Welding inside 18" and 20" Diameter pipe

[Dunme]

Gents,
I have a situation on one of my sites as the contractor was found welding inside a 20" pipe. The weld point is 2.7m from the edge of the pipe while the other end is inaccessible due to installed ISO Bundle. This in my view is an unsafe act, However to advise the contractor on the issue I am looking for standards that supports my action.

Could anyone advise such standards.
Best regards,
'Dunme.

 

[chicopee]

The welding should have been done from the outside, however, the pipe ends should be prepared properly and a backing ring used to ensure full weld penetration.
I am assuming that the welder had to go inside the 20" pipe to weld and consequently I would questioned safety of the welder and the quality of welding.