Welding is a very important joining process and has been used extensively for at least the past 75 years. There is a need to control processes, such as welding, to insure a high quality end result. Over the years there have been many spectacular failures of welded structures, starting with Liberty ship and T-2 tanker failures during WWII, that emphasize this need. Many procedures involving non-destructive and destructive tests are used to study weldments.
Metallographic examination can be performed in-situ by grinding an area on the surface of the weld, its heat affected zones and adjacent base metal (the metal being joined that was unaffected by the temperature of the welding process). This is a reasonably non-destructive evaluation. Destructive examination, where a specimen is removed from either the welded assembly or test coupons, is quite commonly performed. Test coupons are often used to qualify the welder and ensure that the techniques and materials chosen will produce a weld with acceptable soundness and mechanical properties. Post mortems of failed weldments are also examined metallographically using sections removed from the welded assembly, generally after non-destructive examination is completed.
