Dear All

I checked total thermal expansion lenght at same time as changing the ambinet & operating temperature. but but difference of themperature(delta T, 100C)is same

and I found some total thermal expansion lengths were little different.

Material : A53 Grade B, 50m length

case1 : amb. Temp 20C and Oper. Temp 120C, thermal expansion : 61.119mm
case2 : amb. Temp 40C and Oper. Temp 140C, thermal expansion : 62.469mm
case3 : amb. Temp 60C and Oper. Temp 160C, thermal expansion : 63.779mm

Pleae let me know if you know what these differences originated.

Thanks & Regards

Tim Paek

The rate of expansion changes with temperature.

Yes, the RATE changes. Try it for yourself. Go to table C-1 of B31.3 for example, copy the data for Group 1 material into Excel and plot the graph. You'll see that the relationship between temperature and thermal expansion is not exactly linear.

Does anyone know offhand whether the published values are averaged relative to standard ambient conditions, or if the rates are instantaneous?

I.E. If I have a material at 1000°, and rates are provided in ~100° increments, ought I calculate length increases from ambient-100, 100-200, 300-400, 500-600, 700-800, 900-1000 to calculate a total length grown, and then back out an average coefficient of thermal expansion should I want to simply calculate ambient-1000°?

In most cases, I suspect it doesn't matter. In cases where you have dissimilar materials welded together, it makes a big difference.

Thanks.