SPExSPE

[TransMech]

Hi all,
Does somebody has such experiences which is requested SPExSPE seats?
Thanks.

 

[Kreot]

Hi,
Not 100% sure excactly what you mean, but SPE X SPE seated valve is common and in use for many applications not requiring double barriere. Can also refer to it as a DBB.
To be able to give you a good answer i need to know the purpose of the valve

 

[LittleInch]

stiaf,

If I've understood this right, SPE x SPE does not count in anyone's books as a DBB as there is no second block, for which you need one DPE seat at least. Even then lots of people / companies don't accept DPE ba;; valves as a DBB - see plenty of debate on this forum on this point.....

The question isn't very clear, but I agree with you - this is basically a standard ball valve able to seal in a single seat in both directions, but no need for a body pressure relief.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Kreot]

Hi,

Be sure not to confuse DBB and DIB. For a DIB you need a second block ( e.g double piston downstream for trunnion ball).
You can choose to use a DPE x DPE or SPE X DPE dependent on what you need the barriere for.
A DBB valve has 2 seating surfaces to have seat sealing against pressure from both upstream and downstram the valve (SPE X SPE). This gives you only a single barriere, not double. If you need a double barriere, there is a need for a DIB valve.
For a DIB valve there is also a need for cavitydrain valve to verify the upstream barriere.

 

[Markgood]

This is a constant subject of confusion API 6D defines a Double Block and Bleed Ball valve as a valve with SPE (single piston effect) seats on both sides of the Ball these are designed to self relieve. You can also have DIB - 1. & DIB - 2 which are double isolation and bleed valves. The former has two double piston effect seats DPE which seal in both directions and therefore traps fluid in the central cavity and therefore must be fitted with a relief device on liquid duties to avoid damage from thermal expansion. The later DIB - 2 has one SPE seat and one DPE seat with the SPE seat normally relieving to the upstream

 

[Dean8573]

Single piston effect by Single piston effect would indicate to be that a cavity relief ball valve has been requested. this is readliy available and would require the valve to be trunnion mounted i think

 

[Roberto1956]

If it is a trunnion ball valve, SPE x SPE and according to API 6D, the maximum inner pressure is 1,33 x design pressure (this is in API 6D). Take care that the pipeline pressure makes a counter back pressure and you have to consider during the design or during the inspection test at the bench.
So, if you pressurize the cavity with the nozzles unde atmospheric pressure, the maximum inner pressure will be 0,33 x design pressure because at this time of test you do not have the pipeline back pressure.
The API 6D does not makes mandatory the use of a bleed on cavity. You have to ask it during purchase order.

 

[Kreot]

The cavity relief is determined by the spring force of the seats(normally 7-10barg). If you pressurize the cavity of a closed ball valve with atmospheric pressure at upstream and downstream flange, the seats will relief the pressure when you reach the spring set point (more or less the same as a PSV).

 

[Roberto1956]

The cavity relief of a SPE shall be designed for no more than 0.33 x rating pressure with the nozzle under atmospheric pressure. The PSV set pressure for the same valve as DPE shall be between 1.1 to 1.33 x rating pressure.

 

[potus101985]

Hi stiaf,

Query on your statement, "A DBB valve has 2 seating surfaces to have seat sealing against pressure from both upstream and downstram the valve (SPE X SPE). "

For a valve to have a DBB function, is it a requirement to have both pressures on upstream and downstream? What if pressure on downstream is equal to zero?

Cheers,

 

[JohnGP]

If pressure on downstream seat is zero then you don't have positive double isolation. API 6D points this out.
Cheers,
John

 

[Roberto1956]

If you have a trunnion ball valve, SPE x SPE, pressure on upstream, pressure on cavity and atmospheric pressure on downstream. In this case, during the increasing of pressure on the cavity, the relief will occur to the weak side or downstream port side. Anyway, the pressure on the cavity shall not be more than the rating pressure x 0.33. This is the attention point. If you have rating pressure at both sides the cavity will not reach more than pressure rating x 1.33.

 

[Kreot]

It is not a requirement to have pressure at both upstream and downstream seat, but a SPEXSPE will give only you a single barriere independent of which side the pressure is coming from.
The SPE seats are designed to reliev overpressure in the cavity (as Roberto1956 are stating).
My main point is to clarify the confusion between a DBB and DIB (as also Markgood mention), as i see that alot working with valves in the plant. Many people think it is always safe to work downstream a valve as long as the valve is classified as DBB.

 

[Krausen]

SPE x SPE = DBB (Only one positive block with pressure on either side. Seats can self-relieve themselves to either side.)
DPE x DPE = DIB-1 (Two positive blocks regardless which side pressure is on. Seats cannot self-relieve themselves. External DTR required.)
SPE x DPE (or DPE x SPE) = DIB-2 (Two positive blocks with pressure from DPE side of valve. Only one positive block with pressure from SPE side of valve. SPE seat can self-relieve itself.)

DIB-2 is the style of API6D valve becoming the norm for many operation groups in the pipeline industry.