NDE to detect corrosion under riser clamp

[MATEGRITY2009]

Hi everyone,

refer to MFL pigging inspection result, the pipeline found 30% wall loss located at under rider clamp area and the RWT is less than the require thickness of ASME B31.8. As you already knew the MFL is screening NDE method so, the problem is how we can inspect and confirm the exact metal loss of the pipeline without remove the riser clamp?

anyone experience with this, please advise...

Thank you

 

[matschka]

Years ago I coordinated and supervised a team of NDE techs at a major oil refinery in the Bay area. We were tasked with inspecting existing pipe to determine the extent of corrosion both inside and outside of the pipe. We used two,(2), NDE methods, UT and RT. The UT was used first
to detect interior corrosion.If corrosion was found we would determine the depth by subtracting
the corrosion amount from the published wall thickness of the schedule of new pipe. All the findings would go to the refinery engineers for their review.Sometimes they would request an RT of the corroded area also.The RT procedure for this was to use an (RT Standoff Procedure).I had never heard of it before. The NDE company had qualified this procedure and the refinery had accepted it. The procedure was to set up the 'pill' some distance away from the corroded area. Of course they had (standoff) (distance away from pipe wall) specifications for various pipe sizes.The developed film showed the longitudinal pipe walls and the wall thickness's and of course the corrosion would show up as hills and valleys etc. The RT film was given to the refinery engineers and they would determine whether to accept as is or to 'cut out' the affected areas or fittings.I hope this information helps.

 

[SJones]

With the riser clamp in place, external measurement techniques, such as GWUT/LRUT, will only ever be 'screening,' although that could depend on the reliability required for any ensuing FFS assessment. See what you can get and compare it to the MFL to see if achieves an increased accuracy.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.