IRM and Construction Support: Advanced ROV Operations for Experienced Pilots

Inspection, Repair and Maintenance (IRM) and construction support represent the highest-complexity end of ROV operations. The tasks demand not just vehicle skill but a deep understanding of subsea structures, survey instrumentation, and the engineering intent behind each inspection or installation task. Pilots who excel in this environment combine operational precision with technical knowledge — they understand why they are performing each task, not just how.

Structural Inspection: GVI and CVI Techniques

General Visual Inspection (GVI) and Close Visual Inspection (CVI) are defined in DNV-RP-C210 and IMCA M 140, and the distinction matters in practice. A GVI is a survey of the structure from a sufficient standoff distance to observe the overall condition — marine growth patterns, gross structural deformation, dropped object damage, and anode depletion. A CVI requires the ROV to approach to within 150–300mm of the structure to identify specific defects — cracking, corrosion pitting, coating breakdown, and weld defects. CVI requires stable piloting in close proximity to structure, often in current, and demands systematic coverage of defined inspection segments rather than opportunistic camera passes.

FPSO Turret and Mooring Inspections

FPSO turret inspections are among the most demanding IRM tasks. The turret geometry — hawse pipes, chain tables, mooring leg attachment points, swivel stack foundations — creates a complex environment with limited access and significant marine growth accumulation. Cleaning is typically required before inspection, using either rotary brush systems or high-pressure water jetting tools. Plan the cleaning pass systematically: document the pre-clean condition, clean in defined sections, and inspect each section immediately after cleaning before moving on. Attempting to clean the entire structure and then inspect it creates the risk of contaminating cleaned areas with dislodged growth from adjacent sections.

Spool Piece Installation Support

Spool piece installation is a multi-ROV operation in most cases, requiring precise coordination between the vehicle managing the spool and the vehicle monitoring the connection points. As the support ROV pilot, your role during the final approach and make-up sequence is observation and communication — not vehicle movement. Establish your observation position before the lift begins, confirm it with the lead pilot, and hold that position. The worst spool piece incidents occur when a support ROV repositions during the final approach and creates a tether interaction with the lift wire or the installation ROV's umbilical.

Flooded Member Detection

• Flooded member detection (FMD) is conducted using ROV-mounted gamma ray or ultrasonic instruments — know the operating principles of the specific tool you are using before deployment
• Instrument calibration checks at the start of each inspection session are mandatory — do not skip them regardless of schedule pressure
• Approach angle to the pipe member matters for both gamma ray and ultrasonic FMD — confirm the required geometry with the inspection engineer
• Mark the start and end of each member measurement run precisely — positional accuracy determines whether anomalies can be relocated on subsequent surveys
• Water flooding produces a specific instrument signature distinct from partial flooding or internal corrosion products — understand what you're interpreting
• Data quality flags during acquisition should be recorded in the dive log in real time, not reconstructed from memory during post-dive reporting
• Structural node areas often require customized tooling approaches — discuss with the inspection engineer before attempting standard approach geometry

Cathodic Protection Surveys

CP surveys using silver/silver chloride half-cell reference electrodes are a standard IRM task, but the quality of data is entirely dependent on technique. The electrode must be in firm contact with the steel substrate (or within the defined contact proximity for non-contact systems) for the required reading stabilization time — typically 5–10 seconds for a stable potential reading. Rushing CP surveys produces data that is commercially worthless and may trigger a re-survey requirement. Structure your approach to each anode and measurement point deliberately: position the ROV, stabilize, place the probe, hold for stabilization, record, move on. The temptation to rush in a long CP survey campaign is real; the cost of poor data is worse.

As-Built Surveys

As-built surveys document the final installed position of subsea infrastructure and are compared against the design drawings to confirm installation accuracy. The ROV's acoustic positioning system, combined with an inertial navigation system (INS) or ultra-short baseline (USBL) positioning, provides the georeferenced position data. Heading accuracy is as important as position accuracy — document the ROV heading at each measurement point, not just the position. Metrology data, where required, must meet tolerances defined in the project metrology specification, typically in the range of ±10–25mm depending on the application. Understand the specified tolerance before the survey, so you can assess data quality in real time.

Managing Multiple Client Deliverables