Neumatic Test

[alejo2003]

I have this doubt: In the company that i work for we have a column that has been working for 30 years (with several hover hauls). We want to make a neumatic test of the vessel. The Working Pressure is 0.4 Kg/cm2 (5.688 psi). I've reading that the testing pressure in neumatic test is 1.25 times the design pressure when the vessel is new, but we have a procedure for testing the vessel at 1.5 times the working pressure of the vessel. The company who made the vessel recomend 7.5 psi for testing it. What do you all think? In our procedure the neumatic test could be 1.25 times the working pressure (in that case wold be 7.11 psi in our column, very close to the value recomended for the suplier)?

 

[Harold53]

alejo
First of all I think you should check de design code for the column, but anyway most codes limit pneumatic test up to 5 psi. The pneumatic test is a dangerous operation because of the air compressibility, so if you have a leakage the pressure does not drop as quick as with water and normally this become a crack.
In addition, if you have flat bottoms or caps, you must have provision to reinforce this surfaces in order to avoid deformation

 

[imok2]

"The company who made the vessel recomend 7.5 psi for testing it". DO this and get it certified, then if anything goes wrong with the vessel you would be protected and have a claim against the manfg.

 

[imok2]

This my interest you:
Pressure testing shall be performed as per ASME Sec VIII, UG-99 or UG-100 for pressure
vessels or as per ASME/ANSI B31 code series for pressure piping. It is the responsibility of
the design engineer to use hydrostatic or pneumatic pressure test values consistent with the
latest revision of the applicable code.
As a guideline, the pneumatic test pressure shall be at least equal to 1.1 times the maximum
allowable working pressure. Whereas, the hydrostatic test pressure shall be at least equal to
1.3 times the maximum allowable working pressure for vessels designed using ASME
Sec VIII and 1.5 times the maximum allowable working pressure for piping systems designed
using ASME/ANSI B31 code series.
Please read this!!!

http://www-esh.fnal.gov/FESHM/5000/5034.pdf

 

[jte]

alejo2003-

This really belongs in the Boiler and Pressure Vessel Engineering forum. There are several reasons to test a vessel. The only time you must meet the original code of construction is when the vessel is new or when you have made repairs or alterations to it. Even then, it is not unheard of for an AI (please, please don't ask me what an AI is!) to require a hydrotstatic test pressure less than 1.3 or 1.5 times MAWP (adjusted for temperature). For a 30 year old vessel, the proper hydrotest multiplier would be 1.5x. I won't mention pneumatic tests other than to state that if you have to ask these questions (and I'm glad you did!), you shouldn't be fooling around with pneumatic testing.

Don't forget to go to the "personal profile" link at the top left of this page and fill it out. It helps for us to understand the perspective you're coming from. You can see mine by clicking on the "jte" at the top of this post.

imok2-

"DO this and get it certified..." What would that accomplish? The original Code fabricator would have zero liability 30 years later even if they were still in business.

Interesting that the Fermi document you referred to contains some things with which I'd take issue. For one thing, the proper hydrotest multiplier for Section VIII repairs or alterations (without a reduction by the AI) would be based on the original code of construction, not current edition. For Div. 1 vessels, that means 1.5 or 1.3. Also interesting that the Fermi document does not consider a brittle fracture failure mode. The allowable water temperature range is 50 to 90°F. Fifty °F may be well below the MDMT for some vessels. Ninety might not be enough either. I recently calc'd the MDMT for a carbon steel vessel which, at full pressure, was 95°F. I wouldn't want to be the guy who stated that a 55°F test temperature would be ok! No mention of water quality for use during the test. Go ahead and use local sea water to hydro those stainless vessels! Sheesh!

Alright, enough ranting!

jt