RiskTopics Standby Diesel Engine Reliability September 2016 Diesel Engines are frequently used as the Prime Movers for standby or emergency systems such as Fire Pumps, Generators, Barring Drives and so on. They are expected to be reliable and to start immediately every time. However, to ensure this, they need to be installed and maintained to an acceptable standard. This RiskTopic looks at the standards that should be expected. Note: This document does not cover Fire protection arrangements. Introduction Diesel Engines are the work-horses when it comes to standby and emergency drive units (Prime Movers). They are found in all industries and locations attached to a wide range of machines including Fire Pumps, Water Pumps, Generators, Fans and so on. They may also be installed to provide back-up drive to other critical process equipment such as Blowers, Cement Kilns and other rotary equipment. They are frequently abused and neglected, with inadequate installation standards and poor maintenance standards. It is unsurprising that they do not always perform as expected and when this happens, major damage or loss will often follow. All equipment requires good standards of installation and maintenance and Diesel Engines are no exception. If they are to perform their function, they must start and run when required. If this is not the case, they can only be regarded as an ornament. The following standards of installation and maintenance are provided as a guide to good practice. Guidance Installation standards Where Diesel driven units are installed for emergency use, they should be installed as dedicated emergency or standby units and have no secondary function.
For high risk installations, where the failure of the installed unit would result in a critical failure, significant damage or life threatening situations, consideration should be given to installing duplicate/redundant units. Each unit should be completely independent and not share any common services or features. All Engines and their connected drives should be securely fixed to rigid foundations or mounted on a rigid steel skid frame designed to withstand the forces and vibrations generated by these engines. The foundations and/or frames should be designed to conform to OEM requirements and should allow for the engine and its driven components to be aligned accurately to within OEM requirements. Engine installations should be enclosed to make them secure from unauthorized access. Appropriate weather protection should be provided to include Sun, Wind, Rain, Dust, Humidity and environmental pollutants. Secure guards should be fitted to prevent contact with rotating or high temperature components. Standby generator installations should be designed to provide sufficient power for the systems or equipment being protected. The installation of significantly overrated units is not recommended. All installed standby systems should be fitted with appropriate monitoring to detect, alarm and trip the engine in the event of deviation from manufacturer s specified operating parameters. (see appendix list below) Note: In the case of Diesel powered fire pumps, these monitored parameters should not trip the engine when operating under emergency conditions. Maintenance All Diesel Engines, their control systems and the equipment that they are connected to must be included in the site planned maintenance program. This program should include a regular service carried out by a trained technician (Frequently this will be the service agent for the engine, but this is not essential.) The service schedule and frequency should be based on Original Equipment Manufacturers (OEM) recommendations. Note: Emergency standby engines may not run sufficient hours over a period to trigger OEM maintenance schedules. In these circumstances, a suitable maintenance schedule must be agreed with the OEM to suit the particular installation and proposed engine duty. Only manufacturer approved spares including fuel and oil filters should be used. As part of the planned maintenance program and in addition to any OEM recommendations, all Diesel Engine installations should be subject to routine visual inspections by competent personnel, checking the condition of electrical and mechanical items. The maintenance program should include regular run testing of the installation. The simulation testing must include the operation of all relays and signal sensors to simulate a genuine emergency start situation, such as power failure, fire alarm activation etc. Lubrication oil should be sampled periodically to test for water, acids, debris and wear products. Samples should be taken monthly and at operating conditions, as part of the engine run test. 2
