PMI - low nickel 316L pipe welds

Date 10-21-2009 17:44

Having a problem with low nickel in the welds scanning with a XRF spectrometer. Checked pipe and it is around 10.5-11.0 and undiluted filler metal is 11.5-12 which matches the certs that were provided (we require actual chemistries). When we check the welded joints we are getting 8.75 to 10.5 with the majority of readings around 9.5. The pipe sizes are 3/4"-3" sch 40. I was expecting the values to be at least around 11 for the weld metal since there is dilution. I checked some 304L/ER308L pipe and everything scanned OK. I even had one welded up in front of me and got the same results after welding. Scanner is calibrated, new battery, and we checked it on some other known parts. All reading look normal which makes me believe the scanner is working correctly. Any suggestions??

By 3.2 Inspector (***)

Date 10-21-2009 17:49

Have you checked the instrument on a sample, which is known to be 316L?
How thick is your last bead on the welds, which you get the low readings?

3.2

By Superflux (****)

Date 10-21-2009 19:07

Are there any fluctuations in your Chrome or Fe %? Have you or are you able to get a reading in the HAZ? Perhaps the Ni is migrating out of your test/sample zone? In conjuction with 3.2s idea, have you ground down the cap and taken a reading?

By Superflux (****)

Date 10-21-2009 19:11

Smearing of wire wheel material on the surface of hot welds can affect your readings.

By jrupert (*)

Date 10-21-2009 20:57

We checked the scanner on a calibrated 316L surface and the readings are within tolerance. The last bead varies. Some are flush with the surface and some are up to a 1/16th of an inch. Width is around 1/4" to 3/8". We have tried grinding the cap off and checking as well as welding back a cap on top and scanning with little benefit. We have tried with different brushes and techniques with little results. It would be difficult to nail down the HAZ since the area it analyzes is about 1/2" Dia. We did notice a small increase in Nickel scanning a weld on a 1" dia vs a 3" diameter pipe, but still below the spec.

By CWI555

Date 10-21-2009 22:18

Try lowering your heat input and see what you get with the nickel.

By jrupert (*)

Date 11-02-2009 14:41

Posting a follow up to close this out. I welded up another sample of 316L pipe welded with 316L weld wire (two welds). I scanned it with our XRF scanner and got about 10.5 for each. Set it to a test lab to have it scanned with their XRF scanner and it came out a 9.5 for each. I then had them perform OES and the results were 11.6 and 12.0. I think there are several factors that may be effecting the results. (1) the weld is smaller than the XRF scanner window (2) bead geometry (3) bead contour/preparation (3) microstructure???? (4) scanner algorithm for calculating Ni based on feedback. Client accepted all of the results based on the mock up chemistry.