The 3 Reliability Growth Models: The Duane Model, The AMSAA-Crow Model & The Crow-Extended Model

Summary

This video introduces three key models for measuring reliability growth: the Duane Model, AMSA-Crow Model, and Crow Extended Model. The Duane Model tracks cumulative mean time between failures over operation time, with a steeper line indicating greater reliability growth. The AMSA-Crow Model uses test phase data to estimate failure rates and monitor reliability growth over time. The Crow Extended Model refines the AMSA-Crow by categorizing failure modes and considering the effectiveness of corrective actions. These models provide valuable tools for understanding and improving equipment reliability.

Takeaways

• 😀 The Duane model uses cumulative mean time between failure (MTBF) over cumulative operational time to measure reliability growth, producing a straight line when logarithmic values are plotted.
• 😀 A steeper line in the Duane model indicates higher reliability growth, while a flatter line suggests slower or no reliability growth.
• 😀 The AMSA Crow model estimates the instantaneous failure rate and mean time between failures during a test phase, using parameters beta and gamma for future predictions outside the test.
• 😀 Beta and gamma are shape parameters calculated from the test period, which are then used to measure failure rates and reliability growth after the test phase in the AMSA Crow model.
• 😀 The AMSA Crow model helps identify whether failure rates are increasing or decreasing over time, indicating if reliability is growing or declining.
• 😀 The Crow Extended model builds on the AMSA Crow model by categorizing failure modes into A, B, and D modes, based on whether corrective action is taken during or after the test phase.
• 😀 A-mode failures do not receive corrective action, B-mode failures are corrected during the test, and D-mode failures receive corrective action after the test phase.
• 😀 The Crow Extended model incorporates the concept of 'fixed effectiveness,' meaning that some corrective actions may not completely eliminate failure modes, leaving a residual failure rate.
• 😀 The concept of fixed effectiveness helps evaluate the impact of different corrective actions on reliability growth, identifying the most effective strategies for improving reliability.
• 😀 By combining the Crow Extended model with knowledge of failure modes and corrective actions, organizations can improve the reliability growth of their equipment.

Q & A

What is the purpose of the Duane Model in reliability growth?

The Duane Model is used to track reliability growth by plotting cumulative mean time between failures (MTBF) over cumulative operational time, with the slope of the plot indicating the rate of reliability improvement.

How does the slope of the Duane Model's plot reflect reliability growth?

The steeper the slope of the Duane Model's plot, the greater the reliability growth. A flatter slope indicates less reliability growth.

What key metrics does the Duane Model use to measure reliability?

The Duane Model uses mean time between failures (MTBF) and operational time as its key metrics for measuring reliability.

What is the primary assumption of the AMSACROW Model during its test phase?

The AMSACROW Model assumes that the test phase is a good representative of how the equipment will behave outside the test, using test-derived shape parameters (beta and gamma) to estimate failure rates and MTBF.

How are the parameters beta and gamma used in the AMSACROW Model?

Beta and gamma are shape parameters calculated from the test phase data. They are then used to predict the instantaneous failure rate and MTBF outside of the test phase.

What is the difference between the AMSACROW Model and the Duane Model?

While the Duane Model focuses on plotting cumulative MTBF against operational time, the AMSACROW Model estimates instantaneous failure rates and MTBF based on test data and uses shape parameters (beta and gamma) to predict reliability growth.

What are the three types of failure modes categorized in the Crow Extended Model?

The three types of failure modes in the Crow Extended Model are: A Modes (failure modes with no corrective action), B/C Modes (failure modes with corrective action during testing), and BD Modes (failure modes with corrective action delayed until after the test phase).

What does the concept of 'fixed effectiveness' mean in the Crow Extended Model?

Fixed effectiveness refers to the idea that corrective actions may not fully eliminate a failure mode, leaving a residual failure rate that the model takes into account when assessing reliability growth.

How does the Crow Extended Model help determine the most effective corrective actions?

The Crow Extended Model evaluates the residual failure rate after corrective actions and helps identify which actions have the most positive impact on reliability growth, especially by considering the effectiveness of different types of corrective actions.

What is the role of reliability growth models like Duane, AMSACROW, and Crow Extended in equipment maintenance?

Reliability growth models are essential tools for analyzing, tracking, and improving the reliability of equipment over time. They help determine whether reliability is improving, suggest corrective actions, and guide maintenance strategies based on data-driven insights.