Fatigue Crack Growth Rate Properties of SA508 and SA533 Pressure Vessel Steels and Submerged-Arc Weldments in a Pressurized Water Environment

Abstract

The Stage II fatigue crack growth rate (FCGR) properties of four base materials (SA508 Class 2a; SA533 Grade A, Class 2; SA508 Class 3a; and SA533 Grade B, Class 2 steels) and two automatic submerged-arc weldments (SA508 Class 2a and SA533 Grade A, Class 2) were developed in a pressurized water environment at 288°C (550°F) and 13.8 MPa (2000 psi) at load ratios of 0.20 and 0.50. The pressurized water environment FCGR properties of these four pressure vessel steels and two submerged-arc weldments were generally conservative compared with the appropriate American Society of Mechanical Engineers (ASME) Section XI water environment reference curve. The growth rate of fatigue cracks in the four base materials, however, was considerably faster in the pressurized water environment than in a corresponding 288°C (550°F) baseline air environment. The growth rate of fatigue cracks in the two submerged-arc weldments was also accelerated in the pressurized water environment but to a lesser degree than that demonstrated by the corresponding base materials. In the air environment, fatigue striations were observed independent of the material and load ratio, while in the pressurized water environment some intergranular facets were present. The greater environmental effect on crack growth rates displayed by the base materials in comparison with the weldments was attributed to a different sulfide composition and morphology.