress corrosion cracking of x70 pipeline steel in near neutral ph. Tests were performed by slow strain rate testing at 90 c and at 60 c. Mechanisms of highph and nearneutralph scc of underground. 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. Us70249b1 method for detecting near neutrallow ph stress. Stress corrosion cracking of x80 pipeline steel in nearneutral ph environment under constant load tests with and without preload. Stress corrosion cracking scc in nearneutral ph environment remains a major concern for high pressure pipelines transporting oil and gas in canada since its first discovery in 1980s. The role of stress in the scc of linepipe steels in near neutral ph environment, as in other scc systems, is complex. This paper describes results of an ongoing research program investigating crack growth of api x65 and x52 line pipe steels in a low ph cracking environment using a jintegral technique. Corrosion fatigue and nearneutral ph stress corrosion cracking of pipeline steel and the effect of hydrogen sulfide article pdf available in corrosion houston tx 612 february 2005. 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.
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. 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. Intergranular stress corrosion cracking scc of pipelines has been known to cause pipeline failure since the 1960s and is associated with a high ph, above 9, in the electrolyte in direct contact with the external pipe surface. Effect of co 2 on nearneutral ph stress corrosion cracking.
Nearneutral ph scc usually occurs under polyethylene tape pe tape coated pipelines, at locations where the coating becomes disbonded andor damaged. Cepa recommended practices for managing near neutral. Environmental effects on the susceptibility and crack. The ph of the test solutions were kept near neutral by addition of 10 mm phosphate buffer of ph 7. Stress corrosion cracking of x80 pipeline steel in nearneutral ph. Nearneutral ph scc this type of transgranular cracking mode of scc was initially.
Stress corrosion cracking scc is the growth of crack formation in a corrosive 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. Such cracks grow over time and can ultimately lead to pipeline failure. Scc in pipelines is further characterized as high ph scc or nearneutral ph scc. Environmental effects on nearneutral ph stress corrosion cracking in pipelines w. It can lead to unexpected sudden failure of normally ductile metal alloys subjected to a tensile stress, especially at elevated temperature. Abstractstress corrosion cracking scc tests were conducted on american petroleum institute api grade x70 line pipe steel using smooth. The ph was maintained nearneutral in the lab tests by continuous purging of the test solution with co2n2. Near neutral ph stress corrosion crack initiaion under simulated coating disbondment. An overview of nearneutral ph stress corrosion cracking in. Mechanistic studies on stress corrosion cracking of pipeline.
It was demonstrated in this investigation that ssrt can differentiate the severity of various soil. Environmental aspects of nearneutral ph stress corrosion cracking. 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. These soils were collected from pipeline sites where near neutral ph scc has been observed. The environmental factors that increase the cracking susceptibility include higher temperatures, increased chloride content, lower ph, and higher levels of tensile stress.
Integrity management of stress corrosion cracking in gas. A variety of laboratory experiments and models have been developed to address different aspects of this complex problem. Environmental effects on the susceptibility and crack growth. Stress corrosion cracking of x70 pipeline steel in near. This paper is aimed at providing an overview of stress corrosion cracking scc of pipeline steels exposed to nearneutral ph environments and corresponding integrity strategies being developed based on the understanding of the cracking mechanisms determined. In the preassessment step, allied corrosion or the owneroperators personnel will collect historical and current data for the purposes of analyzing and prioritizing the threat of stress. Fullscale stress corrosion crack growth testing of an x70 spiral. Transgranular stress corrosion cracking of highpressure pipelines in contact with solutions of near neutral ph r. This paper is aimed at providing an overview of stress corrosion cracking scc of pipeline steels exposed to near neutral ph environments and corresponding integrity strategies being developed based on the understanding of the cracking mechanisms determined.
Stress corrosion cracking of natural gas pipelines in lowph environments is a serious problem for the gas transmission industry. 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. We are now pleased to make our report to the board pursuant to section 15 of the. Near neutral ph stress corrosion cracks nnph scc are developed under coating disbondments on the external surface of pipelines where the surface of pipeline is exposed to the soil solution. When stainless steels are fully immersed, it is rare to see chloride stress corrosion cracking at temperatures below 60 c 150 f.
