The Experimental Investigation Of Stress Corrosion For 34CrMo4 Alloy Steels In Wet H₂S Environment

In oil and gas exploitation, processing and transport process, the hydrogen sulfide stress corrosion is a serious problem all the time, which is also the key factor affecting the life and reliability of the oil and gas industry equipment. In this paper, we based on possible stress corrosion cracking problem for vehicles compressed natural gas (CNG) cylinders in wet H2S environment, taking into account the differences in the quality of natural gas in different areas and the actual working conditions of cylinder. Through the slow strain rate testing, study the stress corrosion cracking sensitivity of 34CrMo4 steel in different H2S concentration under room temperature.Assembly and commissioning a new type of pre-crack extension tensile corrosion equipment, which does a preparatory work for promoting the wider use of this equipment. And through pre-crack tension growth test, study the impact of different loading methods on the stress corrosion crack growth rate of 34CrMo4 in the case of average loading rate is the same, which provide a basis for the safety evaluation and life prediction of gas cylinders. It is also significant to guide the safe production.The main conclusions are:(1) With the increase of hydrogen, the stress corrosion sensitivity of 34CrMo4 steel is increased by logarithm function rule y = 0.1831Ln(x)-0.403.(2) High concentration (1000ppm, 1500ppm and 2000ppm) range, the stress-strain curve does not exist yield platform, almost linear rise and a sudden break in the rising process.(3) With the increase of hydrogen, 34CrMo4 steel surface passive film is damaged, fracture morphology is gradually changed from ductile fracture to the transgranular fracture cleavage or quasi-brittle fracture cleavage.(4) The impact of different loading methods on the crack growth rate is not obviousi n the case of average load rate is the same, but both of them show more obvious stress corrosion sensitivity.