Lesson 6 – Fault analysis and fault rectification

In this lesson, we will delve into the concepts of machinery failures, their analysis, and the steps involved in rectifying faults effectively.

Understanding Failures

  • A failure is a state in which a machine cannot perform its intended function or has lost its wear reserve (WR) needed for functioning.
  • Failures can disrupt production systems and result in significant losses, making it crucial to analyze their processes, causes, and consequences.
  • Methods exist for detecting potential failures that haven’t occurred yet and for analyzing failures that have already happened.

Types of Failure Analysis

  • IEC 50 (191):1992 introduces methods for both prospective failure analysis (predicting potential failures) and retrospective failure analysis (analyzing past failures).
  • Additionally, weak-point analysis is a method closely related to these concepts.
  • The term “damage analysis” is also used interchangeably with failure analysis, as failures often lead to damage, impacting machinery operability.

Diversity of Damage States

  • Between nominal or new pseudo-potential and complete failure, there exists an infinite range of damage states.
  • Damage effects are diverse, usually stochastic (random), and interconnected. Understanding these is crucial for design, manufacture, use, and maintenance.
  • Three main types of failures are gradual (soft failure), delayed (B-sign), and sudden (hard failure), each with distinct characteristics in terms of duration and impact.

Failure vs. Malfunction

  • ISO IEC 50(191):1992 defines a failure as a condition where a product can’t perform its intended function, except during preventive maintenance or planned activities.
  • Failures are a part of a process, often triggered by wear and tear caused by various stresses during the operational state.
  • Technical failures occur during the process, affecting components but not necessarily causing a malfunction.
  • Failure indicates a change in component quality due to identifiable causes, interpreted as an oc¬osity.
  • A technical defect can occur during manufacturing or repair, which is different from a failure.
  • Reliability is linked to failure, with higher reliability indicating a lower probability of failure.
  • Failure is a process resulting from the deterioration of components during operation, reducing their technical reliability.

Reliability and Unreliability

  • Technical unreliability is defined as a component or sub-assembly’s failure to perform its functions correctly under specific operating conditions for a defined time.
  • This condition doesn’t always lead to failure, as sometimes unreliable components can still operate acceptably under certain conditions.
  • Practical understanding of these concepts helps in identifying issues and improving machinery performance.

Failure types according to the duration and extent of the failure (figure 5.1)

  1. gradual failure (e.g. due to a condensation phenomenon)
  2. delayed failure
  3. sudden failure (e.g. a pneumatic hose fitting puncture) 


  • Failures are conditions where machinery can’t perform its intended function or loses its wear reserve.
  • Analyzing failures, both prospective and retrospective, is crucial to minimize disruptions and losses in production systems.
  • Damage states can vary widely, impacting machinery operability, and are essential to consider in maintenance.
  • Recognizing the differences between failure, malfunction, and technical defect is vital for effective problem-solving in machinery maintenance.

Read the textbook from the 40th page. You can find the textbooks’s content on this link.

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