We are working on an LNG plant and have been having a discussion within the team relating to valves for use in cold service, ie below -46degC and orientationSo far we have been working to a conservative approach of installing all valves in services with a design temperature of -46degC and below in a horizontal pipe, with extended spindles orientated vertically or within 30deg of vertical (in practice, all are vertical but we have the option).My understanding is the vertical extended spindle is to prevent cryogenic liquids reaching the packing by providing for a vapour pocket above the liquid level.On this basis, a question has arisen in relation to valves in cold vapour service and orientation requirements.We have Relief valve lines designated as being in vapour service (mixed refrigerants) with design temperatures of -170degC and an operating temperature of -80degC. Currently we are providing extended bonnet valves for these conditions, installed with the spindles in the vertical. However, considering the discharge line block valves, although these lines are designated with a -170degC DT, for the majority of the time, they will be at ambient temperature, and regardless, will never be operated when subjected to low temperature.So, the questions are as follows:1. Do valves at -46degC and below in vapour service require extended spindles?2. If yes, do they need to be installed with the spindle vertical?3. Do valves in flare service which are normally at ambient temperature need extended spindles? (even if DT is below -46degC)4. If yes, do they need to be installed with the spindle vertical?I agree that the benefit of a vertical (or near vertical) extended spindle installation is to ensure a vapour pocket to prevent the stem seal packing from being exposed to the cold liquid. But there is also a safety related issue. Please take a look to he attached pdf, which offers good (IMO) advices.

MORE NEWS