How the use of acid inhibitors prevents flash rusting during acid cleaning?

Author: Shubham Karnani

One of the crucial aspects of metal infrastructure maintenance is the regular cleaning process. Within this domain, Acid Cleaning emerges as a pivotal method renowned for its efficacy in eradicating rust, scale, and contaminants from metal surfaces across diverse industrial sectors. However, amidst its utility, a notable challenge looms: the occurrence of flash rusting. This phenomenon entails the rapid onset of rust, swiftly spreading across metal surfaces upon exposure to oxygen and moisture. It serves as a significant indicator, suggesting potential salt contamination, heightened humidity levels, or a combination of both factors. In the perpetual endeavour to combat corrosion, the emergence of flash rusting introduces a compelling element to the narrative of metal preservation.

Let us first try to understand what’s and whys of flash rusting. It is a rapid corrosion process that occurs when metal surfaces, stripped of rust and contaminants through acid cleaning, react with oxygen and moisture from the atmosphere. The freshly exposed metal becomes highly susceptible to oxidation, leading to the formation of iron oxide or rust. This type of rusting typically occurs within minutes after cleaning operations are completed. The rate of flash corrosion depends upon the amount of dissolved oxygen in the water, impurities present in the water, the amount of ionic compound on the metal surfaces, and the total drying time.

As we all know corrosion creates various effect that weakens the integrity of the entire infrastructure. It's not just about the visible damage – it's the ripple effect. It leads to losses worth over 900 thousand crores in India Annually. "As India moves towards a USD 5 trillion economy goal, dealing with a challenge like corrosion in projects should be a key focus area, said Rajamani Krishna Murti, president of Indian Stainless-Steel Development"

Role of Acid Inhibitors

Acid inhibitors are chemicals added to acidic solutions during the cleaning process to prevent flash rusting. These inhibitors also prevent corrosive reactions of acids with metal surfaces, extending longevity and reducing operational costs. By forming a protective layer, they shield the metal from direct contact with acids, inhibiting corrosion and enhancing durability. They combat corrosion, control its impact, improve resistance, prevent rust, and provide essential surface treatment.

Working Mechanism

  • Passivation: These inhibitors create a passivation layer, which act as a barrier, reducing the reactivity of the metal with free acid ions.
  • Chemical Reaction Inhibition: These complexes effectively block active sites on the metal, reducing the rate of oxidation.
  • Film Formation: Some form a thin film over the metal surface, creating a physical barrier that shields the metal from acid elements. This film helps prevent the initiation of corrosion reactions, thus minimizing the risk of flash rusting.

Variants

Different types of acids require specialized inhibitors for effective metal protection during cleaning processes:

  • Inhibitor for hydrochloric acid: Forms protective films to shield metal from corrosion during acid cleaning, ensuring durability in corrosive environments.
  • Inhibitor for sulfuric acid: Reduces corrosion rates and extends equipment lifespan in corrosive environments by forming protective films on metals during acid etching.
  • Organic Inhibitors: Compounds like amines, phosphates, and organic acids adsorb onto metal surfaces, forming protective films that inhibit corrosion during acid cleaning.
  • Inhibitors for sulfamic acid: Comprising diethyl thiourea, stabilizers, and surfactants, these inhibitors act as semi-foaming acidic corrosion inhibitors, ideal for pre-formulated descaling. Effective on various metal surfaces including Copper, Brass, Nickel, Tin, Lead, Zinc, galvanized surfaces, and all steel types.

In essence, specialized formulations tailored to each acid type are essential for effective corrosion prevention during cleaning processes. With Chemtex Speciality Limited's expertise and innovative solutions, the battle against corrosion takes a significant step forward, ensuring a brighter and more durable future for metal-dependent industries.

Visit for more information: https://www.chemtexltd.com/products-and-solutions/performance-chemicals/corrosion-inhibitor/acid-corrosion-inhibitor/