LAUSR

Abstract The article considers stress corrosion cracking (SCC) prediction models for pipes steels describing main stages of the process, their rates and implementation conditions. A number of tests, namely: electrochemical, corrosion-mechanical, mechanical, operational life tests, X-ray tests of layer-by-layer texture and residual stresses, analysis of micro and dislocation structure, were carried out for X70-steel pipes manufactured in Germany and USSR, after these pipes had been operated within the gas pipelines for a long time. It was shown that the texture nonuniformity of steels and residual process stresses in pipes are the parameters characterizing resource for growth or slowdown of cracks at initial stages. The cyclic tests did not identify any indicators of fatigue growth and significant changes of dislocational structure in the areas close to the cracks ∼0.2δ deep (where δ is the pipe wall thickness). During static and low-amplitude cyclic loads in the test environment with pH = 5.5…7.0 the rate of crack growth accelerates with available component (sulfide, carbonate, or phosphate) stimulating the anodic dissolution. It was found out that SCC-cracks not deeper than 0.2δ were not dangerous for pipelines reliability; on exposure of corrosion environment the forecasted growth rates of such defects did not exceed 0.3…0.4 mm per year, apart from cracks located in the welded joints and along the weld-fusion line. Growing of the 0,2δ deep SCC-cracks would stop without electrolyte.