Unexpected EDS Results

[swall]

I'm finishing a failure analysis on some broken 302 stainless springs that were used in an animal watering system. The springs were exposed to well water and had a nice uniform coating of rust. There was a prominent sulfur peak--this did not surprise me, as sulfur in well water is not unknown. What WAS a surprise were peaks for strontium and barium. I would be interested in your thoughts about possible sources of these two elements. They appear to be incidental, playing no role in the failure (which was fatigue).

 

[metengr]

The source could be from either well water or river (ground) water.

 

[CoryPad]

Strontium chromate is used in conversion coatings, and barium sulfate is an additive in many polymeric coatings.

 

[EdStainless]

I believe that they are from the well water. They water is probably coming from at least two different underground formations, one rich in S and the other rich in Ba and St. They mix and at a certain temp reach solubility limits.
BaS is nearly insoluble once formed.
Unless you see a lot of biofouling and micropitting I would say that they had no roll in the failure.

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Plymouth Tube

 

[Maui]

Swall, was it strontium-90 that you detected? Strontium-90 is a radioactive isotope of strontium produced by nuclear fission with a half-life of 28.8 years. It has only two sources - nuclear power plants, and the fallout from atmospheric testing of nuclear bombs in the 1950s and 60s. What level did you detect? And is the place where the water was sourced from near a nuclear plant?

Maui

http://www.EngineeringMetallurgy.com

 

[swall]

Maui--I don't know if it was Strontium 90. (I am old enough to know about strontium 90 from fallout, though). Would EDS even distinguish this from normal elemental Strontium? The peak was showing 1500 counts. For comparison purposes, the O peak was at 3500 counts. The only information I have on the location was that it was Minnesota. I have completed my report and supplied it to the engineer of record on the project. Up to him to make the next move, if there is to be further inquiry.

 

[redpicker]

One way to check for Sr90 is to see if you detect x-rays with the electron beam off. Being a beta emitter, Sr90 will excite the sample to produce a characteristic x-ray spectrum without the use of the electron beam. Of course, this alone isn't absolute proof of Sr90, but it would be proof of a beta emitter, and an analysis of the spectrum would give you what elements are present and you could find out from them which ones had isotopes that were beta emitters.

IIRC, the characteristic x-ray spectrum is not affected by isotopes, so EDS wouldn't tell you, other than being able to detect a beta emitter.

rp

 

[Maui]

There are 3 nuclear power plants in Minnesota that I am aware of: Elk River, Monticello, and Prairie Island. It would be interesting to know the location and if the radioactive isotope is what you actually detected.

http://www.EngineeringMetallurgy.com

 

[EdStainless]

It can be more informative to take some of the surface scale/residue, divide it into small lots.
One option is to view them with a microscope equipped to measure the optical properties such as index of refraction.
Another option is to weigh them, then was with various solutions (water, nitric acid, sulfuric acid, and so on).
You can reference a mineralogical handbook for solubility of various compounds/phases.

As far as the failure goes I would be much more concerned about signs of corrosion than the actual surface films.

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Plymouth Tube

 

[swall]

Redpicker--that might make an interesting project. EdStainless--I did not see any signs of corrosion on either the fracture or on the spring coils. The residue seemed to have been deposited on the springs in a fairly uniform layer.