Anyone know why the thermal expansion coefficient in API-650 is different than B31.3.

Example, At Design Temperature of 200°F, it has 6.67 instead of 6.38 x 10^-6 per in.-°F per B31.3?

Also, API-650 does not gives the Thermal expansion Coefficient at 70°F. I could not interpolate the values between temperature 70°F and 200°F without it.

Thanks.

If you see at the bottom of table P-1 given in API 650 App- P, a note is given as,

Mean coefficient of thermal expansion, going from 20°C (70°F)
to the temperature indicated.

So at 70 deg F, our change in temperature is zero so, thermal expansion will be zero,

For interpolation you can use value of expansion coefficient as 0 at 70 F

That is not correct. If you look at B31.3 Table C-3 Thermal Coefficients.

The values given are between 70°F and indicated Temperature.

From 70°F to 70°F, it has 6.07 miu in./in.-°F.

Anyone aware of this?