I have two- 304 Stainless steel tanks, steam jacketed in bottom half, that hold a broth solution at 140-160F. Our first issue involves a reddish/brown and purple appearance in the dome area--air contact area/no product contact. An application of (HCL/phosphoric/surfactants) foam cleaning solution will clean this to a clean, mirror image. Sodium hydroxide/potassium hydroxide solutions (3-6% total alkalinity) with 50-200ppm free chlorine (bleach) applied through a spray ball does not impact this appearance at all. Do you know what this is and what will remove this without using an acid or bleach type cleaner? Our second issue appears to be related to acid that was used to clean the tank. On the steam jacketed portion of the tank, a terrible white spotted appearance has occured, supposedly after acid cleaning. The acid product was foamed throughout the tank, during which the steam may or may not have been left on in the jacketed area . My personal view it that the tank spotting has occured over a period of time, that it is more tied to a process change (which introduced more inorganics and insoluble acid salts), and is much more pronounced in one tank. We tried hand wiping with concentrated acids, caustics, and solvents with no improvement in appearance. We have buffed the tank with 1000 grit with success. What happened to cause this and are issue 1 & 2 related?

We have been unable to extract any significant amount of the scaling material using acid, caustic, or solvents--MEK, etc. Any recommendations on getting a sample?