Vessel field pneumatic testing with piping together 1

[jtseng123]

Dear,

We have vessels with welded nozzles for LNG service. Shop has done hydrotested per UG-99(b)and code stamped. Field already welded all pipes to the nozzles and will go through pneumatic testing the entire system since isolation of the piping is not possible. For sure any pre-caution will be taken and follow very strict safety procedures. The question is, can we air pressurize to the original water test pressure per UG-99(b)? or we have to use reduced pressure per UG-100 (1.1x MAWP x stress ratio) ? Will the mechanical warranty be voided ?

 

[mk3223]

I think you may be pneumatic test at pressure higher than 1.1x MAWP. But, why?
IMO, if agreed a pneumatic test and complied with Code, there is no need to test the system to the pressure used for the hydro testing.

 

[Mec.tec]

In case of pneumatic testing additional requirement(MPI/DPT) of ASME VIII-1 should be met.

 

[chicopee]

Isolation of the piping is not possible you stated which is not consistent with NFPA 58 since you will need valves between piping and tank connections.

 

[jtseng123]

Dear all,
I think I did not make my question clear. Let me try it again:

I have a new vessel (code stamped RT-3)shop hydrotested at 500 psig and already at job site. Any changes on the vessel shall be governed by NBIC from now on.

If I want to re-test the vessel for some reasons, says adding a new nozzle, adding clips, welding external piping and want to test together with piping, etc., per NBIC, I shall re-hydroetst at 500 psig per the original code of construction. However, due to cleanness service, can I pneumatic test at 500 psig instead of using water ?
Note that regardless using air or water, we are not altering the test stress at the vessel during re-testing, only the media changed from water to air. We see no reason to follow UW-50 for NDE since vessel was already painted and stamped. We also see no reason to follow UG-100 for using reduced air test pressure (1.1x )since this is a post construction activity at site, not at shop prior to getting a stamp.

What is your thought or site experience?

 

[chicopee]

Do not test with air as it could be very dangerous. If you use water, I would definitely crib the tank in the middle for additional support as I would not rely on the two end piers. While filling the tank with propane, additional amount of methanol is normally added to cope with moisture within the tank and this is routinely done in our Northeast region of the US. Same method should be used in your case.

 

[susan_cui]

pneumatic test not allowed based on currently status. the reason is:
1. firstly, test pressure is not different.
acc. to ASME VIII-1, hydrostatic test pressure is 1.3 times LSR, but pneumatic test pressure is 1.1 times LSR.
so if you do pneumatic test with hydrostatic test pressure, which is not safe and not allowed
2. secondly, additional NDE required acc. to ASME VIII-1 UW-50
3. design drawing and calculation is based on hydrostatic test, in case pneumatic test performed, which is a deviation

maybe leakage test could be done after piping connection.

 

[Genetix]

Based on your original post, you may be talking about golden joints right?
Pressure vessel fabricator was able to hydrotest the vessel by extending the spool and adding temporary flange for hydrotest purposes and the cut the temporary flange and additional pipe spool after hydrotest acceptance and then later bevel. Tie-in pipe will be welded at site. These type of joints are called golden joints. IMO, I believed that there is no reason to follow NBIC because the vessel have not been operational yet. For golden joints, after welding, we normally ask client waiver for pressure testing (water or air), and proposed to verify the integrity using full NDE only (MT/PT + RT and or UT) and later be leak tested using nitrogen or dry air by commissioning team with much lower pressure.

 

[Genetix]

"quote"
Note that regardless using air or water, we are not altering the test stress at the vessel during re-testing,
"unquote"

Hydrotest at shop vs hydrotest at site is different for skirt supported vessels. Stresses will be different since hydrotest at site is at erected condition. If in case hydrotest at site is allowed, can the bottom section shell and head and skirt withstand erected condition hydrotesting.

 

[jtseng123]

Genetix,

We always design vessels to be good for field hydrotest in operating condition. Foundation and vessel itself will not be a concern.

The purpose is not just to test the golden joint, but all other piping joints which are by welding. Flange connection is not allowed for this service.

For sure all NDE will be done on the piping joints without saying, but to test at lower pressure is not only violating B31.3 code, but also can not guarantee the golden joint will be good during operating.

NDEs do not guarantee vessel will be good for service. It is used to minimize defect prior to hydro or air test. Code allows no NDE on vessels, however, hydro or air test is required to get a stamp. The NDEs required per UW-50 is only to detect more defect prior to air test, to prevent it burst or sorry after fabrication. However our vessel is already past hydrotest and at site, and to put the same test pressure into the as-built vessel but substituting water with air is not alternating test stress and shall not be an issue in my opinion.

 

[MJCronin]

Remember, the MBAs, project managers and PMPs NEVER TAKE ANY RESPONSIBILITY if something goes wrong and people get hurt. If the test is successful and there are cost or schedule time savings....it is because of their superb management skills ..... if people die, well, its because of engineering incompetence

Pnuematic testing stores an incredible amount of energy in the system !!!

https://www.engineering.com/Designe...as-an-Alternative-to-Hydrostatic-Testing.aspx

http://www.eng-tips.com/viewthread.cfm?qid=352388

Wisely, ABSA has written a procedure on when and if this type of testing is acceptable. Large responsible organizations do this kind of thing .... Sloppy, b*tthole organizations, run by arrogant over-caffinated MBAs, do not

http://www.absa.ca/wp-content/uploa...ard_Pneumatic_Test_Procedure_Requirements.pdf

MJCronin
Sr. Process Engineer

 

[A clark]

Genetix,

I disagree with you statement that the NBIC does not apply, The vessel is Code stamped it doesn't matter if it has been placed in service. The NBIC permits pneumatic pressure testing for repairs at a pressure sufficient to ensure leak tightness, for Alterations it must be in accordance with the Code of construction.

