Calculating Gas Flow Rate for a Hot Tap

[pcs1034]

Help, please.

Where can I find information on how to calculate the gas flow rate required through a main carrier pipe in order to weld a split full encirclement saddle on the line? This is necessary to permit the welding root pass to the outer pipe while providing enough heat transfer to keep the weld from "burning through".

I appreciate any responses. PCS1034

 

[CRG]

You may find helpful information from the supplier of the split tee. Have you talked to them regarding this question?

You might find something at the following link:

http://www.tdwilliamson.com

I have a proprietary welding procedure specification; however, I am not authorized to share it. The specification is based on a 1994 Edison Welding Institute Report. The information given in the specification gives a method to determine the acceptable envelope of heat input based on the carbon equivalency, pipe thickness, and a field test cooling rate. Note that the cooling rate is not calculated; but instead, field tested with the flow. Even if you come up with a calculation method, it would be prudent to find a copy of the 1994 EWI Report to confirm that you don’t have excessive HAZ hardness burn-through.

 

[CRG]

Oops, last sentence above should be, “Even if you come up with a calculation method, it would be prudent to find a copy of the 1994 EWI Report to confirm that you don’t have excessive HAZ hardness or a potential for burn-through.

 

[SJones]

Gas flow rate restrictions are more to prevent excessive hardness and brittle zones than to prevent burn through. As well as the EWI work, try looking at PRCI or getting hold of some British Gas (Transco) documentation. Low hydrogen SMAW with downhill suitability and smallish diameter electrodes will also be of benefit for the first passes. If the worst comes to the worst, do your weld test simulation mock-up with flowing water.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/