During a run test, all Diesel Engines should be run for sufficient time to ensure that the engine reaches steady state operating conditions with regards to water temperatures, oil temperatures and pressures. This time varies depending on the engine size, age and ambient temperatures, but is generally 30 minutes or longer. The frequency of this test will vary depending on the criticality of the engine, but will usually be weekly for fire pumps and monthly for standby generators. Avoid excessive running on low or no load, as this can cause sludge and carbon to deposit on the valves reducing performance and fouling injectors. This may also introduce the hazard of Wet Stacking which is a condition that may occur in diesel engines running at low capacity. Under these conditions unburnt fuel may pass through the exhaust side turbo charger and into the exhaust stack where it will adhere to the walls of the stack, potentially resulting in performance issues and fire hazards. The engine should be run at full load at least annually to ensure that it maintains its performance. For generators, this can be a problem if the installed test system has not been designed to provide sufficient dummy load. For Fire pumps, this is satisfied by the annual pump testing. The load testing is also important for the driven Fire pump, Generator, Gearbox etc. and also the switchgear to ensure that they work under stress. (Where generators are required to synchronize with another electrical supply, then the synchronization system should also be tested.) Where the ambient temperature can fall to low levels, the engine block should be fitted with block heaters. These maintain the lubrication system and the water system at a temperature high enough to promote quick starting. In some locations heating of the diesel fuel may also be required to prevent Waxing. Except for fire pumps where the engine cooling is through flow (using fire water from the supply), all engines with closed cooling systems (Radiators or Heat exchangers) must contain Anti-Freeze and water conditioning chemicals that fully comply with OEM specifications. Electrical Installations Starter batteries are preferred to pneumatic or hydraulic starters. The batteries should be located close to the engine but in a position where they are at minimum risk of physical damage. They should be protected from weather and frost. The batteries should be designed for heavy current and should be oversized to provide maximum starting current under repeated use. Battery terminals should be covered to prevent shorting of the terminals. Provision should be made for ventilation of charging gasses (Hydrogen). The batteries should have a dedicated charging system that is designed for continuous use and capable of maintaining the batteries in peak condition. Batteries should be maintained and tested according to the manufacturer's recommendations. This will include electrolyte gravity testing and load testing. They should be replaced according to manufacturer's recommendations or sooner if test results indicate deterioration or cell failure. Battery life can be maximized if the environmental temperature is controlled to around 15-20C (59-68F) For critical installations, the switchover from normal power supply to emergency supply should be automatic. This should include the automatic isolation of incoming supplies and all unnecessary electrical 3
loads that might overload the generator. The testing of this switchover system should be part of the scheduled Engine run test. Accidental connection of the generator to the external supply must be prevented by suitable incoming phase isolation interlocked to the generator isolators. For high risk installations, dedicated cabling should be considered between the generator switchgear and the protected electrical load. Fuel tanks Where Diesel Engines are used as part of Standby or Emergency installations, they should be supplied from a dedicated fuel tank containing sufficient fuel for continuous running for a period determined by risk assessment. Allowance needs to be made in this calculation for periodic test running. Only fuel that complies with the OEM engine specification should be used. For multi-fuel engines a dedicated tank is required for each fuel. Routine samples should be taken of any fuel in the fuel tank to check for water, contamination or poor fuel quality. The use of Bio fuels is not recommended for emergency standby engines, as this can deteriorate with time and ambient temperature and develop sludge or acids that will block or damage the fuel system. Appropriate precautions need to be made to reduce the potential for fuel contamination by weather, insects, unauthorized interference etc. Tanks should be fitted with filtered breathers and strainers. Isolation valves need to be fitted for maintenance and safety reasons, but in normal use they should be locked open or have their handles removed. Diesel units over 750kW (1,000HP) should be fitted with both inlet air and fuel shut off valves to prevent them continuing to run on after an emergency trip in the presence of volatile fumes The fuel tanks should be fitted with level gauges and water traps and drain taps. For high risk installations a remote level sensor may be required. Conclusion Standby engines are used to provide a reliable and flexible back-up drive too many processes and most commonly to Fire Pumps, Water Pumps and Emergency Electrical Generators. In all cases it is expected that the engine will start and run as required when required every time. To ensure that this is the case, good standards of installation and maintenance are required to keep the engines in top condition. Poor installation, or a failure to adequately maintain an engine installation will result in poor reliability and the risk that it will not perform or start when required. References NFPA 25: Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems 4
