B31.1 Vacuum Piping and Out of Roundness 2

[ColonelSanders83]

Hello All,

I am currently designing a geothermal power plant piping system in which we are using an expensive refrigerant as our working fluid. One of our operating cases is a full vacuum during working fluid evacuation. Thus I am designing the piping to handle a 15 psi external pressure as well as the internal pressures it will see during operation.Some of the lines are of substantial diameter 30-48 inches.

I would like to use ASTM A53 Gr. B, but I have found out that A53 piping has an out of roundness allowance of 2%, rather than the standard 1% for most other piping specs.

The BPVC section VIII div 1 UG-28 to UG-30 referanced by B31.1 all seem to be based on a 1% out of roundess. (per L.C. Peng book Pipe Stress Engineering)

Due to the sensitivity of external pressure calculation to out of roundness, how do I correct the calculation to properly account for the additional 1% of out of roundness in A53 pipes?

A question properly stated is a problem half solved.

Always remember, free advice is worth exactly what you pay for it!

http://www.ap-dynamics.ab.ca/

 

[MikeHalloran]

I suggest you calculate the collapse pressure yourself.

The calculation method in this paper:
"Effect of Initial Eccentricity on Collapse Pressure of Circular Beam Tubes", S. Yadav
Fermi National Accelerator Laboratory, Batavia IL

http://www.flab.gov

Gives results that seem to correlate well with a single data point collected/estimated from an expensive incident associated with pressure testing of jacketed tube.



Mike Halloran
Pembroke Pines, FL, USA

 

[doct9960]

ColonelSanders83,

If your pipe meets the permissible variations in ASTM A 53, you don't need to adjust your external pressure calculations. Paragraph UG-80(b)(10) of BPVC Section VIII, Div. 1 says...

Vessels fabricated of pipe may have permissible variations in diameter (measured outside) in accordance with those permitted under the specification covering its
manufacture.

 

[racookpe1978]

But isn't that for variations in thickness (assuming a constant roundness)? He is concerned baout variations in roundness forcing a collapse of the pipe. (Inside pipe pressure is an easier case than vacuum for roundness because inside pressure will tend to reduce variation and reduce roundness problems, but a vacuum will exaggerate roundness problems.)

How many feet of pipe?

Could you consider running the pipe through a lathe or pulling a die through to smooth it out? It would reduce wall thickness - and be expensive! - but for a few large bore thick-walled pipes it might be worth the effort.

 

[ColonelSanders83]

MikeHalloran:

Thank you for that paper reference, thats goes straight into my vast and evergrowing collection of usefull stuff.

doct9960:

I think you may be on the rigth track with your statment, the only thing I need to know to close the loop is if A 53 is an allowed piping material for vessel fabrication in the BPVC. If you could point me to were this is hiding in the code I would be most appreciative.

racookpe1978:

The lengths are between 30 and 100 feet in length.

As usual managment is pressuring for lowest cost and while both of your solutions are valid we have niether the capacity to do it ourselves nor the money to get it done. It would be cheaper to go to more expensive pipe.



A question properly stated is a problem half solved.

Always remember, free advice is worth exactly what you pay for it!

http://www.ap-dynamics.ab.ca/

 

[doct9960]

ColonelSanders83,

SA-53 is listed in Table UCS-23

 

[doct9960]

Forgot to mention that ASME SA-53 is identical with ASTM A53 except for the additonal testing & NDE on ERW pipes (para. 11.1.1) and some editorial corrections to Table X4.1.