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Part 2: Boiler Components Present Maintenance Challenges
March 2012 -
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Each boiler component presents managers and technicians with unique maintenance challenges.
Drums. These are a boiler's most expensive component. The most common maintenance issue is corrosion. PM technique include wet fluorescent magnetic particle testing (WFMT), a nondestructive examination method of all major welds, select attachment welds, and some ligaments. If the test finds corrosion, technicians can use ultrasonic thickness testing (UTT) to assess metal thickness.
Headers. The most common maintenance issues are corrosion, erosion, and metal fatigue. PM techniques include inspecting welds using WFMT or dry-powder magnetic particle testing. Technicians also can use a video probe to assess waterside cleanliness, noting buildups of deposits or debris that could obstruct flow. They also can inspect superheater headers and water-circuit headers.
Main steam piping. These components often suffer the same damage as headers. Common maintenance issues include corrosion, erosion, and metal fatigue. PM techniques should include conducting inspections using WFMT, as well as inspecting non-drainable and sagging horizontal runs with a video probe or UTT to detect internal corrosion or pitting.
Tubing. The largest number of forced downtimes for boilers results from tube failures. The most common maintenance issues include steam-side or waterside deposits retarding heat transfer, flow obstructions, corrosion, fatigue, and erosion. PM techniques include visually inspect tubing to detect discoloration, distortion, swelling or surface damage. Technicians also can use UTT to determine tube thickness.
De-aerators. Maintenance issues include shell welds corrosion on the interior diameter surface. PM techniques include inspecting welds using WFMT.
Air openings. Maintenance issues for these components, which are used for combustion, include obstructions and leakage. PM techniques include visually inspecting for obstructions and debris.
Feedwater piping. Common maintenance issues include flow assisted corrosion. PM techniques should include using a video probe to inspect as access allows or using UTT where corrosion is suspected.
Flue-gas vent system. The system conveys combustion gases to the outside. Maintenance issues can involve obstructions, leaks, and back-pressure on the boiler. PM techniques include removing obstructions, repairing leaks, and cleaning. For long stack lengths, options include shortening the run or using fans to assist flow of flue gases.
Pilot and main burners. Common maintenance issues include an improper flame and yellow-orange streaks caused by dust. PM techniques include: visually inspecting burners; removing, brushing, and vacuuming; and adjusting the firing rate to produce a blue flame where the thermocouple is completely immersed in the inner cone and glows cherry-red.
Safeties. Maintenance issues include scale, as wall as wear-and-tear. PM techniques include blowdown to trip test the primary and auxiliary low-water cutoffs. Technicians also should clean the site glass and test scanners by taking the flame away to see if the boiler ignites.
Part 1: Balancing Boiler Maintenance Costs and Benefits
Part 3: Essential Boiler Preventive Maintenance
Part 4: Product Focus: Boiler Maintenance