Ammonia MAWP Requirements

[jgibbs22]

Hi Everyone:

Does anyone know the reason why Fed OSHA has a unrefrigerated Ammonia styorage vessel MAWP requirement of 250 psig? Cal OSHA has a similair requirement, but is for 265 psig? Was talking with the State about getting a vessel equivalent to ASME for ammonia service that only needs to operate at 100 psig, and they said it has to have a MAWP of 265 psig, PERIOD! When I asked the reasoning for this requirement, their response was "I don't know". can anyone shine some light on this? thanks!

J

 

[vpl]

jgibbs22

Can you ask your OSHA person what section of the California code applies? If I have that, I would probably be able to find the equivalent section in the Federal Code and work back to the "Statements of Consideration" -- which may or may not tell you why the Feds went with 250 psig. Without it, it would be a bit more difficult as I'm not that familiar with OSHA requirements -- doable, but would take longer, and it would depend on how much time I was willing to spend.



Patricia Lougheed

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[jgibbs22]

Thanks Patricia! The seciton of the California Code is Title 8, Section 458, part 3 (d)...

(d) Except for tanks used in refrigeration systems, any tank used for the unrefrigerated storage, transportation, or utilization of NH(3) shall be designed and constructed in accordance with the ASME Code for an allowable working pressure of at least 265 psig.

 

[adamuk]

The design pressure of vessels containing cryogenic or liquified gases will be based upon the vapour pressure at the maximum expected in service temperature. You would reach 265psig at at somewhere between 40 and 45degC. That's the "why"

Adam Potter MEng CEng MIMechE

http://www.ax-ea.co.uk

 

[MJCronin]

I believe that adamuk is spot-on....its all about the vapor pressure at peak design temperature.

Another important source of design information for Anhydrous Ammonia Systems is ANSI K61.1-1999/CGA G2.1-1999....published by the Compressed Gas Association.

Like the ASME/ANSI codes, this Standard was developed by business/achedemic leaders in the compressed gas field.

K61.1 states that the minimum design pressure for non-refrigerated containers (containing anyhdrous ammonia) shall be 250 psig.

There are many other mandatory details regarding relief devices, piping, hoses etc...

My opinion only....