Failure Reason for Valve Stem of 17-4PH Stainless Steel

The stem of a nuclear-grade manual globe valve in a power plant (made of 17-4PH martensitic stainless steel) was broken after running for about 6 years. The reasons for the failure were analyzed through macro inspection, chemical composition analysis, and mechanical performance testing. The results showed that the grain boundaries of the matrix material were coarsened, and in the seawater system, more pitting pits appeared on the surface of the valve stem, and the combined action of pitting corrosion and intergranular corrosion eventually led to the fracture of the valve stem. Inadequate corrosion resistance of the material in seawater environment and improper heat treatment process were the main reasons for valve stem fracture.