Maintenance L3

• Reliability Centered Maintenance (RCM)


  The process of determining the most effective maintenance approach

  
• RCM employs


  • Predictive Maintenance (PdM)
  • Preventive Maintenance (PM)
  • Corrective maintenance (Run-to-Failure/reactive)
  • Proactive Maintenance techniques

  
• RCM


  • Maintenance decisions are based on maintenance requirements supported by sound technical and economic justification

  
• Important goals of RCM


  • To develop design-associated priorities that can facilitate PM
  • To gather information useful for improving the design of items with proven unsatisfactory, inherent reliability
  • To develop PM-related tasks that can reinstate reliability and safety to their inherent levels in the event of equipment or system deterioration
  • To achieve the above goals when the total cost is minimal

  
• RCM ensures


  • The right maintenance is performed at the right time, by the right people, in the right way, with the right training & tools

  
• RCM considers


  • Scheduled maintenance based on failure characteristics in operating context
  • Design changes
  • Training improvements
  • Operational changes
  • One time changes
  • Run to failure when cost effective and no safety/environmental concerns

  
• RCM


  • Less corrective maintenance
  • More proactive approach

  
• RCM Acknowledges Four Types of Maintenance Tasks

  • Time-directed (PM) – Scheduled when appropriate
  • Condition-directed (PdM and real-time monitoring) – Performed when conditions indicate they are needed
  • Failure finding (one of several aspects of Proactive Maintenance)
  • Corrective (CM) Equipment is run-to failure. This is acceptable for some situations and some types of equipment.

  
• Failure Mode, Effects and Criticality Analysis (FMECA)


  A design technique that is used to identify and investigate potential system weaknesses. It includes the necessary steps for examining all ways in which a system can fail, the potential effects of those failures on system performance and safely, and the seriousness of these failures.

  
• Two most common methods to approach fault analysis


  • Failure, Mode, Effect & Criticality Analysis (FMECA)
  • Fault Tree Analysis (FTA)

  
• FMECA


  Starts from the lowest levels of the system and considers the effect at the top level of the system of a failure at the lower level.
• FTA


  Starts with a possible failure mode of the system, and then works down to see what could cause it.
• FMECA is the preferred approach when:
• FTA is the preferred approach when:
• Steps to perform FMECA

  • Define system requirements
  • Accomplish functional analysis
  • Identify failure modes
  • Determine causes of failure
  • Determine the effects of failure
  • Identify failure detection means
  • Rate failure mode severity
  • Rate failure frequency
  • Rate failure mode detection Probability
  • Analyze the failure mode criticality

  
• Purposes in performing FTA:
• Fault Tree Symbols


  • Rectangle
  • Circle
  • Diamond
  • Triangle A
  • Triangle B
  • AND gate
  • OR gate
• Steps to perform FTA


  • Define system, analysis associated assumptions, what constitutes a failure, etc
  • If the simplification of the scope of the analysis is necessary, develop a simple system block diagram showing relevant inputs, outputs, and interfaces
  • Identify undesirable or top fault events to be analyzed and if necessary develop fault trees for all top-level events
  • Identify all the causes that can make the top event occur using fault tree symbols and the logic tree format. More specifically, using deductive reasoning highlight event that can lead to the occurrence of the top event
  • Assuming the causes of the previous step as intermediate effects, continue developing the logic tree by identifying the causes of these intermediate events
  • Develop the fault tree to the lowest level of detail as required
  • Perform analysis of the completed fault tree with respect to understanding the logic and the interrelationships among various fault paths, gaining insight into the unique modes of product faults, etc
  • Determine appropriate corrective measures
  • Prepare documentation of the analysis process and follow up on identified corrective measures

  
• Calculate the probability of occurrence for the top event "Room without light" if the probability of occurrence of all events is 0.02.
• Develop a fault tree for the top event "Vessel loses propulsion"

  
• Calculate the probability of occurrence for the top event "Vessel loses propulsion" if the probability of occurrence of all events is 0.02.