AWS approved welding certification indicates that a welder has completed a nationally recognized test which demonstrates his/her ability to perform a sound weld for a specific process in accordance with industry standards.
There is no universal test to certify welders as there are many different codes, standards and Welding Procedure Specifications (WPS) that regulate welding. Instead, welders must complete individual tests for each standard and process for which they require certification. Depending on the processes (SMAW, GMAW, GTAW, and FCAW), the metals (steel, stainless, aluminum, etc) and the variables (thickness, direction, position, joint design, etc), a welder may need to take several tests, in various processes and positions in order to satisfy employer and industry requirements.
An AWS test is a practicum exam, meaning the welder must successfully perform a hands-on demonstration of the weld process being tested in accordance with the AWS welding standards. In addition to passing the AWS acceptance criteria of a visual inspection conducted by an AWS Certified Welding Inspector, this weld may undergo mechanical testing and/or radiographic examination (destructive and/or nondestructive testing) in accordance with the qualification test procedure.
To learn more about AWS codes, standards and specifications, welders should refer to the relevant AWS publications available at http://pubs.aws.org/.