Life prediction by mechanistic modeling and system monitoring of environmental cracking of iron and nickel alloys in aqueous systems

Advances in developing scientific and engineering methods to control environmental cracking are discussed. Quantitative understanding of the crack advance process is given for types 304 and 316 stainless steels, A508B and A533 low alloy steels, and Inconel 600 and Inconel 182 alloys in high temperature water in terms of the film rupture mechanism. Mechanistic modeling predicts with good accuracy the crack growth data in various laboratory specimens and nuclear components over a wide range of environments, materials and stressing conditions. The practical use of such mechanistic understanding is discussed in terms of the validity of testing methods, design and life evaluation criteria, and operating specifications. An overall approach for component life management is proposed which integrates mechanism-based crack growth rate laws, in situ crack growth damage monitors and environmental sensors. This approach has been extensively developed, validated and applied in plant in preliminary form to cracking of nuclear system components.