Morning guys,
The weld length is based on the circumference of the pipe (QW 304.1 (b)) and I am pretty sure that the circumference referenced is meaning the OD of the pipe, not the ID.
A single 2" pipe (60.3 mm OD) has been the standard size used for years for welder qualification, this gives approx 180 mm weld length.
Hope that helps,
Regards,
Shane