STAINLESS STEEL SEAMLESS PIPE ASME SA312 TP904L B674 UNS N08904 1.4539

STAINLESS STEEL SEAMLESS PIPE ASME SA312 TP904L B674 UNS N08904 1.4539

TP904L is a high-alloyed super-austenitic stainless steel (UNS N08904, W.Nr. 1.4539) designed for exceptional corrosion resistance in highly aggressive environments. By adding molybdenum (Mo) and copper (Cu) to the chromium-nickel matrix, its performance far exceeds that of conventional 304 and 316L stainless steels, particularly in reducing acid media and chloride-bearing solutions.

Why 904L is "Super" Austenitic

1. Superior Resistance to Reducing Acids – The combined addition of Mo (4.0–5.0%) and Cu (1.0–2.0%) is the key. This enables 904L to withstand sulfuric acid up to 70°C (158°F) at various concentrations, and phosphoric acid and acetic acid over a wide range. It also provides excellent resistance to chloride-induced pitting, crevice corrosion, and stress corrosion cracking (SCC).

2. Extra-Low Carbon & Weldability – The ≤0.02% carbon content prevents chromium carbide precipitation at grain boundaries during welding. This effectively eliminates the risk of intergranular corrosion, giving 904L excellent weldability without the need for post-weld heat treatment in most cases.

Key Limitations & Selection Notes

Temperature Limit – 904L is not designed for ultra-high-temperature service. Its recommended maximum long-term operating temperature is approximately 450°C (840°F). Above this, its mechanical strength and creep resistance diminish significantly.

Specific Media Limitations – While excellent in reducing acids, 904L performs worse than molybdenum-free stainless steels (e.g., 304) in strongly oxidizing acids like nitric acid. In hydrochloric acid, it is only suitable for very low concentrations (1–2%).

Some of the quality tests carried out by us includes:

904L Chemical Composition %