MPI of martensitic stainless steel

  • MPI of martensitic stainless steel

    Posted by leo on 27/11/2021 at 8:07 pm

    We have placed order for 13%Cr tubing (API 5CT L-80) which has premium threads cut on both sides of it.
    As per our specification, it calls for wet fluorescent MPI of threads. Now, vendor has come up with clarification that wet florescent MPI would cause contamination of iron oxide particle with stainless material. They are now proposing Liquid penetrant inspection (LPI) in lieu of MPI.
    As far as we know, 13%Cr material is a martensitic stainless and it still attracts a fair magnetism since it is ferromagnetic in nature and moreover, wet florescent MPI is more sensitive than LPI for threaded area.

    What we believe that LPI costs less compare to wet florescent MPI and that’s why, they are proposing LPI. Does MPI cause contamination on 13% Cr material ?

    Please advise your comments

    caleb charles replied 5 months, 3 weeks ago 2 Members · 1 Reply
  • 1 Reply
  • Positive Material Identification (PMI)

    caleb charles

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    28/11/2021 at 4:43 pm
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    If the specification requires MPI as the primary inspection method that is what you should apply unless an approval plan is obtained from the customer. That being said is standard practice to remove all residual inspection materials after testing, therefore no contamination shall be present upon completion.

    I would be more concerned that 13%Cr material may oxidize after being exposed to water if FPI process is applied. That type of contamination can damage surface finis and be difficult to remove from threads.