Hydrotest for Routine Repair 2

[fabtank]

Is a re-hydrotest required for routine repairs?

We have a Section VIII Div. 1 vessel recently completed and now we must weld a small bracket inside.
This will qualify as a routine repair and we are not altering the pressure boundary other than welding about 3".
Do we need to re-hydrotest the vessel after this addition?

 

[metengr]

No, hydrotesting is not required for routine repairs under the NBIC or API 510 provided the vessel has been completed (stamped and originally hydrostatically tested). You can perform NDT after the weld repair or a pressure test.

 

[macmet]

Metengr,

I would just like you to clarify you comment above. You are saying that after a routine repair it is required to,

A) Hydro

or B) other form of NDT such as Xray

Correct?

 

[metengr]

(B).

First, a hydrostatic test as defined by the code of construction is either 1.3 or 1.5X MAWP or design pressure.

Under the rules of the NBIC for repair or routine repair - you need to verify the integrity of the repair by either a pressure test (with water or gas) OR NDT (surface or volumetric).

You are not required nor should one perform another hydrostatic test on any weld repair or routine repair once the pressure retaining item has been completed (per ASME code).

 

[macmet]

So in terms of the OP's question...

A hydro is not required, but a "liquid pressure test" or another form of NDT is?

 

[macmet]

I just asked because the term "hydrostatic test" is often used after a repair, but technically it is a liquid pressure test, not a hydrostatic test.

 

[metengr]

macmet;
Yes, you are correct. The NBIC has definitions and a pressure test is NOT a hydrostatic test. A hydrotest means nothing.

Pressure Test — A test that is conducted using a fluid (liquid or gas) contained inside a pressure-retaining item.

Hydrostatic Test — A liquid pressure test which is conducted using water as the test medium.

 

[fabtank]

I would just like you to clarify you comment above. You are saying that after a routine repair it is required to,

A) Hydro

or B) other form of NDT such as Xray

So for our application what would be the most appropriate form of NDE? PT examination?
We are only adding about 6" of fillet weld on the shell to mount a bracket.

 

[metengr]

Liquid PT or wet MT.

 

[fabtank]

Update:
When we reviewed this with our AI and he said it would have to clear with the state of Utah.
The state of Utah did not accept our proposal to do a Liquid PT test for this routine repair.
They mandated that we must perform a pressure test unless is was not practicable, and extra cost or inconvenience do not make it impracticable.

 

[metengr]

The Jurisdiction has the final say, sometimes you can persuade other times you don't.

 

[racookpe1978]

Is this a "weld" to a pressure-bearing part of the actual wall of the pressure vessel, or is this new weld holding a "bracket" that is merely attached to the wall?

 

[MJCronin]

I believe that this is an important topic and should be turned into an "eng-tips FAQ"

IMHO, There is a lot of confusion out there about pressure vessel repairs and the meaning of terms

MJCronin
Sr. Process Engineer

 

[racookpe1978]

QA me on this: When I use these terms, a "pressure test" is made after assembly by the usual fluid (water for example) up to the normal operating pressure as a check for leaks after disassembly or opening.

A hydrostatic test, on the other hand, is done after construction or replacement with "new" parts that have not been previously hydro'ed. (The new part or repaired part difference is discussed above.) The hydro static test is a formal test made at controlled rates to a pressure greater than NOP, held for a soak period, then inspected. Once a Hydrostatic has been done, only a pressure test is needed before the next startup - again, unless a new part is added or a major repair done. For most new construction, a flush is also run, usually as part of the fill before the hydro.

If just an simple unbolt-and-inspect-and-rebolt has been done, then a simple operational test (controlled startup, leak check before and at NOP, then a complete startup) is required.

 

[metengr]

First, you have to determine which code is applicable. If it is code of construction, you have no pressure test for boilers and pressure vessels, it is a final hydrostatic test to complete code stamping requirements.

Second, once the vessel has been completed above, any subsequent weld repairs can be performed using the National Board Inspection Code (NBIC), or if a pressure vessel, NBIC or API 510.

For repairs (not alterations) you have pressure testing, which can vary from static head to no greater than 1.5X MAWP. The wide range of pressure is provided by the NBIC to allow flexibility to owner/users for conducting a pressure test to verify the integrity of a weld repair, nothing more.

In lieu of pressure testing, NDE can be performed. HOWEVER, it is up to the Inspector, and if applicable, the Jurisdiction to make the final call. As I said, I have been involved for many years and sometimes you can persuade other times, a pressure test is used because the organization making the final decision is more comfortable.

 

[jte]

... because the organization making the final decision is more comfortable.

Indeed, sometimes ignorance is bliss.

[rant] What frustrates me with situations like this is that it is all too easy for a government official to make some determination which has the sole advantage of making it easy for him/her but has in fact no advantage in terms of public safety or reliability and has the definite disadvantage of adding unnecessary cost and effort, and is not within the intent of the engineering organization which created the standard.

It is indeed more difficult and requires more capability and confidence for an official to evaluate a proposal based on its engineering merits. I respect those agencies with people like this - and yes, I deal with a few which are definitely capable of an intelligent discussion.[/rant]

 

[DekDee]

How do you "pressure test" a bracket on the shell wall ?

 

[metengr]

You are pressure testing the shell wall and attachment weld to ensure no leaks and no structural issues under pressure.

 

[DekDee]

Sorry metengr,
Just trying to get my head around it.
I am familiar with hydrostatic and pneumatic leaks tests but not sure what a pressure test is.
If I use a liquid for the pressure test what is the difference between that and a hydrostatic test ?
If I use a gas for the pressure test what is the difference between that and a pneumatic test ?

Cheers,
DD