ASTM A380 – Standards for Cleaning and Passivation of Stainless Steel

In the first of a series on standards for cleaning and passivation, we’ll take a 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 (section 1.1), but many of the techniques outlined may be used to clean and passivate systems already in service (section 1.2).

Stainless Steel

Stainless steels are in heavy use in a wide array of industries, from pharmaceutical and medical device manufacturing, to nuclear energy and aerospace manufacturing, to breweries, wineries and distilleries, to general food and beverage producers, owing to its sufficient strength, toughness and, most especially, its strong resistance to corrosion at a reasonable cost.  Stainless steels can have a variety of different compositions, but all are iron-based with some relatively small portion of carbon (hence the steel) and at least 10% chromium (Cr) by weight.  It is this chromium content that serves as the chief component of its corrosion-resistant oxide surface, improving the defenses of the steel against chemical attack. ASTM A380 mostly concerns itself with removing exogenous (i.e., arising from external sources) iron, rust, grease, oil and other contaminants (section 1.3) as a means of enhancing the alloy’s passive surface (section 1.1.1.2). Lowering the iron to chromium ratio on the surface of the steel makes way for the formation of a more chromium-rich oxide coating that enhances the corrosion resistance of the surface.

Cleaning Processes & Techniques

To achieve each of the desired precleaning, descaling, cleaning, and passivation effects, respectively, several techniques are prescribed as options.  Precleaning (section 4.1) is a rough first pass at removing bulk contaminants from the part(s) in question, and is accomplished with the use of vapor degreasers, alkaline or emulsion cleaners, steam, or high-pressure water jets.

The descaling process removes tightly bound oxides formed during fabrication and/or extended use (section 5.1).  This can be accomplished chemically with acid (sulfuric, nitric and/or hydrofluoric) solutions, molten alkali or salt baths, and other more proprietary formulations (section 5.2).  Immersion in the chemical bath is preferred when feasible, but other methods of achieving desired contact times with the descaling (also known as pickling) agent can be used, such as swabbing, spraying, partially filling and rotating/rocking the part (section 5.2.3), followed by thorough rinsing to remove the cleaning agent entirely.  It may also be feasible to descale the parts mechanically (section 5.4), and the standard provides specifications for appropriate materials and techniques, and more thorough descaling will still likely require at least a brief acid dip after mechanical removal (section 5.3.4).

The cleaning process (section 6) generally involves removal of other surface contaminants from the metal, and a wide variety of techniques are available to suit specific needs.  Methods overlap, unsurprisingly, with the aforementioned precleaning methods, as well as some of the descaling methods, and can include alkaline cleaning (section 6.2.1), emulsion cleaning (section 6.2.2), solvent cleaning (section 6.2.3), vapor degreasing (section 6.2.4), ultrasonic cleaning (section 6.2.5), synthetic detergents (section 6.2.6), chelate cleaning (section 6.2.7), mechanical cleaning (section 6.2.8), steam cleaning (section 6.2.9), water-jetting (section 6.2.10), and acid cleaning (section 6.2.11).  Each of these methods is discussed briefly, outlining key strengths, concerns, and critical parameters for monitoring and control, such as temperature, contact time, and specific composition, appropriate to the part(s) in question and their ultimate purpose.

Passivation Treatment

After cleaning, a specific passivation treatment is often desired, and these are outlined in greater detail in specification ASTM A967 (our next standard in the series). Regardless of the above method(s) selected, a final rinse and/or wipe down will be required (section 6.4) to ensure removal of the cleaning and/or passivating agents.  When these methods are applied to installed systems, the cleaning and passivating solutions, as well as the final rinse, is circulated through the systems (section 6.6).

The standard also includes sections on testing and inspection (section 7) and general precautions to take throughout the planning and execution of the selected processes (section 8).

Astro Pak frequently makes use of alkaline and phosphate-based detergent solutions for the cleaning of existing systems and employs pH-controlled acidic chelating solutions for effective descaling, especially the removal of iron oxides known as rouge formed over time in stainless steel systems. Astro Pak calls this specific form of descaling “derouging”.  Methods used for passivation will be covered in the next installment of the series on ASTM A967.

Conclusion

If you have further questions about how Astro Pak can meet your specific needs for cleaning and passivation per ASTM A380, whether for new parts yet to be put into service, or for existing installed systems in need of cleaning, derouging and/or passivation, please contact us and our team of experienced professionals will work with you to develop a solution to meet and exceed your expectations.

About the
Contributor

Bradley Hostetler

Bradley Hostetler

Bradley Hostetler has recently joined Astro Pak filling the role of metallurgist in Astro Pak’s Technical Services Group. Bradley holds a Bachelor’s degree in Materials Engineering from California Polytechnic State University, San Luis Obispo and a Master’s in Materials Science from Carnegie Mellon University. He comes from the metal production industry and has both research and work experience in steel and specialty alloy melting. Bradley has experience participating and presenting at various AIST (Association for Iron and Steel Technology) and NACE (National Association of Corrosion Engineers) conferences during his time as a student.

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