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.
In the USA, welder qualification is performed according to AWS D1.1, ASME Section IX and API 1104 standards, which are also used in some other countries. Some States have their own Welder Qualifications that supersede AWS Qualifications, but most defer to AWS, ASME or API.
In Canada, welder qualification is carried out according to CSA Standards and ASME. The ASME code is typically used for pressure vessel and pressure piping applications, and CSA Standards are used for structural, general manufacturing and non-pressure applications. There are 3 major CSA Standards to which welders may be qualified: CSA W47.1 for steels (including stainless steels), CSA W47.2 for aluminum, and CSA W186 for reinforcing bars. Under these CSA standards, welder qualification testing is carried out every 2 years by the Canadian Welding Bureau to ensure ongoing competence.
In Europe, the European Committee for Standardization (CEN) has adopted the ISO standards on welder qualification (ISO 9606), to replace the old European EN 287 series.Operators of automated welding systems are certified according to EN 1418. In Europe welders are often certified by third party Personnel Certification Bodies, like The Welding Institute (TWI/CSWIP). Welders involved in the manufacture of equipment that falls within the scope of the Pressure Equipment Directive must be approved by a competent third party which may be either a notified body or a third-party organization recognized by a Member State.
Once a welder passes a test (or a series of tests), their employer or third party involved will certify their ability to pass the test, and the limitations or extent they are qualified to weld, as a written document (welder qualification test record, or WQTR). Normally this document is valid for a limited period (usually for two years), after which the welder must be retested. However some Qualifications are only valid for a single project, while others are unlimited as long as welders do not go beyond a specified length of time without performing that specific type of welding (this period is typically 6 months). Welders must maintain a log to demonstrate they have maintained their Qualifications.