Welding and concrete?

[mikehaugen]

A while back I cut down some posts at work. They are 6" round tubing filled with concrete- not sure if it's 1/4" or 3/16", I'll have to check. I cut them flush with the concrete floor with a torch and boy was there a lot of popping. Anyway, I want to weld some together but not sure if it is a good idea. I would plan to weld some angle to them for 3 point brackets for counterweight.

I would have to imagine that there is still some sort of moisture in them and would possibly build pressure inside. Since they are round I don't anticipate a lot of contact area, so at most I'm thinking maybe 3/4" long welds. Would enough heat build up from short welds like that? Do you think they will blow up in my face? Am I worrying too much?

 

[dragoneggs]

Hmmm.... an interesting question. My guess... and yes it is worth :2cents:, but how much more I don't know. You should be fine as I would expect the metal tube to expand more than the concrete with the introduction of heat. This is based on their relative coefficients of thermal expansion. The steel 'alpha' is about 50% greater than that of concrete.

 

[mikehaugen]

Hmmm.... an interesting question. My guess... and yes it is worth :2cents:, but how much more I don't know. You should be fine as I would expect the metal tube to expand more than the concrete with the introduction of heat. This is based on their relative coefficients of thermal expansion. The steel 'alpha' is about 50% greater than that of concrete.

From what I understand, the problem with concrete and heat is the moisture contained in it will become steam.

 

[dragoneggs]

This is probably an excellent question for Shield Arc! My gut says the pipe, along with expanding, will also dissipate the heat much more than the cement so the amount of water that would get 'superheated' and pressurized will not be enough volume to burst it if you are welding short lengths... but I wouldn't take my guess as gospel. I am sure you would rather hear from someone with experience. I will try to shut and and just tag along here.

 

[mikehaugen]

This is probably an excellent question for Shield Arc! My gut says the pipe, along with expanding, will also dissipate the heat much more than the cement so the amount of water that would get 'superheated' and pressurized will not be enough volume to burst it if you are welding short lengths... but I wouldn't take my guess as gospel. I am sure you would rather hear from someone with experience. I will try to shut and and just tag along here.

You are probably right, it's kinda what I was thinking but I still had my concerns.

 

[Shield Arc]

:laughing::laughing::laughing::laughing::laughing:WOW! This brings back memories! I remember this happening to me on my first job right out of welding school. I cut something with a torch on a concrete curb. Luckily I used my welding hood instead of burning goggles. When the concrete blew up in my face and hit the hood I couldn't imagine what happened.:shocked::shocked:
The heat from the torch or welding is just heating the water trapped in the concrete, and it will blow out! I'd say just protect yourself the best you can. And don't let anyone in the area while your working on this.

 

[Gary Fowler]

As long as the ends of the pipe are open as in not a welded steel cap on both ends, any steam generated is going to be able to vent out between the pipe wall and the concrete. I wouldn't worry about it. IF you are going to weld some of these back together (concrete exposed near the weld), you may want to chip out the concrete a bit from the weld area. I don't think it will "blowup" but it could send some popping concrete into your weld puddle that would contaminate it and make it very weak.

By the way, all aggregate (rocks) will pop like that when heated, it doesn't have to be just concrete, so protect yourself when welding or cutting around gravel or concrete when heat could transfer into these objects.

 

[ThomasH]

A while back I cut down some posts at work. They are 6" round tubing filled with concrete- not sure if it's 1/4" or 3/16", I'll have to check. I cut them flush with the concrete floor with a torch and boy was there a lot of popping. Anyway, I want to weld some together but not sure if it is a good idea. I would plan to weld some angle to them for 3 point brackets for counterweight.

I would have to imagine that there is still some sort of moisture in them and would possibly build pressure inside. Since they are round I don't anticipate a lot of contact area, so at most I'm thinking maybe 3/4" long welds. Would enough heat build up from short welds like that? Do you think they will blow up in my face? Am I worrying too much?

I moved some 6" pipes one time, which were concrete filled and not capped, to new locations, and welded them on top of new pipes that were sticking out of the concrete 2". It was interesting to hear all of the popping going on inside the pipe. The concrete appeared to be dry, but as you might expect it had plenty of moisture, and there were lots of explosions going on inside while I was welding. Considering that aggregate was exploding inside, I *sure* wouldn't want to be welding on something that had exposed concrete on it. What I was doing worked, but sounded plenty scary.

 

[Shield Arc]

When this bridge project across Lake Washington was just about completed we had to remove the 24-inch pipe filled with concrete under every pier table next to the concrete columns. I got everything set up to do it, but got transferred to the Metro tunnel project down town Seattle before the work actually started. The guys used these thermal lance to cut the pipe.
https://www.youtube.com/watch?v=EV4r7OKkXmU

 

[beeforty]

I remember in Hi school shop someone spilling molten metal for a casting project and metal and concrete splattering everywhere! It is the moisture in the concrete or its crystalline structure that causes it to spray both crete and metal at you!