[Fron]

Hello!

So I been wondering for a while, say you have pre-fabbed a pipe arrangement and are to weld it up to a existing pipe arrangement, and say that arrangement carries a flamable liquid exc gasoline, how would you approatch it? Shut of nearest valves and purge from nearest thread / possibility?

I`ve been thinking if you can shut off two sides of a pipeline and drill a hole in the bottom and thread it (this will be a shitty thread, and will most likeley not hold to good, but it will hold enough to keep argon flow and not add oxygene). And drill a hole in the top, and do the same procedure, but instrad of argon hose, put a exc; 1/4" valve to remove the air / control argon.

Do someone have any experience?

[DLewis0289]

You are doing two things, (a) talking about in-service pipe work and (b) scaring me.

Couple options for your general knowledge, THIS IS NOT A PROCEDURE for you to attempt.

You can make the pipe safe, with the appropriate LOTO and evacuation, clean/purge and write a JSA (Job Safety Analysis) outlining the procedure up to and including explosimeter use and frequency.

Or you can perform a hot tap on existing piping with valve, connect your new piping and open the valve.

If you find this work interesting watch some You Tube videos put out by T.D. Williamson (The only equipment I will use for this type of work)

[Poland308]

Definantly a project that requires direct supervision by someone with experience on that spacific pipe material, and with the chemicals or similar ones to what you will be working on. Live lines and flammable chemicals is not a time to be thinking what should I do now. The answer to any unanswered questions in a scenario like this is usually (PIPE BOMB) !!

[exnailpounder]

Don't even think about it!
I was on a job at Citgo refinery and a couple of "pros" cracked open a live line of crude, it rained down on a gigantic electric motor that was driving a pump and they burned half of the FCC down.

[Poland308]

In truth all scary things aside. It can be done safely with proper training. Ideally the line would need to be water flushed and tested to verify it was free of anything flammable. And also open to atmosphere on one or both ends. Even then it might require a purge with an inert gas like nitrogen. Depends a lot on the makeup of the liquid and its properties as well as existing pipe configuration.

[plain ol Bill]

What you are talking about is called a hot tap in the trades. I have done it on natural gas lines by welding a weld on pipe fitting to the pipe or vessel. Then put a gate valve on the fitting, open the valve and drill thru the valve into the pipe. Pull the drill and shut the valve off. Doing this will make you want to check your shorts and put on a clean pair as required.
If a drilled hole I not big enough you are going to have to shut down the line, put a pig on each side of the area you will open if possible and purge the crap out of it. Again - check your shorts frequently.
DO NOT ATTEMPT THIS UNLESS YOU ARE EXPERIENCED DOING HOT TAPS OR HAVE A DEATH WISH. In case you DO have a death wish please send me an email letting me know where you will be doing this work so I can be sure to be a couple of states away - OK.

[Otto Nobedder]

Fron's opening line, "So I've been wondering for a while..." suggests he's not planning to do this tomorrow based on internet advice, but rather was wondering how it's done.

The preferred procedure is called, "double-block and bleed", meaning the line can be shut off and locked out on both sides of the work area, bled (drained), and then flushed/cleaned/purged through the bleed line.

A second option is to double-block the section and completely remove the spool so it can be properly cleaned, purged, and worked on the bench.

If complete isolation is not possible, the fault is in the original engineering and/or construction. This is one of many cases where hot-tap work is required, else the entire system must be shut down and purged.

Steve S

[DLewis0289]

I am with Bill, I am TDW trained and have done hot taps and stopples on everything from Anhydrous Ammonia, Nat Gas, Hydrocarbon, etc. Biggest I have ever done was a 24 inch hydrocarbon. No matter how well trained or how many I have done there is always a pucker factor. (the dispatcher may lower the pressure to 800 psig or so, big deal if it goes wrong)

Even the best "engineered" plans can go wrong. Circa 1982, I was at a chemical plant and the request was easy, hot rod a 2" hole in the top of a 2000 gal stainless steel "chilled water" tank and then weld a 2" ss coupling on it. Valves were shut and chained but they did not break them and put blinds in. Safety guy checked (sniffed) and approved hot work permit. The two guys dicked around for about an hour before they started after the explosimeter check.

