There are different welding codes for procedure qualification and welder qualification like API, ASME Section 9, AWS Standards, European standards. What is the selection criteria for choosing the one?
Application (pressure vessels, piping, structural, water), country of placement/usage (EN for most european things, ASME e.g. for pressure vessels in USA), and design code. The latter will typically involved the application, whereas country for usage may typically determine the design code (e.g. EN 13445 for european pressure vessels and ASME VIII-1 for american vessels). Jurisdiction can also dictate the required code.