Flange temp derating - CSA vs ASME

[302Hugo]

I had a discussion with a coworker about some piping and we disagreed. We have a crude pump station and the pump discharge piping is 600 ANSI rated and the pipeline is rated for 1440 psig. Our pump discharge PSV is set at 1440 psig. But we are running our crude at about 175F.

So derating the flanges we should have our set point at about 1395psi, should we not? My co-worker thinks there is something in CSA that states we are able to use the 1440psig because that is what the pipeline is rated for.

I didn't think there was a difference between CSA and ASME to determine derating for temperature for flanges?

 

[BigInch]

Don't know your Confederate States of America code , but if it was a pipeline operating in the USA under T49.192 or under B31.4 you must derate the pressures when operating at temperatures over 120F.

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"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[302Hugo]

Thanks for the reply. Although, more or less I was wondering about the site piping and derating of the site flanges (ASME B16.5).

If we were operating at 175F with 600 ANSI flanges on the discharge, wouldn't we need to design our piping / have our PSVs set at 1395 psig to protect our site piping?

 

[JLSeagull]

Specify which CSA codes applies to this derating discussion. My copy of CSA B51.03 Boiler, Pressure Vessel, and Pressure Piping Code refers to substantial efforts to harmonize CSA with the USA and International codes and standards. CSA is covered with references to the ASME B&PV code and many of the piping standards.

Consider the more restrictive standard especially if ASME B16.5 is more conservative than some other reference. Also, verify that the connections exclude stainless steel or other alloys if you plan to operate toward the top of ASTM A 105.

 

[ColonelSanders83]

Your coworker thinking there is something in CSA won't cover you in the event he is wrong. Err on the conservative side and set your PSV to 1395 psi until he can definitively prove otherwise (i.e. show you line and verse). You should also not confuse what a specific pipe can handle (the 1440 psi) with what the system can handle (the 1395 psi of the lowest rated components). A piping system is the sum of its parts and is pressure and temperature rated to the WEAKEST component. The pipe is usually the weak link, but apparently not in your case.

 

[302Hugo]

The CSA code would be Z662. That is what was confusing me. As far as I know CSA doesn't state anything about derating for ASTM flanges, and if it did I would assume it refers to ASME B16.5.

I understand the weakest link is what you design for. That's interesting, because with all of our facility piping the flange rating (after temp derating)is always the weakest link (outside of some instrumentation).

 

[BigInch]

Flanges AND PIPE allowables at elevated temperatures are not automatically good for a 1440 psig or whatever rating you might have that was specified/calculated at a base temperature (120F). The potential derating applies to all components depending on their lessened yield strength at elevated temperatures. See the material allowable stress tables in B31.4. If CSA references B31.4 then the derating for all components apply.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[302Hugo]

BigInch, you're right. For some reason I had my horse blinders on and was thinking everyone uses A106B pipe for everything, ha ha. A106B pipe doesn't start to derate until 500F (I believe).

 

[302Hugo]

Ok, I've got my answer!

What the issue was with my co-worker is that he was talking about CSA certified flanges, not ASME certified. As per CSA Z245.12 Table 1 Note (2) "Pressure ratings are for temperatures lower than or equal to 120C"...and for PN 100 (Class 600) flanges the rating is 9930 psig.

So now we need to find out 2 things. What exactly the operating temperature is, and if the flanges used were CSA certified.

 

[jmiles]

Odds are your flanges are not CSA rated flanges, most times people do a spec break at the first flange above ground to make things simpler, and significantly cheaper, sure one or two planges and fittings built to CSA standards are not too bad, but you dont built much above ground pipeing thats dual rated cause ti costs too much money.

Also most pipeline grade materials are higher strength but thinner wal, to save on costs, hence why transition pieces are used when coming above ground.

My guess is you will have to set the PSV to 1395 and call it a lesson learned, but hey who knwos you might luck out.