E-mail : inquiry@ronsteel.comPhone : +8615308477503
We are committed to providing one-stop service for steel pipe products to customers around the world.
Why we should usually inspect stainless steel pipe? There is a phenomenon must be mentioned is Corrosion Under Insulation. Corrosion under insulation (CUI) is a type of corrosion caused by environmental exposure and lack of proper insulation around stainless steel pipelines. CUI can lead to weakened structural strength, increased maintenance costs, and decreased energy efficiency. Therefore, to prevent CUI, it is important to inspect stainless steel pipelines regularly, and ensure that proper insulation is applied and maintained over time. The chromium in stainless steel creates a passive film of chromium oxide which increases resistance to corrosion, however this does not make stainless steel corrosion-proof.
Austenitic stainless steel, also known as 300 series stainless steel, is the most common type of stainless steel used in piping systems, accounting for about 70% of all stainless steel production. Corrosion under insulation (CUI) is a frequent issue with Austenitic stainless steel piping systems due to the difficulty in detecting localized corrosion. CUI often manifests as pitting corrosion or stress corrosion cracking and can be difficult to detect due to its localized nature and the difficulty in detecting corrosion when stay-in-place insulation is used.
Pitting corrosion occurs when corrosion eats away at the surface of a metal, forming small holes or cavities, it is the second reason why inspect stainless steel. Alloys like stainless steel, which are normally resistant to corrosion due to a passivation layer, are actually the most susceptible to pitting corrosion. If the passivation layer is compromised and then attacked by corrosion, the corrosion will not spread on the metal’s surface but will instead penetrate inward. This type of corrosion can cause stress cracking and, if a pit occurs in a critical point, can cause immense damage.
Moreover, stress corrosion cracking is a type of corrosion that can occur in metals when the metal is placed under tensile stress, in combination with a hostile environment. It is especially common in stainless steel and other metals that contain high amounts of chromium. When the metal is placed under tensile stress, small cracks can form and grow, eventually leading to structural failure. Stress corrosion cracking is difficult to detect with the naked eye, as the cracks are often very small and can spread rapidly. Austenitic stainless steels are particularly vulnerable to corrosion from chlorides, such as chlorine, seawater, and certain cleaning solutions.
Chloride corrosion induced stress cracking is a form of corrosion that is more likely to occur at temperatures between 100 and 200°F due to higher chloride deposits and moisture levels. It can be especially dangerous for stainless steel pipes, as the 300 series alloy is susceptible to corroding chemicals such as chlorides. When the pipe is exposed to such chemicals and is also undergoing large amounts of stress, the potential for cracking is much greater. Stress corrosion cracks can start out small, so it’s important to choose insulation carefully to reduce the risk of corrosion.
Stainless steel piping is susceptible to ultra-localized corrosion due to its different ferromagnetic properties compared to other types of piping. This means that specialized inspection techniques must be used for adequate corrosion detection. These methods may include visual inspection, ultrasonic testing, and/or specialized test instruments. Our next article will provide an overview of the different corrosion detection methods for stainless steel piping.
