Stress corrosion cracking scc in engineering thermoplastics is commonly observed in the form of a microcrack colony within a surface layer. Stabilized austenitic stainless steels sss have since been widely used in the petroleum refining industry because of their resistance to sulphidic corrosion and polythionic acid stress corrosion cracking scc, as well as of their excellent strength and toughness. The model used to predict crack growth did not take into account all potential uncertainties in the predicted crack growth, which resulted in cracks. Four types of mechanically and chemically assisted cracking that may occur in industrial equipment include. Stress corrosion cracking led to pipeline explosion near. Stress corrosion cracking in polyethylene coatings of steel pipes todays approach to stress corrosion cracking in polyethylene coatings of steel pipes for standard applications in water and gas distribution systems merely considers the coating types featuring the low peeling resistance of the early editions of din 30670, i. While it is rare, formed parts can develop fractures after they are placed in service. Environmental stress cracking in polyethy lene takes place because of interlamellar failure, which in turn is caused by relaxation of tie molecules. Resistance to this mode of failure can be best gauged through constanttensileload testing, while taking into account the differences in. Scott freddie torres kapl4798 june 1994 prepared for the united states department of energy prepared by knolls atomic power laboratory p. The action of either a tensile stress or a corrosive liquid alone would not be. Stress corrosion cracking scc is a phenomenon experienced from time to time in stainless steels.
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. Stress corrosion cracking ptfe fittings and dip pipes. Hence, an important design factor for pe pipes became commonly known as environmental stress cracking resistance escr, which led to the development of mdpe. Mdpe exhibited excellent scg and stress crack resistance, and dominated pe pipe manufacture for 30 years until the development of bimodal hdpe pe100. Canadian cases have occurred in very specific conditions that exist in only a small proportion of the regions where pipelines operate.
Pipeline corrosion and cracking and the associated. Pipe subjected to this stress testing is coated with an active organic solvent, and twice the nominal pressure of the pipe is applied. Corrosion resistant pex pipe will not pit or stress corrode. Environmental stress corrosion cracking resistance of high. Circumferential stress corrosion cracking is a rare cause of pipeline leakage. Environmental stress cracking can take place through continuous crack growth or via a stepwise progressive mechanism of cracking and arrest, depending on the molecular structure of the plastic, the composition of the chemical agent, the level of stress, and other environmental conditions. Water entering the insulation and diffusing inward will eventually reach a region of dryout at the hot pipe or equipment wall.
Above 390 f, external stresscorrosion cracking is normally not experienced. Four factors, are required before stress corrosion cracking can occur. Field investigations have also confirmed that most of cracking took place at the pipe junction 3. Environmental stress cracking in polyethylene takes place because of interlamellar failure, which in turn is caused by relaxation of tie molecules. Water entering the insulation and diffusing inward will eventually reach a. Oct 21, 2016 circumferential stress corrosion cracking is a rare cause of pipeline leakage.
The nature of polyethylene pipe failure plasticstoday. 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. Corrosionpedia what is stress corrosion cracking scc. The stress required to cause cracking of stainless steel may result either from fabrication or operation or shutdown. This research taken an industrial focus, as a result, test methods were selected. The investigation found that the pipeline ruptured due to stress corrosion cracks on the outside surface of the pipe, and that the polyethylene tape coating applied to the exterior surface. Ultrasonic, external corrosion, stress corrosion cracking, scc, calibration. What causes stress corrosion cracking in pipelines. Highph scc failures of underground pipelines have occurred in a wide variety of. Westcoast energy had a stress corrosion cracking hazard management plan in place for the pipeline, but the extent of the existing cracking on the segment of pipe that ruptured was not identified. The individual crack propagation stage is critical in determining the lifetime of pipe.
The failures of water pipes were traced to two influences. The investigation found that the pipeline ruptured due to stress corrosion cracks on the outside surface of the pipe. After eight continuous hours, the pipe must show no. Compared to the life of the pipe when no corrosion is present, the basic role of the. Corrosion, as an electrolytic process, requires the presence of.
Kellan stress cracking test this test measures the strength of polyethylene pipe against active chemical reagents while the pipe is under stress. Stress corrosion cracking led to pipeline rupture in. Plastics fail due to stress that is applied over time. Stress cracking sc is recognized as one of the major concerns for high density polyethylene hdpe pipes.
