Wet Insulation on an Outdoor Condensate Tank
A 10,000 L horizontal condensate tank outdoors is insulated with 50 mm fibreglass and an aluminium jacket. The jacket has several holes, the insulation is wet, and the carbon steel shell shows pitting and scale. The tank normally operates at 80°C, but it will be isolated and drained for a weekend. The outdoor temperature is -5°C, and light snow is forecast. Access is from a fixed ladder and a small work platform; the tank has a 25 mm nozzle and a 500 mm manway. The client wants the old insulation removed and the tank re-insulated and jacketed by Monday. The nameplate is readable, but there is no insulation drawing and no record of the last inspection. The plant maintenance lead says the pitting is “only surface rust” and wants you to cover it before the weekend ends.
1. What are the removal and waste-handling precautions?
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Isolate, lock out, drain, and verify the tank is at a safe temperature before removal. Barricade the area and use PPE for cold, wet, and contaminated insulation. Do not dry-sweep; bag wet insulation and debris to prevent release. Because the tank is old and the insulation condition is unknown, treat suspect fibrous material as a potential asbestos-containing material until sampling or records confirm otherwise; if suspect, stop and arrange qualified abatement. Segregate waste by type and follow local disposal requirements. Inspect the shell as insulation is removed and photograph pitting and scale. The reasoning is that wet insulation can hide corrosion and may contain biological or chemical contamination, and unauthorized disturbance of asbestos creates a serious health and regulatory risk.
2. How should the tank surface be prepared and inspected before re-insulation?
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Remove all old insulation and jacketing, then clean the shell to bare metal using the method specified by the coating manufacturer, such as abrasive blasting or power-tool cleaning. Inspect for pitting, scale, weld defects, and coating damage. Measure pit depth and extent; do not rely on visual judgement alone. Apply a primer or coating compatible with 80°C service and with the insulation system, and allow it to cure fully. Do not insulate over moisture, frost, or uncured coating. Install dry insulation and weather-tight jacketing with proper overlaps and seals. The reasoning is that corrosion under insulation often starts at breaks in the jacket, and coating the shell before closing it in is the main opportunity to stop further attack.
3. The maintenance lead wants you to cover pitting that is 3 mm deep over about 20% of the shell. What do you do?
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Stop and do not cover the pitting. Report the measurements and photographs to the client and a qualified engineer. A 3 mm pit over a large area may reduce shell thickness below acceptable limits and may indicate active corrosion under insulation. Request thickness testing and a fitness-for-service assessment before re-insulating. If repair or a revised coating system is required, complete it first and obtain written direction. Document the decision. The reasoning is that insulation would hide a potentially progressing defect, and covering it without engineering review could lead to leakage or tank failure.