Steam boiler systems are complex with not only the physics of the mechanical side to worry about but the chemistry of the waterside as well. There are many problems that can occur that will affect the boiler reliability. Normally, the mechanisms that lead to failures in a steam boiler system can be identified, if you know what to look for.
Here are 5 common causes of waterside failures, with pictures and descriptions to help you recognize them.
Oxygen Pitting Corrosion
Appearance: Well-defined pits that can penetrate the metal wall of a pipe or tank. Corrosion by-product deposits (tubercles) may cover the pits.
Location: Boiler tubes, deaerators, feed water tanks, feed water lines, economizers, condensate return lines, and condensate receivers.
Causes: Incomplete dissolved oxygen removal from the feed water, oxygen intrusion in offline boilers and other equipment, and mixing cold makeup with hot condensate.
Corrective Actions: Ensure proper operation and venting of the deaerator or feed water tank, feed oxygen scavenger in the correct location, maintain adequate residuals, and adequately store offline boilers.
Carbonic Acid Attack
Appearance: Thinning or grooving in the sides and bottom of heat exchangers and condensate return line. Typically first noticed at threaded joints that are leaking.
Location: Steam distribution and condensate return lines.
Causes: Breakdown of the naturally occurring alkalinity of the makeup water, which forms carbon dioxide (CO2). The CO2 flashes off the steam to form carbonic acid in the condensate.
Corrective Actions: Reduce feed water alkalinity, keep feed water temperature > 77°C (open feed water tanks), ensure adequate venting, and add appropriate condensate treatment chemistry.
Overheated Tube
Appearance: Thick-lipped failures have thick and ragged edges. Thin-lipped tube failures have uniform knifelike edges with no evidence of metal cracking or irregular tearing.
Location: Economizer and boiler tubes.
Causes: Thick-lipped failures caused by long-term overheating can result from abnormal firing rates, flame impingement, or deposits/scale. Short-term overheating due to complete blockage of water or low water conditions that are inadequate to absorb the heat causes thin-lipped tube failures.
Corrective Actions: Both can be controlled by maintaining proper boiler water chemistry, minimizing deposit/scale formation, ensuring proper burner alignment, and ensuring adequate boiler operation.
Cavitation
Appearance: Intense metal attack characterized by localized deep, circular pits.
Location: Feed water pumps (most common), condensate pumps, steam traps, blowdown lines/valves.
Causes: Formation and then immediate implosion of bubbles in a liquid that occurs when it is subjected to rapid changes in pressure. Turbulent flow may also promote this type of attack.
Corrective Actions: Install slipstream around the feed water pump, lower the feed water temperature, increase the feed water suction head, reduce turbulence, and eliminate rapid pressure changes.
Boiler Site Glass Failure
Appearance: Gradual thinning or internal grooving of the glass.
Location: Boiler sight glass.
Causes: Exterior deterioration (erosion) of the glass from a poorly installed or leaking gasket or excessive condensate formation in the upper steam area of the sight glass. Interior deterioration of the glass from pure, hot condensate will dissolve the glass (i.e., silica).
Corrective Actions: Eliminate leaking gasket and mica shield installed to protect glass from the cooler air, which can cause excessive condensation in the upper steam area of the glass.
Chem-Aqua has the knowledge and expertise to help safeguard your boilers and other types of water systems. We offer a wide range of treatment programmes to protect your systems from corrosion, scale and biofouling damages.
Contact us today and learn how we can help you manage your water treatment challenges, optimize your water systems and generate energy and water savings.
