Abstract
This paper considers the factors influencing the formation and development of stress corrosion defects detected during the inspection and overhaul of the main gas pipeline section. The surveyed gas pipeline is made of large diameter steel pipes made by controlled rolling, produced by various companies, with the predominance of pipes produced by the Khartsyzsk Pipe Plant (KhPP). The correlation between the geometric parameters of defects is described, which makes it possible to estimate the depth of cracks by external parameters. Mechanical tests by cyclic loading of samples containing cracks, based on the site operation data for the last 11 years, showed no crack growth in the absence of a corrosive medium. Micro-X-ray spectral analysis of metal and corrosion products showed no trace of the influence of hydrogen sulphide and nonmetallic inclusions (sulphides) on the development process of SCC. According to the results of the research, the process of development of stress corrosion on the main gas pipelines located in the European part of the Russian Federation is described. The organization operating the gas pipeline is recommended to take into consideration the results of this work during drawing up their repair plan.
Highlights
More than a third (36%) of accidents occur on the main gas pipelines (MG) of the Unified Gas Supply System (UGSS) belonging to «Gazprom» PJSC as a result of the development of stress corrosion defects or stress corrosion
About 2,000 CWN defects were detected per year by methods of in-tube flaw detection (ILI) by magnetic shells; with the use of electromagnetic-acoustic projectiles (EMA) this figure reaches 10,000 defects per year [4]
The density of the SCC defect distribution detected by the nondestructive testing (NDT) during the overhaul was more than 97 times higher than expected by the results of the ILI
Summary
More than a third (36%) of accidents occur on the main gas pipelines (MG) of the Unified Gas Supply System (UGSS) belonging to «Gazprom» PJSC as a result of the development of stress corrosion defects or stress corrosion (hereinafter referred to as SCC). A large number of SCC defects are revealed by methods of nondestructive testing (NDT) in pits and during major overhauls. The absolute majority of defects detected by all inspection methods (almost 92%) have a measured depth of less than 10% of the wall thickness [5, 6]. SCC crack of different depths was identified or is more likely to be detected in more than a million pipe sections during the surveys [7,8,9]. This statement is consistent with the current trend to increase the number of small defects found
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