Corrosion Control in Boiler Systems

Corrosion in boiler systems cannot be isolated entirely from a number of other concomitant problems that have a direct effect on the type, amount, and location of corrosion, and the functioning of the boiler. These problems, which are considered along with corrosion, can be identified as scale, sludge and carryover. 

There are a number of locations in a boiler system where various types and amounts of corrosion can occur. These locations can he grouped in three generalized locations preboiler, boiler, and postboiler. 

The preboiler system is defined here to include feed water pumps and lines, and auxiliary equipment through which the feed water is pumped prior to actually reaching the boiler. If not restricted, one could include a vast variety of units in which the makeup water is conditioned, but which in themselves are not essentially a part of the holier system. This definition then includes such equipment as stage heaters and economizers. 

Using this definition, one finds both corrosion and deposit problems in the preboiler system that can manifest themselves as general corrosion, pitting, or erosion-corrosion. The deposit problem can result from either deposition of suspended sohds that should have been removed earlier in the clarifier unit, or else it may be caused by formation of adherent calcium, magnesium, or iron scales. 

Corrosion can attack iron, copper, or nickel. General corrosion or pitting may occur for conventional reasons, e.g. dissolved oxygen, low pH, presence of deposits, stagnant areas, stress in the metals, defects in metal composition, or surface conditions. Dissolved oxygen often will cause pitting attack when coupled with certain other conditions, such as deposits on the metal surfaces or 

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