What are the difference between ASME B31.3(Petroleum refinery piping) and B31.1(power piping).

In a "nut shell":

- the SIFs are different
- the allowables are different
- the expansion coefficients are different
- the code stress equations are different

There are other differences as well.

The expansion coefficients are different?

Well, doesn't that just beat all?

yes...

the piping knows what code its being used in....

LOL sad isn't it? I believe (hope) the two codes will eventually resync on expansion coefficients.

Also there is a huge difference in the calculation of in-plane versus out of plane bending stresses.

B31.1 uses a simplified one SIF approach (the maximum) for in and out plane where B31.3 uses two separate values. The end result... I can conceive of situations where the reported maximum stress for the same system analyzed by the two codes would show different locations being the highest stress point.

Also there are other numerous SIF differences...

Thanks ....

One thing I still don't understand. Why should there be different codes for designing ? The pipe material is same, so are the temperature-pressure-fluid-insulation-boundary conditions etc. Can't we have one single code which defines everything ?
Regards,
John Wright

You probably would like egg in your beer as well! LOL At one time there was only one code B31.

As time went on other industry needs surfaced.... one of the biggest industries that had may unique requirements were cold piping systems.

I was because of unique needs that B31 Became B31.1, B31.3 etc.

If you compare closely B31.3 and B31.1 you will find vast differences in materials and fabrication.

Now as for design it is my opinion that certain tasks should be the same across codes... hoop stress, fatigue SIFs etc.

But the codes are consensus-based committees and some members just don't care about what the other code says about certain things.

I suggest you do some detailed studying and if you ever get a chance attend a committee meeting or two and you will understand what should really be the same and what shouldn't.