Request pdf stress corrosion cracking in plastic pipes. Sc is a brittle failure that occurs at a stress level lower than the shortterm. Mar 04, 2020 the report says the explosion was caused due to stress corrosion cracking. Stress corrosion cracking led to canadian pipeline rupture, fire. A deterministic modeling of slow stress corrosion sc crack growth. 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. 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. Stress corrosion, also known as stress corrosion cracking, is a type of corrosion that occurs due to the simultaneous action of a corrodent and a sustained tensile stress. Exposure to outdoors environment causes surface oxidation. This thesis studies the resistance of hdpe pipeline materials to environmental stress corrosion cracking due to the exposure to asp chemicals. Steel is an affordable, strong, readily available, and wellunderstood material that. Stress corrosion cracking scc results from strongly coupled thermomechanochemical processes, and is sensitive to material composition and morphology. Ogf article canadas safety board finds stress corrosion. The cepa report on circumferential stress corrosion cracking.
Chlorinerich water can cause stress corrosion cracking, which causes cracks and breaks in the clamps and renders them ineffective, according to the suit. This mechanism is characterized by corrosion in the microscopic granular composition of a metals surface. Stress corrosion cracking led to pipeline rupture in prince. Thermoplastics like polyethylene and polypropylene are subject to environmental stress corrosion cracking when exposed to strong oxidizing acids such as sulfuric acid. However, in some instances, stabilized austenitic sss have been found to be susceptible to pitting, crevice. Experimental and theoretical investigation of stress. Aug 01, 2008 get a handle on stresscracking in hdpe bottles one of the first applications for blow molded hdpe bottles was the replacement of glass for bleach packaging. A jointstock enterprise, possessing a gross investment of rmb 82 million, registered capital of rmb 20 million. This type of failure is referred to as stress corrosion cracking scc. According to astm d883, stress cracking is defined as an external or internal crack in a plastic caused by tensile stresses less than its shortterm mechanical.
Experimental and theoretical investigation of stress corrosion crack scc growth of polyethylene pipes byoungho choi, alexander chudnovsky, rajesh paradkar, william michie, zhenwen zhou, pak meng cham. Metallic pipes form the backbone of cooling systems in nuclear power plants. Experimental and theoretical investigation of stress corrosion crack. Made of highdensity polyethylene hdpe, it stands up to freezethaw cycles and resists corrosion and stress cracking. For example, pipe coated with polyethylene material is shielded from cathodic. Environmental stress cracking esc is one of the most common causes of unexpected brittle failure of thermoplastic especially amorphous polymers known at present. Stresscracking resistance an overview sciencedirect topics. The term eac is used to describe all types of cracking in pipeline that is influenced by the environment and stress. Corrosion problems during oil and gas production and its. It is typically used in gravityflow drainage applications. Observation and modeling stress corrosion cracking scc in engineering thermoplastics is.
Mechanism of cathodic disbonding of threelayer polyethylene. It can lead to unexpected sudden failure of normally ductile metal alloys subjected to a tensile stress, especially at elevated temperature. Stresscracking resistance an overview sciencedirect. Figure 46 polyethylene tape helical tent cepa 1997. Experimental study of stress cracking in high density. Stress corrosion cracking scc is a common problem for polymers and composites that serve under a combination of mechanical stress and chemically aggressive environment. Scc occurs as a result of a combination between corrosion and tensile stress. In response, the board said, westcoast revised several aspects of its inspection practices and integrity management program for this pipeline. Epri looks at highdensity polyethylene for pipes in nuclear plants. It is generally not well understood, and can, given the right conditions, cause catastrophic failure. Plastic failure through environmental stress cracking. This vulnerability is more pronounced as both the temperature and concentration of the acid increases. Experimental and theoretical investigation of stress corrosion crack scc growth of polyethylene pipes.
Stress corrosion cracking scc results from strongly coupled thermomechanochemical. We are now pleased to make our report to the board pursuant to section 15 of the. As the designation indicates, the basic prerequisite for the occurrence of stress cracking is the presence of stresses. Corrosion is related to the susceptibility of the material to the environment, while stresses may be residual, external or.
