Pipe Stress

Replace the tired pipe with new stuff to the same specification, and you can't go wrong, Mildred!

Why not ask your ME?

The allowable stress cannot possibly that high. You are misreading some numbers, or worse yet, concepts.

Hey, it's 3,787 bar.

No wonder the guy needs help, lots of help.

You are confusing pressure (of contents within the pipe interior) with stress (within the pipe wall). The OP is confusing allowable stress with ultimate (or yield) stress, depending on which is used in his local code.

That's why I don't do pipe. Ever.

I also never do two shows a nite. Beetlejuice

The question is not clear! What do you need to know?

Did you mean to ask if you need to include fittings or valves in the test section?

I am let to believe that there would be some fittings - the pressure test fittings - that would be exposed to the test pressure. Anyway everything in the systems needs to meet the system specs.

Rephrase your questions and come out of the anonymos hiding and I am sure somebody can guide you in the right direction!

Your pipe supplier can give you the allowable stress for the grade of pipe you intend to purchase. The stress you quoted is way higher than I would expect. Also you failed to mention the pipe diameter which is critical in calculating the allowable pressure. Recheck your calculations and good luck.

What was the reason why the pipe is being replaced to anyway? Knowing this will point you to do the proper analysis..

thank all for your comments!!

rearranging the question

I am currently checking stress on a section of pipe to be replaced

The conditions are:

1.       existing pipe: OD 18¨, API 5L Gr X65, thickness 0.625¨, ca: 0.0625 ¨

2.       purchased by the client pipe to be replaced: OD 18¨API 5L Gr X65, thickness 0.625 ¨, 206 bar hydrostatic test

3.       Design Factor: 0.72

4.       ASME B31.4

The replacement of the pipe is in the crossing of a river, because the tube is observed. It's been 27 years since it was built. The hydrologic studies indicate that the pipe must be buried 5 m from the level of the river scour

The client wants to validate the specifications  and stress of the pipeline, to validate if the same material and thickness? hence the confusion

I think I can verify is the buoyancy and verify if the tube during construction is able to withstand loads the weight of the earth and the passage of heavy machinery. I'm right? Is there anything else I can do?

When I calculate the Sh get 46,800 psi.

When I determine Sa also get 46,800 psi, is this correct? I'm doing wrong?

Thanks in advance for your feedback

So sorry for my poor English

Using the formula for

Straight Pipe under internal pressure from 304.1.2

P = (2St/D)xE

where S = 46800

t = 0.625

D = 18

E = 1

Design Factor = 0.72

I get an allowable internal pressure of 2340 psig.

It is all straight forward except the yield stress of S = 46800. This has the largest effect on allowable pressure. Be absolutely certain of the allowable stress you are assuming.

You must also check structural factors such as the span between supports and other physical parameters.

thank Mr Dave

the material is API 5L GrX65, then:S=0.72x65000=46.800 psi

According to B31.4, P=2925 psi. My question is if I should calculate hoop stress? when I calculate the hoop stress also is 46,800 psi. that's one of my concerns is that I am doing the right thing? 

other physical parameters, can be more specific?

thanks