NDT for Hot tap - welding a NPS 6 "O-let" unto a NPS 12 pipeline 2

[macki2009]

I am preparing to weld a NPS 6 O-let branch unto a NPS 12 mainline. the welding procedure does not specify any details about NDE/NDT, a colleague says we have to use liquid penetrant after each pass, can anyone shed more light on this scenario, please. which is better, magnetic particle testing or liquid penetrant for this application

 

[Dosequis]

Though these methods have inherent detection strengths and weaknesses, in my experience the materials usually determine which NDE method is used. Typically, magnetic particle is preferred when the base metals can be readily magnetized. I believe the simplest reasoning has to do with the fact that liquid penetrant inspections are more time consuming due to required "dry" and "dwell" times.

Another consideration is that "dry magnetic particle testing" can be performed on hot metal, which is obviously advantageous in the scenario of "NDE every pass". With wet MPI and LPI, liquids would quench a weld that hasn't sufficiently cooled, making the process much more time consuming in your scenario.

Generally, in terms of sensitivity, these methods are comparable. That said, there are several different kinds of MPI and LPI to consider as well, if increased sensitivity is required.

 

[macki2009]

Dosequis, thank you for your response, much appreciated.

 

[SectionIX]

Visual Testing is the most effective test.

We've found that dry MT of the root pass along with a final inspection [once cooled] using a wet method (white/black or fluorescent) is very effective. Shear wave inspection of the connection is advised as well; the main challenge is finding a Level II/III NDE technician who can perform the shear wave and interprete the results. I would avoid LPI as removal of the penetrant is rather labor intensive as the weld bead will generally retain an inordinate amount of penetrant. This generally results in over cleaning that removes too much penetrant, reducing the effectiveness of this method.

 

[weldstan]

Prior to placing the olet fitting on the run pipe, UT inspect for thickness to assure no corrosion degradation in the location. Recommend MT after the root pass, hot pass, 1/2T locations and completed weld.

 

[macki2009]

thank you section IX and Weldstan