Compare with the field.
Published inspections, a transparent model, and an honest view of sensor accuracy.
Quepos marina · North breakwater, outside
A marine breakwater, not a bridge. The published April 2016 underwater survey contains grouped thickness measurements, not individual sensor histories.
- Steel
- ASTM A690
- Member
- AS-500 sheet pile
- Nominal wall
- 12.7 mm
- Cell diameter
- 18.6 m
- Exposure age
- 7–8 years
- Method
- Diver-assisted UT
Figure 7 · below-water series
Derived from bin edges
Bounds on sample mean loss
2.1% modeled loss
What the divers measured
Counts within published thickness bins · April 2016
Wall thickness (mm)
Four readings lie in the 12.5–13.0 mm bin, which crosses the 12.7 mm nominal wall. They are retained; nominal dimensions and inspection measurements need not match exactly.
The source uses 11.0 mm sheet piles in smaller, 12.2 m cells. This comparison uses only the 12.7 mm north-breakwater group.
Run the reference simulation
Published dimensions + adjustable linear loss model
Years of exposure · thickness in mm (truncated axis)
Gray rectangle: grouped-survey mean bounds at age 7–8. Blue dashed line: simulation, not measured history.
Model minus observed mean: 0.154 to 0.654 mm. Positive values mean the model predicts a thicker wall. This is a comparison of aggregate values, not a paired accuracy score.
The initial 0.035 mm/year setting comes from our temperate immersed-steel baseline. This survey concerns unprotected tropical marine steel. Changing the rate to match the survey is calibration on this dataset, not independent validation. The 7.5-year default is an assumed midpoint, not a known installation date.
Inspect the data and calculation
Mean bounds = Σ(count × lower or upper bin edge) / 37. Loss bounds = 100 × (12.7 − mean bound) / 12.7, reversing the bounds. The interval reflects grouping, not confidence or sensor uncertainty. Nominal wall is the baseline; it was not a measured initial wall for every point.
| Thickness interval (mm) | Underwater readings |
|---|---|
| 10.5–11 | 2 |
| 11–11.5 | 1 |
| 11.5–12 | 12 |
| 12–12.5 | 18 |
| 12.5–13 | 4 |