Corrosion occurs when metals (by acid or electrolytic action) attack metals. The metal is eaten away similar to the generalized rusting of an automobile fender. Corrosion increases maintenance costs, results in premature replacement of equipment and causes unnecessary safety risks.

Corrosion occurs where levels of oxygen or carbon dioxide are high, where pH values are low, where contact occurs between dissimilar metals and in damp environments or corrosive atmospheres.

Basic corrosion in boilers results primarily from the reaction of oxygen with the metal.

Stresses, pH conditions and chemical corrosion have an important influence and produce different forms of attack.

Caustic Stress Corrosion or Caustic Embrittlement :

The combination of high stress and high caustic concentrations eventually led to destructive cracking of the boiler vessel. It occurs when hairline cracks appear in highly stressed areas due to high concentrations of alkaline salts that liberate hydrogen, which is then absorbed by the iron in steel, effectively changing its physical properties.

This condition is caused largely by boiler water with pH values 11+ and manifests itself in high-temperature areas of the boiler. Unless embrittlement problems are constantly monitored & controlled, they will take their toll in higher fuel costs, increased safety risks, unnecessary downtime and equipment replacement.