EngiMetric Arena / Diagnose the Failure
Diagnose the RO train that lost output despite more pressure
Competency Fault diagnosis primary Systems and balances supporting Evidence interpretation supporting
What you should take away: Read normalized RO performance together with pressure drop, and separate fouling from a change in feed salinity or a sensor fault.
The situation
What is happening
An RO train is compared with its commissioning baseline. The operator has raised feed pressure from 55 to 58 bar, but normalized permeate flow is 17 % below baseline and feed-to-concentrate pressure drop has risen from 1.0 to 1.6 bar. Salt passage has increased slightly. Choose the diagnosis the normalized record supports.
Given
| Quantity | Value | Unit | Note |
|---|---|---|---|
| Baseline feed pressure | 55 | bar | Commissioning record. |
| Current feed pressure | 58 | bar | Raised by the operator. |
| Baseline pressure drop | 1.0 | bar | Feed to concentrate. |
| Current pressure drop | 1.6 | bar | Same train, current record. |
| Normalized flow change | -17.1 | % | Corrected to reference temperature and baseline net driving pressure. |
Assumptions this challenge makes
- Feed TDS and temperature are unchanged between baseline and current records.
- The membrane area is unchanged and the same train is being compared.
- Normalization follows the analyzer’s ASTM D4516-style reference conditions.
Your call
Your answer
Hints
- Look at the two normalized signals together: permeate flow and pressure drop. What kind of change raises one and lowers the other?
- The operator raised feed pressure, yet normalized flow is still below baseline. That means the extra pressure is compensating for a loss, not creating a gain.
- A rise in pressure drop points to the feed-concentrate flow path. The analyzer deliberately reports a direction, not a foulant identity.
Your answer Engine result
Where that comes from
Each limit, checked
Why
- The analyzer normalizes the current permeate flow to the reference temperature and baseline net driving pressure. Even after that correction, flow is 17.1 % below baseline.
- Pressure drop has risen from 1.0 to 1.6 bar, a 60 % increase. That is a hydraulic restriction in the feed-concentrate path, not a change in osmotic pressure.
- Salt passage has increased by about 0.17 percentage points, which can accompany fouling but is not the dominant signal. Feed TDS and temperature are unchanged, so a feed-salinity explanation does not fit.
- The supported diagnosis is fouling, scaling or plugging of the flow path. The analyzer’s own guidance is directional: verify with the plant log and the membrane maker before assigning a specific foulant or starting a clean-in-place procedure.
- Raising feed pressure can mask the production loss temporarily, but it also increases the stress on the membrane and the energy use. It does not correct the underlying restriction.
What this challenge does not establish
- The analyzer normalizes with a fixed temperature-correction approximation; the membrane maker’s own factor supersedes it when available.
- A single baseline and current record cannot distinguish fouling from scaling, plugging or mechanical damage without inspection and water analysis.
- Instrument bias is not detected by the model; field verification is required.
- The model does not predict cleaning effectiveness or membrane remaining life.