Dad and I were on the other side of the plant and felt the ground shake, Illinois not California. We took off running towards where we new the tank was at. I swear on my eyes, I still remember the guy's name was Joe Thatcher and his fire watch / helper was Jim Morgan. Joe is standing on the ground, lense blew out of his hood and his Carharts were smoking. As soon as he pierced the rod through the tank, it exploded blowing one of the dish heads clean off the vessel destroying a canopy on the building next to it. blew all the windows out of the main office. Thank God Jim had been standing on the other end of the tank. Joe had been straddling, SITTING ON TOP OF THE TANK.

Chilled water tank, WTF? HOW? It served a process that had a shell and tube condenser, one side chilled water, process side Cyclopentane or Cyclohexane I can't remember. In the time between the sniff and the guys starting it developed a tube leak and the process side was at a higher pressure than the cooling side AND one of the gate valves leaked by, or was missed (people started going into CYA mode real fast) thus filling the chilled water system with highly explosive vapors.

[Fron]

First of all, thanks a lot for good answers.
Secondly this is not something that is going to be tested. The reason for this topic is straight out of curiosity. And how this "situation" is handled in other places in the world.

But how do you guys approach a gasoline tank repair if someone brings it by your shop?

[rick9345]

First of all, thanks a lot for good answers.
Secondly this is not something that is going to be tested. The reason for this topic is straight out of curiosity. And how this "situation" is handled in other places in the world.

But how do you guys approach a gasoline tank repair if someone brings it by your shop?

Garden hose fastened to tailpipe of Internal combustion engine running outside of shop(carbon monoxide)constant purge(CO is inert).I use it for in field work and shop. Welding around flammables including old shop rags not for the faint of heart that don't think first.Like building a house of cards,one wrong move it all falls down.

[DLewis0289]

What you are talking about is called a hot tap in the trades. I have done it on natural gas lines by welding a weld on pipe fitting to the pipe or vessel. Then put a gate valve on the fitting, open the valve and drill thru the valve into the pipe. Pull the drill and shut the valve off.

And to clarify I am sure he is talking about a hot tap machine connected to the gate valve on the natural gas line, not a "Black and Decker" drill, which would be fine for water if that was all you had.

For small jobs

11032_p01.gif (5.07 KiB) Viewed 742 times

[welding@60]

FIRST OF ALLDO NOT ATTEMPT IF YOU ARENT EXPERENCED ENOUGH TO READ WELD PUDDLE as for gasoline tanks have succesfuly repaired by hot water dawn dishwash cleaning and purging with co2 diesel fuel tanks off cat scrapers I have cut open with o/a co2 purge keep purge going until done welding coustmer is more than happy to pay for co2 and premimum rate to get machine back in dirt as for hot gasoline piping 15yrs ago was up dating 8inch load line by plumbing from old under ground line being put out of service to existing above ground line running 1500ft to storage tank started out by pre fab rolling 45 sweep with 150# slip on flanges now to cut 8 inch hot line first welded on 2inch thread o let and hot tapped line was previously drained and open to air high and low in pipe supports still allows for pooling of live gasoline cut line with hand operated pipe cutters ahead of hot tap pucker tight not get spark removed section reach as far behind tap as we could and installed fire proof balloon type pipe plug and aired up tight next came in front of tap installed 8inch sewer plug and tightend next put 12inch long riser on thread o let filled void between plugs to top of riser with water now 2 barriers between welding area and live gasoline line now set in pre fabed sweep tacked in good took flanges apart complete all welds then pull out plugs still pucker up real tight if you get to the point you don't you are getting to confident that's when things can go terribly wrong

[cornmuse]

What you are talking about is called a hot tap in the trades.

Gas company here had (still have for occaisional use) a special valve they would weld on the gas main. Flowing gas carrys away the heat, they had to really crank up the heat (ox/acet) to make their welds. Had a local welder who among other things, made hot taps on up to 8" water mains, mostly for hydrant "tee's", both steel & transite pipe. Some cities would not allow shutting off certain mains, so, this guy did his thing for us.

-c-