Creep of ex-service 0.5CrMoV steel at low strain rates

The high-sensitivity helicoid spring specimen technique was used to investigate creep response of ex-service low alloy steel having detectable creep damage. The creep conditions were selected to be close to those under which the material was used, that is 560 °° C and 34 MPa. Three specimens were prepared from the segment of main steam pipeline having radial, tangential and axial orientation with respect to the original pipeline axis to reveal potential anisotropy introduced by previous creep deformation. Results were compared to creep curves obtained on the unused generic low alloy steel under the same conditions. The ex-service steel creeps considerably faster, mainly during the transient period. Unfortunately, the chemical composition of the steel does not match its specification so it is not clear which part of the difference can be attributed to the creep damage. Some differences were observed between different specimen orientation, so the anisotropy introduced by the creep damage can be observed. More experiments are needed to determine any potential contribution to the residual-life assessment.