Definition - What does Caustic Cracking mean?
Caustic cracking is a form of stress corrosion cracking most frequently encountered in carbon steels or iron-chromium-nickel alloys that are exposed to concentrated hydroxide solutions at temperatures of 482°F (250°C).
This phenomenon mostly occurs in boilers where caustic soda (NaOH) has been added in small amounts to boiler water to prevent scaling. However, caustics (alkalis) may become concentrated amounts in crevices around rivet heads and at hot spots. When combined with the considerable fabrication stresses around rivet holes, this can cracking of the steel boiler shells and tube plates.
Caustic cracking is also known as caustic embrittlement.
Corrosionpedia explains Caustic Cracking
The following conditions are necessary for this type of cracking to occur:
- The metal must be stressed
- The boiler water must contain caustics
- At least a trace of silica must be present
- Some mechanisms, such as a slight leak, must be present to allow the boiler water to concentrate on the stressed metal
Caustic cracking can be prevented through:
- Control of stress level (residual or load) and hardness
- Avoiding alkalis
- Use of materials known not to crack in the specified environment
- Controlling temperature and/or potential