UT of inservice welds

[sree60]

Hi members

The pressure vessel ( in service) nozzle welds are required to be tested by manual UT . The vessel is PAINTED. Can UT be performed over paint? The calibration is always done on an unpainted reference block. How is the compensation done for the error introduced due to the paint . Any info or reference will be appreciated

Sree60

 

[TTT]

It's been a while since I have ut'd any welds but have never heard of doing shear wave inspections of welds through paint! The paint must always be removed at least the standoff distance for that angled probe.

 

[ndeguy]

Not necessarily "always". You can perform the following extra trests before UT on a painted surface: -

1. close visual inspection of paint for adhesion to steel substrate
2. compression wave inspection of paint steel interface to ensure uniformity of the bond.
3. paint thickness inspection of coating for any large variations in coating thickness which could cause mode conversion variations and or attenuation losses.
4. check for transfer losses/gains when comparing your cal block to your inspection surface. Transfer losses can be high when testing from a painted surface

 

[Duwe6]

Concur w/Ndeguy. Proper, well adheared paint is easy to work through. Problem is 'what attenuation is the paint causing?'. Typically, that is not a 'real' problem. Good welds usually remain good after you add 2-5 dB to compensate for the paint. Bad welds, especially cracks and Lack-of-Fusion are rejectable even before adding a gusstimated attenuation correction.