Chemical Cleaning Stainless Pipe Using Nitric Acid

A. A small caveat: Keep in mind chromium is attacked by strong warm alkaline solutions, so with prolonged contact you may preferentially etch some of the chromium from the stainless. The net effect is the contact surfaces will turn streaky/brown from the ferric oxide which will appear after you enrich the surface with iron in this manner. However, the iron oxide is susceptible to most acids and the acid rinse may, in fact, restore the iron/chrome balance and leave the surface with the metal oxides which make stainless, well, stainless. If you are merely looking to passivate the system, I would think the H2O2 you plan to use in the system will be more than sufficient to keep the stainless surface well oxidized.

Are are you trying to clean or remove some contaminant from the system? If so, is the contamination on the ID of the tubing soluble in detergents? Maybe an ionic surfactant rinse followed by some distilled water would be sufficient. A good commercial product for this might be LF2100 or Micro-90 from International Products--both low foam, high surfactant cleaners that do not contain silicates. Dale

A. Richard, cleaning stainless steel piping with a 10% solution of caustic soda [affil links] at 150 °F and for four hours seems like a hammer & tongs approach to cleaning. You could use a commercially available alkaline cleaner designed for recirculation at lower concentration and a shorter cleaning time and get better results. I'm not an expert on cleaning prior to peroxide service but I suspect the removal of all organic materials is critical. The surfactants in the commercial alkaline cleaner will significantly improve the organics removal compared to caustic alone.

Rinsing with a 1% solution of nitric acid will remove any traces of alkalinity or hard water deposits left by the alkaline cleaning. It will not passivate any cut, abraded or welded stainless steel surfaces though. A higher concentration of nitric acid or a formulated passivation material is needed to do that.

A. If this is newly installed stainless pipe, and it is your desire to improve the chrome content of the ID, thereby improving resistance to corrosion, then you should only use a degreasing solvent sufficient to remove any oils or preservatives that may be present from the manufacturing process. Then we recommend chelant circulation to improve the surface chrome content by reducing the iron content.

A. Hi Stefen. ASTM A967 is the general spec for passivation of stainless steel for non-aerospace and non-medical applications. It will tell you what you must comply with for passivation. ASTM A380 is a general guideline for cleaning stainless steel. Good luck.

Regards,

A. Hi Sumi. A312 is not a type of stainless steel. Rather ASTM A312 is the spec you are looking for and covers austenitic stainless steel pipe including types 304, 316, and others :-)

After you comply with that spec/code will come the next question of what you are using the pipe for. In general, cleaning, pickling, and passivation will be required -- but please tell us the application (unless you are simply selling A312 pipe to your customers). Good luck.

Regards,

  Thank you so much Ted for responding.
Yes you are right, this was a question asked by a customer to our sales person in General. Later when I checked the code, it said that pickling, blasting and surface finish are not mandatory if the pipes are bright annealed. But we didn't know for what the pipe was used.

Thank You for your time.