Caustic Stress Corrosion Cracking
Definition - What does Caustic Cracking mean?
'Caustic embrittlement' was first used to describe the cracking of riveted mild steel boiler plates due to local deposition of concentrated hydroxide at temperatures of 200 to 250 o C (400 to 480 o F). It was later known as 'stress corrosion cracking' which is in turn replaced by 'caustic cracking'.
- Stress corrosion cracking (SCC) is the growth of crack formation in a corrosive environment. It can lead to unexpected sudden failure of normally ductile metal alloys subjected to a tensile stress, especially at elevated temperature. SCC is highly chemically specific in that certain alloys are likely to undergo SCC only when exposed to a small number of chemical environments.
- Chloride stress corrosion cracking (CLSCC) is one the most common reasons why austenitic stainless steel pipework and vessels deteriorate in the chemical processing and petrochemical industries. Deterioration by CLSCC can lead to failures that have the potential to release stored energy and/or hazardous substances.
- Caustic Stress Corrosion Cracking No. Corrosion in Caustic Solutions. Corrosion by caustic (sodium or potassium hydroxide) at all concentrations is easily handled at room temperature with a variety of metals and alloys, including carbon steels. It becomes increasingly more corrosive with increasing temperature and concentration.
- Stress corrosion cracking (SCC) of nickel-based alloys. Environments that may cause stress corrosion cracking in nickel alloys include hot caustic solutions, high temperature water and hot and wet hydrofluoric acid. This chapter addresses the cracking behavior of nickel alloys in industries such as chemical process, nuclear power generation and in oil and gas exploration and production.
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.
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Caustic cracking is also known as caustic embrittlement.
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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