Experimental study on stress corrosion crack propagation rate of FV520B in carbon dioxide and hydrogen sulfide solution

• Stress corrosion cracking of FV520B in imitation nature gas environment.
• Crack propagation rate test by wedge opening loading specimens.
• H2S plays the major role in the stress corrosion process.
• Microscopic morphology shows a typical brittle fracture of FV520B.

FV520B steel is a kind of precipitation hardening Martensitic stainless steel, it has high-strength, good plasticity and good corrosion resistance. Stress corrosion cracking (SCC) is one of the main corrosion failure mode for FV520B in industrial transportation of natural gas operation. For a better understanding the effect on SCC of FV520B, the improved wedge opening loading (WOL) specimens and constant displacement loading methods were employed in experimental research in carbon dioxide and hydrogen sulfide solution. The test results showed that the crack propagation rate is 1.941 × 10−7–5.748 × 10−7 mm/s, the stress intensity factor KISCCKISCC is not more than 36.83 MPa m. The rate increases with the increasing of the crack opening displacement. Under the condition of different initial loading, KISCCKISCC generally shows a decreasing tendency with the increase in H2S concentration, and the crack propagation rate showed an increasing trend substantially. For the enrichment of sulfur ion in the crack tip induced the generation of pitting corrosion, promoting the surrounding metal formed the corrosion micro batteries, the pit defects gradually extended and connected with the adjacent pit to form a small crack, leading to further propagation till cracking happened. Fracture microscopic morphology displayed typical brittle fracture phenomena, accompanying with trans-granular cracking, river shape and sector, many second cracks on the fracture surface.