Standard practice for use of mattssons solution of ph 7. Stress corrosion cracking of x70 pipeline steel in near neutral ph solution subjected to constant load and cyclic load testing. This paper is aimed at providing an overview of stress corrosion cracking scc of pipeline steels exposed to nearneutral ph environments and corresponding. Understanding the effects of hydrogen, hydrostatic testing. Stress corrosion cracking of linepipe steels in near neutral. Sutherby b a department of chemical and materials engineering, university of alberta, edmonton, canada b transcanada pipeline limited, calgary, canada abstract stress corrosion crack scc growth mechanisms in pipeline steels exposed to near neutral ph environments are not well. The original 1997 cepa stress corrosion cracking recommended practices hereafter referred to as the practices were prepared and made public by cepa in response. Environmental effects on nearneutral ph stress corrosion. Near neutral ph stress corrosion cracking nnphscc, which occurs when ground water penetrates under the pipe coating, causes longitudinal cracks to develop on the surface of pipelines.
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. Pdf corrosion fatigue and nearneutral ph stress corrosion. Delanty introduction the majority of instances of stress corrosion cracking scc in highpressure gas pipelines has been associated with the propagation of intergranular cracks. Abstract over the past fifteen years, field dig programs have identified specific soil environments that are particularly potent in promoting near neutral ph scc of underground pipelines coated with polyethylene tape.
Environmental aspects of nearneutral ph stress corrosion. Intergranular stress corrosion cracking scc of pipelines has been known to cause pipeline failure since the 1960s and is associated with a high ph, above 9, in the. Characteristics of nearneutralph stress corrosion cracks. This research is aimed at understanding nearneutral ph scc. 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. Sutherby b a department of chemical and materials engineering, university of. Stress corrosion cracking of natural gas pipelines in low ph environments is a serious problem for the gas transmission industry.
Nnph scc initiation and early stage of growth is mainly governed by the dissolution process of steel. Prioritization of scc susceptible pipeline segments is performed utilizing the following factors. An overview of nearneutral ph stress corrosion cracking. 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. Growth of surfacetype stress corrosion cracks in near. Nearneutral ph stress corrosion crack initiation under. Nearneutral ph stress corrosion cracking susceptibility.
Abstract nearneutral 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. Cepa recommended practices for managaing nearneutral ph scc 1 of 158 3rd edition, may 2015 executive summary this 3rd stedition of the cepa recommended. Stress corrosion cracking scc in nearneutral ph environment remains a major concern for high pressure pipelines transporting oil and gas. Du and coworkers investigated the influence of ac on the stress corrosion cracking scc behavior of pipeline steels in high ph and nearneutral ph solutions. Rosen 15 types of pipeline cracks inspection solutions. Highph and nearneutral ph scc of pipelines rosen group. Continue monitoring for scc while managing integrity for other issues such as corrosion. While there is general agreement on a role for hydrogen in th. This paper describes results of an ongoing research program. Stress corrosion cracking scc, a form of environmentassisted cracking, has caused 24 major pipeline failures in the canadian oil and gas pipeline system. Cepa recommended practices for managing near neutral ph.
Effect of potential on scc initiation for pipeline steel. 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. What causes stress corrosion cracking in pipelines. Environmentally induced cracking of api grade steel in near neutral ph soil environmentally induced cracking of pipeline steels in contact with soil have been investigated. Stress corrosion cracking, underground pipeline, pressure fluctuation, hydrostatic testing, near neutral ph overview currently, there is a poor understanding of the effects of pressure related parameters operating pressure, pressure fluctuations, and hydrostatic testings on external stress corrosion crack propagation in pipelines in. Stress corrosion cracking of linepipe steels in near. Corrosion fatigue and nearneutral ph stress corrosion cracking of pipeline steel and the effect of hydrogen sulfide article pdf available in corrosion houston tx 612 february 2005 with. The two patches can be characterized as containing either dense cracks or sparse cracks, based on their spatial separation. The environment primarily responsible is diluted groundwater containing dissolved co2. Fullscale stress corrosion crack growth testing of an x70. Corrosion fatigue and nearneutral ph stress corrosion. Abstract the application of strainbased design for pipelines requires comprehensive understanding of the postyield mechanical behavior of materials. Environmentally induced cracking of api grade steel in near. Effect of co2 on nearneutral ph stress corrosion cracking.
