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Industrial Passivation And Passivating Services: What Are They & Why Are They Necessary?

Industrial Passivation And Passivating Services: What Are They & Why Are They Necessary?

 

Simple exposure to air or water, or exposure in the presence of electrochemical processes, can cause corrosion in many metal materials used in industrial settings [1]. Passivation and passivating processes improve the corrosion-resistance of treated metals, thereby decreasing metal stress and the associated risk of part failure. Most commonly associated with stainless steel parts and equipment, the passivating process is an often-underutilized management tool for corrosion. Industrial firms with known vulnerabilities to or substantial maintenance costs caused by corrosion should consider using any one of several passivating processes to reduce the deterioration of metal parts and equipment due to environmental damage. In this article, we will explore passivation and passivating processes in greater depth, including their appropriateness for and benefits to businesses operating in industrial settings.

 

What Is Industrial Passivation?

Passivation involves forcing or prompting the development of an outer layer on metal to protect it from environmentally caused degradation [1]. More specifically, forced passivation in industry settings includes the use of a chemical solvent (often an oxidizing agent) to create an inert coating that is less likely than the metal’s natural surface to chemically react with air or water [2]. Spontaneous passivation treatments involve the application of naturally corrosion-resistant barrier metals, like zinc, nickel, or chrome, which form a metal-oxide bond on the surface of the treated item in order to increase its resistance to corrosion [3].

In application with stainless steel material, for example, the forced passivating process involves treating all parts with an oxidizing agent — most often citric or nitric acid — which then strips free iron from the surface by means of chemical dissolution [2]. This leaves behind a thin oxide layer that is tightly bound to the surface of the steel [4]. The resultant chromic oxide layer is significantly more resistant to rust than stainless steel. That said, passivation is not always permanent, especially in high-intensity industrial settings and/or for parts that experience significant agitation, friction, or wear-and-tear in the presence of reactive oxygen or water environments [5]. Regular maintenance of industrial parts and equipment treated via passivating processes should involve regular re-treatment. Conversely, spontaneous passivation, like happens with galvanization, involves dipping metal parts in a hot zink solution which (under normal environmental conditions) prompts spontaneous, natural passivation at the conclusion of galvanization.

 

What Are The Benefits Of Industrial Passivation And Passivating Treatments?

The most significant benefit of passivation in industrial settings is the reduction of corrosion-related stress in, damage to, and failure of parts treated via passivating processes. What’s more, passivating treatments have the additional effect of cleaning contamination accrued during manufacturing from the surface of treated parts/equipment. This reduces the risk of product contamination during use while also increasing the part/equipment’s durability and overall capacity for continued safe use over time [6].

Further, passivating treatments are dramatically more environmentally friendly and safe for use than other industrial cleaning and corrosion-resistance treatments. Most notably, non-passivation treatments, like the use of epoxy or polyurethane resins, can pose risks to human health and sensitive environmental systems. This is because these treatments contain known-ecotoxin bisphenol A (BPA), which releases over time to the potential detriment of humans and the known detriment of aquatic life exposed to material runoff [7]. Non-passivating treatments can also present human health threats due to their porous surfaces, which quickly become breeding grounds for bacteria and viruses) [8]. Additionally, their flammable, highly meltable compositions and tendency to emit potentially carcinogenic (and definitely cardiovascular-damaging) vapors [8]. Industrial passivation and passivating treatments are comparatively low-risk to both humans and the environment.

 

Common Misconceptions About Industrial Passivation and Passivating Treatments

Forced passivation, the process described above, is often confused with other acid-bath and electrochemical treatments for metal parts/equipment. However, passivation accomplishes different goals than other chemical treatments like pickling and electropolishing. Specifically, where passivating treatments remove surface contaminants and install a corrosion-resistant oxide layer, pickling cleans away this oxide layer, as it makes it difficult to machine or otherwise modify the metal. Electropolishing supports greater passivation than is possible through standard passivating processes, as it smooths out and fully removes micro burrs, micro cracks, pits, and other imperfections, yielding corrosion resistance that is up to 30x greater than that of forced or spontaneous passivation treatments [9].

Further misconceptions about passivation assert that the effects of passivating treatments are universal and permanent. This is patently untrue. Though the oxide layer installed by passivating treatments does seal and protect against corrosion in many circumstances, it is not appropriate for all industrial applications — nor is it immutable, especially in the face of damage and electrochemical exposure [4]. Also worth considering is that passivation is only useful when the processor knows the specific alloy of the metal being treated; using the wrong passivating solution can actually damage the integrity of the metal [10].

 

Is Industrial Passivation Necessary?

Yes and no. Manufacturing can (and nearly-always does) leave free iron and other contaminants on and embedded in the surface of metal parts. While not entirely necessary for parts to function, passivation removes these contaminants to prolong the lifespan and increase the user-safety associated with the parts [9]. Further, specific machining processes, like welding, can damage and transform the surface of the metal in ways that actively facilitate corrosion/rusting [11]. In those cases, passivation represents the best option for damage- and loss-prevention available to businesses operating in industrial settings. This ultimately reduces maintenance and replacement costs, thereby increasing overall revenue. That being said, in the case of poor-quality (discolored, sugared) welds, passivation and passivating treatments can do little to protect or seal the metal against environmental damage. As a result, additional corrosion prevention treatments may be necessary to achieve the same level of benefits and cost-savings in some situations.

When deciding whether (and what kind of) passivating treatments may be necessary for their metal parts and equipment, industrial firms should consult with a qualified passivation processor. An experienced professional can determine the unique passivating treatment needs and/or impediments based on the manufacturing and machining conditions of the parts, their function within the broader context of operations, and their specific alloy composition(s). Processors who make passivating treatment determinations without considering the conditions, context, and composition of targeted metals should not inspire confidence. Instead, seeking more information from a qualified processor presents the greatest potential benefits to industrial firms.

 

References:

  1. https://www.corrosionpedia.com/definition/860/passivation
  2. https://www.besttechnologyinc.com/passivation-systems/what-is-passivation/
  3. https://www.gimeco.com/hot-dip-galvanizing-process/galvanizing-procedure/passivation/
  4. https://www.reliance-foundry.com/blog/passivation
  5. https://www.pureflowinc.com/wp-content/uploads/2015/02/WhyPassivateSS.pdf
  6. https://www.durcomfg.com/stainless-steel-passivation/
  7. https://www.ncbi.nlm.nih.gov/pubmed/28704774
  8. https://www.thefabricator.com/thefabricator/article/safety/3-health-and-safety-concerns-of-traditional-anti-corrosion-coatings
  9. https://www.ableelectropolishing.com/resources/frequently-asked-questions/passivation-necessary/
  10. https://www.marlinwire.com/blog/finishing-your-steel-electropolishing-vs.-passivating-stainless-steel
  11. https://cougartron.com/blog/passivate-stainless-steel-welding/
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