Hydrostatic Test on Propane Storage Tank

[chicopee]

Mass. Fire Marshall office requires that a hydro at MAWP be performed on a second hand propane storage tank. We are of the opinion that this is not necessary and that we can check for leaks at welded joints when the tank is filled with propane and when the pressure is near MAWP. Our external inspection and ultrasonic test of shell and heads revealed the tank to be in good condition. Comments are appreciated.

 

[metengr]

The concern by the Chief/Jurisdiction is probably the condition of the seam and girth welds of the propane tank. Unless you can attempt to provide a 100% volumetric examination of the welds, and with the thickness of the shell and heads plead your case in lieu of a hydrostatic test - the Jurisdiction has final say.

 

[aclark]

Metengr is correct the Jurisdiction does have the final say.

However it is normal to have a pneumatic teat performed on a propane tank due to the moisture issues. Most Code shops pneumatically test these tanks in production using chambers. you could do a UT of all Cat A and B welds and a Mt or PT of nozzles and attachments. RT is not normally feasable due to lack of a manway for internal access.

 

[metengr]

alclark;
In production, yes, you are correct. The key here is the fact that the tank had been in service, and apparently an Operating Certificate or permit is required. The hydrostatic test is typically a default approach that many Jurisdictions use to justify fit for service criteria. I don't necessarily agree with this because there are alternative methods to assure safe operation of a pressure retaining item. In my dealings with Jurisdictions, they are reasonable folks provided you have a game plan ahead of time and tell them what is the situation and your corrective action. If you approach the Jurisdiction and ask them for guidance, they will take the path of least resistance - hydrotest.

In this case, since this is a used tank, the Jurisdiction is probably falling back on using a hydrostatic test to assure adequate design margin in the event the tank has suffered from internal corrosion that would not be detected by spot UT for thickness testing or assuring full penetration welds. Perhaps a visual inspection could be performed using a borescope or other fiber optic camera as is permitted in Part RB of the tank interior, in conjunction with UT of the shell/head thickness and UT of the welds. Also, do we even know if this tank was built to Section VIII, Div 1 was stamped, and the age?

 

[GenB]

I am new to propane tanks and I wonder if any other liquid other than water can be used (because of moisture and not of explosive nature as LPG),
can be used in lieu of the danger pneumatic on a used vessel
genb

 

[aclark]

metengr:

Thanks for the remark about us Jurisdictions being reasonable. I was wondering seeing as how LP is non corrisve, it may be that the Fire Marshall is not familar with ASME and National Board. In my state LP tanks also fall under the Fire Marshall and not the Boiler and Pressure Vessel Div. Also how big is this tank? Is it a domestic tank or a large storage bullet? Also has it always been in LP service?

We currently have a request to take some 50,000 gal storage bullets built in the 1940's and convert them to compressed air service. We have lots of questions for the owners.

 

[deanc]

Does this LP tank have a manway? If so talk to the Jurisdiction and doing an internal. If not think metengr has the best answer.

aclark: Strongly suggest you get the Jurisdiction in on this ASAP if you have not already done so. They may just tell you no.

Have you cut coupons for analysis? Are you going to Wet MT all the seams? Will you do new calcs to current Code or 1940?

Sounds like fun to me.

 

[aclark]

deannc:

I am the Jurisdiction, and we have lots of questions for the owner of these vessels. We have required that the calcualtions be per the origional Code.

Also most domestic 1500 gal and 750 gal LP tanks do not have manways.

 

[metengr]

aclark;
One of these days, I hope to see you at the NBIC main committee meeting?

 

[jte]

aclark-

You state that you req'd the calc's "be per the original Code" but didn't state which edition. I presume you meant the 1940's era editions.

How do you interpret NBIC Interpretation 95-19 which states that The term "original code of construction" refers to the document itself, not the edition/addenda of the document. Repairs and alterations may be performed to the edition/addenda used for the original construction or a later edition/addenda most applicable to the work?

And... for what its worth, though I've butted heads with agency AI's and jurisdictions, I'll agree that they tend to be reasonable.

jt

 

[PAN]

aclark,
The test at MAWP (corroded condition) should be acceptable in this case.

I understand that the moisture issue may be concerned. However, drying after hydrostatic test should be the normal practice. Pneumatic test for the used vessel is prohibited in my company's standard.

 

[chicopee]

This tank is 18000 gallons and stamped per NB/ASME. Sounds like an internal inspection may be the right approach.
The situation is now getting more complicated with an other PE who has suggested nitrogen to perform this so-called "hydro" but more accurately should be called a leak test. To me a hydro test is testing tanks up to 150% MAWP using water as a medium.