Understanding Corrosion in Water Pipelines: A Guide for Pipeline Designers


Alloy 904

Last updated: March 7, 2016

What Does Alloy 904 Mean?

Alloy 904 is a super austenitic stainless steel which is designed to provide moderate to high corrosion resistance in a wide range of process environments. It is a mixture with a large amount of chromium and nickel along with molybdenum and copper, which allows it to resist corrosion.

The chemical composition of Alloy 904 is:

  • Nickel – 23 to 28%
  • Chromium – 19 to 23%
  • Molybdenum – 4 to 5%
  • Copper – 1 to 2%
  • Carbon – 0.02% max
  • Manganese – 2% max
  • Silicon – 1% max
  • Phosphorus – 0.045% max
  • Sulfur – 0.035% max

Alloy 904 is also known as Alloy 904L.


Corrosionpedia Explains Alloy 904

Industrial nomenclature or the recommended grade for Alloy 904 is: UNS N08904 / W.Nr. 1.4539

Alloy 904 exhibits excellent corrosion resistance from warm seawater and chloride attack. This alloy resists stress corrosion cracking because of its high nickel content. The presence of copper in this alloy also gives it resistance to sulfuric acid and other reducing agents in both extreme and mild temperatures.

Some of the major applications for Alloy 904 include:

  • Wiring in electrostatic precipitators
  • Oil refinery components
  • Seawater cooling devices
  • Gas scrubbing plants
  • Pulp and paper processing industries
  • Acetic, phosphoric and sulfuric acid processing plants


Alloy 904L

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