Deaerator feedwater storage vessel weldment cracking: some fractographic and crack extension details

Abstract

The present paper describes the results of a large field surveillance study aimed at understanding and mitigating crack growth in deaerator feedwater storage vessel weldments. It has been demonstrated that this particular type of cracking was widespread in nature, was primarily initiated at the bottom of significant surface corrosion pits and that subsequent subcritical crack growth was the result of a fatigue fracture process. The fatigue crack growth was made up of two different components, viz. an environmental assisted crack, EAC, portion and a pure mechanical portion. Detailed quantitative fractography established that the fatigue fracture surfaces contained a mixture of fanshaped, cleavage-like facets and rough ductile striated regions and that the proportions of these failure modes dictated the rate of fatigue crack extension. Finally the finding that fatigue was the primary crack extension process in deaerator weldments was further strengthened through a comparison of quantitative fractrography and crack geometry evolution with reported data from the literature.