Material of construction for manganese phosphate tank

A. Hi, Elizabeth. The answer may depend upon whether you are talking about the simple compound manganese phosphate, stored at room temperature, or whether you are speaking of a process tank for a proprietary manganese phosphatization process.

Years ago the company I was with at the time supplied many major manganese phosphatizing process lines to auto and farm equipment manufacturers and we always made everything from the tanks to the barrels to the heating coils from 316L stainless steel. One reason is that 316L retains full corrosion resistance after welding so you don't worry about selective attack along weld lines; another reason is that 316L is one of the easiest materials to reliably electropolish, and you may find electropolishing highly advisable for components like the heating coils which readily 'sludge-up' and need to be cleaned -- electropolishing slows the build-up while making cleaning easier.

Lesser grades may be fine but I don't have any real experience with them since GM, Caterpillar, et al wanted the highest reliability they could get for lines that would operate for decades.

Regards,

A. Hi, Elizabeth,

Manganese phosphate is really mild chemical. I have many years experience that SS316 and SS304 are both safe to be tank material of such chemicals. SS316 is higher grade with molybdenum and contains equal chrome and nickel with SS304; but, SS304 is much less expensive. You may test by dipping both in your manganese phosphate chemicals (hot or cold) for a while to observe the change of mill surface. You may not see any difference, which indicate that both are applicable.