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00:14 Oct-12-2006
Looking for root erosion in thin-walled duplex stainless steel welds

We have air coolers on our plant (oil & gas) part of which consists of a row of 1 inch dia, 1,6 mm to 3,5 mm wall thickness duplex (22% Cr, UNS31803) tubes TIG welded with matching filler metal to an 8 inch duplex header (wt 11 - 18mm). Weld ferrite content range 35% - 65%.

I am no corrosion engineer but it seems that duplex is susceptible to weld root erosion or cracking in case of wet-upset in an H2S environment. So we wish to check the weld roots for such whilst new equipment fabricated from material more-suited to the potential environment are procured.

A simulation test rig of one header with 4 or 5 tubes welded in place is being made for performance demonstration purposes. Do anybody have experience of such configurations? Is low-frequency eddy current a possibility? Or DC MPI - knowing that the permeability variations may produce non-relevant indications. As the material/configuration set-up is difficult to inspect I expect signal interpretation and evaluation will be a problem. Any ideas?