NDT before or after PWHT

[quatle]

Hello everybody

any ASME code don't mentioned NDT after or before PWHT, anyone can explain for me understand why?

 

[BigInch]

Depends on the type of ND test that you are doing and what you are looking to verify. Some tests show no difference before or after. How would you expect magnetic particle or ultrasonic tests to be different when done before and after.

 

[quatle]

Hello BigInch

normally, we performed RT before PWHT as this saves the time and money of having to repair welds and again perform heat treatment on the repair. As the owner we are willing for the contractor to do the NDT before heat treatment, but at his own cost.

The NDT carried out before heat treatment should be the same as the NDT carried out after heat treatment. Generally the NDT before heat treatment has been radiography, but as the owner we have substituted this for UT after heat treatment. The theory being, that the only repairable defects likely after heat treatment (if this has not been performed correctly) is cracking and the preferred method for crack detection in this instance would be UT, so far lack of sidewall fusion defect may insufficient of RT method

RG

 

[BigInch]

So if you already know when to do your NDT tests, why does ASME have to tell you.

 

[DekDee]

quatle,
If you perform RT before PWHT and UT after PWHT you are asking for trouble.
Numerous linear defects can be missed by RT and the weld deemed acceptable (especially lack of sidewall fusion)then the weld will be rejected when it is UT tested.
What is the material ?
What is the applicable code ?

ASME B31.3
(a) For P-Nos. 3, 4, 5A, 5B, 5C, and 15E materials, examinations shall be performed after completion of heat treatment. However, examinations need not be repeated on welds or portions of welds that are subjected to additional heat treatments and have not been repaired by welding.

 

[quatle]

Hello DekDee

Material is CS P1
Applicable code is ASME B31.3

Defection is found after PWHT, that mean we must repair by welding - RT or UT - re-PWHT - UT right?

as ASME B31.3 2014 edition is preheating 95deg without PWHT, we can preheating over 95Deg for repair by welding without re-PWHT

 

[MickMc]

On previous projects clients have stipulated that NDT must be performed after PWHT as the possibilities of cracking etc when stress relieving. Economically it suits contractor to NDT before PWHT in order to find defects in weld before going through PWHT, contractor is of course free to do before and after at his own cost.

 

[racookpe1978]

It depends too on the preheat-maintain heat-post weld heat treatment cycle you're in: If the casting or forging needs to be kept hot from preheat through end-of-PWHT, then you cannot do NDE effectively. UT melts the sensor or coupling fluid, dye penet must be less than 100 deg F, mag particle is possible (sometimes) but may be inaccessible because of heat blankets or access to the weld area for the probe and the person. RT may be impossible for the same reason: The film melts or cannot be pushed into position safely.

Theoretically, the NDE is done after PWHT because cracks "might" occur because of the stress induced in the cooldown. Practically, you try to NDE before PWHT/hydrogen bakeout/cooldown so you DON'T have to reheat and re-PWHT if you find a crack.

 

[weldstan]

quatle,
For P1 materials, ASME B31.3 permits final NDE before PWHT. It is up to the Engineer/Owner to mandate final Code required NDE after PWFT.

 

[quatle]

Weldstan,

where is para in B31.3 permitted performing NDT before PWHT?

 

[weldstan]

Please read carefully Section 341.3.1 (a), which defines for which material P-Nos. require final NDE AFTER PWHT. It can then be inferred that all other P-Nos. may have final NDE before PWHT (or after PWHT when required by Owner/Engineer),