Design a Piping System for ammonia service 2

[usatab]

We are designing a piping system for anhydrous ammonia service basically ammonia filling station. we are using ammonia as non-refrigerated system.

From B31.3 i understand that I lie in Category M Fluid service.(Please correct me if I am wrong). So, for that I suggested to use low temperature CS material i-e ASTM A333 Gr 1 or 6.
But from other sourcing i came to know that if ammonia is used as non-refrigerated we can use A53 or A106 material and if ammonia is being used as Refrigerated then for piping system we will use A333 material.

So, need some advise to clarify this confusion.

Many thanks in advance

 

[moltenmetal]

It is the owner's call whether or not to consider any fluid Category M or not.

Where chlorine is used, it has been my experience that it is seldom considered Category M, so I would be very surprised at an ammonia system being considered Category M unless it were in a confined space or there was some other similar consideration.

As to the selection of material, if there is a reasonable likelihood of autorefrigeration taking the temperature below the limits of A53 or A106, then you need the low temperature material- assuming the "filling station" isn't exposed to ambient temperatures so low that they require low temp material already.

 

[georgeverghese]

There would be many operating cases where this piping would be at less than -20degC; the cost differential to A106B is minimal anyway.

 

[MJCronin]

Be careful .... some US states have imposed their own requirements for piping design, including materials selection:

http://www.mda.state.mn.us/Global/MDADocs/chemfert/nh3/nh3syspipreq.aspx

Some inspection, testing and documentation requirements for completed systems are also mandated by selected states.

Also, it's a good idea to review the extensive OSHA requirements specifically addressing Anhydrous Ammonia:

https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9757

Tell us more about your system design ....

MJCronin
Sr. Process Engineer

 

[moltenmetal]

You can tell from MJCronin's excellent 1st link that ammonia is NOT considered a Category M fluid, as the document talks extensively about threaded joints.

 

[MJCronin]

Thanks, MM,...... Have always found your posts very helpful !!!!

I have always been outraged that neither ASME nor any other authority has developed the testicular fortitude bravery to establish at least a partial list of chemicals that must be considered Category M service.

Time after time the newbie comes to eng-tips to ask his reasonable question for a particular liquid ..

His MBA boss is putting pressure on him

ASME answers the question by performing it's typical prissy dance ...... "Yes.... it might be Category M in this case....OOooh, but not for that case !!!"

Cant we all agree that water is never Cat M and that Phosgene Gas, in any circumstance IS CATEGORY M ?????

?????????????????????????????????????????????????????????????????????????????????????????????????????????????????

MJCronin
Sr. Process Engineer

 

[chicopee]

For what it is worth, don't use brass or any copper alloys in the ammonia piping system.

 

[usatab]

Yes Chicopee we are not using any copper or brass like things.

 

[usatab]

Mr. MJCronin's thanks for such helpful references and comments about Category M fluid.
Basically it is a ammonia filling station that we are designing. Where temperature ranges from 5 to 50 C. But we are operating it at 20 C and 8 barg pressure(ammonia vapour Pressure). From your reference document, it seems that I can use A106 Material as we do not lie in refrigeration system.

Waiting for your further kind guidance.
thanks.