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Boiler Tube Failure Handbook

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Observation

Location

Mechanism

	Appearance	Observation	Locations	Mechanism
	Bulging tube adjacent to field weld	Bulging » Deformation	Waterwall	Long-term Overheat
	Metal thinning on fireside	Deformation » Thinning	WaterwallSuperheater	Smelt/Slag Attack
	External wastage beneath adherent slag deposit	Deformation » Thinning	WaterwallSuperheater	Corrosion From Slag Attack
	External thinning, smooth areas	Deformation » Thinning	Reheater	Fireside Corrosion/Erosion
	Smooth surface	Deformation » Thinning	ReheaterSuperheater	Fly Ash Erosion
	General pitting	Holes, Pits, Gouges » Waterside (Firetube boiler)	Waterside of firetube boiler	Acid Attack
	ID pitting with corrosion tubercles	Holes, Pits, Gouges » Waterside	WaterwallReheaterSuperheater	Oxygen Pitting
	sharply defined hole	Holes, Pits, Gouges » Waterside	Economizer	Corrosion Fatigue
	Severe corrosion on side of tube facing gas turbine/duct burners	Holes, Pits, Gouges » Waterside	Evaporator Section	Multiple Under-Deposit Corrosion Mechanisms Including Caustic Gouging, Phosphate Attack, and Hydrogen Damage
	Undercut corrosion, multi-color deposits (red, white, black). (This is a view of a tube ID following cleaning.)	Holes, Pits, Gouges » Waterside	Waterwall	Acid Phosphate Attack
	Thinning on inside of a U-bend or other change in direction	Holes, Pits, Gouges » Waterside	Economizer	Flow Accelerated Corrosion (FAC)
	Defect at weld bar attachment	Holes, Pits, Gouges » Fireside/Material Flaw	Waterwall	Weld/Materials Defect
	Porosity in weld	Holes, Pits, Gouges » Material Defect	Superheater	Weld Defect
	Thinning from the fireside, pockmarks on external surface	Holes, Pits, Gouges » Fireside	Waterwall	Fireside Corrosion
	Metal wastage	Holes, Pits, Gouges » Fireside	Waterwall	Fireside Corrosion
	Catastrophic failure associated with weld overlay	Cracking » In or near weld or attachment » Transverse	Waterwall	Hydrogen Damage
	Fine cracks around studs	Cracking » Transverse » Not in or near a weld	Studded Waterwall	Thermal Fatigue
	Circumferential cracking	Cracking » Transverse » Not in or near a weld or attachment	Waterwall	Thermal Fatigue
	Forming lap at tube OD	Cracking » Longitudinal » Not in or near a weld	Waterwall	Material Defect
	Multiple tight fine cracks	Cracking » Longitudinal » Not in or near a weld	Superheater	Stress Corrosion Cracking
	Fish-mouth rupture	Cracking » Not in or near a weld	ReheaterSuperheater	Short-Term Overheat
	Fish-mouth opening	Cracking » Longitudinal » Not in or near a weld	Waterwall	Hot Tensile Overload
	Thick-lipped rupture, may be very large window missing or a flap hanging by one edge	Holes, Pits, Gouges	Waterwall	Hydrogen Damage
	Irregular cracking	Cracking » Not in or near a weld	Superheater	Creep
	Short longitudinal cracks with numerous parallel cracks	Cracking » Longitudinal » Not in or near a weld or attachment	ReheaterSuperheater	Long-term Overheat/Creep
	Multitude of cracks parallel to tube	Cracking » Longitudinal » Not in or near a weld or attachment	Superheater	Long-term Overheat/Creep
	Longitudinal crack at bend	Cracking » Not in or near a weld or attachment	WaterwallReheaterSuperheater	Long-term Overheat
	Transverse cracking in the rolled portion of tube where it is inserted into the drum	Near or in weld or attachment	Riser tube at rolled connection in drum	Caustic Induced Stress Corrosion Cracking
	Complete failure at weld	Cracking » In or near weld or attachment » Transverse	Superheater	Thermal FatigueDissimilar Metal Weld Creep
	Transverse crack near support	Cracking » In or near weld or attachment » Transverse	Evaporator	Thermal Fatigue
	Brittle fracture in heat affected zone of a weld	Cracking » In or near weld or attachment » Transverse or Random	ReheaterSuperheater	Graphitization
	Multiple cracks associated with attachment on outside of tube	Cracking » In or near weld or attachment » Longitudinal or Random	WaterwallEconomizer	Corrosion Fatigue
	Longitudinal ID corrosion-fatigue cracks	Cracking » In or near weld or attachment » Longitudinal	Waterwall	Corrosion Fatigue
	Longitudinal cracks adjacent to weld	Cracking » In or near weld or attachment » Longitudinal or Random	Superheater	Wrong material/Creep
	Thick-lipped rupture and adjacent longitudinal fissuring	Cracking » Longitudinal » Not Near Weld	ReheaterSuperheater	Creep
	Deformation and perforation from the outside in	Holes, Pits, Gouges » Fire/Gas Side	Reheater	Mechanical damage
	Complete weld separation	Cracking » In or near weld or attachment » Transverse	Superheater	Dissimilar Metal Weld Failure (DMW)
	Cracks close to attachments	Cracking » In or near weld or attachment » Longitudinal	Waterwall	Corrosion Fatigue
	Severe corrosion gouging at a weld-backing ring	Holes, Pits, Gouges » Water/Steam Side	Waterwall	Caustic Gouging
	Severe pock-marked corrosion on fireside	Holes, Pits, Gouges	Furnace Riser	Corrosion/Thermal Fatigue
	Bulging tube adjacent to field weld	Bulging » Deformation	Waterwall	Long-term Overheat
	Appearance	Observation	Location	Mechanism