What is the minimum field hydrotest pressure for a repair/alteration

[jtseng123]

Dear all,
I search several places but could not find an answer. NBIC only says pressure not to exceed the lesser of 1.5 MAWP and the original test pressure, but does not set the minimum.
I have a small existing vessel gone through modifications at local shop. Without consulting us first, AI and shop decided to test only 10 psig above MAWP, but that is 150 psig less than the oroginal test pressure. They claimed the concern of safety if tested at the original pressure or 1.5 MAWP.

 

[bctarala]

Hydrotest pressure settings vary depends on countrys local code. What you say about 1.5 x MAWP is the minimum setting for hydrotest in new boilers. Here in our country, for mechanical inspection or statutory inspection (renewal of permit)of boiler, we use 1.2 x MAWP, for new and altered boilers,we use 1.5 x mawp. Please review your local code.

 

[metengr]

If using the NBIC, the pressure test for repair is only given as a maximum value because not all repairs need to have full operating pressure or above operating pressure to prove the integrity of the weld repair. Owner/users require flexibility for in-service equipment.

For alterations, the hydrostatic test requirement follows the original code of construction requirements unless alterative approached are agreed upon between the owner/user, inspector and, if required, the Jurisdiction.

 

[DekDee]

metengr,
A bit confused
"If using the NBIC, the pressure test for repair is only given as a maximum value because not all repairs need to have full operating pressure......"
Would not maximum operating pressure be the minimum requirement for a hydrotest ?
Cheers,
DD

 

[metengr]

DekDee;
No, not for repairs. During my previous assignment and now my client routinely performs pressure tests as low as 200 psig for weld repairs to waterwall tubes and internal boiler components to avoid damaging the protective internal magnetite oxide layer. Hydrotest means one using water to pressurize. A hydrostatic test refers back to the original code of construction test.

 

[metengr]

In addition, I should have mentioned the 200 psig "squeeze" after weld repairs was on power boilers rated at 1800-2200 psig operating pressure.

 

[jtseng123]

Thanks and still not get the picture clear what will be the minimum hydrotest pressure per NBIC when AI and shop decide to perform hydrotest on this 7 years old small drum. We are adding three 2" nozzles, welding a vortex breaker and couple of baffles to direct the flow.

If a shop owner working on ane existing vessel fabricated by others, will he be afraid of something can happen if tested at 1.5 MAWP or the orginal test pressure ? How can he prove the integrity of his work without running the risk ? Is tested at MAWP good enough to prove his work?

 

[metengr]

jtseng123;
What is the original code of construction for the vessel? If the hydrostatic test does not meet the original code of construction hydrostatic test requirement of 1.5X MAWP, you do have options;

1. Use the lower hydrostatic pressure test at 1.1X MAWP and perform NDT of the welds related to the alteration work.
2. Re-do the hydrostatic test at 1.5X MAWP and call it a day.

Is this considered an alteration under NBIC or API 510 rules? Adding nozzles does not necessarily fall under alteration, this could be a repair.

The above options must be discussed with the AI and the user for acceptance.

 

[fegenbush]

jtseng123,

For a repair, pressure testing is not required per 4.4.1(e) of NBIC Part 3*. As metengr said, not all nozzle additions are alterations. If the vessel already has the same size or larger nozzle and reinforcement is not required per 3.3.3(i) or (j) of NBIC Part 3*.

For an alteration, pressure testing *may* not be required per 4.4.2(c) of NBIC Part 3*. If the customer does require a pressure test, it must either be to the original code of construction (consult that code for the required minimum pressure) per 4.4.2(a)(1) of NBIC Part 3* or the minimum pressure to ensure leak tightness per 4.4.2(a)(2) and 4.4.1(a)(1) of NBIC Part 3* which is to be determined by the contractor performing the repair. As metengr said, this is common for high pressure boiler applications where full pressure is not required for leak tightness determination.

*my copy is from 2007, but I do not think it has changed

 

[macmet]

I believe this should be up to your AI. We generally like to see between 90-100% of operating pressure, but I usually work with whatever the AI suggests unless it is higher than what I feel is safe for people and the boiler being tested.

 

[ukmet]

Dear jtseng123

Repair or alteration you can follow the rules of API 510.

1.5 x MAWP if the vessel was originally constructed prior to 1999 addendum

1.3 x MAWP if the vessel was originally constructed after to 1999 addendum

It is the MINIMUM TEST PRESSURE requirement. do add the factor of stress at test temp and design temp.

 

[jtseng123]

ukmet,

Normally, we go by NBIC. As has been discussesed so far, it appears no minimum test pressure set by NBIC. It will all depend on AI and end-user to come up with something mutualy agreed upon.

I am not familar with API 510 since we never use that so far. The "minumum" test pressure you cited is the same as UG-99 for new constructed vessel. NBIC must have a reason not to adopt that rule from UG-99 that I am waiting someone to shed the light.

 

[metengr]

NBIC must have a reason not to adopt that rule from UG-99 that I am waiting someone to shed the light.

As a member of the NBIC main committee, the reason is maximum pressure testing flexibility for end users.