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. Stress corrosion cracking cause of 2018 enbridge pipeline. According to astm d883, stress cracking is defined as an external or internal crack in a plastic caused by tensile stresses less than its shortterm mechanical strength. 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. Experimental study of stress cracking in high density polyethylene pipes a thesis submitted to the faculty of drexel university by jingyu zhang. Epri looks at highdensity polyethylene for pipes in. First, the part must be stressed, either from an applied force or due to residual stress usually from forming. Environmental stress crack resistance of polyethylene figure 2 astm f1473 the polyethylene notch tensile pent test this method is used in the united states to test pe pipe grade materials that exhibit high escr values, as this test generally provides more timely results. Stress cracking agents in process streams are not the only cause of scc. Stress corrosion cracking scc is a form of localized corrosion which produces cracks in metals by simultaneous action of a corrodent and tensile stress.
The tsb said although westcoasts stress corrosion cracking hazard management plan recognized stress corrosion, the extent of the existing cracking. Scc is highly chemically specific in that certain alloys are likely to undergo scc only when exposed to a small number of chemical environments. The report says the explosion was caused due to stress corrosion cracking. Stress corrosion cracking phenomena are not limited to polyethylene coatings of steel pipe. Stress corrosion cracking scc in engineering thermoplastics is commonly observed in the form of a microcrack colony within a surface layer of degraded polymer exposed to a combined action of mechanical stresses and chemically aggressive environment. A deterministic modeling of slow stress corrosion sc crack growth process is. In fact, the designs for polyvinyl chloride pvc and high density polyethylene hdpe pipes are based on stressregression or stressrupture curves that are plots of the time to failure under various levels of constant stress. Mar 04, 2020 the investigation found that the pipeline ruptured due to stress corrosion cracks on the outside surface of the pipe, and that the polyethylene tape coating applied to the exterior surface. Stress corrosion cracking is a form of environmental assisted cracking eac. Resistance to this mode of failure can be best gauged through constanttensileload testing, while taking into account the differences in yield point among various polyethylenes. All cases of circumferential scc, to date, have occurred under either polyethylene tape or a polyethylene backed shrink sleeve. A probabilistic modeling of scc initiation is briefly discussed.
Jan 18, 2011 hence, an important design factor for pe pipes became commonly known as environmental stress cracking resistance escr, which led to the development of mdpe. The ducts are smoothwalled pipes with diameters generally around 4. Stress corrosion cracking recommended practices canadian. Failure of 321 stainless steel heater tube in heavy crude oil. The duct and grout then form a double corrosionprotection system for the steel strands. It meets astm f667 specifications and testing requirements. The investigation found that the pipeline ruptured due to stress corrosion cracks on its outside surface. Pipeline corrosion and cracking and the associated calibration. Stress corrosion cracking of polyethylene practical. The geometry of the junction between liner and corrugation creates stress concentration when the pipe is subjected to tensile stress, inducing the likelihood of cracking.
The stress corrosion cracking resistance was measured on new pipes that complied with american petroleum institute api grade x70 with all the pipe lengths being manufactured from steel of the same heat number with the same nominal diameter of 406 mm and wall thickness of 8. Experimental study of stress cracking in high density polyethylene. May 18, 2016 thermoplastics like polyethylene and polypropylene are subject to environmental stress corrosion cracking when exposed to strong oxidizing acids such as sulfuric acid. While the cause of the scc resulted from a multitude of factors, there appeared to be a commonality relating to pipeline coatings. Following the occurrence, the tsb issued a pipeline safety advisory letter to westcoast energy inc. Water that escapes through the corroded fittings may also affect the pex stainless steal clamps. Stress corrosion cracking of gas pipelines effect of. The resulting flexible pipe has greater impact and tensile strengths, improved creep resistance, and performs extremely well at high temperatures and pressures. They have been observed in all products heat shaped from plastic materials.
Stress corrosion cracking scc is the growth of crack formation in a corrosive environment. In a pipeline environment when water comes in contact with steel there is potential for the minerals and gases to create an initial corrosion site that. Pipeline stress corrosion cracking scc corrosion doctors. Residual stresses and stress corrosion cracking in pipe fittings ronald j.