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Boiler Corrosion & Fatigue in Steam and Hot Water Systems

corrosion mechanisms that may be evident in water tube and shell boiler operation

Circumferential Cracking
Form of fatigue stress corrosion, mostly at fire-side bends
Caustic Embrittlement
Occurs under high static stress in concentrations of caustic soda
Necking and Grooving
Waisting of fire-side stay bolts & rods at entry to boiler end plates
Boiler Stress Cracking

A fatigue corrosion in areas of repeated or alternating stresses, usually of low frequency and relatively high magnitude

Air Bubble Pitting
Associated with small bubbles of oxygen adhering to metal surfaces
Fatigue Corrosion

Caused by alternating stress fatiguing of a component,
associated with crazy and circumferential cracking

Stress Corrosion

A consequence of high mechanical stress in a chemically active local environment

Galvanic Attack

Physically weakening electrochemical transformations between dissimilar metals in the presence of an electrolyte

Crazy Cracking

Most commonly occuring in the bore of a fire tube, particularly at bends. Surface has a fissured, wrinkly appearance

Crevice Attack

Occuring along seams between adjacent components, caused by electrochemical and/or chemical stress in the presence of mechanical straining

Scab Pitting

A deep-acting electrochemical cell penetratrating fure-side tube surfaces, although similar structures can develop under less specific circumstances


Consequent upon foaming caused by dissolved salts. Small bubbles aggregate from rough surfaces to form a stable foam, which is carried-over into steam spaces - causing explosive displacement of large quantities of water into (particularly) superheater drums

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