Original paper(Vol.46 No.6 pp.613)
Corrosion fatigue strength of high strength steel welded joint in H2S and CO2 gas environment
Ebara Ryuichiro; Yamada Yoshikazu; Shinohara Hitoshi
Abstract:In order to clarify the influence of H2S and CO2 gas environments on the fatigue strength of high strength steel welded joint, corrosion fatigue tests of 17-4PH T type welded joint were carried out in {H2S gas (5000 ppm) + humid air (353 K, 90% relative humidity)} and 99.9% CO2 gas (353 K, 90% relative humidity) environments by use of a corrosion fatigue testing apparatus in gaseous environment.
The fatigue strength of 17-4PH T type welded joint at 2.0x107 cycles in {H2S gas (5000 ppm) + humid air (353 K, 90% relative humidity)} and in 99.9% CO2 gas (353 K, 90% relative humidity) was 50 and 46 percent lower than that in air, respectively. The influence of H2S gas content on fatigue life was remarkable in H2S gas content ranging 50 to 5 000 ppm. In the humid H2S and CO2 gas environments corrosion pits were observed at the crack initiation area of the fracture surface. While striation was observed at the crack propagation area of the fracture surface. Thus, it is concluded that the initiation of corrosion pits at the crack initiation area is the major cause of the reduction in fatigue strength of 17-4PH T type welded joint in humid H2S and CO2 gas environment.
Key Words:H2S gas, CO2 gas, corrosion fatigue, 17-4PH steel, T type welded joint, corrosive pit