ASTM A967 – Standard Specification for Chemical Passivation Treatments for Stainless Steel Parts
This specification covers several different types of chemical passivation treatments for stainless steel parts. The treatments are the following: immersion treatment using nitric acid solutions, immersion treatment using citric acid solution, and electrochemical treatment. Immediately after the removal from the passivating solution, the parts shall be thoroughly rinsed, using stagnant, countercurrent, or spray washes, singly or in combination, with or without a separate chemical treatment for neutralization of the passivation media. The chemical reactions of the passivating media on the surface of the stainless steel shall be stopped by rinsing of the stainless steel part, with or without a separate neutralization treatment. A chemical treatment shall be applied which will accelerate the formation of the passive film on a chemically clean stainless steel surface. The passivated parts shall exhibit a chemically clean surface and shall, on visual inspection, show no etching, pitting, or frosting. The following tests shall be performed on each lot of stainless steel parts: water immersion test, high humidity test, salt spray test, copper sulfate test, and potassium ferricyanide-nitric acid test. A free iron test shall be used for the detection of free iron on the surface of stainless steel.
1.1 This specification covers several different types of chemical passivation treatments for stainless steel parts. It includes recommendations and precautions for descaling, cleaning, and passivation of stainless steel parts. It includes several alternative tests, with acceptance criteria, for confirmation of effectiveness of such treatments for stainless steel parts.
1.2 Practices for the mechanical and chemical treatments of stainless steel surfaces are discussed more thoroughly in Practice A380/A380M.
1.3 Several alternative chemical treatments are defined for passivation of stainless steel parts. Appendix X1 and Appendix X2 give some nonmandatory information and provides some general guidelines regarding the selection of passivation treatments appropriate to particular grades of stainless steel. This specification makes no recommendations regarding the suitability of any grade, treatment, or acceptance criteria for any particular application or class of applications.
1.4 The tests in this specification are intended to confirm the effectiveness of passivation, particularly with regard to the removal of free iron and other exogenous matter. These tests include the following practices:
1.4.1 Practice A—Water Immersion Test,
1.4.2 Practice B—High Humidity Test,
1.4.3 Practice C—Salt Spray Test,
1.4.4 Practice D—Copper Sulfate Test,
1.4.5 Practice E—Potassium Ferricyanide-Nitric Acid Test, and
1.4.6 Practice F—Damp Cloth Test, and
1.4.7 Practice G—Boiling Water Immersion Test.
NOTE 1: Free iron denotes iron present on the surface of the parts, including but not limited to iron contamination, iron-tool marks, residual-iron salts from pickling solutions, iron dust, atmospheric exposure, iron deposits in welds, embedded iron, and iron oxide.
1.5 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.