Originally Published: September 22, 2023 | Last Updated: September 26, 2023
Contributors: Chris Jones (Global Business Development Manager, Brulin)
Different metal substrates require tailored cleaning solutions; a chemistry that works for one part might be detrimental to another.
Steel often requires cleaning due to heavy lubricating oils from various metalworking processes. Aqueous cleaners, typically highly alkaline, are preferred, and factors like temperature and agitation aid in effective cleaning. However, challenges like pitting or rust may arise.
On the other hand, stainless steel, long celebrated and used for its resistance to corrosion, is chosen where its higher cost is warranted. Yet, its resilience shouldn’t be taken for granted. While many types resist corrosion under normal conditions, certain cleaning chemicals can harm them. While stainless steel can be cleaned using a variety of cleaners, it’s crucial to minimize its exposure to certain acidic conditions.
Cleaning steel is one of the most commonplace practices in industrial parts cleaning, given its widespread application and specific maintenance needs. Due to steel’s inherent challenges in formability, various processes impart different residues on the material, necessitating diverse cleaning strategies.
One of the primary reasons for the presence of thick lubricating oils on steel components stems from drawing or stamping operations. Drawing, which involves pulling metal into a die to create specific shapes, and stamping, which presses or forms metals into desired shapes, both exert significant strain on steel. This necessitates the application of these heavy lubricants, which facilitate these operations by reducing friction, wear, and potential damage.
In contrast to drawing and stamping, fabricating steel in milling, drilling, and cutting operations works differently. Milling is about removing material to shape a component, drilling creates holes, and cutting shapes steel into specific sizes. These activities generally don’t stress the steel work as intensively as drawing or stamping, so the lubricants employed here are lighter in cleaning related measures like viscosity. However, they still incorporate additives that withstand extreme pressure and boundary conditions to ensure smooth operation and longevity of the tools and can adhere tenaciously to the part surface.
Apart from operations-specific lubrication, steel components—whether they undergo intense metalwork or not—often receive protective treatments. For instance, even steel that avoids processes like shearing might get a coat of oil-based rust inhibitors.
These inhibitors in some cases are simply protective barrier layers excluding oxygen. In some cases they are specially formulated and designed to inhibit rust. Their resilience allows steel components to be stored outdoors for extended periods without the peril of corrosion, thereby safeguarding the material’s integrity and prolonging its useful life. This precaution underscores the industry’s understanding of the environmental challenges steel might face, especially when stored in open spaces where elements like moisture can accelerate rusting.
Aqueous cleaners have become an industry favorite for steel cleaning. This includes cleaners of a high alkaline nature. In the context of these cleaners, a pH exceeding 12 counts as “high,” which implies a strong ability to neutralize acids, effectively emulsify oil and grease, and disrupt heavier soil structures on steel surfaces like rust and carbonized soils. This makes them particularly effective in handling the variety of tenacious contaminants that can accumulate on steel over time.
While aqueous cleaners alone are potent, their performance can be amplified under specific conditions.
One of the concerns when cleaning industrial steel parts, particularly cast iron, is the potential for pitting. Pitting is a form of localized corrosion where small cavities or “pits” form on the material’s surface. This is especially prevalent when steel is subjected to highly alkaline solutions, such as those found in certain cleaning agents like alkaline rust removers. These solutions, while effective in tackling rust and other forms of corrosion, can be too aggressive if the exposure time is extended.
The duration of contact between the steel and the cleaner plays a pivotal role in determining the extent of potential damage. For instance, when cast iron remains submerged or in prolonged contact with a robust alkaline solution for extended periods, say around 10 hours or more, the risk of pitting intensifies. As such, it becomes imperative for those involved in the cleaning process to monitor and control the exposure time meticulously. Properly managing this contact time ensures the efficacy of the cleaning process while safeguarding the material from the adverse effects of prolonged exposure to strong alkaline solutions.
