Hi all, I am confused after goin

[Amin1984]

Hi all,

I am confused after going through one P&ID of gas processing facility I have been working. What are the reasons behind using of 2" ball valve upstream multistage RO-restricted orifice for start up pressurization? To my knowledge ball valve is used as on/off valve as if used for throttling it will be damaged while in most areas in facility using globe valve for pressurization
if designer depends on multistage RO-restricted orifice and open ball valve 100% directly?

 

[mk3223]

For clearly understanding the system, if there is a P&ID or sketch can be shared.

In general, it's correct that the ball valve may be used as an on-off function instead of throttling. Since there are RO's on the lines, it sounds that the gas flows of each branch are set by these RO's without throttling required. if doubt, you s=may verify with the Process Engineer or Operation for the design function.

 

[Amin1984]

thanks for your reply
distance between valve and orifice is 2m so if I open valve fully open and above pressure is 68barg is there any problem

 

[mk3223]

Per P&ID, the vessel C-2731 has the operating condition @ 68.4barg and the design condition @ 79barg. The vessel should be fine once the process operating pressure to be kept under the design condition, by assuming that the pressure rating of the piping associated with this vessel is higher than the vessel design condition.

 

[Amin1984]

sorry my question that selection of ball valve for pressurization is there problem to the valve if I open it
or designer depends on multistage RO-restricted orifice and open ball valve 100% directly?

 

[mk3223]

IMO, it may depend on the RO, which is to take the full dP across the orifice as the ball valve is to be open 100% directly. In reality, during the start-up process, the system should be pressurized slowly by modulating the pressure source upstream of the RO.

If the system was pressurized to 68barg first before the ball valve opened, the ball valve can be cracked open in the beginning to slowly pressurize the system downstream, and then continuously open to 100%. But, this may not be an idea start-up procedure since it could result in the damage and cause the leaking through the valve seat.

 

[MortenA]

It can be difficult toopen the main valve if the pressure difference is bigger than say 2 barg (seems like you are aware of this).

I would assume that the RO is there to limit gas flow through the upstream contactor where trays (or packing) may be damaged or liquids carried forward if the flow becomes as high as it could be. The RO is multistage most likely to reduce noise.

Best regards, Morten

 

[georgeverghese]

This set up is similar to many blowdown facilities configured with an automated reduced port ball valve with RO some 1metre or so away from it. This is also company standard configuration for one oil/gas supermajor. There have been complaints from plant operators of seat damage to the ball valve in some instances. Despite these problems, the global company standard hasnt changed. However, one of the major subsidiaries of this company in Borneo deviates from this global guidance and uses an automated globe valve as the isolation valve (as you suggest), and I've not heard of any complaints with this setup. I would presume this is a class V leaktight globe. Your concerns are valid, and in my opinion, the class V leaktight automated globe seems a more reliable setup. If you must make do with the ball valve, maybe a metal seated class V ball trim would be able to withstand the high dp better than the soft seated option. But for small bore lines less than DN80, seat damage is stated to be minimal for a soft seated quarter turn ball valve which is quickly opened.