DNV-RP-C203 is the dominant recommended practice for fatigue analysis of offshore steel structures. Every NCS jacket operator, every offshore-wind monopile owner, every floater designer references it. The standard is mature; the gap is how operationally-captured inspection findings feed the fatigue-life calculation. CoatingPassport closes that gap.

1. What the standard governs

DNV-RP-C203 covers fatigue analysis methodology for steel offshore structures: S-N curves per detail class, stress- concentration factors, design fatigue life requirements, cumulative damage (Miner's rule), and acceptance criteria for fatigue-critical components like K-joints, T-joints, tubular butt welds, and grouted connections.

On the operator side, RP-C203 governs the inputs to in- service fatigue assessment. Initial-design fatigue life is calculated from S-N curves; remaining life accounts for actual operating history, observed damage, and inspection findings. The standard expects findings to be quantitative — depth, length, location — not narrative.

2. Where inspection feeds the fatigue calculation

Crack detection at welded joints. Surface-breaking cracks reset the remaining-life calculation. Initial size + location + confidence drives the engineering critical assessment (ECA per BS 7910).
Coating breakdown over fatigue-critical zones. Coating loss accelerates corrosion-fatigue interaction. S-N curves shift class downward when free corrosion is present. The location of breakdown matters as much as the extent.
Weld-toe geometry observations. Toe grinding, undercuts, weld profile — RP-C203 has explicit stress-concentration treatments for these.
Repair history. Past repairs, weld overlays, plate inserts — each reset the local fatigue class and need to be carried across inspection cycles. The CoatingPassport history array preserves this trail.

3. The structural problem with PDF inspection records (again)

A finding documented as “crack observed at K-joint 12, weld toe, approx 35 mm length, depth unclear” in a PDF cannot feed an RP-C203 calculation directly. The engineering team has to manually re-extract the measurements, transcribe them into the structural-analysis software, and reconcile against the prior inspection cycle's PDF.

A finding emitted as CoatingPassport JSON carries category, severity, confidence, n_frames_supporting, location_on_asset (coordinate system + x/y/z), source_frames, and ai_model_version. Direct ingest into the structural-analysis tool. Drift across inspections observable in the history array. ECA workflow gets the structured input it needs.

4. RP-C203 × CoatingPassport mapping

S-N curve selection remains an engineering judgment — but the input (coating present? free corrosion? cathodic protection adequate?) comes from the passport, not from PDF re-reading.
Hot-spot stress at observed defects calculations need location_on_asset with the right coordinate system. The passport carries it.
Fatigue-life remaining calculations use passport timestamps + history versions to compute elapsed operating cycles since last documented condition.
Inspection-interval optimization per RP-C203 risk-based inspection (RBI) approaches benefits from structured passport drift data — when severity accelerates between two cycles, the next interval shortens automatically.

5. The DNV-Veracity + DNV class-survey path

Hullproof emits a Veracity-ready export (live demo) so the passport plugs directly into the DNV digital ecosystem. RP-C203 severity vocabulary is already mapped; no per-customer translation layer for class-survey handoff.

6. What this means for your fatigue program

Operators investing in RP-C203 fatigue programs gain when structured inspection data feeds the calculation. The payoff is faster ECA turnaround, defensible remaining-life calculations, optimized inspection intervals, and audit- grade trail back to source frames for any subsequent challenge — PSA Norway, class society, insurance, or litigation.

DNV-RP-C203 fatigue — what offshore engineers need from inspection data.