Research On The Influence Factors Of Stress Corrosion Cracking Of X80 Pipeline Steel In Near-neutral PH Soil Environment

Stress corrosion cracking(SCC) is generally defined as the initiation and/or propagation of cracks in the presence of both a sensile tress and a corrosive environment. The occurrence of SCC is commonly recognized by brittle cracking features in normally ductile metals, meaning that the catstrop Hic capablility of SCC is manifested through an effective reduction in fracture tounhness. Consequently SCC is a serious and growing concern in many industries, one which is the pipeline industry.The study of influence factors of X80 pipeline steel in near-neutral p H soil environment was subserved by the investigation of SCC mechanism, SCC sensitivity, crack initiation, early crack propagation, dormancy and upper crack growth situation. For example, in the second line of the west-east national gas transmission project, the soil regime along the pipeline in near-neutral p H soil environment has been investigated. The results show the significance of the study of SCC of X80 pipeline steel in near-neutral p H soil environment. The effect of yield strength, cathodic protection potential and pressure fluctuation on SCC sensitivity of high strength pipeline steel in near-neutral p H soil environment were studied by means of the slow strain rate tension test, the constant loading test, the electric-chemical test, the WOL test and the top load pressure fluctuation test.The results indicate that in the case of no account of cathodic protection, with the increasement of pipeline steel grade, the yield strength increases, and the SCC sensitivity also increase. Along with the potential turning negative, the area reduction, the elongation and the fracture time of slow tensile samples decrease, and the SCC sensitivity increases. When the potential is under the protection potential, the SCC sensitivity is the strongest in neutral p H solution. High load small-scope fluctuation load stress promotes obviously the expansion rate of SCC cracks, while X70 and X80 pipeline steel is not sensitive to SCC under the constant load in neutral p H solution.