Field welding on hydro-carbon pipeline?

[11echo]

I witnessed a field weld on a semi large hydro carbon pipe line (12" - 18") where the welders inserted a "balloon" on a lanyard, inflated it to isolate the hydro carbon vapors in the line, and to further isolate any vapors a synthetic-base mud was mixed and liberally spread at the edge of the balloon and pipe wall. I remember this mud was very slippery, and had a tenancy to fleck off as it dried (welding was done when the mud was wet). This was some time ago, and I have forgotten what the mud was? ...Drilling mud? ...or some specialty mud? Anybody know?

 

[Duwe6]

Sounds like Drilling Mud to me.

If your future needs are just for a branch connection, it would be safer to use the procedure set forth in API-570, and do the welding with flow in the pipe.

Fumes plus air = explosion. Note that the 'mud' was drying out and loosing its seal during this operation. Too risky for me.

Welding heat on the OD of a line with flowing hydrocarbon [or any liquid] = cool, fast-freezing weld and no chance of going "BOOM".

 

[11echo]

Unfortunately that's not the case here. We have to tie-in to existing small diameter piping (3"), so I can't maintain any flow through the lines. Also there are no isolation valves or points on the existing lines to "block" any vapors. What I was hoping to do was cold cut the lines, isolate any vapors, and weld on flanges for a tie-in point. However I will look into API-570 and see if there is another option. THX!

 

[Duwe6]

For a tie-in, use either a "whisper purge" of natural gas, or propane. When the O2 level hits 0.0% and the LEL is off-scale, you are ready to weld. Weld uphill on the root, with the gas flames above the weld puddle. Have a 3/4 or 1" open nipple on the line, at the top, near your buttweld. This will relieve the pressure when the root is welded shut. As long as you have flames -- root gap, then at the nipple -- you have proof of a "too rich to burn" atmosphere inside your pipe. Gas companies use this method regularly.

If the buring whisper purge is too exciting for your Safety dept, you can use a Freeze Plug. Insert two inflatable bladders [plumbers drain plugs] into your line about 2-3 diameters apart. Leave a tube at the top and a hose at the bottom of the outer bag. Fill through the hose, until ALL the air is purged from between your bags -- 100% full of water. Now have somebody like TEAM Industrial put the freeze jacket and thermocouples on your line and freeze the water. As long as the thermocouples show 0-deg F or colder, the ice plug is structural, not just sealed. You should be able to hydro against a 3" Sch40 2-diameter freeze3 plug at 500 psig.

I have done 200 psig on a 20" line, and 3100 psig on a 1" line. Ice is amazing stuff.