# Thermal expansion of steel tube (chain link fence)

A friend is building a chain link fence, and occasionally I drive across the state to assist. The newest problem is that the top rail won’t quite fit into the connector sleeves that I bought from a different vendor.

BUT MY ACTUAL GENERAL QUESTION IS: How much will the inside diameter of the connector sleeve increase if it gets heated up to about 250 degrees Fahrenheit? (From, say, an ambient 80 degrees.)

The sleeve’s I.D. is nominally 1-5/8”. The sleeve is galvanized steel, and the thickness is about 0.06”.

Finding a practical solution to the fencing problem, shouldn’t be difficult — I’ve got some connector sleeves from a different vendor that work okay (a little too loose), and ordering sleeves from the same place we bought the top rail wouldn’t cost much. My question is mostly abstract curiosity. (I’m not great at math.)

Don’t know how many of these you have to connect. But you could probably take a reciprocating saw (of your choosing) with a metal blade and slice/make a cut down the end of the rail pipe to remove some material. Then compress it a bit with some channel lock pliers to make the diameter a bit small and then force it in.

I’d get the right sleeves. It’s hard to say if heating will work, and you don’t want the connector cooling down while you run the pipe through it because it will seize on the pipe. And 16 gauge metal is pretty thin and will cool down fast. Just get the sleeves or rails that fit.

D_hot = hot diameter
D_cold = cold diameter

R (ratio) = D_hot / D_cold

R = alpha x delta_T + 1

alpha (linear thermal exp coefficient for steel) = 0.0000094 in/in F

delta_T = 250 - 80 = 170 F

=>. R = 1.0016

So, 1.625 in (1 5/8 in) will become 1.628 in when hot.

Note - the calc assumes uniform heating, in reality the metal will have hot spots or may not stay Truly circular when heated.

Also - there’s a good chance you will vaporize the zinc (galvanization) and will result in bad corrosion at those spots.

You also risk breathing zinc vapors which is not good. Buy the right size fittings, it’s not worth the risks to your health.

Between 200°F and 300°F the linear coefficient of thermal expansion for carbon steel material is 0.00000667 in/in-°F, based on 70°F reference temperature. So the ID at 250°F would be roughly 1.625 + (1.625)(0.00000667)(250-70) = 1.627 inches.

Not much of an improvement but you can use the same formula to approximate the required heating temperature. You could also cool the rail to reduce the OD.

Yay @Surreal Thanks for independently verifying the calc.

@Surreal and @am77494 – thank you very much for the calculations (and worrying about my health).

And lesser – but still real – thanks to enipla and Tripolar.