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whole casing to be opened rather easily, similar to an automobile hood. The low- pressure turbine also has a horizontal split casing. A case can be opened to allow for internal inspection or maintenance in one working day. Horizontal split casings facilitate the following maintenance and repair actions: • FOD and DOD repair. • Occasionally, a gas turbine requires a trim balance to lower vibration as an engine matures. A trim balance may also be performed to reduce airborne and structure borne noise. There is no need to remove the gas turbine from the ship to balance the unit. • Preventative maintenance actions that incorporate lessons learned after many years of operation can be performed to extend the life of the gas turbine. These actions include performing inspections, updating components with developed life extension capabilities or implement- ing modifications for specific ship op- eration profiles and loadings. By having gas turbine top casing repair in-situ ca- pabilities, the cost of maintenance will be significantly minimized. FOD Repair Case Study At the end of 2017 during a periodic borescope inspection of an international ship, damage was found on the leading edge of a stage 10 compressor blade. The compressor casing was opened in-situ to determine the cause and the extent of the damage, and repairs were made to the turbine in a matter of days and at mini- mal expense. A GE Field Service Representative (FSR) performed maintenance tasks in accordance with the GE technical manual (GEK) for shipboard I-level maintenance procedures. Minimal specialized tooling, a hinge kit and hand tools were used on site by the FSR. The damage was determined to be from FOD and was greater than what was iden- tified by the borescope inspection. That is because a borescope inspection pro- vides a limited view of the airfoils and critical flow path hardware. By visually inspecting the compressor, it was deter- mined that ten other compressor blades had minor damage. The 10th stage blade was replaced while the other blades were blended with honing stones. The root cause was determined to be from loose ship "non-skid" deck sur- face that passed through an incomplete mounted nylon sock on the inlet screen. Top case repair costs are typically less than $100,000. These costs vary on the low end for tasks such as trim balance with no material, to blade replacement(s) or blending in a FOD/stall repair. The work can typically be performed in two to three days. Number of Occurrences of Intermediate Top Case Repair and Maintenance Actions Table 1 provides the number of top case repairs made in the USN in 2017, the RCN in the past 15 years and estimates for the RAN in the context of their re- spective LM2500 fleet size. Preventative maintenance and life ex- tension upgrades make up most of top case events (50% to 86%). This is followed by the need to trim balance the turbine or make FOD/stall repairs (7% to 25%). Variations in percentages reflect different navy experiences. Conclusion Foreign or domestic object damage in- flicted on turbines is an inevitability in demanding maritime environments. This damage should not be casually discount- ed during turbine acquisition decisions or as part the development of a comprehen- sive lifecycle plan. The best way to limit repair and maintenance to thousands of dollars and just a few days downtime is by using a modular gas turbine design with split casings as employed on GE's gas turbines. GE's design approach also supports lifecycle strategies that embrace planned maintenance actions. Scheduled maintenance extends the engine's service life due to changes in the ship's propul- sion plant load profile, or to incorporate technical advances made in turbine de- sign over the years. GE also supports this design philosophy with proven tooling and a global service network. Repairing a gas turbine in-place pre- serves ever-tightening maintenance bud- gets by protecting against the disruptive costs of unplanned engine removals. Most importantly, it substantially miti- gates the operational risk of an engine casualty that reduces the ship's mission capability or impacts availability for weeks or months. This is particularly important in countries that operate a relatively small number of surface combatants with sin- gle gas turbine propulsion systems, which do not have the inherent redundancy to maintain speed required to meet mission objectives. For more information visit ge.com/marine. References 1. "Building on a Marine Power Legacy," 2018 2. "GE Marine Gas Turbines for Frig- ates," April 2018 3. Thompson, B., Badgley Dr. R., Har- tranft, J., "Experience from Expan- sion of On-Board Maintenance for Marine Gas Turbines," ASME Paper 89-GT-232 4. Driscoll, M., Patterson, J., McFe- tridge E., See, C., "Removals for Cause: A 35 Year Assessment of LM2500 Engine Removals by the United States Navy" June 2011 5. "What Price Freedom? Questions Surround LCS 1," Aviation Week, May 9, 2012. PeRSPecTIVe Sponsored Content Navy USN RCN RAN Number of top case eveNts 32 in 2017 Average 3 / year for last 15 years Average 3 / year fleet size: commissioNed ships 400 gas turbines on over 110 ships 24 gas turbines on 12 Halifax frigates; first commissioned in 1992 16 gas turbines on 4 classes of ships: Adelaide and Anzac frigates, Hobart destroyers and Canberra LHD's Table 1: Number of Occurrences of Intermediate Top Case Events 40 AUGUST/SEPTEMBER 2018 www.vanguardcanada.com

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