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API 641 Test

API 641 Test

API 641 Test

What soft seat material is recommended that can withstand "Group A" test conditions of this standard which are 600psig at 500deg.F (methane gas)? I believe TFM/PTFE seats cannot withstand these conditions. Does anyone know any other soft seat material for ball valve to be tested for API 641 Group A or B?

RE: API 641 Test

API 641 do not dictate that soft seat should be used for such test. Why not metal seated? As long as consistent leak rate throughout the test cycle, then it is also acceptable.
•You can refer to ISO 23936-1 for polymers selection and its design parameter. Also incorporating general process medium restriction.
•The design temperature of 150C is based on valve operation under fully-rated pressure/temperature as dictated by ASME B16.5 for flanges.
•API 608, which is the governing standard for floating ball valves contains a table of deratings. In this table, it can be read that at 205 C virgin and modified PTFE have lost their differential pressure rating, while reinforced PTFE has a size-dependent dP between 20 and 50 psi (1.4 and 3.4 bar)

Your question is classic: Can a ball valve design survive static test (API 598/6D/IS)5208) vs stroke test at clean condition (API 641 and many others End User protocol) vs actual field condition (in your case methane; not clean).
Do we need soft seated ball valve at 260oC that could survive dirt and hundreds of valve stroke but still remain Class A aka zero leakage? I don’t think so, soft seat is prone damage and highly unlikely will remain zero leakage up to end of lifetime (unless used in a clean dairy/cosmetic environment at relatively ambient temperature).
Our experiences, yes you’re right, even though PTFE as per ISO is written maximum design temperature of 260oC, however it will loose differential pressure and creep after several stroke at elevated temperature.
Maybe this is achievable for non-operated ball valve, but personally never seen one that can survive hundreds of stroke.
Even at 205 degC, a large number soft seat also fails after stroked a couple of times.
Not really sure if there is a patented polymers that could reach such (if indeed required) temperature limit. Years ago I was approached by Habonim, but not yet have a chance to test one.


All valves will last for years, except the ones that were poorly manufactured; are still wrongly operated and or were wrongly selected


RE: API 641 Test

There are soft-seated floating ball valves that have passed API 641 testing at 600 psig and 500 F. Tests were witnessed by an independent 3rd party. They are usually small size and have modified TFM seats and seals. You can find the manufacturers and materials used in a quick google search for API 641 ball valves.

RE: API 641 Test

Thank you Danlap and BCD for your replies.

The reason we do not want to use metal seats is that we want soft seated valves to qualify for the API-641 Group A/B test. Metal seats can definitely handle the test conditions, but soft seats provide bubble-tight shut-off and lower seat torques for actuation as against metal seats. Therefore, getting a soft seated valve certified to this fugitive emissions standard is critical for us.

RE: API 641 Test

API 641 testing doesn't care about the status of your seat after the test. Nor does it care about "differentiating" the seat material.

All it cares about is your test temperature, the packing material, the stem seal design.

However, i am not sure why you are trying to qualify a PTFE seated valve to 500F.

Luke | Valve Hax | https://valvehax.com/

RE: API 641 Test

HitokiriAoshi ... although the API-641 test doesn't care about the seat condition after the test, our concern is that if we subject a soft seated valve with graphite stem packing to Group A/B test parameters, the soft seats will wear down at 600psig + 500F + 610 mechanical cycles, which will cause the ball to wiggle and that will subsequently lead to uneven wearing of stem packing which in turn can cause the valve to leak from that area. If we test the valve with metal seats to prevent the above issue and the valve passes this test, then I don't think this API standard allows extension of the certification to the same valve but with a different (soft seats) trim.

RE: API 641 Test

Your valve, with graphite packing, and ptfe seat, should be considered a decreased temperature rating valve. and not be running the high temperature tests.

However, if you look at section 11, which specifies valve qualified. you will see that the valves with the "same quarter-turn design" may be deemed to be qualified. except. you will see that it does not talk about the seat at all. This is what i consider a grey area in the standard currently. If you have a client which wants to use you, they will accept the metal seat testing. If you have a client who do not want to use you, they will not accept it. (you'd just have to run a low temp test, which should be easier to pass)

Remember, you do not HAVE to have a third party witness in these grey area. you can propose to do the testing in-house if capable, and provide report to client, if they are hesitant to accept the metal seated testings.

finally, 641 is being updated and will be updated soon, if this is not an emergency i recommend waiting a year.

Luke | Valve Hax | https://valvehax.com/

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