[icedcappucino]

Definition
Phenomenon that takes place in boiler when caustic substances gather in materials of the boiler, especially highly stressed regions such as cracks, tube and tube plate connection, joints, bends, and rivets.

Definition of “caustic”: Strong corrosive alkaline

Chemical formula:

Process
NA2CO3 = Sodium Hydroxide which is usually used for softening of lime soda water in high pressure boilers
As water evaporates (to become steam), the concentration of sodium hydroxide increases + undergoes hydrolysis (H20) -> Sodium Hydroxide (NaOH) + Carbon Dioxide (CO2)

When alkaline Sodium Hydroxide enters the highly stressed regions and evaporates, leaving behind Hydroxide salts which reacts with the boiler material (e.g. carbon steel). This reaction is corrosion which forms Ferrite (oxidised Iron) and causes the material to become brittle, thus this process is named “caustic embrittlement”.

Prevention

– Managing the temperature and potential
– Managing the Hardness and stress level- residual or load
– Avoiding the use of alkalis
– Utilizing material that does not crack when used in a caustic environment
– Using sodium phosphate instead of sodium bicarbonate as a softening agent for boiler water
– Introducing Na2SO4 in boiler water helps in blocking hairline cracks

Source 1
Source 2

• This topic was modified 2 years ago by icedcappucino.

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