Vanguard Magazine

www.vanguardcanada.com AUGUST/SEPTEMBER 2018 39 Sponsored Content customers, GE estimates the cost savings on an annualized basis of using a design with split casings: The United States Navy (USN) saves approximately $45 to $93 million per year; and the Royal Ca- nadian (RCN) and Royal Australian Na- vies (RAN) save $4 to $9 million each per year. The number of split case repair and maintenance actions performed are 32 USN instances in 2017, and an average of three per year each for the RCN and RAN. Repairing an engine in-situ is par- ticularly important on single gas turbine propulsion ships, which do not have re- dundancy. For most surface combatants, the loss of even one gas turbine would se- verely limit the ship in achieving mission objectives, increase the burden to the ship's crew and significantly impact the downtime of the valuable combat asset. GE offers Intermediate level (I-level) repair and maintenance which can be performed on ship, dockside or at a lo- cal facility. Couple that with GE's proven procedures, tooling and global network of expert service personnel, and the cost and time to return the gas turbine to operation is markedly less than sending the component or turbine to a depot or OEM. Note, not all repairs can be made in place; gas turbine removals may still be required due to event severity. How- ever, by having a horizontal split casing, GE gas turbines can be opened in-situ, a thorough and immediate assessment made, and planning initiated to expedite repairs. This paper shares lessons learned that assist the acquisition, maintenance and ship operator communities in the devel- opment of design-for-maintenance re- quirements of a gas turbine, maintenance planning and quantification of lifecycle costs. Oftentimes, maintenance activities are only considered after the ship is at sea when a costly event occurs. Unscheduled Compressor Events Compressor events will unexpectedly oc- cur and they can be classified into the fol- lowing categories: FOD is the ingestion of a foreign ob- ject, salt water, sand laden intake air or material left after the execution of main- tenance tasks such as the ship's structure or tooling. Despite ship personnel robust procedures, training and preventative best practices, ships propelled by gas turbines can be subjected to foreign object inges- tion and subsequent compressor blade damage. FOD by salt water ingestion occurred on the Freedom-class Littoral Combat Ship 1 with damage to a com- petitor's gas turbine. 5 In such an event, the split casing design of the GE gas tur- bine will immediately permit the extent of the damage to be determined and can allow the repair to be made in-situ in a matter of days (see Figure 1). Conversely, engines without split casings require the complete removal of the gas turbine to determine the extent of the damage and make repairs. Some military marine ves- sels also have the added complication of limited space within the inlet duct or ad- equate tooling to facilitate removal of the entire turbine. It is important to immediately determine the extent of the damage visually before resuming operation. Borescope inspec- tions are not always conclusive since dam- age also can be sustained on non-rotating airfoils such as vanes. FOD often impacts multiple blades and can be extensive. Mi- nor damage can result in slight degrada- tion of performance or a compressor that is more prone to stall. With continued operation, minor damage may propagate resulting in subsequent blade separation and significant compressor damage. Figure 2 illustrates a compressor blade that experienced an impact/tear from a FOD event. The blade was determined to be beyond serviceable limits and required replacement. Domestic Object Damage (DOD) is a self-generated event when an internal ob- ject liberates causing impact damage to the engine. DOD also can occur from an engine stall. A gas turbine has the potential to stall when subjected to abnormal operating conditions, or out-of-schedule Variable Stator Vanes (VSV) or bleed valves. GE LM2500 and LM6000 gas turbine designs have horizontal split casings to fa- cilitate easy access, repair and maintenance to internal components. The LM gas turbine design employs specialized hinges and braces allowing the PeRSPecTIVe Figure 2: FOD Damaged Compressor Blade Figure 1: In-Situ Maintenance of GE LM2500 Horizontal Split Case Compressor

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