Stainless Steel Passivation Process

1. Why Stainless Steel Rust Stainless steel is the most durable of metals. Its mechanical properties enable its structures to remain extremely resistant to rust. Nevertheless, corrosion can’t be precluded. But there are ways to minimize the risk of corrosion. Stainless steel’s fine layer of chromium oxide has natural techniques to self-repair when breached or broken. However, if the damage is too extensive corrosion can occur. There are various types of corrosion to be aware of. The most common types are: Pitting Corrosion on stainless steel The passive layer on stainless steel can be attacked by certain chemical species. Chloride ion is the most common of these and is found in everyday materials such as salt and bleach. Harsh pitting corrosion is a localized damage that eats pits into stainless steel. In addition to chloride ion, can be caused by elevated temperatures for extended amounts of time or lack of oxygen to the surface. You can avoid pitting corrosion by ensuring that stainless steel does not come into prolonged contact with harmful chemicals or by choosing a grade of steel which is more resistant to attack. Crevice Corrosion on stainless steel Stainless steel requires a supply of oxygen to make sure that the passive layer can form on the surface. In very tight crevices it is not always possible for the oxygen to gain access to the stainless steel surface thereby causing it to be vulnerable to attack. Crevice corrosion is avoided by sealing crevices with a flexible sealant or by using a more corrosion resistant grade. General Corrosion on stainless steel Normally stainless steel does not corrode uniformly like ordinary carbon and alloy steels. However, with some chemicals, mainly acids, the passive layer may be attacked uniformly depending on concentration and temperature and the metal loss is distributed over the entire surface of the steel. Hydrochloric and sulphuric acids at some concentrations are particularly aggressive towards stainless steel. General corrosion can be quite destructive and happen to the entire surface at once.

2. Galvanic corrosion on stainless steel If two dissimilar metals are in contact with each other and with an electrolyte (e.g. water or another solution), it is possible for a galvanic cell to be set up and to accelerate corrosion of one of the metals. It can be avoided by separating the metals with a non-metallic insulator such as rubber. Less common types of corrosion are: Stress Corrosion Cracking (SCC) on stainless steel Stress Corrosion Cracking is a relatively rare form of corrosion, which requires a specific combination of tensile stress, temperature and corrosive species, often the chloride ion, for it to occur. SCC can occur typically in hot water tanks or swimming pools. But if it does

3. happen, it can be rapid, breaking down the mechanical properties of steel in days rather than months or years. Another form known as sulphide stress corrosion cracking (SSCC) is associated with hydrogen sulphide in oil and gas exploration and production Intergranular Attack on stainless steel Intergranular Attack is also a quite rare form of corrosion. If the carbon level in the steel is too high, chromium can combine with carbon to form chromium carbide. This occurs at temperatures between about 450-850 C. This process is also called sensitisation and typically occurs during welding. The chromium available to form the passive layer is effectively reduced and corrosion can occur. This corrosive harm happens between the grains and can be avoided by using a low-carbon stainless steel or uniform heating and rapid cooling of the steel. However, you can control any type of rusting with Stainless Steel Passivation Process. Removing rust from stainless steel can be a hefty task and it can ruin the visual appearance of the metal and when it is left unchecked, the quality and strength of it can also decrease but you can easily remove corrosion from your steel surfaces with our products. A safe and environment friendly alternative to prevent metals from rusting is through Passivation With Citric Acid. Citric acid is non-toxic and comes from citrus fruits which makes it safe for your use. Our CitriSurf citric acid cleaning process can be your go to partner to free your stainless surfaces from rust and make them shine like new without any hassle.