Caustic embrittlement

This alkaline water enters minute cracks present in the inner walls of the boiler by capillary action.

[2] Inside the cracks, the water evaporates and the amount of hydroxide keeps increasing progressively.

This causes embrittlement of boiler parts like rivets, bends and joints, which are under stress.

What happens is that its molecules will get inside the hair-line crack and block it, as a result of which sodium hydroxide, even if it is there, will not be able to come in contact with iron, and no reaction will be there.

Adding tannin or lignin to boiler water blocks the hair-line cracks and prevents infiltration of NaOH into these areas.