In order to clarify the influence of H
2S and CO
2 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 {H
2S gas (5000ppm)+humid air (353K, 90% relative humidity)} and 99.9% CO
2 gas (353K, 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 2.0×10
7 cycles in {H
2S gas (5000ppm)+humid air (353K, 90% relative humidity)} and in 99.9% CO
2 gas (353K, 90% relative humidity) was 50 and 46 percent lower than that in air, respectively. The influence of H
2S gas content on fatigue life was remarkable in H
2S gas content ranging 50 to 5000ppm. In the humid H
2S and CO
2 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 H
2S and CO
2 gas environment.
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