Allianz Global Corporate & Specialty Why Diesel Engines on ... R - Why Diesel Engines on...¢  diesel

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  • Why Diesel Engines on Fire Pumps Fail Prematurely By Gene Allen, Allianz Energy, Houston

    Allianz Global Corporate & Specialty www.agcs.allianz.com

    Large diesel engines that are used to power fixed fire protection water pumps appear to have a pattern of premature failure due to “overheating.” When diesel engines are used in over-the-road trucks, they normally operate over 6,000 hours before major repairs are needed. However, many of these engines on fixed fire protection water pumps are failing with less than 500 hours of operation.

    In large flammable and combustible liquids handling complexes, the total area of process units can be as large as a small town. Because of the facility size and quantities of flammable liquids, multiple large (2,500 to 5,000 gpm) fire protection water pumps are needed. These pumps are almost always powered by diesel engines and not electric motors because if the facility has a large incident, such as a Vapor Cloud Explosion (VCE), the electrical supply could be impaired. Thus, the diesel engine is the driver of choice for these large fire protection water pumps.

    All Photos and drawings by author except as noted

    Risk Bulletin

    Number 48 July 2014

    Engine on upper left only had 150 hours of operation before the top end overhaul / new head

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  • Two ways to cool a water jacketed diesel engine

    There are two methods of removing/rejecting heat from water jacketed internal combustion diesel engines:

    1. The method used in trucks and cars is circulation of the heated water from the engine through a water to air heat exchanger, called a radiator. Older engine driven firewater pumps, as well as newer, very large diesel firewater pumps, use radiators for cooling.

    In cold weather climates, firewater pumps installed outside would have to be freeze protected.

    For current installations, most fire pumps are enclosed in buildings. If equipped with a radiator, the building can be very expensive because it would require specially designed ventilation systems that allow fresh air into the building and hot air exiting the radiator out of the building. See figure below.

    Fig A.11.3.2(b) from NFPA 20, Installation of Stationary Pumps for Fire Protection, 2013 Edition

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  • Two ways to cool a water jacketed diesel engine (continued)

    2. When a diesel engine is used to power something in an enclosed area, like a boat or other marine application (e.g. engine room), a liquid to liquid heat exchanger is used to cool the engine by exchanging the generated internal heat with the cool “sea water” or “fresh water” from outside the boat. For decades, many diesel engine drivers on fire pumps could be provided with these liquid to liquid heat exchangers instead of radiators. These exchanger equipped engines get raw cooling water from the discharge side of the fire pump. Traditionally, a “shell and tube” type heat exchanger is used. See the yellow exchanger mounted in front of the engine photo below.

    The idea of using water to water heat exchangers has been around in very expensive pleasure boats since the 1920’s. During World War II, between 1938 and 1945, they were produced by the thousands to be used in small to medium sized watercraft, landing craft, service boats, and even fighting craft like the Patrol Torpedo (PT) boats.

    All those boats used one or more water to water heat exchangers, not only to cool the engine, but also to cool the engine intake combustion air from the supercharger. Additionally, the engine room was kept cooler by using the outside water to cool the engine exhaust manifold. The limited space is more than evident when looking at the photo below of a PT boat and its three giant 12 cylinder Packard engines.

    These water to water heat exchangers typically were a standard shell and tube exchanger with the hot engine water on one side and the cool raw water on the other. For corrosion resistance, the choice of metal depended on whether the raw water was “salty” sea water or “fresh” lake or river water. Also, the exchangers were bolted together so they could be disassembled for cleaning at regular intervals. This was done in order to remove foreign material and scaling accumulation before the exchanger plugged and the engine overheated.

    PT boat Engine Room with three Packard V 12 engines Photo with permission of T. Garth Connelly

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  • The death of the radiator on engine driven fixed firewater pumps

    When the economic pressures to reduce costs and expenses came to the energy industry in the early 1980’s, many energy, petrochemical, and chemical companies started outsourcing things like maintenance and engineering. The design of fire protection water systems slowly became one of the items that was outsourced. Instead of an in-plant engineer designing fire pumps and systems, outside vendors took on more and more of the water system projects including new firewater pump design.

