Took out a steam sparger and noticed a small section that had residue on the top of it. I believe it may be caused by a reaction with HCL and moisture creating water and a metal chloride. It felt oily and was a little brown and had small flakes of some sort of buildup. Any information on what this might be will help me be able to trace back the root cause of the problem. I have attached a photo of what I found.
Dear Thomas Cermack
SS 304L(Cr-18, Ni-8)316 SS (Cr-18,Ni-12, Mo-2) has excellent corrosion resistance, but Chloride creates pitting corrosion. The HCl break H+ & Cl- ions,Pitting corrosion of stainless steel due to chlorides would certainly produce a rust-colored product. Passivation can be used to maintain a good corrosion resistant surface of stainless steel process vessel.
Please find attached herewith link about material detail.
regards,
Prem Baboo
Research MATERIAL SELECTION FOR NITROGEN BASED FERTILIZERS PLANTS
You may also see emerald green to dark olive colored liquid residue, which I have always associated with chromium being selected dissolved out of stainless alloys; I have seen this in 316L SS pipe bearing "anhydrous" HCl which may have a few hundred ppm of moisture, at temperatures up to about 50 Celsius.
If this corrosion is of concern you may wish to look at higher alloys, for example the Hastelloys (especially the C grades).
This is the opinion of the author, not of Solvay, and is based on plant experience - but corrosion chemistries are complex, and coupon testing is recommended in selecting materials of construction for corrosive service.
http://www.haynesintl.com/CRAlloys.htm
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