This book is concerned with the two most important aspects of the use of non-destructive testing. Firstly, the effectiveness of procedures to detect and size the defects present irrespective of the geometry, materials involved or environment. Secondly, the reliability of instrumentation and personnel to perform the specified procedures. Validation and certification techniques required for the justification of safe operation of a plant are also discussed. Experts in industries where safety and defect detection are of paramount importance have made valuable contributions drawn from their experience to make this book essential reading for anyone responsible for safety of plant operation. Illustrated throughout, the book is also of interest to mechanical and structural engineers, researchers and inspectors as well as being a useful reference tool for graduate students.