Dear all,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 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!

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