"Stainless Steel Corrosion"

Question:

"My question relates to corrosion products of stainless steel. I am working on an evironmental project where groundwater pollution is being studied. Water wells constructed of stainless steel materials (type 304 I believe) were installed in the mid 1980s. Groundwater samples from these wells have shown fairly high levels of chromium and we can not relate this to historical activities at the site. My questions are about the makup of stainless steel products that are 15 years old and whether corrosion of the stainless steel materials could account for the high chromium we see in the groundwater. The groundwater conditions near the wells in question are not harsh in that the pH is normal, no chlorinated compounds are present, but the total dissloved solids content is pretty high (between 5000 and 10,000 ppm - mostly calcium, magnesium, chloride, etc.) Any information that can be supplied on this topic or literature references would be appreciated."

Answer:

When 300-series stainless steels corrode, the corrosion products will contain base metal elements, including iron, chromium and nickel, as well as oxygen. Therefore, if the stainless steel well components were corroding, then they certaintly could be contributing chromium to the groundwater. However, the 300-series stainless steels normally show good resistance to neutral pH waters; therefore, unless you can correlate the high levels of chromium in the water with evidence that the stainless well components are corroding sufficiently to contribute those levels of chromium (which is not considered likely) then an alternate source may exist. You may also want to verify the ionic or compound form of the chromium, as this information may help in identifying the source. YOu may also want to consider installing a retrievable corrosoion coupon to verify corrosion rates of 304SS in the water by checking weight loss vs. time.

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