The primary standard for friction welding is ISO 15620 'Welding - friction welding of metallic materials'.
In addition, there are a number of other national standards, for example:
USA: ANSI/AWS C6.1 - 1989 'Recommended practice for friction welding'
Japan: JIS Z 3607 (1994) 'Recommended practice for friction welding of carbon steels'
Most larger companies using friction welding processes will have their own internal specifications for friction welding.