Steam Boiler Failures
Steam boiler systems are complex with not only the physics of the mechanical side to worry about but the chemistry of the water side as well. There are many problems that can occur that will impact boiler reliability. The mechanisms that can lead to failures in a steam boiler system can often be identified if you know what to look for. Here are five (5) common causes of waterside failures with pictures and descriptions to help you recognize them.
| Oxygen Pitting Corrosion |
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| Appearance: |
Well defined pits that can penetrate the metal wall of a pipe or tank. The pits may be covered by corrosion byproduct deposits (tubercles). |
| Location: |
Boiler tubes, deaerators, feedwater tanks, feedwater lines, economizers, condensate return lines, and condensate receiver. |
| Causes: |
Incomplete dissolved oxygen removal from the feedwater, 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 feedwater tank, feed oxygen scavenger in correct location and maintain adequate residuals, and properly store offline boilers. |
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| Carbonic Acid Attack |
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| 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 with the steam to form carbonic acid in the condensate. |
| Corrective Actions: |
Reduce feedwater alkalinity, keep feedwater temperature > 170°F (open feedwater tanks), ensure adequate venting, and add appropriate condensate treatment chemistry. |
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| Overheated Tube |
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| Thick Lipped Tube Failure |
Thin Lipped Tube Failure |
| Appearance: |
Thick lipped failures have thick and ragged edges. Thin lipped tube failures have uniform knifelike edges with no evidence of cracking or irregular tearing of the metal. |
| Location: |
Economizer and boiler tubes. |
| Causes: |
Thick lipped failures caused by long term overheating that can result from abnormal firing rates, flame impingement, or deposits/scale. Thin lipped tube failures caused by short term overheating that may be due to complete blockage of water or low water conditions that is not adequate to absorb the heat. |
| Corrective Actions: |
Both can be controlled by maintaining proper boiler water chemistry, minimizing deposit/scale formation, ensuring proper burner alignment, and ensuring proper operation of the boiler. |
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| Cavitation |
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| Appearance: |
Intense metal attack characterized by deep, circular pits that are localized. |
| Location: |
Feedwater 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: |
Installation of slip stream around the feedwater pump, lowering the feedwater temperature, increasing the feedwater suction head, reducing turbulence, and eliminating rapid pressure changes. |
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| Boiler Site Glass Failure |
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| 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 a leaking gasket or from 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, 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 important water systems. We offer a wide range of treatment strategies to protect your systems from corrosion. Contact us today to learn how we can help you manage your water treatment challenges.