PMI Testing with Portable XRF Tester

[wsmith22]

We have a customer asking for PMI testing to verify 316/316L stainless steel materials in a pressure vessel with the ASME SA specification limits. They want to include the PMI tester accuracy in the results. For example, if the accuracy of the tester is +/-0.1 for Cr and the SA specification requires 16.00-18.00, I assume we would need the tester to read between 16.1-17.9 for a match. Would this be correct?

I don't know if this is the standard way to use the tester because the accuracy is narrowing the actual specification range. From what I have read, the testers have algorithms that determine the best match based on the combination of elements.

 

[jmec87]

I would be careful relying on XRF for PMI. A few years ago, I had a few sales reps (from Bruker, Thermo Fisher Scientific, and Olympus) give me demonstrations of their portable XRF testers. All of them had accuracy and repeatability significantly worse than stated in their marketing materials (testing mostly on 4130/4140 low alloy steels), even in ideal conditions, and I felt there was too much risk of both false positives and false negatives for them to be useful to me. XRF also generally can't detect carbon.

If you want to move forward with this, I recommend first getting demonstrations from a few XRF manufacturers to verify that they can meet your required accuracy and repeatability on your planned materials in your normal conditions. As well, clarify in writing with your customer the intended disposition of any materials with questionable or failed XRF results in order to minimize your risk.

 

[weldstan]

You check for both Cr and Mo. We have used XRF for PMI of 316 SS many times in the field. Sample prep and equipment setup is required for best accuracy. Most often we found 304 SS as the mixed material in lieu of 316 the few times mixes were found. On one job there was a near 10% mix.

 

[r6155]

@ wsmith22
If the tester read between 15,9 and 18,1 is correct.

Regards

 

[Dhurjati Sen]

There are standard procedures for PMI testing as well. Those talk mainly about the spot preparation like filing / buffing required before PMI. Also, the number of readings to be taken, what needs to be done in case a few deviations are noted, etc. etc..

It is little deeper than +0.1/-0.1 tolerance.

However, this is usually done in case of welding, to rule out the possibility of erroneous use of filler wire / electrodes.

Surely, you got a rich client, probably somebody from the middle-east!

DHURJATI SEN
Kolkata, India