Influence of Service Exposure on Base and Weld Metal of 1/2 Cr-1/2 Mo-1/4 V High-Pressure Steam Inlet Piping

An investigation was performed on a circumferential weld joint in a 1/2 Cr-1/2 Mo-1/4 V high-pressure steam inlet pipe following the detection of steam leakage in a weld area. The component, 326 mm o.d. × 55 mm wall steam pipe, had accumulated approximately 75,000 hr of service at 566C. A special welding technique had been employed with the 2-1/4 Cr-1 Mo weld metal which created a fully refined heat-affected zone (HAZ) grain structure. The failure path conformed to the contour of the HAZ through more than half of the wall thickness. The cracking was intergranular and had propagated in a narrow zone of material at the intersection of the fine-grained HAZ and the parent metal. For the base metal, the short-time rupture strengths of the service-exposed material were below those of the unexposed material. A Larson-Miller parameter correlation indicated that the nominal operating stress and temperature are in the regime where the rupture strengths for the service-exposed base material are as good as those for unexposed material.