5 replies to this topic

[shekhar dhuri]

Hi,

 

I am working on a very fast track project and we have asked our contractors to submit the their 'Standard Designs' for the Gas Processing Plant (Slug Cather, Sweetening, Dehydration, NGL recovery and Fractionation, Stabilisation). I am reviewing supplier's P&IDs and have observed folloiwng points.

• For Isolation vavles even in case of Hydrocarbon applications, Gate valves have been used instead of ball valves.
• No positive isolation (Removable spool / spectacle blind) is used.
• No PSV sparing is provided.

 

Can you please suggest if i should accept these things ??

 

Regards,

Shekhar Dhuri

[fallah]

Shekhar,

 

Appears the contractors are EPC ones because have included minimum requirements in their designs to lower the project expenditures. Anyway, IMO, at first you should refer to relevant process design criteria submitted by them in their proposals and put your comments as per your budget while are taking care not to deviate from relevant codes and standards.

 

For example, sparing the PSVs isn't a code requirement and there are the plants in which no sparing are considered for such valves due to client/owner request.

[sukanta87]

Regarding to the discussion one thing want to add. Have observed some NG process plants and oil refinery with plug valves as their isolation valve and it's only plug valves ( where line sizes are >= 2"). The main reason behind this philosophy is still unknown.

[shekhar dhuri]

Fallah,

The EPC Contractor has not submitted any process design criteria and we have not asked for it either.  We have provided brief functional specifications to the contractor with a specification of the Gas / LPG and Condensate.  Similarly, the ultimate Client is not involved in any technical discussions.  So, It is us, who have decide if it technically okay or not.

[fallah]

Shekhar,

 

If you are in a position by which you can reject such points in supplier's PIDs, put your comments on mentioned points and ask them to improve the PIDs accordingly...  Actually such points will lead to having operational/maintenance/safety issues....

[farid.k]

This is from my opinion,

• For Isolation valves even in case of Hydrocarbon applications, Gate valves have been used instead of ball valves.

For me, your system is big. the choose of valve is depends so many factor such as fluid type (slurry, dirty, clean service, hazardous and flammable, corrosive etc.), fluid characteristic (gas, steam, liquid etc.), pressure and temperature limitation, operation and maintenance requirement and etc. Based on my experience, we cannot say it is fault to use gate valve for gas service. just that, I’ve found for the gas service, normally ball valve is being used and some standard says, ball valve is more compact and reliable against leakage than gate valve.

• No positive isolation (Removable spool / spectacle blind) is used.

Positive isolation is a procedure whereby physical separation between systems is achieved. Closing valve does not achieve positive isolation. Normally positive isolation shall be provided during hot work to be done, equipment need to hydrostatically tested or inspected, or equipment to be opened whilst other remainder of the unit is still in operation. My suggestion just use valve with flange. Whenever need positive isolation at any point, just close the valve first, drain and put spade for positive isolation.

• No PSV sparing is provided.

 

For me, it’s good to have one spare IF when the situation to service the current online relief valve, we can temporarily isolate that one and run the PSV spare one. Let say you have any alternative method to protect equipment from overpressure during PSV maintenance, spare might be no need. For thermal expansion, for me no need spare.

 

It is good to sit together with the design engineer and do the design review plus challenge the design. They might have their intention why they use gate valve, don’t put the spare and etc2.