NEAR NEUTRAL pH SCC OF GRADE X80 LINEPIPE STEELS UNDER CYCLIC LOADING

摘要

Susceptibility to stress corrosion cracking (SCC) of Grade X80 linepipe steels, which were produced by recent TMCP (Thermo-Mechanical Controlled Processing) technique, controlled rolling (CR) followed by accelerated cooling process (ACC), in near neutral pH conditions was investigated, and cracking behavior was compared with conventional Grade X65 linepipe. Longitudinal strip specimens with small surface notches were cyclically loaded in the NS4 solution with cathodic polarization of -l000mV vs. SCE. No significant difference in susceptibility to SCC was found between Grades X80 and X65 linepipes, both produced by TMCP process, even under higher stress condition for X80 linepipe steel. Hydrogen permeation test reviled the strong effect of hydrogen for the cracking under the SCC test condition. Transgranular cracking and quasi-cleavage fracture were observed as an evidence of the effect of both corrosion and hydrogen embrittlement on near neutral pH SCC.