Metallography helps NDT - some case histories [Paper IX-b]

Metallography and NDT appear almost opposite. One requires sectioning, polishing, etching etc. while the other, being non-dectructive testing, examines without damage or impairing the serviceability of the components. Many times one helps the other to evaluate and accept the soundness of the material or joint. The science of metallography is essentially the study of the structural characteristics and some of the NDT technique such as UT is very much influenced by such characteristics of the material. With the advancement of technology, in some cases metallographic examinations are carried out in-situ and are helpful in deciding the direction of investigation. Sometimes, it becomes impractical to adopt satisfactory quality control techniques and therefore process is controlled by using combination of metallographic examination and statistical techniques. These are illustrated with the help of case histories. (author)