A. Introduction

Depending on the severity of duty required of a heat exchanger when in service, various methods of nondestructive testing are available to provide that the parent material and that the welds deposited are sufficiently free from defect to satisfy the known service conditions. During fabrication radiographic, ultrasonic, magnetic particle, and dye penetrant tests are available inspection techniques. The various design codes specify nondestructive testing in varying degree for different vessel categories, and the choice of technique for a particular application requires careful consideration.

There are internationally recognized certification schemes to qualify personnel for radiographic, ultrasonic, magnetic particle, and dye penetrant testing, and in the case of ultrasonic inspection it is particularly important that personnel are suitably qualified to undertake work of this nature.

If there is any danger of heat treatment cracking, nondestructive testing should be carried out after heat treatment and the design code requirements followed in this respect.

After acceptance of the nondestructive tests, the integrity of the finished vessel is further established by a pressure test, usually hydraulically applied, although in certain circumstances with adequate safety precautions a pneumatic test may be carried out. The stages at which various forms of nondestructive testing are employed are discussed below.