Over time, steel is susceptible to the accumulation of rust and scale, both of which can compromise its structural integrity and visual appeal. Rust is the result of the oxidation process, while scale is a layer of oxidized metal that forms at high temperatures. Both need targeted removal strategies to ensure the steel’s longevity and performance.
For lighter occurrences of rust and scale, a mild acid solution is often employed. This solution is typically composed of phosphoric or hydrochloric acid and is applied at room temperature for short durations. Such treatments are effective for minor surface irregularities without risking damage to the steel.
However, when confronting more severe or heavy-scale accumulation from processes like iron forging, a more intensive approach is needed. Here, the steel is “pickled” in a potent, heated solution of acid, which efficiently breaks down the stubborn scale layers. To ensure that this treatment doesn’t inadvertently harm the base metal itself, inhibitors can be introduced into the mix.
Stainless steel, due to its resistance to rust under typical conditions, is used in applications where the benefits outweigh its higher cost. However, it’s a common misconception to underestimate the care stainless steel parts require. Despite its impressive attributes, the wrong cleaning agents can easily undermine the steel’s inherent strengths. It’s crucial to understand the metal’s nature; while many stainless steel variants resist rust in standard environments, certain types can corrode in acidic conditions.
Stainless steel comes in various grades, each tailored for specific applications and environments. While all forms of stainless steel offer a degree of corrosion resistance, understanding the distinctions between these types is crucial for optimal utilization. For example, Type 304 and Type 316 each have unique properties and require unique care to maintain their integrity.
All stainless steel types need restricted exposure to hydrochloric acid or warm/hot sulfuric acid. While a premium (and pricier) stainless steel grade can withstand hot sulfuric acid, extended exposure to acidic solutions with chlorides, such as hydrochloric acid, can lead to pitting across all stainless steel types.
Stainless steel, despite its name and reputation, is not permanently immune to the forces of nature. When exposed to oxygen, chromium forms a protective oxide layer on the steel part’s surface, acting as a shield against corrosive elements.
Various factors can disrupt this protective layer. Factors, such as high salinity or exposure to aggressive chemicals, specific service conditions like extreme temperatures or mechanical stress, and various metalworking processes like cutting, laser cutting, welding, and several other processes, can disrupt and lead to vulnerabilities in this protective layer, permitting corrosion.
To avoid corrosion on stainless steel parts, it’s crucial to address it promptly to maintain the material’s integrity and appearance. This is where thepassivation process steps in.
Passivation aims to reinforce the metal’s passive nature against rusting. By immersing the steel in a solution of strong citric acid, such as AquaVantage® Passivation, contaminants and free iron on the surface are dissolved, promoting the formation of a more uniform and stable chromium oxide layer. This regenerated protective film ensures that the stainless steel continues to resist corrosive forces, effectively rejuvenating its inherent resistance and extending its lifespan.
When passivating stainless steel, keep these points in mind.
While stainless steel is undeniably robust, ensuring its longevity requires mindful maintenance.
Not all cleaning agents are suitable for every situation, and understanding the specifics of what the steel has been exposed to is pivotal. Employing the right cleaning agent for the task at hand and being attentive to the steel’s response can avert potential issues, maintaining the material’s aesthetics and functionality for the long haul.
Every metal, whether it’s steel or stainless steel, has unique properties that necessitate individualized cleaning and maintenance approaches. It’s not just about ensuring cleanliness or prolonging aesthetics; it’s about preserving functionality, ensuring safety, and promoting longevity.
Staying informed about best practices in material care is more than just a requirement; it’s a responsibility. We urge manufacturers, industries, and individuals alike to invest time in understanding the substrates they work with—and we’re here to help.
Our dedicated team of parts cleaning advisors equips our clients and partners with our knowledge and help apply cleaning solutions in real-time. Contact our team to ask any questions about your parts cleaning process, and we’ll find the right way to improve it that saves your operation time and money.