Mission OC
The Mission OC is a composite oil‑exhaust‑gas water‑tube boiler that delivers up to 120 t/h of steam at 9 or 18 bar(g) and can run on oil, exhaust gas, or both.
Inspector Detail
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Common issues
- Soot fires in the exhaust gas section from unburned fuel deposits building up on tube surfaces
- Fireside tube fouling reducing heat transfer and raising exhaust gas temperature
- Refractory damage or spalling in the furnace
- Burner flame instability or ignition failure
- Waterside scaling when feed water treatment is inadequate
- Safety valve set pressure drifting off its calibrated value over time
- Economizer or tube leaks from thermal fatigue at rolled joints
- Soot blower malfunction leading to progressive fireside fouling
Inspection checklist
- Check feed water treatment chemical residuals (e.g. oxygen scavenger) against the test schedule
- Check boiler water TDS/alkalinity against the test schedule
- Inspect the exhaust gas side for soot build-up
- Check burner flame condition and the ignition/purge sequence
- Function-test safety valves and confirm lift pressure at the next opportunity
- Check level gauge glasses and level alarms
- Inspect furnace refractory condition
- Check soot blower operation
- Check for external leaks or corrosion on the boiler casing and mountings
Service intervals
| Boiler water chemistry testing | daily or per watch |
| Feed water treatment dosing check | daily |
| Safety valve function test | typically annually, with set pressure verified at survey - confirm against class requirements |
| Internal inspection (waterside and fireside) | typically at annual survey when the boiler can be opened and gas-freed |
| Exhaust gas side external cleaning | per the maker's recommendation or condition-based on soot build-up |
Typical wear limits
| Tube wall thickness (UT measured) | renewal is commonly indicated once wall thickness falls to around 70-80% of the original design value - confirm the exact allowable minimum against class rules and the maker's data for this boiler |
Ranges are typical for this design class. Always confirm against the manufacturer documentation for your serial number.
Critical spares
- Burner nozzle/atomizer
- Ignition electrode
- Flame scanner
- Safety valve repair/spare kit
- Manhole and handhole door gasket set
- Water level gauge glass set
Safety
- Pressurized steam system - a leak can cause severe burns; approach suspected leaks with caution and isolate before investigating
- Boiler explosion risk if safety valves are not maintained and tested - this is a life-safety item, not routine maintenance
- Combustion space explosion risk on ignition failure - always allow the purge cycle to complete before firing
- Hot surfaces on the casing and uptake
- Entry into the boiler for internal inspection is confined-space work - requires gas-freeing, isolation and a permit
Class survey
Boilers are subject to periodic class survey - external examination more frequently, full internal examination at longer intervals, commonly linked to the annual/intermediate/special survey cycle; surveyors check safety valve testing and sealing, review water treatment records, and require a hydrostatic test after any significant repair
Components & Design
Component data being added…
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
Integrated composite design. EG section at sea, oil section in port or supplementary. Soot blow EG section regularly.
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