By -
Date 03-06-2006 00:54
Cesar,
I'm not sure the Code addresses your particular circumstance as a "requirement". Unless I'm mistaken, which I'm very often corrected, I don't think the Code Books are books of recommendations, but list essential and non-essential variables necessary to perform Code related tasks. You are asking about Code requirements directly related to purging pipes where supports are being welded. I doubt very seriously that you will find pro or con circumstances directly related to this circumstance. To be honest, your subcontractor is probably right in the fact that the purge is not "required", but that does not eliminate the fact that it might be "necessary" to protect the inside form contamination. You make reference to "my welding subcontractor" on a couple of occasions. This leads me to believe that this subcontractor is working under your direct authority. If you, either as the General Contractor or authoritative contractor, feels the pipes should be purged due to the thin wall pipe, then don't ask his opinions anyway, require it. We know that the reason for purging pipe is to keep the atmosphere from entering the weld pool and causing contamination. If you feel that the welding on the outside is affecting the mechanical properties and corrosion resistance of the inside of the pipe, make the choice for the subcontractor and require it. I do not feel that in every circumstance possible that it is necessary to purge the inside of pipes when welding is done on the inside. I think that wall thickness and heat input and welding process should be the deciding factors. We know that a thin wall pipe (3mm in this case) is more prone to heat related problems on the inside that a pipe of greater thickness (1/2" wall thickness and above).
Now, your decision to reject Metal Cored Gas Shielded welding process for repairs should have been decided by your repair procedure. To arbitrarily say it is not good enough strictly because of the root and HAZ protection leaves a lot for discussion. For example, joint configuration, depth and severity of the repairs, and accessibility should be considered before accepting or rejecting any weld repair process. Cesar, if you have the authority to reject/accept the process to make repairs, then you should have the authority to require/not require the purging of the pipes. Due to the fact that a lot of repairs have limited access, your decision was probably a logical one, but this forum does not have the authority to make decisions without know all the facts. Even then, we are only going to make recommendations (or suggestions) after reviewing all the facts presented to us. There are a LOT of educated and experienced people in this forum that are unselfishly and willing to share experience and latest technology with the rest of the industry, but from a liability standpoint, we are only able to offer our own personal recommendation and suggestion. I'm sure you understand that. Sometimes you might have to make a mock weld using the scenario you are presentiing to us to prove your point to your subcontractor.
Chuck