Reliability Engineering Flashcards

Two components with reliabilities of 0.90 and 0.95 are arranged in series. What is the system reliability?

Answer: 0.855

Series reliability is the product of component reliabilities: 0.90 × 0.95 = 0.855.

Two identical pumps, each with reliability 0.80, run in active parallel redundancy. What is the system reliability?

Answer: 0.96

Parallel reliability = 1 − (1 − 0.80)² = 1 − 0.04 = 0.96.

A Weibull analysis returns a shape parameter (beta) of 0.7. What failure behavior does this indicate?

Answer: Infant mortality with a decreasing failure rate

A beta below 1 means the failure rate decreases over time, which points to early-life or infant mortality failures.

An asset runs with an MTBF of 500 hours and an MTTR of 20 hours. What is its inherent availability?

Answer: 96.2%

Inherent availability = MTBF / (MTBF + MTTR) = 500 / 520 ≈ 96.2%.

In a Weibull distribution, what does the characteristic life (eta) represent?

Answer: The time by which about 63.2% of the population has failed

Eta is the time at which about 63.2% of units are expected to have failed, whatever the value of beta.

What is the main purpose of a reliability block diagram (RBD)?

Answer: To model how the reliability of components combines into system reliability

An RBD shows the series and parallel logic of components so you can calculate system reliability.

Which failure pattern did the Nowlan and Heap airline study find in most components (about 68%)?

Answer: Infant mortality followed by a constant failure rate

Pattern F, infant mortality followed by a constant conditional probability of failure, made up about 68% of the components studied.