spool for butterfly valve in exchangers

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10 years 6 months ago - 10 years 6 months ago #8347 by shishirmtech
spool for butterfly valve in exchangers was created by shishirmtech
When we do the piping, we keep some spool piece in between exchanger nozzle and butterfly valve,why?
But in case of gate valve, its not needed, Why?

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10 years 6 months ago - 10 years 6 months ago #6905 by Jop
Your question is a good one and is loaded with ramifications.
First - In Piping there is a Rule for everything, and for every Rule there will be an exception.

Now let's talk about Valves' Look at your Butterfly Valves. What type are they? They may be the full Flanged type which use normal Stud Bolts on each end just like a Gate Valve. These types of valves do not need the down stream flange to hold the valve in place.
There are through Bolt, Lug type and non-Lug type Butterfly Valves (the lugs are not threaded here) that require a flange on the downstream end because they use through bolts and the bolts need the flange to hold the Butterfly Valve in place. The exception here is a Butterfly Valve that has all threaded lugs. With this type of butterfly Valve you will use Cap Screws on both sides of the Butterfly Valve.
So a partial answer might be something to do with your Butterfly Valves.

The more important issue the overall piping layout around Shell & Tube Exchangers. The piping layout must not only consider the proper piping arrangement for the process and the operation of the plant but it must consider maintenance and safety.

For pure process and operations of the system you could put the valves almost anywhere, against the nozzles or far away from the nozzles.

For maintenance you do not want the valves against the nozzles. There is a work area required to remove the Channel end of an exchanger. The inlet and outlet valves should be located one half meter (18") clear of the back of the Shell body flange.

Some might ask, Why? Most equipment such as exchangers today operate at high temperature and high pressure. They require hydraulic Bolt Tensioners to pre-stress the bolts thus eliminating the potential for leaks. These Bolt Tensioners Require space and lots of people room while doing this work. So, if all the lines to and from the exchanger come from above ground, keep the inlet and out valves out of the maintenance area. So you would have a spool piece anyway.

Now the exception here: If the Exchanger is in Cooling Water (CW) service, the CW would normally be in the tube (the Channel) side and the main CW Headers and branches routed underground, the CW supply would normally rise up out of the ground into the bottom Channel side nozzle. It is not necessary to route this line out of the Maintenance area but you should use a threaded Lug Butterfly Valve or a Gate valve here.

Do it once and Do it Right

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