    These vendor contractors turned to public standards like the National Fire Protection Agency’s Code for Stationary Pumps (NFPA 20) for design information. Because NFPA 20 allowed the water to water exchangers, and fire pump sets with these exchangers are less expensive to manufacture and install, the contractors influenced the firewater pump manufacturers to offer more pumps with water to water exchangers. Industry quickly moved in that direction. Without the experienced in-plant engineer to be the gate keeper on the decision, the radiator equipped diesel engine began to disappear.

    While NFPA 20 provides good information on the design of the emergency bypass piping, (see above), almost all of the rest of the raw water cooling loop, including the heat exchanger design, is left to the discretion of the manufacturer or vendor.

    Premature overheating engine failure is from insufficient heat exchanger cooling

    The “non-mechanical related” premature diesel engine failures that have been reviewed had one thing in common: they all had water to water heat exchanger cooling systems.

    Why are these water to water heat exchanger equipped engines failing?

    1. The raw cooling water flow may be reduced below the minimum recommended rate before the heat exchanger:

    • In some cases, the raw water line is reduced in size at the supply connection to the source water piping, as can be seen in the photos to the right. These small connections may have produced enough cooling flow when the pump was installed, but over time, these smaller orifices can be restricted by rust or tuberculation.

    Raw water Normal and Bypass piping NFPA 20, Installation of Stationary Pumps for Fire Protection, 2013 Edition

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  • Premature overheating engine failure is from insufficient heat exchanger cooling (continued)

    • The inlet water strainers and/or regulator may be too small for the larger diesel engines or may be clogged with debris. It is recommended by some engine manufacturers that the inlet strainers be disassembled and cleaned before each weekly engine churn test, not just blown down.

    During a recent flow test of a new 3,500 gpm firewater pump, when the pump was at rated capacity with 150 psi discharge pressure, the raw cooling water regulated pressure was 35 psi, as expected. When the discharge was increased to 150% of rated capacity, the discharge pressure was

    97 psi, also as expected. However, the raw cooling water regulated pressure surprisingly dropped to 26 psi! Closing the primary supply side valve and opening the emergency bypass side also resulted in 26 psi. But with both the primary and bypass valves open the pressure returned to 35 psi.

    The strainers were clean, so the strainers and/or the regulators on this “new installation” unit were simply too small to allow the correct amount of raw cooling water to flow through the exchanger at the lower inlet water pressure.

    2. Even if the cooling water is flowing at the correct rate, the diesel engine may still overheat if the heat exchanger loses its thermal transfer efficiency due to some plugging and/or internal parts “fouling” (coated with silt or sludge) – see below. Neither the NFPA nor the manufacturers suggest a schedule for internal inspection of the heat exchanger.

    The raw water going to the heat exchanger is expected to be “clean”, maybe even potable water. The strainers on the supply line and even the screen in the regulator (a well-kept secret ) are designed to remove small particles like sand and gravel. Typically, the raw water source for fire protection water pumps

    (at most of the large flammable/combustible liquids processing complexes) is from rivers, ponds, or utility water. These are certainly not potable water sources. These water sources have materials, silt, mud flakes, small shells, biological growth, organics, and slime which can slide through the strainers, but collect in the exchanger due to velocity changes or turbulence. Any time the fire protection water is supplied by these non-potable sources, the inspection of the internal parts of any heat exchanger should be conducted on a regularly scheduled basis.

    FM (Factory Mutual) Approval, a third-party certification organization, has recognized the low flow problem in the raw water cooling loop by requiring an automatic low flow alarm if the raw water flow is reduced more than 75% of the required cooling water requirement. This is a requirement of the FM approval standard for diesel engine fire pump drivers, section 3.6.1.A May 20