Influence of long-term operation on the toughness of 17GS pipeline steel

We study the influence of long-term (30 yr) operation on the levels of toughness and brittle-fracture resistance of 17GS pipeline steel in the presence of notches and cracklike defects. We present the results of low-temperature testing (13–293 K) of specially prepared cylindrical specimens for uniaxial tension. The specimens were cut out from the base metal of an archival (reference) pipe and a pipe taken after operation for 30 yr. It was discovered that long-term operation does not affect the microscopic cleavage resistance Rmc (minimum brittle-fracture stress) of steel and has practically no influence on the strain-hardening exponent. The application of the local approach to the analysis of fracture demonstrates that the toughness of steel after operation decreases mainly as a result of the increase in the yield limit. It is shown that a small (15%) increment of the yield limit increases the critical temperature of the lower Charpy shelf by 40 K and may be responsible for a twofold drop of the crack resistance of steel.