You are  probably right with your assessment of the situation, but you haven't been with that company for long. You are the new kid on the block and you can expect some BS from someone that has low self-esteem.

The chap probably feels like everyone is talking about him and his failure to pass the examinations. He needs someone he can "pick on" to feel better about himself and "tag, you're it" my friend.

As mentions by CT, in a pleasant way tell him that you are capable of fixing your own welds and that you would appreciate the opportunity to learn from your "mistakes". Ask him to show you what you did wrong so you won't repeat them a second time or at least you will know what "skills" you need to "improve". In other words, schmooze the SOB. I bet your "reject" rate will drop dramatically when he has to point out the problems and explain how they don't meet the acceptance criteria.

Welcome to the "School of Life".

As for him inspecting the work; as long as he doesn't accept the CAWI credential, he's free to do what ever tasks the employer assigns to him. However, if he accepts the CAWI credential, he is bound to the code of ethics as is any inspector carrying AWS credentials.

Best regards - Al