Multi -Facets of Metallurgy : Emerging Trends Ed. A mit Chatterjee, A TM 97, Jamshedpur, pp. 131-149 Structural and Component Integrity R. N. GHOSH National Metallurgical Laboratory, Jamshedpur - 831007. ABSTRACT A structure or a component is expected to perform specific functions for a minimum specified period of time. If it ceases to do so, it is said to have failed. The consequence of service failure can be tragic and expensive. There are innumerable cases of engineering disasters resulting in loss of life and property. Therefore, utmost care and attention are required to be given to critical structures / components to ensure that such incidents do not take place. Integrity evaluation performed at regular intervals is a means to ensure absence of such tragic service failure. It also gives us an estimate of its remaining life which is essential to plan future course of action so that it could be used till the very end of its real life. Recent development of powerful non-destructive techniques and availability of modern computational facility at affordable cost has made this a routine exercise for many critical applications. This paper describes the basic principles behind structural and component integrity evaluation and also presents some of our recent experiences. Keywords : Remaining life, Creep, Fatigue, Fracture, Corrosion, Failure analysis. INTRODUCTION Although engineering structures and components are designed to last for a specified period, premature failure does take place for a variety of reasons viz., design deficiencies (lack of knowledge), material selection deficiencies, pro- cessing deficiencies, assembly and installation error, operational and mainte- nance error, and environmental impact. In addition one must realise that every design has a probability of failure. This is because both the material property and the loading are random variables having a mean and a standard deviation. Therefore, inspite of the best effort there would always be a few incidents when the loading may exceed the critical value or the material used may have inferior property. However, depending on the level of factor of safety used, the probabil- ity of failure is always very low (10-1 / 10-1), but it increases with prolonged 131