STUDY OF LOW FREQUENCY FATIGUE CRACK GROWTH RATE da/dN IN H2S ENVIRONMENT

摘要

The fatigue crack growth rate (FCGR) of 4130X steel in H2S environment is investigated in this paper. Modified WOL specimens, soarked in H2S solution of moderate concentration (200×10 -6); were tested on a corrosion fatigue machine at a low frequency 0.0067Hz. The tests were based on a constant fatigue load profile. A computer was used to acquire the load and the displacement from three extensometers used for the calculation of crack size according to the compliance equation. The relations between the FCGR da/dN and the increment of fracture toughness ?K were determined through the Paris fit to experiment data in the case of K below K1SCC and above K1SCC respectively. Thus, our results can be a reference for the determination of the critical crack size of gas cylinders. A comparison of our results with FCGRs in air reported in literature shows FCGRs in H2S environment are much higher than those in air, and H2S concentration and load frequency affects da/dN very much.