 

[david339933]

NBIC is pretty clear on this......You cannot exceed the maximum pneumatic test pressure of the original code of construction, ie: 1.1 times MAWP...UG-100. NBIC Part 3 - 4.4.1(b)

 

[Genetix]

@MJCronin,

Nice post!

@Jtseng,
What I said are based on experience. I'm from contractor side and so far our client agrees on full NDE + leak test. By the way for the piping lines which does not allow flanges for connections, we normally pressure test the piping line first by extending the piping on both ends of the line and weld some blind or temporary flange and then cut to required length and bevel and after acceptance of pressure test and then weld it to the joint on the vessel nozzle. That way we only concern about the vessel nozzle to piping joint (golden joint). In my experience, I have never heard of the problem on those golden joints which are not pressure tested rather full NDE + leak test only.

In the future, I may be able to experience clients which could insist to have those golden joints pressure tested. I would be very much interested on what is the final disposition on your problem. I'm interested also whether the joints of the vessel which are not previously radiographed (since the vessel stamp is only RT-3), will be fully radiographed as per requirements of UW-50 prior to pneumatic testing (which I think is required or if not, should be the wise thing to do prior to pneumatic testing). There could be an issue as to who will shoulder the cause of NDE, the removal and restoration of painting, and the repair of previously non radiograph welds with defects found during NDE prior to pneumatic testing.

 

[A clark]

Genetix,

UW-50 does not require RT. PT or MT is the requirement in accordance with Endnote 71. I suggest you review UW-50 and EndNote 71.

 

[jtseng123]

Genetix,

I don't think UW-50 is applicable. If it is still under fabrication prior to getting code stamp, yes UW-50 is applicable so no one is going to be sorry during testing if something happens. I believe that is the major safety concern from code to ensure better integrity prior to testing, and also reduce test pressure to 1.1 x.


david339933, NBIC says not to exceed original code of construction. My interpretation is the stress level shall not exceed the original code of construction, not what test media can or can not be used (throughout the code, it is the "stress" under concern). If my interpretation is correct, I shall be able to swap water with air and still set the 1.3x as my upper limit since no stress level changed.

 

[david339933]

In your post you refer:
1.) adding clips to a pressure part....this is a repair.
2.) adding a nozzle.....this may be an alteration or repair...depending on nozzle info.

So we definitely have a repair if you are adding clips....see 3.3.3 "Examples of Repairs"

So now knowing you have a repair...head to 4.4.1 as I referenced above....

4.4.1 - Test or Examination Methods Applicable to Repairs
b) "A pneumatic test may be conducted. Concurrence of the owner shall be obtained in addition to that of the Inspector and Jurisdiction where required. The test pressure shall be the minimum required to verify leak tightness integrity of the repair, but shall not exceed the maximum pneumatic test pressure of the original code of construction. Precautionary requirements of the original code of construction shall be followed."

This is telling you that you CANNOT exceed 1.1 times MAWP....and also tells you that you must follow UW-50 NDE requirements. "Precautionary Requirements".

Like I said....NBIC is quite clear on this subject.

 

[Genetix]

@ A Clark.

I acknowledge your correction, sorry my bad.

 

[jtseng123]

david339933,
In my opinion UW-50 does not need to be followed. NBIC says very clearly like you quoted " verify leak tightness integrity of the repair", not any other places.

If you have a as-built code stamped vessel, 25' diameter and 250 ft tall vessel under repair. alternation, or welding a golden weld like my case, you can field re-hydrotest numerous times. You don't need to remove insulation or strip paint in other un-related areas for re-examining. Now due to the dedicate internals and cleanness requirement, you have to use air instead of water, do you think you have to remove all insulation, strip paint, and also remove ladders and platforms in order to preforming extra full x-ray on long seam and conducting examining, or performing any extra NDE for un-related areas just because the re-test media is air?

 

[david339933]

You had referred to clips, nozzles etc, not just a golden weld. Consult your AI....you are attempting to pneumatic test to Sec. VIII requirements, when this weld is outside the scope of the vessel. The vessel does not need retesting in this situation. You are now attempting to pneumatically test a vessel which has never been pneumatically tested, and has no safeguards completed.....consult your AI.
IMO: You are using a much more dangerous method of testing the vessel....one which has safety requirements. If you are hydrotesting again, it isn't a big deal, as the vessel welds have already seen this test....they have not undergone pneumatic testing. Normal procedure is Nitrogen leak test at a much lower pressure....no where near Sec. VIII requirements.


Subject Description: Section VIII, Division 1 (1986 Edition, 1988 Addenda), U-1(e)
Date Issued: 08/25/1989
Record Number: BC89-202
Interpretation Number : VIII-1-89-115
Question(s) and Reply(ies):
Question: Two vessels were fabricated by a Manufacturer in accordance with the requirements of Section VIII, Division 1 and were stamped accordingly. Nozzles with weld end connections were provided on the vessels. Are the field welds for the connections to these nozzles considered within the Scope of Section VIII, Division 1?
Reply: No, see U-1(e)(1)(a).