Butterfly valves

[srisua]

Dear Seniors,

Greetings for the day. Thanks in advance for your support on my query. We are doing detailed engineering for fuel system for 660MW power plant. There are two fuels to be used for lighting up the boiler and for initial heating. They are Heavy fuel oil and light diesel oil. In our scope only fuel oil unloading system alone is there. System to be designed for pressure of 3.5kg/cm2,100cum/hr flow and operating temperature is 50degC. There are two pumps for each fuel system in which one is working and one is standby. Generally we use ball valves for isolation purpose. Now my question is as the pressure and temperature is less, "can we use butterfly valves instead of ball valves for this oil application?".

 

[racookpe1978]

What are your fire reg's for butterfly valves isolating a pressurized, flammable liquid?

During maintenance and construction, ball valves are a bit easier to work with because you can unbolt one side of the valve.

 

[srisua]

Dear racookpe

Thank you very much for your reply. Yes as you suggested ball valves are bit easier than ball valves in maintenance as the same is available in two or three piece construction. But we can also unbolt flanges and can be removed butterfly valve for maintenance.

For butterfly valves we have selected seat material is EPDM and this material will withstand upto 150 degc where as our operating temperature is 50 degC. Ball valve and butterfly valves, both are isolation purpose only. generally butterfly valves will be used in water lines. why cannot we use the same in oil lines as these valves also withstanding temperature and pressure.

 

[MickMc]

Srisua,

No technical reason that butterfly valves cannot be used in services other than utilities as long as client has no objections and material is suitable for medium. My general experience in oil & gas is butterfly valves specified in lieu of gate/ball in sizes circa NPS 8 and above for economic, space saving and ease of installation with concentric type used in water service and double and triple offset in process and/or hydrocarbon service for superior sealing performance.

You can use double flanged type for isolation purposes but not wafer or lugged unless additional spool is used and if positive isolation is required using blind/fig 8 an additional spool is required as even in double flanged type the disc protrudes beyond the body when open.

 

[srisua]

Dear MickMc

Thank you very much for your reply.

In my case I have used wafer type butterfly valve for isolating of duplex strainer with EPDM seat. This strainer will be mounted at pump suction. Duplex strainer containing two bodies, if one body chokes, manual change over will be done to another body. Here operating pressure is atmospheric and temperature is 50 deg C. For main process lines I have used ball valves only. There is a spool piece at one both side of valve and hence disc protruding beyond the valve is not a problem. Now you are requested to please suggest whether my selection of concentric butterfly valve at strainer is a problem or not.

Herewith i am attaching drawing for better clarity

 

[MickMc]

Srisua,

Looks OK to me for manual change over between strainers and I have hopefully auccessfully attached similar layout from a website for a water system showing wafer lug butterfly valves. Whether you can use concentric type will be client driven as they may stipulate between utilities/process/hydrocarbons.

 

[keyepitts]

Standard EPDM is usually not recommended for hydrocarbon exposure; a better material choice would be Buna or Viton, which may still swell in fuel oil service, making the valve difficult or impossible to open and close. Best choice would probably be a valve using teflon as the main elastomer.

 

[srisua]

Mr. MickMc

Thankyou for your suggestion and gone through the photograph sent to you, this is exactly same as my strainer, but the valve showing in photograph is not wafer lug type. May be double or triple offset butterfly valve.

Mr. Keyepitts

Thanks for your suggestion, yes, i should not select EPDM as it my react with hydrocarbons. As suggested PTFE is suitable for oil application.

Regards

 

[MickMc]

Srisua,

Correct photograph shows a lug type and lug or wafer type can be concentric, double or triple offset just a difference in the way it is mounted with both having same face to face dimensions. Double flanged only comes in double or triple offset as far as I am aware and if you have access to copy of API 609 which is governing standard it will guide you.

Be aware of client specifications if any as wafer and concentric disc and seat may only be allowed in water and/or utility service which is common in my experience in oil & gas.

 

[BigInch]

For hydrocarbon service butterfly valves are better only when throttling is needed and usually not used where isolation is required.

Blinds can be used if maintenance is not frequent, however ball or gate valves should be used where frequent access is needed.