Proper Dredge Maintenance Yields Higher Profits
Lastly, dredge manufactures should provide sufficient alarms to warn operators that a hazardous condition or problem exists. These situations should be corrected promptly; the manufacturer or the maintenance personnel should eliminate nuisance or faulty alarms if they occur.
2. Routine sampling and analysis
Routine sampling and analysis provides insight into the health of the dredge and its likelihood to need major repairs in the near future. These major tasks often require more skilled maintenance personnel and additional scheduled service time. The OEM often provides maintenance and testing schedules, but common sense can be used to create a schedule if none is provided.
Diesel engine oil should be sampled and analyzed in a lab at least every 500 hours and hydraulic oil at least every 1,000 hours. The presence of water in the oil during the normal inspection should trigger more frequent testing or immediate corrective action. The analytical results from the testing lab should indicate any required testing schedule change or upcoming corrective equipment repair.
Baseline temperatures of all equipment, including electrical switchgear, motors, and connections, should be taken upon commissioning with an infrared heat gun. Monthly comparative readings should be observed; a high temperature is often an indication of a loose connection or a failing component.
On more critical systems, baseline and semi-annual vibration reading comparisons should be used as an indication of the bearing health and balance of the item. On hydraulic dredges, the dredge pump impeller to front door gap should be checked and adjusted at least once a month.
An ultrasonic thickness tester, or UT tester, should be employed to take readings of the dredge pipeline thickness at the same location to gauge the wear; on mechanical dredges, the same test should be done on the bucket to predict the wear rate. Additionally, once a year, the dredge hull thickness should be checked in several repetitive locations for early indications of coating failure or corrosion. Monthly, bolts holding rotating or vibrating equipment should be checked with a torque wrench to correct the condition and help locate failing components.
3. Performance-based testing
Like routine sampling, performance-based testing generates information on the condition of dredge systems, but also provides important information on the efficiency and energy consumption of the wearing components. This testing is primarily designed to reduce energy costs associated with worn equipment, and many of the tests listed can be automatically performed by the dredge’s control system or PLC.
On hydraulic dredges, the dredge pump should be periodically tested to compare it to a performance curve baseline established when the pump was new. If greater pump speed is needed to achieve the test discharge pressure, a worn impeller is usually the culprit. Lower discharge pressure with higher energy consumption is associated with a worn front liner or shell, or a large gap between the impeller and front liner.
Similar tests can be performed on service water pumps, jet pumps, fire pumps, sand pumps, and silt pumps. Worn pump components consume more energy and should be replaced during the next scheduled maintenance period.
Hydraulic pumps should be routinely brought to their maximum pressure and flow conditions while the power consumption and temperature is recorded. Internally leaking pump valves cause reduction in speed and an increase in temperature. Internally leaking motors and cylinders characteristically operate at lower speeds and with reduced force while still consuming full power. Applying a known load at a set speed and measuring the fuel consumption, turbo boost, and manifold temperature can compute a diesel engine’s efficiency.
4. Scheduled replacement
Often, the scheduled replacement of a component is the easiest way to prevent downtime, if the component is one that does not exhibit wear or failure characteristics prior to failure. On diesel engines, batteries, oil, filters, and belts should be replaced at scheduled intervals even when testing and inspections show it is not necessary. Scheduled engine overhauls and replacements can reduce unplanned failures, as well as allow newer more fuel-efficient engines to be used.
Rotating bearing seals in cutter drives, bearing tubes, dredge pumps, etc. should be replaced annually to prevent unplanned failures. Gears, bearings, friction plates, and brakes in winches, motors, and drives have finite lives and should be replaced prior to failure; OEMs can provide information on the effective life of such components at differing loads. Brushes on DC electric motors should be replaced in batches, as opposed to all at once, to eliminate commutator-seating issues. Ladder and bucket lift cables should be replaced or flipped annually.
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