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June 14, 2010
Littoral Combat Ship (LCS), Gas Turbine Reliability Engineering Implementation
ABSTRACT
The development of the Littoral Combat Ship (LCS) and its life cycle support design objectives were driven by three key objectives: 1) High level of ship mission availability while performing any one of the three mission capabilities; 2) Minimal Total Ownership Cost (TOC); 3) Manning compliment lower than the similar predecessor class of ships. To achieve these concurrent goals, the ship design provides functionality including advanced automation for machinery control, as well as mission function reconfiguration and execution. Unfortunately, information-based automated machinery reliability management decision support was not part of the ship design. This type of decision support is vital in enabling a significantly reduced crew and the advance planning required for executing the scheduled short maintenance availabilities. Leveraging existing equipment monitoring technologies deployed throughout the legacy fleet with the reliability engineering approach on LCS will improve the operational availability of gas turbine propulsion systems and allow executing the ship’s Concept of Operations (CONOPS).
To address the reliability and TOC risks with the initially defined sustainment approach, a Reliability Engineering derived Condition Based Maintenance (CBM) strategy was developed, such that it could be implemented using a proven remote monitoring infrastructure. This paper will describe the Reliability Engineering based CBM approach and how it will be implemented on the LCS-1 and LCS-2 propulsion gas turbine engines and other critical systems to achieve system level operational reliability, the LCS life cycle support design objectives, and defined sustainment strategies.
INTRODUCTION
Given the low ship-board manning level and the distinct operations plan for the Littoral Combat Ship, gas turbine engine maintenance will be conducted almost entirely shore-side. This requires an equipment monitoring and condition assessment infrastructure to enable effective advance maintenance planning and scheduling for the abbreviated in-port availabilities of the LCS.
Maintenance, engineering, and logistics costs are driven by the actions to support equipment failure mode management by either reactive or predictive means. The selection and design of a sustainment strategy that minimizes TOC within the constraints of Mission Availability and ship-board manning is required as part of the ship design activities.
The current Navy approach to achieve the operational and TOC objectives, within the reduced LCS manning framework is:
•A high level of dependence on shore-based support to perform maintenance and repairs between operating cycles
•Continuous Distance Support through a ship-to-shore integrated information system.
•An intent to negotiate a Performance Based Sustainment Contract (PBSC) with the applicable ship-builder
While these three concepts of sustainment support are critical to LCS gas turbine propulsion systems, what is lacking is an innovative integrated information system that can capture the equipment failure risk and maintenance related information, transfer it ashore for analysis and conversion to knowledge, in order to:
•support decisions related to ship-board and shore-side work scope planning
•support decisions on how to manage ship-board and shore-side mission based sparing
•leverage the shore-based PBSC support infrastructure
•capture the accountability and metrics related aspects of the PBSC
The consequence of this is that to have the shore side support teams respond to short notice sustainment requirements, the Navy will have to account for additional annual support costs that were previously handled by ship’s crew. This is due to the need for on-shelf ready materials and the availability of “ready-to-fly-away” distant support teams composed primarily of commercial contractors. Specifically, during the three year ISP period, the respective ship builders will be under a cost reimbursable contract to perform some of the preventive maintenance tasks and most of the corrective maintenance requirements. In order to negotiate a Fixed Price PBSC, within a system availability and performance metrics framework, the risk of system failure will be covered through an elevated cost of logistic footprint. This cost will be equivalent or possibly more, if the Navy assumes LCS sustainment within existing organic infrastructure.
To address the reliability and TOC risks with the initially defined sustainment approach, the US Navy is implementing a Reliability Engineering derived Condition Based Maintenance (CBM) process and system as a more effective sustainment approach within which to develop and implement the LCS gas turbine systems sustainment strategies. This is to be done regardless if the Navy or contractor is responsible for sustainment accountability. Reliability Engineering based CBM is the process of scheduling prescribed maintenance tasks, through the analysis of equipment condition indicating data and operational utilization (stress) data. Current equipment condition and the forecasted risk of failure are estimated using the acquired information, in conjunction with the planned equipment operating (duty cycle) profile. Business rules related to unacceptable equipment risks are invoked ashore, providing accurate advance planning and scheduling of maintenance and logistic support activities, resulting in high mission availability, while minimizing logistic footprint.
As currently defined by the Navy, “CBM” is a maintenance strategy derived from analysis, preferably using RCM. CBM includes maintenance processes and capabilities derived from real or near-real time assessments obtained from embedded sensors and/or external tests and measurements using either portable equipment or actual inspection. The objective of CBM is to perform maintenance based upon the evidence of need while ensuring safety, reliability, availability, and reduced total ownership cost.
In essence, Condition Based Maintenance is pre-planned corrective maintenance, scheduled through risk analysis, as recognized degradations and equipment cumulative wear propagate2, taking into account:
•Safety risk
•Equipment predicted risk
•Mission impact risk
•Cost risks
The Reliability Engineering based CBM approach will allow for a shift from periodically scheduled Preventive Maintenance (PM) and failure based Corrective Maintenance to a maintenance strategy based on predicted machinery failure risk.
The primary intent is to enable early detection of machinery condition change and failure risk prediction which will extend the planning horizon for managing equipment failure modes that have an impact on the defined mission requirements and cost constraints. The Reliability Engineering based CBM will support the reduced shipboard manpower and will support achieving the LCS design objectives of:
1. Increased equipment readiness through a higher systems reliability and availability gained by more effective planning of the work scope to be accomplished prior to and following mission operating periods
2. Reduced cost of O-Level and shore side on-shelf spares and maintenance tasks since a better awareness of equipment health at all times allows for enhanced logistic planning
Download the full PDF:: LCS_Gas_Turbine_Reliability_Engineering_Implementation.pdf
