I am trying to put together a weld procedure for putting a hot tap on a 2" line carrying refrigerant R134a. We have decided to use a split tee fitting and I am trying to develop a welding procedure for this.

Considering this is fairly thin wall pipe, I need to calculate how long it takes before I burn through the wall in order to determine travel speed of the electrode.

Can someone point me in the right direction for some equations for heat transfer, or whatever it is I actually need to accomplish this?

bradsr0138;
Not enough information to provide help.

For starters, what is the pipe material? Copper? Steel?

What is the wall thickness of the 2" line? Fairly thin wall tells me nothing.

You should have a mock-up (same set orientation as in the field with pipe size and fitting) and qualify a welding procedure specification for this hot tap.

You intent should be to fillet weld the split fitting on the OD of the pipe with a hot tap valve.

Review this

http://www.koppl.com/pdfs/Hottap.pdf

The material is carbon steel, material specification ASTM A 53. The wall thickness is 0.154 in. with a min wall thickness of 0.135 in.

I was not so much concerned with actual hot tap procedure. I am more concerned with the transfer of heat from the welding electrode on the OD of the pipe and how long it will take before it burns through to the ID.  

You will not burn through to the ID at this wall thickness. Using conventional welding techniques, our welders can weld on as thin as 0.090" tubing using the GTAW process. As I said, develop a welding procedure specification using same constraints, OD and wall thickness, before trying on the actual pipe. Also, you better qualify a WPS.

bradsr0138;

We used to run sample checks for gas line hot taps if we were unsure of how much penetration we would get into the parent material.

The simplest way to do it is just get a piece of similar material to your carrier pipe (A53 is bog-standard, should be easy enough), and put a run of weld onto it. If you then take your sample, cut through the weld and etch the sample, you will be able to tell exactly how far you are penetrating into the steel...We would also ask the welder to try and penetrate as deep as he could, just so we could measure a worst case scenario.

We did ours with Lo-Hi electrodes and as far as I can remember the max penetration we would achieve with this was 3-4mm. TIG will give you even less

regards

Declan