Failure Analysis and RCA Flashcards

A shaft fracture surface shows smooth, curved beach marks radiating from a keyway corner with a small rough final-fracture zone. What failure mechanism is most likely?

Answer: High-cycle fatigue with low nominal stress

Beach marks from a stress concentrator with a small final fast-fracture zone indicate fatigue under relatively low nominal stress.

In RCA terminology, which category of root cause addresses why an organization's systems allowed a human error to occur?

Answer: Latent (organizational) root cause

Latent roots are the management systems, procedures, and culture that allowed the physical and human causes to happen.

Which piece of evidence is most perishable and should be collected first after a failure event?

Answer: Positions of components, debris, and witness recollections

Physical positions and people's memories degrade quickly, so they must be preserved before cleanup or repairs.

A team keeps replacing a failed pump bearing every few months without asking why it fails. This practice is best described as:

Answer: Treating symptoms rather than root causes

Repeatedly replacing parts without addressing the cause treats the symptom and guarantees recurrence.

What is the main advantage of a logic tree (cause-and-effect tree) over a simple 5 Whys analysis?

Answer: It captures multiple parallel causes and requires each hypothesis to be verified

Logic trees branch to show multiple contributing causes and require verification of every hypothesis.

Which failure mode is a common result of misalignment between a motor and pump?

Answer: Bearing and coupling wear with high axial vibration at 1x and 2x running speed

Misalignment produces elevated axial vibration, often at 1x and 2x running speed, and accelerates bearing and coupling wear.

An RCA trigger criterion states that any failure costing more than $25,000 or causing a safety incident requires formal analysis. What is the main purpose of such triggers?

Answer: To focus limited RCA resources on events with significant consequences

Trigger criteria make sure RCA effort goes where consequences justify it.