We partnered with an FPSO operator to run simultaneous inspections of identical water ballast tanks using ROVs and rope-access teams on an FPSO. By capturing comparable metrics for safety exposure, technical coverage and schedule impacts, we built a practical framework that helps the operator pick the right method for each tank – improving safety and planning confidence.
The challenge
The operator wanted clear, real-world evidence to understand when ROV-based inspections should replace or complement manned entry, and what trade-offs this would mean for cost, safety, schedule, and inspection quality.
Key challenges included:
- Personnel safety exposure from confined-space entry, working at heights and potential heat stress during rope-access inspections.
- SIMOPS constraints (helicopter ops, bunkering, supply boats) that can interrupt manned work, whereas ROVs can often continue.
- Deballasting, ventilation, gas freeing and access preparations required for manned entry versus keeping tanks filled for ROV inspections.
- Establishing like-for-like scope and a fair comparison against LR Special Survey requirements (CVI + UTM).
- Learning curve for ROVs (first deployment on this facility, early tool issues), versus a highly experienced rope-access team.
Our solution
We designed a paired trial on identical tanks, running rope-access and ROV inspections in parallel, measuring key parameters so we could compare “apples with apples.”
What we did:
- Defined comparable scopes aligned to Special Survey (CVI + UTM) and anomaly recording so results could be meaningfully compared.
- Tracked like-for-like metrics: daily tool time, UT points, % scope complete, and SIMOPS-related delays – creating a cost and productivity baseline for each method.
- Set objective decision triggers: a framework to demobilise one team if the projected cost per tank exceeded the other by >30% after a defined trial period.
- Collaborated with the surveyor and facility teams to validate methods, adjust scopes as the trials progressed.
The outcome
The side-by-side trial produced an evidence-based playbook for selecting the right inspection method per tank:
- HSE advantage: ROVs materially reduce confined-space exposure and are less constrained by SIMOPS; this was reflected in the evaluation weighting (HSE ranked #1) and scoring.
- Capability envelope clarified: ROVs are preferred when tanks can remain wet/filled, SIMOPS density is high, or we want to minimise manned exposure; rope-access is preferred for extensive anomaly cleaning or intricate UT in tight spaces.
- Planning confidence: We established realistic duration ranges for Special Survey scopes based on each technique.
- Cost and schedule insight: Rather than a single “winner,” cost-effectiveness depended on scope requirements (e.g. GVI/CVI and UT on good surfaces only vs heavily corroded surfaces requiring descaling to get good UT readings).
Bottom line: the operator now has a clear, defensible way to choose ROV, manned entry, or a hybrid approach – improving safety and making inspection planning faster and more certain.