Appendices Appendix 1 Engine Protective devices The following Protective devices will normally be fitted to general use emergency diesel engines. The particular requirements will be dependent on the engine size, duty and manufacturer specification. Monitored condition. (Using On-Line sensors) Alarm Trip High cooling temperature. Yes Yes Low Lubrication pressure Yes Yes High Lubrication Temperature Yes Yes High Main bearing temperature (only fitted to large slow speed engines) If Fitted If Fitted Power Cylinder Lubrication Low Flow (only fitted to large slow speed engines) High Engine Vibration (only fitted to large slow speed engines) If Fitted If Fitted Engine Overspeed If Fitted If Fitted Turbo Charger Thrust Bearing failure. Low Lubrication pressure. High Lubrication Oil Temperature. Overspeed Engine Run. (For all auto start emergency power units) If Fitted Yes If Fitted Auxiliary Oil pump running (only fitted to large slow speed engines) Crank Case over-pressure. (only fitted to large slow speed engines) If fitted this is usually part of the engine start control sequence. If Fitted Note: In the case of Diesel powered fire pumps, these monitored parameters should not trip the engine when operating under emergency conditions. Note: Large slow speed engines such as those used for power generation may also be fitted with additional sensors to monitor the engine health and performance. These may include the following: High/Low crank case oil level. High Lubrication Oil Pressure Low coolant level Low coolant flow High exhaust gas temperature. 5
Appendix 2 General Diesel Engine Maintenance schedule Equipment item Activity Frequency Notes Fuel Tank level Visual / Weekly / Tank level sensor (If fitted) Solenoid valve operation (if fitted) Visual Weekly Required under NFPA 25 for fire Visual / Test Weekly Required under NFPA 25 for fire pumps Fuel strainer. Clean Quarterly Water in tank Clean Annually The ingress of water into the fuel tank may indicate environmental issues or poor tank breather operation. This condition should be investigated. Water in fuel system separator. / Clean Weekly / See above Flexible hoses and fittings Visual / Weekly / For leaks, damage or deterioration. Tank vents & Breathers / Test Annually See above Rigid piping including fixings and fittings. Visual Annually For leaks, damage or deterioration. Lubrication System Oil Level Visual / Weekly Oil Change/Test 50hr or Annually Whichever soonest. Oil should be sampled and tested prior to changing to monitor oil and engine condition. Oil Filter(s) Change With Engine Oil Lubrication oil heater.( If fitted) Weekly Required under NFPA 25 for fire Crankcase Breather Visual / Change 6
Equipment item Activity Frequency Notes Cooling system Level Visual / Weekly Antifreeze/Water Treatment / Test 6 Months Water to heat exchanger (if fitted) Clean heat exchanger (if fitted) Weekly Required under NFPA 25 for fire Clean Annually Required under NFPA 25 for fire Water Pumps Visual Weekly For leaks. Flexible hoses and fittings Visual/ Weekly For leaks, damage or deterioration. Block Heater (if fitted) Weekly Intake air Visual / Clean Annually Exhaust System Leakage Visual / Weekly / Condensate Trap Weekly Drain. Insulation Visual Weekly / Excessive back pressure Test Annually Exhaust system integrity Visual Annually Flexible pipe sections Visual During engine test. For damage and leakage. Battery System Electrolyte Level Weekly Battery Terminals Visual / / Clean Quarterly For cleanliness and absence of corrosion. Battery casing and containers. Visual For leakage, damage, corrosion 7
Equipment item Activity Frequency Notes Specific gravity/state of charge. Test 6 monthly If automatic charging and battery conditioning are fitted. Battery Charger Visual Weekly For operation, equalization charge and condition. Electrical System General condition. Visual Weekly Wiring for condition and terminals for tightness. Annually Operation of safety systems, sensors and alarms. / Test 6 monthly For function, condition. Replace fuses every 2 years. Panels, cabinets, switchgear and controls. / Clean 6 monthly For function, security, sealing, dust and condition. Circuit breakers or Fuses. Visual / Required under NFPA 25 for fire Circuit breakers or Fuses. Change 2 years Required under NFPA 25 for fire Note: For more details related to Diesel Engines for Fire Pumps, please refer to NFPA 25 8.5 and Table 8.5.3. Note: Engine maintenance scope and frequency should always meet or exceed the Manufacturer s recommendations. 8
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