LNG plant, valve selection and orientation 1

[MJS996]

Hi

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 orientation

So 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?

Any background info on extended spindle valve selection and orientation would be appreciated.

Thanks in advance

 

[ione]

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.

You can also find something here

http://www.eng-tips.com/faqs.cfm?fid=566

 

[JLSeagull]

I saw a post with NGL used where I thought that the OP meant LNG. In this case perhaps the term LNG applies to NGL. LNG is liquified natural gas as in liquid methane or natural gas that is cooled to minus 259 degrees Fahrenheit, minus 162 degrees Celsius. NGL is natural gas liquieds such as propane etc. Atmospheric propane is near -40 degree F and degree C. The lowest temperature in the NGL demethanizer is about -150 degree F, -101 degree C.

 

[itascot]

Most high performance butterfly valve manufacturers will state that the extended bonnet is specifically designed to avoid packing freezing, this would cause problems in sealing function, the other reason for extensionis so that you have space to insulate pipeline & valve body from external temp. at the same time keeping packing at a safe distance from cold fluid. The 45° angle installation is also preferred by the HPBV manufacturers. A vertical installation means that any foreign bodies would be in hub area (the areas where offset butterfly valves have most rubbing in) and could cause premature wear in this area between metal seat/Seal ring.

 

[belowzero]

Take a look at FAQ 774-566 its for Cryogenic valves but also relates to low temp valves such as you require.
The shaft can be as much as 45 degrees from vertical if the extension is long enough, try and comply with a known standard such as shell's then you cannot go wrong, these have been put together after a lot of research, although the extensions will be short it is really important never to get a valve packing frozen by providing insulation up the extension, the extension must be in open air unless in a cold country where trace should be used.
These questions appear to be asked almost every year, try a couple of searches in cryogenics and this forum for low temp /cryogenic standards.
B

 

[belowzero]

To answer your questions though:
1. Yes depending on what standard you want to comply with.
2. Installation should be no more than 45 deg from vertical.
3. Yes, these valves will typically get to lower temperatures.
4. As Q2

Stem position and length apply to any type of valve, ball, gate TOSV etc etc
Extensions should be designed with actuator weight and position taken into account when ordered.