Digging up gas lines

[MChalkley]

Does anyone know how much danger is really involved in digging up gas lines? As in: How often do they blow up and why?

I busted one last Saturday and the police and fire departments evacuated the whole block. Then the gas guy came, got out a clamp with a ground rod attached to it, strolled over to the pipe, and sqeezed the pipe shut. That was it.

So, my next question is: Does anyone know of a source for these tools? I saw a couple of them in an Internet search, but they're $300!

 

[njrqs]

Mark

Ok so you buy the tool and then each time you dig one up you just close it off and cover it up hey????

Shonky /w3tcompact/icons/laugh.gif

 

[EdKing]

I think the biggest danger with gaslines is the fact that a deisel engine will have a tendency to "take off" if it draws the gas in. It's like dumping the throttle wide open with no governor.

 

[gordon]

Good news is that the gas actually only will burn in a very narrow percentage of air mixture. To much gas and it won't explode and not enough gas and it won't even ignite. But when your in that nice window of 2.5-8% range of gas to air it sure does make for some pretty colors and even sometimes a nice BOOM to go with it.

Ever figure out why backhoe insurance is so costly?

Gordon

 

[JATO_RaT]

Mark, many times natural gas lines are broken by backhoes out here. Our gas company PG&E broke a very high pressure one at the job we were on and to us it was a huge deal. A massive dust storm from the escaping gas, the smell everywhere. I just wanted to run. The gas guys stood around laughing about how they do this all the time, no big deal. They weld right on the gas line while the line is hot. I don't get it. I know you need the right air mixture, but good grief, how and when do you know when that is. About the most costly thing to dig into is anything phone line related with one exception. On our nearest cross road at my old house were two aircraft petroleum lines to the 2 military air bases. Touch the outside with a hoe and it was automatic to shut the lines down, evacuate them and clean them. Intial minimum cost was $50,000. Puncture it and I believe you just shoot yourself to take the easy way out. No one uses hoes around them, they get out the shovels. Rat...

 

[billfires]

Rat, we have a $2500 meter that measures the LEL and UEL (lower & upper explosive limits) of flammible gases. Different gases have varying ranges where they will explode. I generally trust the people that deal with these things on an almost daily basis but also keep in mind that most "incidents" happen to people that are considered "experts" in their field.

Bill C

 

[Bird]

<font color=blue>how much danger is really involved in digging up gas lines</font color=blue>

A lot! Mark, I did gas leakage surveys for natural gas companies in '93 and '94. I think you need 4% to 15% natural gas to ignite it (different percentages for other gasses). So a trained and experienced guy can work reasonably safely in high concentrations of gas (so long as he has enough oxygen to breathe), but with high concentrations at a leak, how many people are going to know where, at the perimeter of the leaking gas, is the right concentration to ignite?/w3tcompact/icons/wink.gif And it doesn't take much of a spark to set it off (I notice you mentioned his ground rod on that clamp).

And another thing about digging up gas lines . . . what kind of pipe? There's still some cast iron lines out there, black pipe, wrapped pipe, and "plastic" pipe. Different techniques to repairing them, too, of course. I checked some gas mains that had been in the ground for over 70 years in Pennsylvania.

I'm one of those social pariahs who still smokes, and had several people ask me if it wasn't dangerous for me to be searching for leaks while smoking a cigarette./w3tcompact/icons/laugh.gif I always told them it was the safest time there was, because I was using instruments that would pick up minute quantities of any combustible hydrocarbons. I used a "flame pack" that would pick up the tiniest quantities (even from decomposing vegetation at times) and also a "combustible gas indicator" that would measure the concentration. It was an interesting job.

 

[Egon]

Usually its best to hand expose all lines when doing hoe work. They can be located and marked. The plastic lines have metal tracers with them.

Diesel equipement working around hydrocarbons should be equiped with a positive air shutoff so the engine can't run away or ignite the leak. In many places this is a requirement when using diesel engines.

Plastic pipe under low pressure can be bent back on itself to seal off the ends. The clamps for metal pipes are readily available at stores supplying oilfield supplies.

Its best to evacuate the area when there is a gas leak and let the utility company take over. They should isolate the line and let it bleed down to zero presure and then proceed with a repair suitable to the type of pipe in question.

The real bad leaks are those involving gasses heavier than air as they pool and can ignite at any time an ignition soure is encountered. Usually the leading edge of such a pool will be within the comustible range. Some of these leaks are purposely ignite to reduce hazard of large explosion.

Just some thoughts.

Egon

 

[Golfgar4]

<font color=blue>"How often do they blow up and why?"</font color=blue>

Mark,

I cannot tell how often they blow up, but I can tell you that it can happen. A few years ago, one of our City crews was doing a minor excavation in our downtown area. They had called Diggers Hotline and all locates had been marked. At least they thought so!/w3tcompact/icons/sad.gif They hit a line that no one knew was there, and the two middle buildings in the block blew up! /w3tcompact/icons/shocked.gif

The back hoe was blown backward about 20' and the operator, who survived, landed about 40' away! As far as anyone knows, the explosion was caused by sparks as the bucket cut into the gas line.

Fortunately, no one was killed or seriously injured as this occurred during the lunch hour and almost all of the occupants were away from the buildings.

 

[hosejockey2002]

It's actually a good thing when the gas ignites when the line is broken, as long as there are no structures too close. When the gas is burning, you can see exactly where it is and it doesn't have a chance to accumulate. Of course, it's usually not very good for the machine that hits the line!