Thermal Relief Valve Requirements on LNG Lines

[gmedrano]

Does anyone know of any codes or standards for multiple TRVs on long LNG lines? API 521 doesn't state anything about multiple TRVs and I couldn't find anything on NFPA 59A regarding the subject. Any help?

 

[EGT01]

I don't have experience with LNG but I'm curious about what your concern is regarding multiple thermal relief valves and thought I would see what I could find.

If you are in the US, you may want to review the Code of Federal Regulations, Title 49 CFR Parts 100 - 199. In particular

http://ops.dot.gov/regs/1999/part193.htm

but I didn't really see anything regarding the number of relief valves.

Since you are talking about thermal relief, I would assume the pipeline design pressure must be high enough to preclude the need for liquid vaporization. However, it seems that the required design pressure may likely be above the critical pressure and you might experience either liquid or dense phase thermal expansion. In either case, it would seem that as long as you provided the required relief area, it wouldn't matter how many valves you used unless you are thinking there is some other criteria that may require a certain number of valves.

I really didn't find much on the internet but I thought these links were interesting

http://www.shell-usgp.com/lngsasrae.asp

http://www.lngfacts.org/

http://www.slc.ca.gov/Division_Page...IR/2Part2-DescriptionoftheProposedAction2.doc

 

[dmjmhn]

Needs sizing information for thermal relief valve on exposed (aboveground) vacuuum jacketed LNG pipeline. Particularly thermal expansion coefficient for LNG, specifc heat of liquid LNG as these are the parameters required for thermal relief valves.

 

[Tonylmiller]

Is this a very large pipeline? Normally thermal relief requirements are very small.

Tony Miller
Cornerstone Engineering Group, p.c.

http://www.cegpc.com

 

[jbmr]

I only have experience of single TRVs in such cases, with a valve larger than the standard 3/4" x 1" for long lines if the calculation according to API521 section 3.14 / API520 shows that this is required.
However I agree with EGT01 and don't think that it is wrong to have multiple TRVs providing the relief area is sufficient.
I am not sure about how the set pressures should be staggered though...

Rgds

jbmr

 

[PAN]

gmedrano,
If the long line has several block valves, several thermal relief valves may be necessary. I do not know the code or guideline for the minimum length to install at least one thermal relief valve between block valves. However, the size of the thermal relief valve always in small size as jbmr's comment.

 

[dcasto]

Under any code or rule you may fall under, you'd want to do everthing possible to send the vapors somewhere first before activating a typical relief valve. Even uder DOT rules a PSV is not required. You could install multiple control valves that open and send the LNG to a VRU long before the system reaches MAOP. But if feel that you need a typical relief valve as a last resort, make sure you take into account all the line insulation and everthing as you size it.

 

[davefitz]

Are there any lessons learned regarding the heat abosorbed by the pipeline during fires, such as the 30 Aug2005 Nigeria or the 30 aug 2004 Ghislenglien Belgium events?

(Strange coincidence- both occured on 30 Aug. )