Stainless steel pipes are widely used in many industries as a seamless and welded pipes for its excellent corrosion and oxidation resistance, but stainless steel pipes does not include corrosion resistance, it was reduced by the presence of different surface oxides on the pipe stainless steel. The most common of these oxides, chromium oxide, is produced when the chromium in the alloy reacts with the oxygen in the air.
At 300 C chromium oxide is stable and forms a passive film over the pipe material. This filme prevents oxygen and other corrosive substances from reaching the alloy. At 800 C however, chromium oxide becomes unstable and is easily oxidised by oxygen, leading to the reduction of the stainless steels corrosion resistance.
Austenitic stainless steel is an iron-based alloy with at least 10% chromium and is typically used in making seamless and welded pipes. Its corrosion resistance is attributed to its high nickel content. Nickel, when in contact with oxygen, forms a thin protective oxide film that covers the pipe surface and helps prevent corrosion.
Austenitic stainless steel is also known for its high toughness and good ductility, which makes it ideal for use in applications involving pipe bending and welding. It has a high temperature resistance and good resistance to acidic, neutral and caustic media. However, it should not be used in applications that require higher strength or higher temperatures where it can become brittle.
Stainless steel pipes come in a wide range of shapes and sizes, so it is important to select the right grade for your application. There are a few common grades of stainless steel pipes such as 316, 316L, 304, 304L, and 321. Each grade has different properties and characteristics that make it more suitable for certain applications.
316 and 316L stainless steel pipes have higher levels of molybdenum and chromium, making them more resistant to extreme corrosion and pitting than other grades of stainless steel. They are often used in applications involving outdoor structures and structures exposed to salt water or harsh chemicals.
304 and 304L stainless steel pipes have a chromium-nickel-manganese (CNM) composition, which provides the steel with good strength and toughness. They are more resistant to heat and are ideal for applications where high-temperature oxidation resistance is required.
321 stainless steel pipes have higher levels of titanium, which gives them increased strength, ductility, and resistance to a wide range of corrosive agents. They also have good weldability and formability, making them suitable for welding and bending processes.
The welding process for stainless steel seamless and welded pipes requires special precautions to ensure good components compatibility and weldability. It is important to preheat the components before welding to reduce strain hardening and improve the weldability of the material. The welding procedure should be designed to reduce heat input and minimise heat affected zones. This prevents the formation of hot tears or damage to the pipe material.
In addition, it is important to use welding consumables with the same chemical composition as the base material. This reduces the risk of forming cracks and other weld defects that can reduce the pipe’s strength and service life. Prolonged exposure to ductility also affects the stainless steel’s mechanical properties, so materials must be handled properly to prevent cracking.
Finally, stainless steel pipes should be inspected and tested regularly to ensure the pipe meets the necessary standards and requirements. This includes visual and electromagnetic inspections to identify defects in the welds, as well as nondestructive testing to ensure structural integrity.
Overall, stainless steel pipes are a reliable and durable choice for many industries and applications due to their corrosion and oxidation resistance, high strength and good weldability. However, it is important to select and inspect the right grade for your application and ensure proper welding and handling of the material to prevent any issues.
