In the first of a series on standards for cleaning and passivation, we will look at ASTM A380/A380M – 13, Standard Practice for Cleaning, Descaling, and Passivation of Stainless Steel Parts, Equipment and Systems. This standard is written primarily with the initial cleaning of new parts and assemblies in mind but many of the techniques outlined may be used to clean and passivate systems already in service.
Introduction – Passivation Definitions
The introductory section of the specification provides a clear set of definitions on the term passivation as it pertains to stainless steel. The spec provides three definitions for passivation as:
- Section 1.1.1.1: “the process by which a stainless steel will spontaneously form a chemically inactive surface when exposed to air.”
- Section 1.1.1.2: “[the] removal of exogenous iron or iron compounds from the surface of a stainless steel by means of a chemical dissolution.”
- Section 1.1.1.3: “the chemical treatment of a stainless steel with a mild oxidant… for the purpose of enhancing the spontaneous formation of the protective passive film. Such chemical treatment is generally not necessary for the formation of the passive film.”
When Astro Pak mentions passivation, we mean a combination of the second and third definitions. Our chemical process of passivation removes exogenous iron at the stainless steel surface for the sake of enhancing the corrosion resistance of the already existing, chemically inactive oxide layer.
Descaling
The first chemical process mentioned in A380 is descaling. Descaling removes tightly bound metal oxides adhered to the stainless steel surface. These oxides are typically formed as a result of the metal’s primary solidification, welding, or heat treatment. Descaling can occur chemically (pickling) or mechanically through processes such as sanding, grinding, and abrasive blasting. A380 recommends a combination of nitric and hydrofluoric acids and to pickle for a maximum of 30 minutes at a time to prevent over-pickling (etching). If pickling is only partially effective, the spec suggests intermittently scrubbing the metal surface with a stainless steel or fiber brush to facilitate scale removal.
Cleaning
ASTM A380 mentions 11 cleaning processes in its section for cleaning. The cleaning chemistries introduced are: alkaline, emulsion, solvent, detergent, chelate, steam, and acid cleaning. Cleaning techniques mentioned are: vapor degreasing, ultrasonic cleaning, mechanical cleaning, and water-jetting. A380 does not provide specific chemical concentrations or detergents for cleaning, but it includes some suggestion for process parameters when discussing cleaning techniques. Astro Pak prefers alkaline solutions or synthetic detergents for cleaning, but has experience with all eleven methods presented in this spec with exception to water-jet cleaning.
Before a discussion on passivation concludes the cleaning section, A380 provides instruction on cleaning welds and weld-joint areas. A380 recommends cleaning the surface to be welded at least several inches back from the joint itself. Cleaning methods for the process side of the finished weld match exactly those first introduced in the descaling section. The external or non-process surface of the weld is not required to be cleaned by the spec, that decision is left to the system owner/purchaser.
Passivation
Passivation, per the second and third definitions mentioned above, is not explicitly required per ASTM A380, the specification leaves the responsibility to the final user of the piping system on if the system should be passivated. The subsection of passivation directs the reader to both the spec’s appendix and ASTM A967 for effective passivation chemistries. The appendix of ASTM A380 contains a table detailing pickling processes (Table A1.1) and passivation processes (Table A2.1), featuring time and temperature ranges plus chemical blends necessary to pickle or passivate various stainless steel grades. Table A2.1 is not an exhaustive list of passivation chemistries however, A380 defers to ASTM A967 for a more comprehensive list. In previous revisions of A380, no mention of A967 existed with respect to other chemistries outside of Table A2.1. From the 2013 revision onward, any chemistry mentioned in either A380 or A967 to be a compliant passivation method. Because of this new language, Astro Pak’s proprietary Ultra Pass passivation chemistry conforms to both A380 and A967, instead of A967 only.
Inspection and Process Considerations
The main content of ASTM A380 ends with a discussion on cleanliness inspection, passivation acceptance tests, and safety considerations for chemical use and pumping process fluids through piping systems. Common inspections techniques include white and blacklight inspections, wipe testing with white or black wipe, and a pattern dry inspection. The spec introduces two tests for passivation acceptance that are also included in ASTM A967 and will be commented on more in that post. Further considerations mentioned in this section include a discussion on the process fluid flow level required to remove finer contamination particles, proper safety equipment to protect the cleaning technician from chemical attack plus protect the equipment from contamination, and proper storage procedures for the chemicals used to clean.
Conclusion
If you have further questions about how Astro Pak can meet your specific needs for cleaning and passivation per ASTM A380, whether of new parts yet to be put into service, or of existing installed systems in need of cleaning, derouging and/or passivation, contact us. and our team of experienced professionals will work with you to develop a solution to meet and exceed your expectations.
