Horizontal hydro of verticall vessel 6

[jharper]

It is my understanding that when hydro testing a vertical vessel in the horizontal position, that the test pressure must be increased to accomodate for the static head. The fabricator has stated that the Code does not require this and therefore will not test higher than the Code calculated value 1.3 x MAWP x Sc / Sh.

It is a 14' OD x 50' T/T vessel.

Any inisght?

 

[nickelkid]

If your MAWP was calculated correctly static head has been accounted for. I believe your fabricator is correct.

 

[vesselfab]

yes, the mawp is accounted for in opperating position with mawp at top of vessel and liquid loads applied if they are there.

Code shop hydro test does not allow for static head and the shop guy here is in the right unless the user has it in spec.

Many Users have in their spec that design must be capable of withstanding a hydro in operating condition...but that is a whole other question and set of calcs.

 

[jharper]

Thanks guys. It's a requirement in our specs, but reading UG-99 have to agree with you and the fabricator that it is not CODE required.

Thanks again.

 

[prex]

I have to strongly disagree with the above positions.
First point, RCHandy, is that MAWP and design pressure are always intended at top of vessel. So static head is indeed accounted for in calculating MAWP, but only because it is subtracted from the calculated local allowable pressure to come back to vessel top.
Second point is that weight of contents is classified as an additional loading with respect to pressure (UG-22) and is therefore to be considered separately.
Third point: see last sentence of UG-99(b).
My conclusion, jharper, is that it is a code requirement that the static head is accounted for in your situation.
To be convinced of that, just think of a very tall vessel with a low design pressure, where the local pressure at bottom in operating conditions could be dominated by the static head. With your conclusion such a vessel might well be tested at a pressure lower than the operating pressure!
Note however, on the other hand, that parts of the vessel located near the top might be overstressed by such a test and this condition would limit the hydrotest pressure.

prex

http://www.xcalcs.com

: Online engineering calculations

http://www.megamag.it

: Magnetic brakes for fun rides

http://www.levitans.com

: Air bearing pads

 

[JoeTank]

I concur with the first three answers, so the vote is now 4 to 1.

Joe Tank

 

[JoeTank]

We need a re-count... it's now just 3 to 1

Joe Tank

 

[JLSeagull]

Is this vertical vessel a separator; or suction scrubber that would not normally be more than 20% full? Does it matter in the testing protocol if the vessel is not intended to be nearly liquid full? Is the test pressure significantly greater (such as 1000 psig) than the additional liquid head?

 

[jharper]

The vessel is low pressure (3 psig design) and does not even need to be Code Stamped; however, our client requires it to be Registered regardless.

The vessel will operate from 10% to full and should typically be at atmospheric pressure.

The test pressure is only 4 psig, however, with static head the test pressure would be ~ 21 psig at the top (tested horizontally). According to Div 2 rules for hydrotest allowables, the top head can only be tested at 17 psig max. I have asked the fabricator to test at 17 and they have refused.

I am also at a disadvantage since I was not involved with writing the design specification. My company did not get involved with the project until after the vessel was purchased by the client. We got involved for drawing and calculation review since our company was designing the rest of the plant associated with these new vessels.

I beleive if you follow the Code, you only have to test to 4 psig. Had my company written the spec, there would have been no question since our standars require static head to be accouynted for in horizontal testing of vertical vessels. Regardless of whether this is covered by Code or not, I believe that it is required. And the Code allows a higher pressure when agreed to by all parties with calculations presented to the AI (but AI has the right to reject the vessel if any distortion is present during testing).

Thanks to all.

 

[nickelkid]

Points well taken; there is no doubt that some designs require and can have an adjustment test pressure accounting for the caveats mentioned. The design stage is the best time to verify that the specifications have been incorporated correctly. IMO without the proper support documentation or knowledge of it, the fabricator was right for his stance in this situation.

 

[Christine74]

In my experience, when a fabricator proposes to hydrotest a vertical vessel in the horizontal position, the very first thing the Authorized Inspector asks for is whether or not the additional hydrostatic loads have been properly accounted for in the test.

-Christine

 

[jamesl]

There is no need to consider static head for vertical vessel during pressure test. Code interpretation VIII-1-95-27 has a clear answer for this one.

 

[nickelkid]

Interpretation: VIII-1-95-27
Subject: Section VIII, Division 1 (1992 Edition, 1993 Addenda); UG-99(b)
Date Issued: January 12, 1995
File: BC94-414

Question (1): Does the last sentence of UG-99(b) of Section VIII, Division 1, "All loadings that may exist during this test shall be given consideration," require that the static head that exists in a tower in the vertical position must be considered when determining the test pressure in the horizontal position?

Reply (1): No.

Question (2): Does UG-99 specify in which position a vertical tower must be hydrotested?

Reply (2): No.