Chemical Considerations
Historically the Pharmaceutical, Bio-Technology and Medical Devices industries have employed mineral acids such as Nitric and Phosphoric, and even Electro-Polishing to attempt to clean and Passivate Austenitic Stainless Steels. These have demonstrated mixed and/or transitory results especially when stainless components are subjected to long term corrosive media, including WFI and Clean Steam.
Research indicates that the vast majority of pit initiation on Stainless Steels originates from sulfide inclusions, and in particular MnS particles, which act as preferential sites for attack. Nitric acid solutions do a good job of removing the sulfide inclusions from the surface. However, Nitric Acid does not dissolve Aluminum, and once the primary sulfide sites are removed, then the secondary Aluminum sites become the primary sites for corrosion. Aluminum is a major contaminant in Stainless Steel.
Phosphoric acid will do a good job of removing the ferric oxide from the surface, and will in effect increase the chromium content at the surface through removal of surface iron. Like nitric acid, phosphoric acid will not address the Aluminum inclusions.
Electro-Polishing is a Chemical/Electrical means of “leveling out” the peaks and valleys on the surface of a material. No “dissolution” of impurities takes place. Often other impurities are introduced to the surface through the contaminated “Electrolytes”.
Corrosion / Rouge removal as performed by C.I.P., LLC. uses biodegradable organic chelating agents, which are less toxic, less hazardous, less corrosive, and are the only proven method of achieving true Passivity. C.I.P., LLC. incorporates the latest available Scientific and Technological advances in Chemistry and Metallurgy.
No two systems will ever be exactly alike. Therefore, it is ridiculous to assume that any “Standard Recipe” procedure can be expected to achieve the desired results of rendering a Stainless Steel surface clean and Passive. Because the Human Eye can’t see Passivation, scientific equipment and measurements must be utilized to determine a point of Passivity. The following is a delineation of the metallurgical determinants that fashion the essence of the C.I.P., LLC. pH targeted multi-staged Precision Cleaning and Passivation operation, as well as a synopsis of the technique used. Naturally, precise aspects concerning the materials and operational methods utilized will differ from system to system. The on-sight analysis is what determines the “fine tuning” of each chemical stage during every project.
Additionally, the correct chemical concentration, along with the proper operating temperature and flow velocities, as well as the proper contact times are all essential criterion for a successful Passivation Project. Equally important are the means by which Compounded Chemicals are Buffered, the pH which the solutions are maintained, the prevention of Halogens ever being used, the protection against Ferric Ion Corrosion, concern for Fe precipitation and proper rinses between stages are equally imperative.