Fully welded Ball valve - Seat pneumatic test failure after shell test 2

[Ilam]

HI Engineers!

I'm a procurement engineer from Oil & Gas Indusry in UAE , we ordered Fully welded ball valve 16" Class 600 ,from a Malaysian manufacturer for our metering skid project, since those valves are tight shut off valves, they have to be tested at Field ( in UAE before installing to meter) as per API 6D.

Note: Valve has been accepted in FAT without any issues for below tests, however in field test the results
1. Hydrostatic Shell test ( 1.5 time rated pressure) - Passed in FAT & Field Test
2. Hydrostatic Seat test ( HIgh pressure pressure)- Passed in FAT & Field Test
3. Pneumatic seat test ( Low pressure)- Passed in FAT & Failed in Field Test

The valve manufacturer claims there are possibilities of seat insert memory( PTFE) get affected due to half open shell test, this may result in failure during pneumatic test.

We also have same kind of failures in same project with a different manufacturer from Italy & India also. The percentage of failure is around 40% of ordered valevs.

Kindly advice on the shell test impact on the seat memory and if someone has faced similar issues in past.

Thanks in advance

 

[bcd]

Yes it is true that leaving a ball valve with PTFE or similar soft sealing material in the partial open position may cause an indentation of the seat where it crosses the ball port.

 

[HitokiriAoshi]

what's your test sequence?

here is your likely issues.

1) sand, y'all got lots of sand, which can damage the seats.
2) soft seat issues, if you had the valve half open, or it was staged for a long time, the ball can be not round, causing the soft seat memory issue. there are workaround.
3) gearbox adjustment issues. the cheaper the manufacture, the more likely you need to tweak the stops to find the sweet spot, play with it to see if you can find it
4) testing orientation. Depending on orientation, it can be easier or harder, or impossible to pass. This is because trunnion valves are not perfect dimensions and the ball can lift and move. If they used soft spacers on the trunnions to reduce torque etc, they may have been crushed over time.
5) hardened lubrication, the lubrication or other things may have gotten around the springs and back of the seat retainers, hardened and making it difficult to provide the necessary pre compression pressure to seal low pressure.
6) crushed seats, too high of a seat pressure test, can crush the seat causing failure in the low pressure test.
7) testing order, you can try to help the valve pass by doing a high pressure seat test, directly follow by a low pressure air test, and switch to the other side. The pressure will help the seat conform to the ball better.

good luck, can help more if needed, but the above should solve most issues. also.. testing pressure on low?

Luke | Valve Hax |

https://valvehax.com/

 

[Ilam]

Thanks Mr. Hitokiriaoshi for your elaborate responses. It was very helpful. We are suspecting only seat memory issue, Can you explain further on the below
1. Any standard or reference that seat test will damage the seats
2. Any standards referring that the testing sequence(high pressure seat test, directly follow by a low pressure air test, and switch to the other side) can be changed. The valves are not designed to operate in half opened conditions.

Note: The worst part in this case is many valves have been cut and no Root cause Analysis found.

 

[HitokiriAoshi]

Please check note C on Table 1 of API 598, i believe MSS standard and maybe API 608 may make reference to it.

This is a touchy subject at standards writing organizations, but it's a fact. Smart end users may opt to test valve seat at 100% pressure instead of 110% to verify seat integrity. especially if you are going to be operating the valve at about 70% max rating anyway per design.

No standard specify the sequence in downstream standard. There are no exact sequencing. The only requirement is for high pressure pneumatic test, which must follow a hydrostatic testing due to safety reason.

Luke | Valve Hax |

https://valvehax.com/