Effect of Strain Rate on Stress Corrosion Cracking of X80 Pipeline Steel

Stress corrosion cracking susceptibility of X80 pipeline steel was investigated in a simulated soil solution using slow strain rate tensile(SSRT) tests.The simulated soil solution was based on the chemical compositions of alkaline Gansu soil in northwest of China.The tests were conducted at different strain rates.The fracture surfaces and secondary cracks were observed using scanning electron microscopy(SEM).The results showed that strain rates had an important role on SCC of X80 steel in simulated soil solutions.Corrosion and mechanical factors have different influences during the SCC processes at different strain rates,which results in the variety of SCC.There was the highest SCC susceptibility at the strain rate of 1.0×10-6s-1.Combined effect of corrosion and mechanics leads to high SCC susceptibility.When the strain rates were lower than 1.0×10-6s-1,enough long corrosion time results in the corrosion of crack in this strain rate range.The crack propagation is restrained.Thus,slight decrease of SCC susceptibilities occurs.As the strain rates were higher than 1.0×10-6 s-1,SCC susceptibilities were low obviously.In this high strain rates range,the mechanical factors have more effect on SCC than corrosion factors,which mainly lead to mechanical fracture of specimens.