08:16 Oct-02-2006 Godfrey Hands Engineering, PRI Nadcap, United Kingdom, Joined Nov 1998 284
Re: Inspection underneath riser clamps ----------- Start Original Message ----------- : Gents, : Could any body suggest a suitable NDT method for the inspection of offshore risers underneath riser clamps? : I would much appreciate your comments on the "applicability of LRUT technique" for such inspections. : Thanks, : Prasad ------------ End Original Message ------------ Dear Prasad, It is good to be in contact with you again. You will be aware that NDT Consultants in the UK market the SwRI MsS Long Range UT system. Your Alex (from Velosi) saw our system in use in Kuwait earlier this year, and whilst we were there, we were sucessful in detecting CREVICE CORROSION under clamps on gas lines with the equipment. This was confirmed in each case by removal of the clamps and manual UT of the area (but in some cases, manual UT was not necessary because of the extent of the corrosion being clearly visible). We have no experience on risers, but because we use Torsional Waves, there should be no leakage of waves into product (as you will get with Longitudinal waves), and therefore we expect this to be very possible. Please contact me for more information, or else speak with Alex.
An important factor that would contribute to the success or otherwise of LRUT inspection is the means by which the clamp is attached to the riser. Do the risers have a neoprene (or similar) insert between clamp and riser wall - if so that should help the technique as there is no metal to metal interface for leakage (irrespective of whether torsional or longitudinal waveform is applied). If your product is gas then Longitudinal waveforms will not 'leak' into the product - this is only a possible effect on liquid filled lines. There is certainly at least one manufacturer that provides both Longitudinal and Torsional combined in the same tool as default. In any case a full technical appraisal should be made to determine inspectability and also establish what level of sensitivity you expect from this particular application.