Reliability and Maintainability in Industrial Systems

Posted on Nov 3, 2024 in Other subjects

REVIEW QUESTIONS

Infrared Thermography

Infrared thermography is a technique that allows for non-contact, distance measurement and accurate display of surface temperatures. Human eyes are not sensitive to infrared radiation emitted by an object, but infrared cameras can mediate the energy with infrared sensors. This allows us to determine the surface temperature at a distance, in real time, and without contact. The display uses a color scale, where each color represents a different temperature, with the highest temperature being white.

Applications:

  1. Power lines
  2. High and Low Voltage Installations
  3. Electrical panels, connections, terminals, transformers, fuses, and connectors
  4. Electric motors, generators, coils, etc.
  5. Reducers, brakes, bearings, couplings, mechanical clutches
  6. Furnaces, boilers, and heat exchangers
  7. Industrial cold and air conditioning installations
  8. Production lines: cutting, pressing, forging, heat treatment

Reliability and the Bathtub Curve

Reliability is the probability that a component or system will perform its intended function flawlessly during a given period and under established conditions.

To understand reliability, consider the following:

  1. Reliability-unreliability
  2. Density of failure
  3. Failure rate or life
  4. The bathtub curve

The bathtub curve is a graph representing the failures during the lifetime of a system or machine. It is named for its resemblance to a bathtub cut lengthwise.

It has three stages:

  1. Initial failures: This stage is characterized by a high failure rate that decreases rapidly with time. These failures may be due to defective equipment, improper installations, equipment design errors, lack of equipment operation knowledge, or the lack of proper procedures.
  2. Normal faults: This phase has a lower and constant failure rate. Failures do not occur due to inherent causes within the equipment, but rather due to external random causes. These causes include acts of God, improper operation, inadequate conditions, and other unforeseen events.
  3. Failures of wear: This phase is characterized by a rapidly increasing failure rate. Failures are caused by wear and tear of the equipment due to the passage of time.

This is one of twelve established forms of failure modes for equipment, systems, and devices.

Maintainability: Key Features and Influencing Factors

Maintainability refers to the likelihood that a facility, machine, or part, if damaged, can be repaired within a specific time (tr) when maintenance operations are conducted according to defined procedures. It can be defined as the ease of performing maintenance.

Three key factors influence the repair time of a machine:

  1. Proper design
  2. Proper maintenance organization
  3. Proper implementation of the repair

Design factors include:

  • Complexity of the machine
  • Weight of its components
  • Visibility and accessibility of components
  • Standardization and miniaturization of components
  • Interchangeable components
  • Ease of assembly and disassembly

Organizational factors include:

  1. Labor management
  2. Personnel training
  3. Sizing of the maintenance template
  4. Efficient parts management
  5. Decentralized maintenance
  6. Availability of documentation

Performance factors include:

  1. Labor skills
  2. Suitable tools for the job
  3. Measurement and verification instruments
  4. Testability
  5. Work preparation

Vibration Analysis: Description and Applications

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Predictive Maintenance

Definition:

Predictive maintenance is based primarily on detecting a failure before it happens, allowing time to correct it without disrupting service or stopping production. These controls can be carried out periodically or continuously, depending on the equipment type, production system, and other factors.

Diagnostic instruments, equipment, nondestructive testing, lubricant analysis, temperature checks of electrical equipment, etc., are used for this purpose.

Advantages of Predictive Maintenance:

  1. Reduces downtime
  2. Allows for tracking the evolution of a defect over time
  3. Optimizes maintenance personnel management
  4. Checking the status of machinery, both periodically and accidentally, allows for creating a historical record of mechanical behavior
  5. Provides knowledge of the exact time limit for action without involving the development of a glitch
  6. Enables informed decisions on stopping production lines for critical machines
  7. Supports the creation of internal operating procedures or the purchase of new equipment
  8. Allows for knowledge of the history of actions, which can be used for corrective maintenance
  9. Facilitates failure analysis
  10. Enables statistical analysis of the system

FMECA Method of Fault Analysis

The FMECA (Failure Mode, Effects, and Criticality Analysis) method is a technique that helps assess the probability of failure occurrence and its consequences for the use of a computer-machine production system.

Identifying the potential failure of a component, feature, or set of equipment allows for evaluating the possible detection frequency, gravity, and criticality, and proposing actions to organize preventive control and coordination, thus decreasing criticality.

The FMECA allows for a precautionary approach. The starting point is that the working group has a good understanding of the facility’s behavior, existing production systems, and similar elements within the company.

The analysis consists of three phases:

  1. Qualitative: Highlights failures
  2. Quantitative: Calculates the risk
  3. Corrective action: Implements a corrective action plan

The FMECA is characterized by:

  1. Being formalized group work
  2. The proactive analysis of a device’s effects
  3. The use of a simple and objective approach
  4. The existence of clear criteria

Differences and Similarities Between the Bathtub Curve of Electrical and Mechanical Components

The bathtub curve has three areas: initially, the failure rate is higher due to the recent installation of the equipment and the resulting lack of immunity to the environment, quality failures, adjustment problems, settling of components, etc. In the case of mechanical equipment, where tribological processes are crucial, this phase corresponds to intrinsic damage from the manufacturing process or design. In contrast, this period is almost negligible in electrical systems.

In the electronic domain, the initial phase has a very long slope, reducing the failure rate at the end of the stage. In the mechanical domain, the slope is much less prolonged, and the failure rate remains very high at the end of the stage. During the lifespan, the failure rate in the mechanical domain is higher than in the electronic domain, although they are both similar. The last stage is much shorter in the mechanical domain. We can say that the bathtub curve in the mechanical domain is closer to the normal bathtub curve.

Concept of Availability and Factors Affecting It

Availability is the probability that an asset will perform its assigned function when required. It depends on how often failures occur in a given time and under specific conditions (reliability) and how much time is required to correct the failure (maintainability).

Several definitions of availability:

  • Average availability and operational availability practically coincide and are the main indicators of maintenance efficiency.
  • Inherent availability is intrinsic to the machine and is determined by the manufacturer during the design phase.
  • The maintenance service impacts availability by improving the inherent availability provided by the manufacturer through preventive maintenance, work preparation, and corrective maintenance.
  • The maintenance service improves operational availability through logistical support.
  • A machine is considered highly available when, in the event of damage, repair is very rapid, meaning it is maintainable.

The operational availability of a facility depends on:

  1. Its design and structure
  2. Ongoing preventive maintenance
  3. Time spent on preventive maintenance while the facility is stopped
  4. Active repair time
  5. Logistical and administrative time
  6. Passive repair time

Logically, higher average maintenance leads to increased availability, but not linearly. Instead, high availability corresponds to a large increase in the maintenance quality index.

Half-Life Curves of a Part and Choosing the Proper Maintenance Technique

The average life of a part is plotted on a graph with the number of parts on the vertical axis and operating hours on the horizontal axis. There are two parameters: R (oscillations of the probable life) and V (lowest life expectancy).

If a part has a very low average life and very little swing, choose MHT (Maintenance Hard Time) as predictive maintenance would not be profitable. If the probable life oscillation is high, choose MOC (Maintenance on Condition).