MNT.6:5 - Archetypal Grounding
For PS17 in configuration C41, the constructed decision is how to meet the required normal duty after the next planned outage, not how to guarantee an indefinite bearing life. MNT.4 supplies the abnormal, increasing condition account; vibration magnitude alone does not choose replacement. The case additionally supplies an existing machine-specific inspection and diagnostic account identifying a localized defect in the installed bearing’s rolling contact. Its relevant mounting and lubrication findings support replacement under the unchanged design basis rather than correction of an ongoing mounting or lubrication defect. These are explicit diagnostic premises for this teaching case, not conclusions obtainable from the three vibration values alone.
The operating assessment supplies a distinct premise: a permitted lower-duty assignment for this unit still meets the full present district-heating demand until the planned outage two days away. This is not XRI-09’s reduced-capacity outage, whose separate bound remains four hours. Normal demand then returns, and that lower-duty assignment cannot meet it. This two-day boundary is a service and supported-use boundary, not a predicted time to bearing failure. Continued use remains within the supplied condition and protection limits; losing one of those limits reopens the operating response immediately.
| Live response | Effect and consequence under the supplied case conditions | Place in the answer |
|---|---|---|
| Continue unrestricted use without intervention | Leaves the diagnosed defect in place, while the available condition assessment does not support unrestricted normal-duty use over the receiving period. | Does not provide a supported answer to the required use. |
| Use the permitted temporary restriction | Reduces the present demand on the affected unit and meets current service needs within its supported conditions; it neither removes the defect nor supplies the later normal duty. | A usable bridge to the outage, not a substitute for restoration. |
| Replace the applicable bearing at the planned outage | Removes the identified local defective component. Preparation, testing and hand-back provisionally fit MNT.7’s 225-minute demand within the 240-minute bound. Replacement introduces intervention risk and still needs applicable parts, protected work and functioning verification. | The supported restoration recommendation, conditional on those operative requirements. |
| Stop immediately | Avoids further running of the affected unit but causes service loss that the permitted bridge avoids under the present facts. | Not the preferred present response; return to the operating/protection decision if the bridge loses its supported conditions. |
The recommendation follows from the combination: the restriction meets only the short receiving need, whereas replacement addresses the identified defect and has a bounded usable opportunity before normal demand returns. Neither the vibration rise nor the availability of an outage would establish that comparison alone. The spare applicability/certification return remains outstanding. The finished advice is therefore “use the supported temporary arrangement and recommend replacement at the suitable outage, subject to applicable part and operative work conditions,” not “begin replacement now.” If the part or full window does not become usable, the team must reopen the service arrangement; it cannot silently extend the temporary restriction.
Why this bearing deteriorated earlier than comparable units remains unresolved. The supplied diagnostic basis supports removing the present local defect, but does not establish that replacement prevents every recurrence. That stronger causal uncertainty does not defeat this bounded recommendation; it limits the claim to the present restoration question. Actual resulting functioning and resumed-use authority still require their separate MNT.10 and MNT.11 returns.
Suppose an existing inspection instead shows that a shared mounting defect would make another bearing replacement ineffective. That evidence changes the alternatives and reopens the choice. The team returns the mounting or engineering question instead of repeating the same repair.
In the shared-specialist case, a less urgent job can be deferred only if its failure consequence and operating conditions support that choice. The arithmetic showing that both jobs cannot fit identifies the conflict; it does not decide which consequence to accept.