Pressure Testing Pipework (CWP / DP and WP)

[DW1006]

I am looking to have some pipework pressure tested to 750psi, to allow us to certify the pipework to have a Working pressure of 600psi.
However, I have just noticed that within this pipework structure there are two valves (butterfly I recall) on the system which are stamped with “740CWP 0 @ 445°F”
Im not to familiar with what the Cold Working Pressure mandates. I understand its saying that the max operating temp is 445°F when running at 740CWP, but what does this mean with regards to SWP and DP.
During the pressure test the pipework will be charged with nitrogen, and will remain at ambient temp. As im nowhere near the 445 degree F does this mean im good to before a pressure test to 750psi, to allow a Working Pressure of 600psi, gain at ambient temp.
Any advice would be fantastic.

Regards

Dave

 

[LittleInch]

The way I read that is that they are good for 740 psi at CWP defined as up to 100F / 38C in MSS SP 110 I think.

After that they derate down to 0 (ZERO) psi at 445F. I suspect they are rubber lined? So good for 600 psi up to about 150F at least.

So for ambient temp testing at 750 psi they look good to me but need to be open.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

Pneumatic testing

https://www.pipingengineer.org/pneumatic-testing-of-piping-systems/

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[DW1006]

So, ive been doing a bit of research, and would people agree with the following.
I think when we talk about hydrostatic testing this is CWP. My understanding is I don’t think the water is actually heated, but running an ambient test for anything that operates up to 230C is good enough.. CWP is a ‘safer’ way of conducting a pressure test as in the event of a failure as you do not get a sudden release of energy as you would with a gas failure. They are generally conducted at the manufacturer or by a test house under very controlled conditions. However, hydrostatic tests are difficult to perform in the field where we are, and some parts are not suitable for water ingress (corrosion) hence why we have used N2 as in the event of a sudden release of energy the source would not ignite (no O2 obviously).
Happy to be corrected.

 

[LittleInch]

Yes I believe that testing is basically at CWP temperatures. Note that based on the data, the valves start to de-rate after 38C.

Nitrogen or air makes little difference I feel - the issue for pneumatic testing is mainly the stored energy.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

Pneumatic testing should be a last resort. If I was conducting a safety review, I would ask why you cannot use a corrosion inhibitor and expect to hear a very good reason.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[EdStainless]

If this is a system of any size then pneumatic testing at these pressures is very hazardous.
Will this be bunkered?
Including the top to prevent launching any material?
And no personnel within a very long distance.
The gas does not matter, air poses no more risk than N2.
You need a very detailed safety and risk assessment.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[DW1006]

Cheers all for your advise and input. Regarding safety questions, all extremely valid and all correct in what you are saying. Due to the nature of the facility and what it is used for, water is not an option. Pressure test will be carried out in a controlled, restricted area, and by competent people, under the watchful eye of BV. Full ATP and RA have been carried out, and pressure test is in accordance with SAFedPSG21 and ASME B31.3.
Fantastic advice, and good to see everyone is taking safety seriously
In my company, nothing gets over looked (well im sure it probably does, but not the little things haha - Big company, big safety wigs, lots of safety ideas and campaigns

 

[LittleInch]

That's good.

I do think you need to dig out the data sheet on that valve to understand what its pressure temperature rating is and what temperature it will operate at

But testing is fine at ambient temperature.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[DW1006]

Cheers. For clarity, the pipework once certified to operate at 600psi max, and will contain clean dry air at ambient temperature. It will never operate at an increased temperature.
I guessing, this particular section of spool with the valves stamped 740CWP at 445°F must have been originally tested somewhere in house using water - ive no records for for this though unfortunately. Its certainly never seen any water while it has been installed.
Would this be your assumptions to? Its first i have ever come across something stating CWP. Throughout all of our facilities and pipework, the flanges have only ever had SWP and DP stamped and the class. Hence my confusion

 

[LittleInch]

CWP is just another version of the flange or valve rating used in B16.5 There's no correlation between that and testing in water, though the valve castings may have been tested at the vendors works - check out the data sheet and test records for the valve.

Think it comes more from the steam industry back in the day hence why there is an upper temp limit with one assume a gradual slide in MAWP from 740 psi to Zero psi over the range 100F to 445F You keep saying 740 at 445, but your OP said CWP 740, 0 @ 445F. BIG difference.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[r6155]

Try with Acoustic Emission Examination during pressure test, see ASME V

Regards

 

[GD2]

DW1006,
One statement you made is erroneous. 740 CWP@445 F is wrong. 740 psi is at room temp upto 100 F. LittleInch had clarified at his first response.
You plan to certify the piping at 600 psi (at room temperature), it will be absolutely fine with the valves.
By pneumatic test of the piping system ( N2/air) ar 750 psi, the system DP will be 682 psi@100F
Keeping the MAWP 600 psi@100F, the system will be safe.
One more thing I want to recommend is that always relate pressure to corresponding temperature. In design world pressure alone does not make sense.

GDD
Canada