API 622 about Valve Packing type testing 2

[NGiLuzzu]

With reference to thread408-40826, I've been informed that API standard 622 about "Type Testing of Process Valve Packing for Fugitive Emissions" is now under development.

Has anybody read some draft?
Does anybody know the date planned for final pubblication?

Thanks, 'NGL

 

[gasketguru]

I doubt if I have the very latest version, but the original API 622 draft was intended to be a test for the packing, whereas ISO 15848 is for the whole valve. A standardised test rig is proposed (1" stem, ¼" packing), and emissions measurements are based on EPA Method 21, measuring ppm methane, but with a vacuum chamber style bagging of the gland to capture the leakage. It is a block valve type of test with 1500 stem cycles and 3 thermal cycles. There are also corrosion tests and tests for volatile content and lubricants etc.

In terms of the emissions measurements, it is more realistic than the levels given in the ISO 15848. The stem movements can be linear or rotary, and of course certain types of packing sets might only perform well on one kind of movement, so it would be interesting to ensure that any given packing set is tested both ways, depending on your requirements.

 

[NGiLuzzu]

gasketguru,
in the meantime I could read Ballot Rev. 1 (dated August 25, 2005) of the API std. in object, whose title is "Type Testing of Process Valve Packing for Fugitive Emissions".

In general terms, I can confirm your abstract (fugitive emissions type test with detail of the test fixture; ambient and high temperature corrosion tests; other packing materials tests).

This testing procedure is mainly intended for packing Manufacturers, but paragraph 1.4 states that "suitability of packing tested to this standard may be confirmed by re-testing the packing in the actual valve in accordance with" the same fugitive emissions type test procedure.

From the valve Manufacturer's standpoint, this clause is quite "dangerous" as it may open the door to greedy and costly Customer requirements (which could result particularly difficult to satisfy for European Companies, as methane is required instead of helium, flame ionization VOC analyzer instead of mass spectrometer and so on...).

What is your opinion?

Thanks and Regards, 'NGL

 

[gasketguru]

I think the idea of the API test is really that it helps to rank the packings to give some confidence before the valve manufacturer conducts an expensive ISO 15848 test. Note of course that 500 ppm methane is also far easier to achieve than the ISO A, B, and C levels which are a lot tighter as far as I can see. (Compare the volume leak rates with those in the API 453 equations for example.)

Also, most people can understand figures like 500 ppm methane, far easier than something like 10E-06 mbar.l/sec/m or whatever of helium, which is impossible to measure and relate to compared with typical on-site refinery LDAR programme measurements. (These would be done with a flame ionisation detector calibrated with methane of course…)

I personally suspect that many valve buyers may already be a little confused about how to compare the ISO test results from one manufacturer to another. The piece in the API about re-testing in a real valve is because the test rig is never the same as your valve – packing diameter, stem material, packing section etc. will all influence sealing performance, especially in thermal cycling, which has a very significant effect. I am not sure how much of the ISO test is actually achievable – especially if you have a large diameter stainless stem in a butterfly valve going to low temperatures for example.

Maybe another good thread for this forum would be for people to say what ISO levels they have already achieved (albeit anonymously). This would be in terms of classes (block or control valve endurance 1, 2 or 3, and tightness A, B or C) with whatever kind of valve (ball, butterfly, gate etc.) and packing type (graphite, PTFE and so on…)

I have seen a lot of ISO testing and believe that some things may not be reasonably achievable. The API is more practical than the ISO, though some of the tests may still be superfluous to practical requirements in the real world.

 

[NGiLuzzu]

Interesting post, gasketguru!

Let me be a bit suspicious about ISO 15848-1 type tests results, as the standard is, in my opinion, intrinsically wrong.
This because it applies helium even with a vacuum to something (graphite or PTFE) that is intrinsically permeable to helium and really act as a "sponge" or a "soak" for such little molecules...!

About that, please take also a look at thread408-150132 (in particular my post dated 21 Mar 06, 3:34), thread408-143739 and thread408-115884.

Thanks and Regards, 'NGL

 

[gasketguru]

Absolutely right - the ISO levels are very tight indeed. If you consider a 25mm diameter stem for example, then class A with helium is listed as 4.4E-07 cc/sec. This would be equivalent to a volume of a 30mm diameter sphere per year. This would not be possible to detect on a refinery valve in an LDAR programme of course. The EPA 453 emissions estimate protocol gives “default zero” as being 7.8E-06 kg/hr for all stem sizes, so even with methane as a light hydrocarbon, this would be a sphere of nearer 440mm in diameter by comparison, at room temperature.

However, it is possible to get good ISO test results given the right conditions and packing etc. We have seen class A tightness with packed glands on block valve tests. Beware of thermal cycling. Note that “ambient temperature” qualifies you from –29°C to +40°C, but I think that if you were to cool the valve to –29°C from room temperature, then you would probably see a leakage increase due to stem shrinkage, especially with a relatively large stainless stem. Hence it would be interesting to see what test results had already been achieved over various temperature ranges with different generic valve and packing types.