Understanding Corrosion in Water Pipelines: A Guide for Pipeline Designers


Caustic Environment

Last updated: October 15, 2017

What Does Caustic Environment Mean?

Caustic environments refer to environments that are corrosive, capable of burning, and harmful to materials and humans. Caustic environments enhance the caustic cracking of materials. A small amount of caustic substances—like alkaline sodium, potassium and ammonium carbonate-bicarbonate solution—causes the intergranular stress-corrosion cracking (SSC) of steels in buried pipelines. It also produces SSC in treating plants where CO2 is removed from the natural gases.

Highly concentrated caustic soda in a boiler-operating environment causes the caustic embrittlement of boiler tubes, which leads to boiler failure.


Corrosionpedia Explains Caustic Environment

A caustic environment is a corrosive environment that is mostly filled with caustic substances. The most well-known caustic substance is caustic soda. The presence of caustic soda in a boiler causes the embrittlement of boiler tubes. Here, caustic soda is applied to prevent scaling in boiler tubes.

A caustic environment can be formed in both homes and industries. In a home, many household products contain caustic substances, such as laundry detergent, soap and batteries. Some antibacterial soaps also contain caustic substances.

Although molten sodium at high temperatures and high pressure causes rapid SSC of stainless steel, anhydrous caustic does not cause this corrosion. Besides sodium salts, other alkali metal compounds also cause similar corrosion.

A caustic solution has varied effects on different alloys and metal elements. For example, the corrosion rates of aluminum alloys in caustic solutions are severe, and even mildly alkaline solutions cause aluminum equipment to corrode. Strong and warm caustic causes the rapid general corrosion of titanium by stripping the oxide film. In these two cases, stress-corrosion is very rare. Some metals like zirconium show good corrosion and stress-corrosion cracking resistance of 50–90% NaOH up to 500°F (260°C), but it is more expensive than nickel components.

A caustic environment leads to caustic corrosion. This occurs when caustic is concentrated and dissolves the protective oxide layer of a metal’s surface, exposing the base metal to the corrosive environment.


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