Local creep damage effects on subsequent low temperature fatigue crack growth behaviour of thick-walled pressure vessels

•Local creep damage was introduced into C(T) specimens by interrupting CCG tests.•Material pre-straining was conducted to limit plasticity ahead of the crack tip.•Plastic pre-straining was found to have insignificant effects on the FCG behaviour.•Reduced FCG trends were found in the presence of creep damage.•Local creep pre-straining and change in the cracking mode caused reduced FCG rates. The influence of prior creep damage on the subsequent fatigue cracking behaviour of thick-walled pressure vessels has been thoroughly investigated in this study. Creep damage was introduced into fracture mechanics specimens by performing creep tests at 550 °C and stopping them after reaching a desired crack length. Using this experimental methodology, creep damage was successfully introduced ahead of the crack tip in the form of intergranular voids and microcracks. In order to assess the creep damage effects, in the absence of significant plasticity, on the structural integrity of thick-walled pressure vessels the material was uniformly pre-strained under compressive plastic deformation prior to the specimen manufacture, thus hardening the material. Fatigue tests were performed on specimens with and without creep damage and the results were compared with each other. Moreover, metallurgical investigations were conducted to understand the influence of microstructural damages, as a result of creep loading conditions, on the fatigue cracking behaviour of the material. The results from this study show a clear reduction in the fatigue cracking rate in the presence of creep damage local to the crack tip. The findings have been discussed in terms of the effects of static creep loading conditions and microstructural damages on the subsequent fatigue cracking behaviour under cyclic loading conditions.