In certain Low temperature and cryogenic applications ,shell specifies valve bonnet to be non extended.. to be more specific it states the valves to be non operable valves (ref shell MESC 77/200).
what are the service or requirements to go for these valves..

You may have opened "a can of worms" with this question.

Basically, the Shell Specification 77/200 covers valves in service between -20 deg c and -196Deg C and specifies these as "operable" valves. Valves with operating temps between 0 and -20 Deg c are deemed non operable.

This is debatable however, as some people claim that the design temp determines whether the valve is operable or not. So if the design temp is -25Deg C then this could be an operable valve.

Now this is where it gets confusing! Technically an operable valve/ball valve is only so if it is fitted with an extended bonnet. If the design temp is -50deg C (this deeming it operable) but the valve is not offered/required with an extended bonnet, then it is not covered within 77/200!!!

Basically though if you have a valve operating below -20Degc (Operating or Design temp) and it is fited with an extended bonnet then it is deemed OPERABLE and thus must fulfill the requirements of 77/200.

IF, your valve has a design/operating temp warmer than -20Degc then it is NON OPERABLE.

IF your valve has a design/operating temp between -20deg and -196degc and does not have an extended bonnet, then it SHOULD be OPERABLE, however 77/200 does not cover this type of valve!

Just to give some advice.... if you do have a valve operating below -50/-60 deg C i would STRONGLY advise that you offer an extended bonnet!

I think i know where you are going.. Basically a valve can be deemed non-operable by Shell, if they for example specify a valve with a design temperature below -20Deg C, however they state that the valve will not meet these low temperature conditions and thus is not required to operate at low temperature.

Thus SHELL could deem the valve "NON-OPERABLE".

Depending on your valve type, the length of a standard bonnet and the packing type used in your valve, it may not be neccassary to offer an extended bonnet at -40 Deg C.

For example, a globe control valve, may be working on a service where the design temperature is -46 Deg C and may be operating below -20 Deg C.... however the packing type offered is PTFE Chevrons and is suitable up to -50Deg C... so an extended bonnet is not required to protect the packing. Because it is not offered, and to decrease the overall cost (thus making the valve more competitive) it is offered with a standard bonnet.

As i said the confusion is caused in instances like this, because Shell may deem this Operable because it is operating below -20, but it isn't covered by 77/200 because it does not have an extended bonnet.

To be very general (which i do not like been) the valve is only going to be "operable" if it is made from a grade of 300 stainless (which is suitable to -196 Deg C)... operable testing would subject the valve to cryogenic temperatures, which other materials may not be suitable for...

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