Stress corrosion cracking in pipelines sciencedirect. Environmentally induced cracking of api grade steel in. In the case of near neutral ph scc, the cracking environment. Initiating near neutral ph scc in the laboratory under stressing conditions that are representative of those on an operating gas pipeline has proven very difficult. Abstract the environmental effects on the susceptibility and crack growth of nearneutral ph stress corrosion cracking scc were characterized using mechanical testing, hydrogen. Stress corrosion testing of copper in near neutral sulfide. Abstract the environmental effects on the susceptibility and crack growth of near neutral ph stress corrosion cracking scc were characterized using mechanical testing, hydrogen permeation and potential drop measurements. Abstract nearneutral ph scc has been one of the major remaining concerns to pipeline safe operation. Effect of potential on scc initiation for pipeline steel in. All existing crack growth models were developed based on the results obtained from tests either under constant load for the case of scc or under constant stress.
Near neutral ph scc usually occurs under polyethylene tape pe tape coated pipelines, at locations where the coating becomes disbonded andor damaged. Different soils were prepared in order to determine their physical, chemical and bacteriological characteristics. A18308 integrity management of stress corrosion cracking in gas pipeline high consequence areas has been added to your cart. Scc in pipelines is further characterized as high ph scc or near neutral ph scc. The above mentioned results of tensile tests of miniaturized samples fig. Nearneutral ph stress corrosion cracking nnphscc, which occurs when ground water penetrates under the pipe coating, causes longitudinal cracks to develop on the surface of. Note that the ph here refers to the environment on the pipe surface at the crack location, not the ph of the soil itself. Note that the ph here refers to the environment on the. Instances of tgscc have been associated with dilute solutions with ph values in the region of 6. In this article, the impact of plastic prestrain on nearneutral ph stress corrosion cracking scc susceptibility of welded x70 steel was investigated with a slow strain rate tensile ssrt test.
In the preassessment step, allied corrosion or the owneroperators personnel will collect historical and current data for the purposes of analyzing and prioritizing the threat of stress corrosion cracking. Combined effect of alternating current interference and. Stress corrosion cracking of brass in ammonia solutions was carried out with guidelines given by astm standard g3798. Microstructural effect on nearneutral ph stress corrosion cracking.
Influence of strain rate on the stress corrosion cracking of x70 pipeline steel in dilute nearneutral ph solutions. Transgranular stress corrosion cracking of highpressure. Nearneutral ph stress corrosion crack initiaion under simulated coating disbondment. The ph of the test solutions were kept near neutral by addition of 10. Nearneutral ph stress corrosion cracks nnph scc are developed under coating disbondments on the external surface of pipelines where the surface of pipeline is exposed to the soil. Observations of corrosion product formation and stress. 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. Also, the environment at the bottom of a pit will become more acidic.
Ground water can then penetrate under the damageddisbonded coating, become trapped and form a suitable environment for corrosion and cracking. Environmentally induced cracking of api grade steel in nearneutral ph soil environmentally induced cracking of pipeline steels in contact with soil have been investigated. Stress corrosion cracking scc in near neutral ph environment remains a major concern for high pressure pipelines transporting oil and gas in canada since its first discovery in 1980s. Circumferential scc high ph or near neutral occurs where the environmental conditions are right and the peak stress in the pipe is axial. Lowph stress corrosion cracking of natural gas pipelines. Near neutral ph stress corrosion cracking assessment using bayesian network modeling. These recommended practices represent an overview of the methods used by cepa member companies to manage near. Two patches of nearneutral ph stress corrosion cracks scc, as developed on a pipeline steel during service, have been characterized. Stress corrosion cracking on canadian oil and gas pipelinesscc scc scc scc scc scc scc. No matter how well these pipelines are designed, constructed and protected, once in place they are subjected to. Axial stresses are usually created by the pipe bending to follow the ground profile or additional loads imposed by ground movement landslides, subsidence, etc.
1382 1428 1129 54 1045 1579 483 233 1187 1220 815 69 1111 1137 1050 675 759 388 256 290 745 781 973 793 30 1666 262 1638 189 1163 522 1471 1194 1396 1532 1021 218 1088 396 976 1138 708 1116 1400 390 1472 559 68