Bang!!!

[hankj]

Hi, guys.

Enlighten me, if you will.

I have several 18" lengths of 8" steel pipe - 3/8" wall. Broke an irrigation line - 2" schedule 40 PVC, and decided that a piece of this steel pipe cut in half lengthwise would make good protection for the buried repair. As I finished the first cut with th O/A torch, the pipe spread violently about 1", accompanied by a loud bang similar to a 12 ga.

Was it due to the way the pipe is made or was it just the result of expansion from the heat of cutting?

Sure made me jump. Learn something every day!

Be well.

hankj

[HAWK]

hankj,

I think you will get the same result if you try it again! By the time you get to the end of the pipe there is not much left to hold it together. When that last "thread" holding the pipe together is severed something has to give. You have filled the pipe with a lot of heat creating a lot of expansion. All that energy has to go somewhere.

I have had 20' sections of 1/4" wall steel case pipe do the same thing, but not with as much force. By the time I get to the end of the pipe a lot of cooling has taken place and the wall is much thinner as well.

Be careful! Think what could happen. See below:

On a different note: A crew was working in front of me on a capped section of 20' x 8" ductile iron pipe. This was a termination pipe in a water line and was supposed to be dry. Unknown to the crew a samll water leak had sprung several days earlier and compressed all the air in side the pipe. When the worker removed the last eyebolt the end cap blew off and sailed over 100 yards taking his knee cap with it!

[Blondie_486]

Hankj & Hawk,

Recently at work I was working on a project that had 5" schedule 160 that had to be split in half. The sections were 6" long and I decided to cut them on the vertical bandsaw. I stood them up on end and when I got through the wall of the pipe on the first cut they snapped apart with a loud pop. I wasn't really hogging the work so not that much heat had been generated. I'm figuring that it most likely is in the way the pipe is formed that when you cut it lenght wise it springs back apart.

Now I've cut pierced tubing the same way and with a torch and not much spring to it mainly because the pierced tubing starts out as a round bar then the center is pierced to turn it into tubing.

It would be like comparing a piece of tubing that you made using 2 seperate processes. The first process would be to take sheet stock and form it in a roll and then squeeze the edges together and weld it. The second process you take a piece of round stock and chuck it in a lathe and bore the inside out.

In the end you could have 2 pieces with the same ID and the same OD. but When you went to split them which do you think would be most likely pop open? Of course the one that you had formed from flat stock, you would release the tension caused by the forming process. Pipe begins life as a coiled steel. I've had the opportunity to see pipe being made and my brother works for a company that makes tubing products for the automotive industry. It's really quite something to see.

Blondie

[HAWK]

Blondie,

Thanks for the info. I was wondering about different methods of manufacture. Hankj is right it will startle you!

[Blondie_486]

Hawk,

You're right it will startle you. Even though I know it's coming sometimes it still makes me jump. Especially if some one else is doing the cutting.

Blondie

[hankj]

Thanks for the disussion, guys. I knew you'd come through!

The whole thing just makes me realize that one needs to be thinking about what's going on all the time when working on materials whose properties can be altered by the process.

Be well.

hankj

[Blondie_486]

Hankj,

Yes we need to be especially careful with how we work with materials. Some can kill you if not handled properly. Any time you try to dissect something that's been formed and welded such as pipe when you split it open it will spring on you. Just think if it had been a 48" diameter boiler shell that had been made of 2" GR70 boiler plate. We've had to cut a couple of those apart because the sub arc welder had a problem and the weld had to be completely removed and start all over again. When we got to the end those sounded like a cannon went off. Fortunately we were able to stand back from them when they were being cut. One of them split apart with such force it jumped off the rollers it was sitting on.

Blondie