Minimum thickness of bent pipe (ASME VIII-1)

[marty007]

Hey,

I've run into this a few times now, and finally had a need to develop a good design guideline. I was wondering what approach others take.

So the question is, what do you define as your minimum thickness for a bent pipe for use in ASME VIII-1?

In my opinion, this issue is not covered in ASME VIII-1, so I decided to apply U-2(g) and take a page out of ASME B31.3 / B31.1. In these codes, there is a formula presented for minimum pipe wall thickness at the extrados/intrados region of a bend. In B31.3 this is presented in paragraph 304.2.1. Essentially a variable (I) is calculated based on the pipe diameter and bend radius. The standard pipe wall thickness formula is then used, but the allowable stress (S) is divided by this factor (I). With this method the pipe bend ends up having three minimum thicknesses: one at the outside of the bend (extrados), one at the sidewall, and one at the inside of the bend (intrados).

So, for ASME VIII-1, could we use this same approach? The formula for (I) would be taken from ASME B31.3, and is used to divide the allowable stress (S) in the ASME VIII-1 shell thickness formula.

What does the community think of this approach?

Cheers,
Marty

 

[SnTMan]

marty007, not familar with the piping Codes, but it sounds U-2(g) to me.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[metengr]

The minimum thickness for bent tube or pipe must be the minimum thickness as for straight tube or pipe, look at UG-31, which applies to tubes used as tubes or shell. The concept is the same where UG-27 provides for the minimum thickness of tube or shells under internal pressure.

So, your approach should be to use the minimum thickness from UG-27 but the original thickness for bending to account for wall reduction could certainly be used from one of the piping codes, as you stated.