Welder certification is based on specially designed tests to determine a welder’s skill and ability to deposit sound weld metal. The main part of the welder’s test consists of welding one or more test coupons which are then examined using non-destructive and destructive methods. The extent of certification is described by a number of variables, which include the specific welding process, type of deposited metal, thickness, joint design, position, backing, and others. Most often, the test is conducted in accordance with a particular code. Depending on product requirements the test can be administered under the auspices of a national or international organization, such as the American Welding Society (AWS), or American Society of Mechanical Engineers (ASME), but manufacturers may specify their own standards and requirements as well. Most certifications expire after a certain time limit, and have different requirements for renewal or extension of the certification.