NDT for in service inspection of cast stainless steel piping and welds

Depends on what your (or the client's!) spec says.
Depends on the shape of the fitting (or casting or forging) and what the purchase spec is from the repairing company.

For stainless steel, UT is sometimes required for piping, but not just "in general" down a piping run. UT is tough to read, you get a lot of funny reflections off of fittings, elbows, bends, valve bodies, flanges, etc and so the other tests are preferred. The pipe is pedigreed from the supplier, so the concern is the field or shop weld joining the pipe to something else.

Welds on that SS piping run? Often a VT on the root pass and always a VT on the final weld - depends on thickness of the pipe wall; almost always a PT (dye penetrant) on the final weld since mag particle (MT) doesn't work on SS.

Mag particle usually replaces the PT on a CS (P1) pipe. Often MT is used on CS-CS structural fillets on a "sample count" basis: 2 in 6, 4 in 12, 6 in 20, etc. Bigger the weld buildup, more likely the MT is run.

RT (X-ray) tests on pressure piping are frequently required - depends again on what the spec and weld process and test plan say. Don't guess, you have to read (in detail!) your own documents and be able to justify each step (or each "i amnot going to do this" decision) back to the source document, page, and paragraph.

Thanks for the reply. I read some documents about the challenge of UT on cast stainless steel due to course grain and anisotropic structure. Since UT is normally used on ISI, just wonder, for the PWR which used cast stainless steel for primary piping, what NDT is used? UT or RT?

Thanks

Andyweld

I've seen both; though primarily RT for the stainless steel piping.

A lot depends on when and why they're doing the NDT.

Patricia Lougheed

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It's very, very hard to use RT to "measure" any sort of "thickness".

RT (any X-ray for that matter) goes "through" the metal or target, then exposes a photographic plate or CR tube or solid-state recorder on the far side.

what do you "measure" to determine thickness of what material the x-ray goes through? How do you calibrate your measurement device, and how do you assure repeatability between x-ray shots, materials, and different operators and x-ray readers? The RT can take of photo and find cracks or inclusions or voids. But it cannot measure thickness.

UT sends a sound wave into the steel or target material, gets a reflection off the far side, and creates a unique pulse when the echo returns to the near side. That IS a "calibrate-able" and repeatable test - at least on one part metals with smooth sides.

So, why would you use anything but UT on a simple In-service inspection? You don't want to break the pipe or heat exchanger or casting apart and look inside.

In our Swedish utilities do we normally use UT for all advanced volumetric testing. UT is often combined with ET in order to be sure to detect all surface breaking defects.

When UT is applied for primary systems, is it in the absolute majority of the cases mechanized systems that are used.

Mechanized UT is used from the outside in the majority of the cases. For a few external pump BWR applications is UT/ET used from inside the disassembled pump.

One are that might be a bit tricky to test is the cross-over leg, especially the welds running lengthwise, this might require some rater special equipment.

One company that has done a lot of mechanized UT/ET testing at PWR’s and BWR’s world wide is Wesdyne TRC.
Also Siemens KWU, nowadays AREVA Erlangen has done some rater fascinating through wall UT testing in thick cast austenitic stainless steel pump housings at Swedish utilities.

So it can be done, it is merely a matter of how much money it can cost.

Hi Andy

This paper may be of interest.


You will find many more of potential interest by searching the database of ndt.net

Hope this helps.

Happy New Year