Welding techniques are continually changing and evolving, while at the same time inspection techniques are improving in their ability to spot small defects and inclusions.
Modern Welding Techniques
Shielded metal arc welding (SMAW) is susceptible to defects so it requires a highly skilled welder to ensure the weld that has little to no defects. As a result, submerged welding techniques that keep the weld area clean were developed. These methods use either an inert gas shield or the weld area is covered by a shielding granulated flux. This is known as submerged arc welding (SAW).
Some form of filler wire is required. In tungsten inert gas (TIG) welding, a tungsten electrode makes the arc and the wire is fed by hand, while with metal inert gas (MIG) welding the feed wire acts as an electrode and is fed automatically. It is now common to use pulsed current because this reduces heat input and can improve the welding process.
Welding of critical equipment must be performed in terms of a welding specification prepared by an experienced and qualified engineer. The welding method, filler rod material, the size of the weld and the number of passes as well as the inspection techniques to be used are all specified. This will be reviewed and approved by the Quality Inspector (QA).
Traditionally, visual inspection of welds was common, occasionally supplemented by radiographic inspection of a certain percentage of the weld. It is not out of the ordinary for a 100 percent weld inspection to be required, which will require full radiographic inspection. An alternative to radiographic inspection is ultrasonic inspection. Using ultrasonic sound diffraction supplemented by pulse echo techniques, the accuracy of ultrasonic inspection is almost as foolproof as that of radiography.
The American Welding Society (AWS) and ASME provide guidelines for welder certification. In general terms, welders are coded to perform certain work based on a combination of practical experience, qualifications and the ability to weld sample coupons as listed in the work specification. Generally, a welder is coded to perform certain types of welding only, and coding has to be renewed regularly. Apart from AWS and ASME, third-party authorized inspection agencies may be accredited to perform welding inspections and approvals.