Material Selection for LNG Storage Tank

[MrTank]

Hi Experts,


If natural gas is liquefied (methane CH4) at -260F and the transport pressure is 4 psi, should the mdmt be -260F and design pressure be higher than 4 psi?



-MrTank

ôI have not failed. I've just found 10,000 ways that won't work.ö
-Thomas A. Edison

 

[weldstan]

The MDMT is normally specified as either -320 F or -325 F, the approximate temp. of liquid nitrogen at which impact testing is done for welding procedures and some materials.

 

[MrTank]

Thanks. What about the pressure? I assume it will be designed under API 620 as API 650 maxed out at 2.5 psi internal.

-MrTank

ôI have not failed. I've just found 10,000 ways that won't work.ö
-Thomas A. Edison

 

[fegenbush]

MrTank,

API 620 will be required as API 650 does not permit refrigerated service. It would be prudent to rate the vessel for enough overpressure to permit proper relief valve operation.

 

[JStephen]

I would be inclined to get somebody a lot more familiar with that kind of service involved in the design and/or specification. Not a good area to experiment.
If it's a fairly small tank, it might be just as easy to use ASME.

 

[weldstan]

Understand that the pressure at the bottom course of a 100+ ft high, tank shell will be considerably greater than 4 psi.

 

[MrTank]

Thank you for your input guys. This is not a job but rather it is just for my own curiosity. In case I get asked, I already know what to answer based on your feedback. So feel free to answer.

Weldstan,

Yes I understand the concept of pressure head. Thanks.

JStepehen,

I have no problem hiring an experienced engineer if a job like this is thrown my way but I would like to understand as much as I can before I do.


-MrTank

ôI have not failed. I've just found 10,000 ways that won't work.ö
-Thomas A. Edison