Reliability Engineering. Module 3. Proactive Techniques - Definitions

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Evelyn Goodman
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1 Reliability Engineering Module 3 1 Proactive Techniques - Definitions Functional Failure: The inability of an asset to meet a desired standard of performance. Failure Cause: The circumstances during design, manufacture, and use which have led to failure. Failure mode: The cause by which a failure is observed. When identifying each failure mode, the failure effects are also recorded. The process of identifying functions, functional failures, failure modes and failure effects yield surprising and often very exciting opportunities for improving performance and safety 2 1

2 Classification of Failures by Combination of Suddenness and Degree Critical Failure Failure which is likely to cause injury to persons or significant damage to material Major Failure Failure, other than a critical failure, which is likely to reduce the ability of a more complex item to perform its required function Minor Failure Failure, other than critical, which does not reduce the ability of a more complex item to perform its required function Repetitive Failure Recurring inability of a system, subsystem, structure or component to perform the required function 3 Reliability Improvement Failures Primary or secondary Potential or Functional Catastrophic or gradual What is the impact? The key to improving the status quo is the study and avoidance of FAILURE 2

3 Process for Conducting Analysis of Repetitive Failures 1. Monitor plant or equipment performance 2. Identify repetitive system/component failures Sources of repetitive failure data are: Number of maintenance man-hours by system or component Number of maintenance work orders by system or component Maintenance backlog (by system) Control instruments out of service Achievement of maintenance performance goals Safety system unavailability Number of unplanned facility shutdowns Lost production time Number of incident reports Data Gathering FMEA (Failure Mode Effect Analysis) Defective Function Event Frequency Loss Per Yearly Component Causing Loss Occurrence Loss Interview Process Knowledgeable people (operators and mechanics) 6 3

4 Process for Conducting Analysis of Repetitive Failures 3. Establish priorities for solution and allocation of resources This can be achieved by performing the following: A.. Ranking identified problems using Pareto Analysis Pump Seals Vital Few Shaft Coupling V Belts Hydraulic Cylinders Trivial Many Drive Pump Clutch Bearings Brake Roll Bearings Photo Cells Gear Drive Reasons 7 Process for Conducting Analysis of Repetitive Failures B. Providing a framework for the allocation of resources. C. Focusing attention on problems identified as the most important to the achievement of the Dept./Plant s operational and safety goals. D. Considering the following in the ranking process: Overall plant performance goals Reliability Centered Maintenance (RCM) studies Plant Safety Analyses/Technical Specifications Cost in man-hours, dollars, exposure or lost production due to recurring failures 8

5 Process for Conducting Analysis of Repetitive Failures. Assign problems for analysis based on the following: A. Match the problems to available resources (staff and money) B. Determine the complexity of the problem ( clear definition of the problem and expected improvement in performance) C. Select the size and composition of the problem solving team D. Provide a schedule which allows for effective feedback and timely completion of the task.. Analyze problems/determine root cause based on the following: A. Collect all relevant data (CMMS, PdM, etc.) B. Analyze the component and/or system failure 9 Process for Conducting Analysis of Repetitive Failures C. Determine the root cause of failure ( RCFA) D. Develop a list of potential corrective actions 6. Recommend corrective action 7. Select corrective action Evaluate and prioritize possible corrective actions Factors to consider are: Achievement of the improvement goals Ease of implementation Resources required (manpower, cost, schedule) to implement the corrective action Time necessary to implement the corrective action 10

6 Process for Conducting Analysis of Repetitive Failures 8. Implement selected corrective actions by performing the following: Assign corrective actions to individuals, departments or teams for implementation Establish schedules and milestones Review schedule periodically to ensure progress is being made Adjust schedule/or resources if necessary 9. Evaluate results of implemented corrective actions Monitor system performance (PdM and system data should be used) Determine whether the improvement goals have been met 11 Significant Event Tracking Team 1 Type Loss Assigned 2 3 Quantity Loss System/Subsystem Physical 1 Root 2 Causes 3 Human 1 Root 2 Causes 3 Recommendations Responsibility Source: Maintenance Management, E. Jones 12 6

