Which of the following may be used to qualify a welder?

Mechanical tests are central to qualifying a welder as they provide direct evidence of a welder's ability to produce sound welds under specified conditions. These tests typically include tensile tests, impact tests, bend tests, and other assessments that evaluate the physical properties and integrity of the welds produced. By subjecting welds to mechanical tests, one can objectively measure the strength, ductility, and toughness of the weld metal, and ensure that they meet the required standards and specifications.

In contrast, while written examinations may assess a welder's theoretical knowledge, they do not demonstrate practical skills. Visual inspections of previous works can offer some insights into a welder's past performance but lack a standardized method for ensuring current competency. Oral interviews may evaluate a welder's understanding or thought process but also cannot confirm tangible skills or adherence to welding standards. Thus, mechanical tests are the most definitive method for qualifying a welder.