Extended Bonnet valve

[Erkamal]

HI Friends,

I am working on steam valve.

Valve Input : Pressure : Max. 2500 PSI
Temperature : 325 Deg C.
I want some idea about stem packing. which seal will be useful for such type of high temperature condition?

Any Thumb rule or design calculation for extended bonnet height? and on which height , the stem seal should have to be located?

I feel that I should use extended bonnet and graphoil seal for valve.

Regards
Kamlesh

 

[hsbcn]

What DN bore are we talking about?

I work with valves in exotic alloys at alloy-valves.com. This is me on Twitter and LinkedIn. Let's connect!

 

[Erkamal]

Hi frds,

I will be DN 100 .

 

[mohan55]

You can use graphite stem seals following ext. Bonnet height as per bs6364

 

[Erkamal]

Hi Frds,

Thx for your value added answers.

I am designing angle type control choke vale. and now distance is only 150mm from valve inlet centre to bonnet seal surface. i will do up to to 250 mm but all stem and other design will change.

So does any graphoil seal help me to reduce bonnet extension?

Thx

 

[Chandramouli Attili]

Hi,
I am new to Valve design.
May i know where Extended bonnet valve will be used!

 

[Danlap]

Extended bonnet (length) is minimum length for vapor space. Which is required in order for medium/service when it reaches Bottom Packing soft ring/seals (for instance), the temperature will be in range (Design temperature seals) for it to perform optimal sealing capability (read: contain the medium inside the pressure envelope), external leakage wise. Nowadays it is called Fugitive Emission.
At some extend it may influence the Hand wheel Operating force, so EN 12570 should also taken into account.

Cryogenic valve (below -50 deg Celcius) use the term of Extended Bonnet and High temperature valve (the threshold slightly differ between some standards) use the term of Heat Dissipation Bonnet.
Special (expensive and not easy to fabricate) soft material capable to meet below (for cryogenic) and or above (for High temperature) of this threshold.
However please bare in mind, that most of these materials are patented. And probably will be improved in the next 5 years or even not available any longer.
By those account, expected lifetime of Upstream valve (let say 5 years) and Downstream/ Refinery (let say 20 years) should consider the availability of the same material as well on the next refurbishment window. Shall this is the case.

Highly recommend to use standard minimum length of Bonnet extension regardless the seal you use, unless special case applied such as the end user aware of this, spatial constraint in the Plant, etc.
It would be easier for the End user successor and HSE auditor shall something happened with this valve in the future.
PS: Purchasing of soft goods today to be installed in the next 5-20 years refurbishment window are definitely not recommended.
Just some toughts

Regards,
MR

Greenfield and Brownfield have one thing in common; Valve(s) is deemed to "run to fail" earlier shall compared to other equipments

 

[mbelly84]

@mohan55, bS6364 is a standard for cryogenic services (-50°C to -196°C), not high temperature.

 

[Erkamal]

Thx frd,

Dear Svuce , valve can be used in geothermal application.

Hi Frds, I have just selected material , it should be nickel base alloy for hight temperature application .and doing some calculation at elevated temperature.

Dear 19081984 , you are right about BS6364 . and it is cryogenic service. so confuse that can i use this bonnet hight reference from BS 6364 for high temperature or not?

Cause, max. temp is 325 deg C in my valve design.

 

[Erkamal]

Dear Muktiadi,
Your reply is very informative,
Thx for reply.

 

[Danlap]

Dear Erkamal,

Your welcome.
Extended Bonnet for High temp / Heat dissipation bonnet minimum space length is derived from ASME B16.34, ASME VIII Div. 1, and End user - manufacturer Best practice.
Sorry cannot elaborate more on that in this forum.

A simple approach, using several Hypothesis / assumption as follow:
a. Disregarding the usage of Asbestos based packing (obsolete/withdrawn due to health/environment issues) even though it is proven for High temp service.
b. No elastomeric material and or O-ring used
c. In general: Standard packing used is Graphite based (Die formed / Braided yarn / Ring, etc.) with Graphite purity of 98% or more

PS: Graphite is susceptible for oxidation shall in contact with high temperature above 400/450 degree Celcius directly​

By that reason, service temperature 325 deg Celcius (measured at valve bore) do not requires extended Bonnet.
If above 400/450 deg Celcius, ask the calculation from manufacturer using heat transfer software or other method to see what is the minimum length.
Shall it is unavoidable to use standard valve (without extended bonnet) for High temp, as long as the service is not critical for safety reason, then one of the mitigation is replacing the packing periodically.

regards,
MR

Greenfield and Brownfield have one thing in common; Valve(s) is deemed to "run to fail" earlier shall compared to other equipments