904L smls pipe

904L is a low-carbon, high-nickel, molybdenum austenitic stainless acid-resistant steel. It has good activation-passivation transition ability, good corrosion resistance, good corrosion resistance in non-oxidizing acids such as sulfuric acid, acetic acid, formic acid, and phosphoric acid, and good corrosion resistance in neutral chlorine-containing media. It is resistant to pitting corrosion and has good resistance to crevice corrosion and stress corrosion. It is suitable for sulfuric acid of various concentrations below 70°C. It can withstand acetic acid and formic acid of any concentration and temperature under normal pressure. It also has good corrosion resistance in mixed acids. Metallographic structure of 904L stainless steel: 904L has a completely austenitic structure. Compared with general austenitic stainless steel with high molybdenum content, 904L is not sensitive to the precipitation of ferrite and α phase.

Corrosion resistance of 904L stainless steel: Since the carbon content of 904L is very low (maximum 0.020%), there will be no carbide precipitation under normal heat treatment and welding. This eliminates the risk of intergranular corrosion that normally occurs after heat treatment and welding. Due to the high chromium nickel molybdenum content and the addition of copper, 904L can be passivated even in reducing environments such as sulfuric acid and formic acid. The high nickel content also results in a lower corrosion rate in the active state. In pure sulfuric acid in the concentration range of 0~98%, the service temperature of 904L can be as high as 40 degrees Celsius. In pure phosphoric acid with a concentration range of 0~85%, its corrosion resistance is very good. In industrial phosphoric acid produced by wet processes, impurities have a strong impact on corrosion resistance. Among all kinds of phosphoric acid, 904L has better corrosion resistance than ordinary stainless steel. In strongly oxidizing nitric acid, 904L has lower corrosion resistance than highly alloyed steels that do not contain molybdenum. In hydrochloric acid, the use of 904L is limited to lower concentrations of 1-2%. within this concentration range. The corrosion resistance of 904L is better than that of conventional stainless steel. 904L steel has high resistance to pitting corrosion. Its ability to resist crevice corrosion in chloride solutions is also very good. The high nickel content of 904L reduces the corrosion rate in pits and crevices. Ordinary austenitic stainless steel may be sensitive to stress corrosion in a chloride-rich environment at temperatures above 60 degrees Celsius. This sensitivity can be reduced by increasing the nickel content of the stainless steel. Due to its high nickel content, 904L has high resistance to stress corrosion cracking in chloride solutions, concentrated hydroxide solutions and hydrogen sulfide-rich environments.