OL Series (Oil-Fired Auxiliary Boiler)
Alfa Laval Aalborg (formerly Aalborg Industries, Danish, acquired by Alfa Laval in 2011) is the world's leading manufacturer of marine boilers with an estimated 40-50% market share. The OL series is the standard auxiliary boiler on motor vessels of all sizes — from coastal to VLCC. Water-tube construction with natural circulation, oil-fired. The OL boiler supplies steam for heating, tank cleaning, fuel oil preheating and as a drive for steam-driven cargo pumps on tankers.
Components & Design
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Technical Data
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Common failures & inspection points
Internal visual inspection of all steam/water tubes; perform pressure test if suspected; seal leaking tube with conical stop valve after steel wire brush cleaning of tube ends. Leaking tubes must be renewed.
Check DP transmitter unit (external reference/variable leg, 4–20 mA output); feedwater control valve functional test; sight glass for cracks, contamination; test alarm function in control unit
Test two safety valves under full-load steam: pressure build-up 7 min. max. +6% working pressure permissible (water tubes); pop-point of each valve max. ±3% from set pressure; class notation: perform opening + accumulation test under classifier supervision
Inspect furnace walls and refractory lining visually (min. 2x/year); check for cracks, moisture, soot deposits. Check lower tube plate (insulation + form refractory). After 3–4 weeks operation: perform blow-down, inspect/clean boiler, remove sludge
Hydrostatic test: fill boiler with water 21–65 °C (water tubes max. 71 °C). Pressure: 1.5× MAWP (non-entry) or 1.25× MAWP (entry). Secure safety valves with clamps. Check all seal surfaces, rivets, welds for leaks. Class notation: every 2 years (up to 8 years), then annually
Class survey: water side (steam drum, water drum, all tubes) check for corrosion/cracks/deposits; fire side (furnace, flue gas path) check for soot/flocking (min. 2x/year). Man holes (top/bottom) permit access. If necessary use ultrasonic/endoscope for deeper defects
Type-general inspection and maintenance points for this equipment category — not model-specific.
Service & Maintenance
Burner nozzle inspection weekly. Feedwater treatment daily (pH, chlorides, dissolved oxygen). Soot blowing after each firing on HFO. Water-side inspection at annual survey. Hydraulic test every 5 years per Class.
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