AV-6N

Common issues

• Soot fire (most dangerous, often due to insufficient soot blowing or oil ingress)
• Tube leakage from corrosion/erosion (internal due to poor water treatment, external due to acidic soot)
• Soot accumulation (reduces heat transfer efficiency, increases back pressure, fire risk)
• Water hammer (can damage tubes and piping, often due to improper drainage or cold feedwater introduction)
• Low water level damage (overheating of tubes, deformation, potential rupture)
• Refractory damage (cracks, spalling, leading to casing overheating and reduced efficiency)
• Soot blower malfunction (stuck lances, worn nozzles, steam/air supply issues)

Inspection checklist

• **External Visual Inspection**: Check for signs of corrosion on casing, piping, and supports. Inspect insulation integrity and look for any steam/water leaks from flanges, glands, or access doors.
• **Gas Side Inspection (when cold)**: Open access doors to inspect for soot accumulation on tubes, tube sheet condition, and refractory lining integrity (cracks, spalling). Check for any signs of tube deformation or damage.
• **Water Side Inspection (when opened)**: Inspect for scale, sludge, and internal corrosion on tubes and drum surfaces. Check condition of internal fittings, feed pipes, and blowdown connections. Verify cleanliness of water level gauge connections.
• **Soot Blower System**: Verify operational readiness. Check lances for straightness, nozzles for wear/blockage, and ensure proper steam/air supply pressure and drainage. Confirm full travel of lances.
• **Safety Devices**: Test pressure relief valves (manual lift, verify set pressure if possible). Test low water level alarms and automatic shutdown systems. Check high pressure alarms.
• **Feedwater System**: Inspect feed pump operation, non-return valves, and ensure proper feedwater quality is maintained through regular water treatment and analysis.
• **Drainage & Blowdown System**: Check drain and blowdown valves for leaks and proper operation. Ensure condensate return system is functioning correctly.
• **Exhaust Gas Path**: Verify exhaust gas dampers operate correctly and are free from excessive soot. Check functionality of exhaust gas temperature sensors.
• **Control & Monitoring System**: Review local and remote control panel indications, alarm history, and verify functionality of interlocks.

Service intervals

Typical wear limits

Ranges are typical for this design class. Always confirm against the manufacturer documentation for your serial number.

Critical spares

• Soot blower nozzles and lances
• Manhole/handhole gaskets and sealing rings
• Water level gauge glass and cocks/valves
• Pressure relief valve spring and sealing elements
• Control system sensors (pressure, temperature, level probes)
• Tube plugs (for emergency isolation of leaking tubes)
• Refractory repair material (cement, anchors)
• Feedwater pump mechanical seals/gaskets (if integrated)

Safety

• **Soot Fire**: The most critical hazard, leading to severe damage, potential explosion, and personnel injury. Requires immediate and correct response.
• **Over-pressurization**: Failure of pressure relief valves can lead to catastrophic rupture of the economizer. Regular testing is paramount.
• **Scalding/Burns**: From hot surfaces, steam, or hot water leaks. Always wear appropriate PPE.
• **Confined Space Entry**: Hazards during internal inspections (asphyxiation, falls, heat stress). Requires strict adherence to permit-to-work systems and safety procedures.
• **Hot Exhaust Gases**: Risk of burns during inspection or maintenance if not properly cooled down and isolated.

Class survey

Class surveyors typically focus on: 1. **Internal Inspection**: Thorough examination of both gas side (soot accumulation, tube condition, refractory integrity) and water side (scale, corrosion, sludge, tube integrity, internal fittings). 2. **Hydrostatic Pressure Test**: Typically performed every 5 years, to 1.25 times the maximum working pressure, to verify structural integrity. 3. **Safety Valve Test**: Verification of lifting pressure, blow-down, and re-seating pressure. Certification of safety valves is required. 4. **Alarms & Trips**: Functionality test of critical safety devices, including low-low water level shutdown, high pressure alarm, and other interlocks. 5. **External Condition**: Assessment of insulation, casing integrity, foundations, piping connections, and absence of external corrosion or leaks. 6. **Documentation Review**: Scrutiny of maintenance logs, water treatment records, previous survey reports, and safety valve certificates. 7. **Soot Blower System**: Operational check and condition assessment to ensure effective cleaning.