Cryo ball valve for LNG -FIRE SAFE CONCEPT

Dear Specialists ,
Doing some consultancy LNG terminal and LNG Shipbuilding.
I am looking for an answer/guidance about minimum requirement to consider a ball valves to be fire safe or not.
My focus will be on valves having a size below 8” inches as everyone know that for valves having a larger size (more mass) the actual Fire safe test is not relevant as energy for heating the body will “not” affect the trim due insufficient allowed burning time according the code EN ISO 10497, API 607, API 6FA.

As mechanical engineer it obvious for me that the valves to have at the minimum the some clear feature to pretend succeeding the test.
For example one of the candidate supplier present his valves “Ball valves Top entry” as fire safe however the seat arrangement “piston type “ is equipped with fragile lip seal in PCTFE or modified PTFE.
It is clear that those lip seal alone will not hold for long at elevated temperature.
Some other supplier have Graphite ring as backup which seemed more appropriate.

Any though on this ?


Tory

 

[PeterIgg]

Hi Tory

You really have to go back to the respective manufacturers for an answer on this one. Fire safe sealing is achieved in a variety of ways, one of which is for the seals to 'burn out' and allow components to move and create a 'metal to metal' seal and NOT necessarily rely on, say, a graphite seal. Realise that the valve only has to have limited operability after a fire.

 

[Tori Azuko]

Hi Peter and all ,

I know the theory of various ball valves design and I ask here to have an others opinion and more the feeling from the community on this subject.
For example, talking here about Trunnion mounted ball valves and internal leakage only.

The way the spring loaded piston seat need to move against the ball to touch the metal contact when the soft seat melt is not the main concern area as those system is proven.

The concern is the sealing of the piston seat itself , if the piston seat’s seal have the same melting point (modified PTFE lip seal ) than the soft seat itself.
We could consider that both will melt at the same time therefore the leakage will not occur at the contact Seat /ball but around the piston between the body (seat pocket).

Here an example of an valve's internal having soft parts (soft seat + piston seal ) both have the same melting point but manufacturer claim it is fire safe !
good mechanical sense will say no at all.

 

[gerhardl]

Hello Tori,

Please also be reminded that a valve intended to withstand a fire, normally is required to have a fire-safe certificate or is sold with a factory-approved 'firesafe-design'. The last usually means that the factory has experience with fire-safe valves and that valves with this design has been tested and certified by the factory, but that the one with fire-safe design could be of another dimension or pressure class.

See also earlier general discussions, for instance thread 408-263955

In addition bear in mind that during a firesafe test the valve is filled under full pressure with water, then is in flames of high temperature for 30 min., and after this cooled down to 100 degrees. Leakage over the seat and inside out is measured during the process (minimum leakage required), and the valve must be able to be operated at least one time afterwards.

I cannot see that this can be proven for a sceptical customer purely by design drawings, without some practical test, especially if fully certified alternatives excists commercially available.

 

[gerhardl]

Hello Tori,

I did not see your comment before I answered, but still see my general answer as relevant. The particular point you raise is interesting as an engineering question. I would say generally yes, under circumstances the piston sealings could melt, for instance under certain orientations of the valve in a given fire.

If this then gives a significant leaking or not is an open question, and should be proven by a physical test for similar constructions by the same manufacturer.

If not yet done: does the valve leak with all soft seat seals and piston seals removed? If yes. what is required for the valve not to leak?

 

[mk3223]

IMO, the fire-safe valve is required by Codes to be certified by going through the testing with the specific testing guidelines and duration. As the valves having different designs of the seal types or material, the manufacturers is responsible to show the proof if the valve passes the specific Code testing.

 

[Tori Azuko]

Hi All,

Thank you for your great feedback ,

For the one who had the opportunity to see a fire safe test on valves <6" the body is [highlight #EF2929]hot red[/highlight]
and water are vaporized and no way the lip seal in direct contact with the body remain in place (this is were it create some questioning about fire safe on valves equipped with lip seal only).
Nevertheless I receive several fire safe certificat and some refer to a drawing , I assume those drawing must be part of the documentation
as Fire safe code explicitly mention that no change from the tested design is allowed.
(for exemple some fire safe certificate acc API607 4th edition in 1998 user must be certain the valves did not change in 20 years).


Kind regards,

 

[Tori Azuko]

Hi Gerhardl,

I did not find the thread 408-263955 ??


Regards,

 

[NGiLuzzu]

Tori,
maybe you'll find some more information trying to read some of these old posts:

- thread408-388739

- thread408-299055

- thread408-229575

- thread408-392566

- thread408-64692​

Regards,​

/'NGL​