Among others, some of the most frequent problems are caused by:

• The heat flow is high at the front of the tube sheet, where the hot gases coming from the process are received. Both the tube sheet and its ferrules (which are also lined with refractory) can create localized hot spots, resulting in water-side fouling and corrosion problems (metal Dusting, SCC)
• Concentration corrosion, known as ductile or caustic embrittlement. Phenomenon occurs with waters with high OH and occurs in heat transfer areas.
• Steam blanketing at the top of horizontal tubes. This occurs when the water flow is not sufficient to promote wetting of the interior of the top surface of a horizontal generator tube, allowing evaporation to dryness.
• Nucleate Boiling or Departure Nucleate Boiling (DNB) caused by a heat flux. DNB can occur anywhere in the boiler if the surface of a tube receives too much heat or if a deformation of the tube surface causes a vapor pocket to form a localized area that allows caustic concentration by evaporation.
• Accumulation of deposits on the tube wall. Porous deposits allow boiling to take place inside the deposits, concentrating sodium hydroxide.
• Solids accumulation on the bottom plate of the standpipe of vertical waste heat boilers.
• Damage to the ferrules of the boiler inlet tube sheet with hot gas tubes. In many cases, the concentration of corrosion cells has developed immediately adjacent to the end of the hot gas inlet protection ferrules. If water velocity, chemical treatment and solids removal are not sufficient to provide a proper cleaning, deposits will accumulate on the irregular surface provided and heat will concentrate there creating Metal Dusting.
• Displacement rupture or Ceep Rupture is the second leading cause of waste heat boiler failure and is a failure of the metal resulting from overheating. Displacement rupture results when heat input is excessive (process gas is too hot or flow is too high) or when heat is not transferred efficiently to the boiler water. When either condition occurs, the boiler metal exceeds its plasticity point, blisters and thins by stretching until it no longer contains the steam-water mixture at operating pressure and fails.
• Superheater creep rupture caused by poor steam purity. Steam purity is the third source of problems in waste heat boilers. When the purity of saturated steam is poor, it drags solids that deposit in the superheater. Deposits will also occur in rotating equipment such as turbines.
• Some hot gases generate corrosion problems in the cold part of the recovery units due to the content of corrosive gases.