7 Root-Cause Failure Analysis (RCFA) In some cases, plant equipment fails repeatedly, and failures are accepted as a normal idiosyncrasy of that equipment. Recurring problems such as short bearing life, frequent seal fracture, and structural cracking are symptoms of more severe problems. Often, the symptomatic problem is fixed and frequent repairs continue, resulting in high costs for parts and labor and decreased mission support reliability. While condition monitoring (PdM) can identify most equipment faults at such an early stage, the program does not include discovering the underlying reason for the faults. 13 I N P U T Predictive Maintenance Findings Vibration Analysis Lube oil analysis Thermography Process indicators Active Failures Past or future failures which were selected from the FMEA, equipment history, and Pareto analysis Preventive Maintenance Findings Material inspection Mech/Elec. Inspections Operational inspections P R O C E S S Failure Analysis Open to all possibilities Test hypotheses - Why? Why? Why? Drive towards the Root Cause O U T P U T Procedural/System Standardized Operation PdM/PM Maintenance Practices Performance Excellence Technological/Equipment Improved Design Maintenance Prevention 1 7

8 Goals of Root-Cause Failure Analysis (RCFA) RCFA proactively seeks the fundamental causes that lead to facility and equipment failure. Its goals are: Find the cause of the problem quickly, efficiently, and economically Correct the cause of the problem, not just the effect (use of the Why s) Provide information that can help prevent the problem from recurring Instill a mentality of fix forever 1 How to Find the Root Cause? Take each reason of failure of a system/equipment and define the root causes by asking the W1H Questions 1. Who could cause the problem?. Where is the problem happening? 2. What could cause the problem?. Why? Why? Why? 3. When is the problem happening? 6. How could the problem happen? REASON OF FAILURE ROOT CAUSES Who What When Why How Who What When Why How 16 8

9 Table 1 provides an abbreviated Root Cause Failure Sheet for electric motor stators Root Cause of Failure Mode for Electric Motor Bearings Failure Mode Mechanism Reason Root Cause Comments Lubrication Contamination Seal failure Bearing seized Cleanliness (This includes Insufficient Oil leak seals, shields, Procedural lubrication Excessive Procedural system, and Wrong type Procedural lock nuts.) Fatigue Metallurgical Inherent Excessive temp. Excessive load Imbalance Misalignment Fit-up Application Surface distress Installation Procedural Contamination See lubrication Storage Procedural Electrical Insulation Welding 3. Failure Mode Identification Sheet 17 Common Root Causes Dirt: causes blocking (engine oilways), jamming, product quality problems (food), and might cause misalignment when getting in clamping mechanisms. Inadequate lubrication: causing excessive wear or failure of the lubricant itself. Dis/mis assembly: corroding welds, rivet structure, split pins. Incorrect set-up or operation: wrong speed, sequence, wrong materials, starting up too quickly, inappropriate use of emergency stops, machine can be misaligned or out of calibration. Incorrect process or packing of materials in packaging plants: inadequate material 18 9

10 Example: Eastman Chemical Investments in Proactive RCFA/RCM year Training Resources Projects Potential Savings - RCFA: $ 6.07 M from all active projects 19 Failed-Part Analysis This proactive process involves visually inspecting failed parts after their removal to identify the root causes of their failures. More detailed technical analysis may be conducted when necessary to determine the root cause of the failure. Bearings are generally the weakest equipment components. Only 10 to 20 % of bearings achieve their design life. The root causes of bearing failures may relate to improper installation, poor lubrication practices, excessive balance and alignment tolerances, or poor storage and handling techniques. Failed-bearing analysis provides methods to categorize defects such as scoring, color, fretting, and pitting and to relate these findings to the most probable cause of failure 20 10

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