steel pipe expansion

ed broderick_2

Realizing there is expansion and contraction, how much larger should I make the 1 1/4 riser hole? This is black pipe not copper. Thank you to the Steam Pros. Ed

Tony Conner

What Matters Most...

...is the length of the pipe. The diameter will increase as well, but you're talking about such small dimension, that you'd likely have a hard time measuring it unless you had calipers. The formula for steel pipe expansion is:

inches/100 feet of pipe = 0.00804 X the delta-T in *F

When you figure out the fraction of 100 feet that the OD of 1-1/4" pipe represents (actual OD is 1.66 inches) this is a tiny number.

If you're planning to insulate this line, you should make the hole big eough to allow for it. If nothing else, you will likely get some expansion on horizontal runs under or over this riser. That may move the vertical line to one side of the hole or the other anyway.

Tim Gardner

One mistake I made as a DIY homeowner was to allow the riser to touch a piece of wood as it squeezed by. I should have cut the wood a bit more. I now hear it every time it fills with steam and when it cools. It makes this clicking sound, a little like a dripping fawcet. I didn't know what it was until a retired plumber mentioned that this can happen. Now that I know what it is, It doesn't bother me as much, but I'll do it right next time. I might even open the wall again someday and fix it.

So I'd make the whole big enough that there's plenty of clearance on all sides, especially if the same pipe has to thread multiple holes.

Dave DeFord

If my math is right..

your formula would result in 1.0854 inches of expansion over 100 ft at 135 deg F rise in temp. Is that right? It just seems like a lot.

Tony Conner

That's..

...what you get. Quite often, you won't actually see the end of the line move that much. The pipe will often squirm a bit along it's length, and take up some of the expansion. We used to figure that the 125 PSIG steam system I worked on would expand almost 2-1/2" for every 100 feet. When you've sometimes got 600 or 800 feet of line (length of a city block), it adds-up - especially when there is 6 or 7 blocks in a straight shot. There would have to be a manhole at each intersection with anchor points, and another manhole in the middle of the block, with a pair of expansion joints back to back, each taking over 6" of travel. We always measured the joints when they went in new, so we could see how much expansion we actually got, when the lines were valved-in. If the calcs said you'd get a foot, the actual expansion would usually be 9" or so.