Handbook-Testing & Inspecting

3 Sampling. Every part that is constructed cannot be completely tested to determine just how strong it is, because such a test would destroy the part. Yet it is important to know just how strong each part is. Such assurance can be obtained by a combination of four factors: 1. A procedure that has been proved to give the desired results. 2. A control of operations such that the procedure will be followed exactly all along the line. 3. Constant inspection to make certain that operations are being performed correctly and that materials meet specifications. 4. Occasional testing to make sure that unforeseen factors are not creeping in. Translated into welding these four factors are carried out in the following manner: Procedure Qualification. In the first place it must be proved that the procedure will give the required results. A workman who has proved himself to be a good operator over a period of time is used in developing a method of making a weld. The welds made by that operator are then completely tested to determine whether the results desired are being obtained by the procedure used. As soon as the desired results are obtained, the procedure has been established. That is what is known as a procedure qualification. Other operators are then tried out on the proved procedure and as soon as the welds they make will also withstand testing, those operators are qualified to follow the procedure. Procedure Control. As the proved welding method then goes into use in production work, a procedure control is established so that continued satisfactory work can be assured. Constant Inspection. As work progresses and as more parts are turned out by the production operation, they are examined to make certain that the factors that can be determined by inspection methods are what were expected. Periodic Inspection. From time to time parts are taken from the production line and tested to destruction to make certain that the three factors already discussed are given the desired results. The frequency with which destructive tests have to be performed is determined from experience and from the severity of the requirements.