Pipeline and Cable Inspection: What ROV Pilots Actually Do on Survey Jobs

Subsea cable and pipeline inspection is a core ROV service across the oil and gas, telecommunications, and offshore renewable energy sectors. Whether you are surveying a 30-year-old hydrocarbon export pipeline or a newly installed inter-array cable for an offshore wind farm, the fundamental inspection principles are the same: follow the route, document the condition, measure the burial depth, identify anomalies, and report accurately. This guide covers the practical techniques used for cable and pipeline inspection with ROVs.

Route Survey Methodology

• Follow the pipeline or cable route at a consistent height and speed for uniform video coverage
• Maintain the camera angle to show both the product and the surrounding seabed
• Use the ROV positioning system to correlate video with geographical coordinates (KP markers)
• Record heading, depth, altitude, and speed continuously throughout the survey
• Note all crossings, approaches, and proximity to other infrastructure
• Document the seabed type and condition along the route

Free-Span Detection and Measurement

Free spans occur where the pipeline or cable is unsupported by the seabed, creating a gap between the product and the seafloor. Free spans are significant because they expose the pipeline to vortex-induced vibrations (VIV), which can cause fatigue damage over time. ROVs detect free spans visually and measure them using sonar, laser scaling, or calibrated camera systems. The key measurements are the span length (along the pipeline), the span height (gap between pipeline and seabed), and the shoulder geometry at each end of the span.

Burial Depth Measurement

• Mechanical burial assessment tools (jetting probes) deployed from the ROV
• Sub-bottom profiler systems mounted on the ROV for continuous burial depth measurement
• TSS (pipe tracker) electromagnetic detection systems for ferrous pipelines
• Manual probing at discrete points for spot-check verification
• Compare measured burial depth against the design requirement (typically 0.6 m to 1.0 m cover)
• Document any areas where burial depth is below the minimum specification

Anomaly Classification

• Use a standardized anomaly classification system (typically defined in the project scope of work)
• Common anomaly categories: coating damage, dents, buckles, corrosion, third-party damage, debris
• For cables: armor wire damage, bending anomalies, exposure, and scour
• Assign severity ratings based on the classification criteria provided by the client
• Photograph and video-record every anomaly with clear scaling references
• Record the anomaly location using KP (kilometer point) or coordinate references

Survey Data Management

• Maintain a continuous event log during the survey with timestamps and KP references
• Record all anomalies in the event log as they are observed
• Ensure video recording is continuous and time-stamped for post-survey review
• Cross-reference still images with video timestamps and KP positions
• Compile a preliminary anomaly register before the end of each survey shift
• Use ThrusterLog to maintain structured dive records that link to the survey event log

Reporting Standards

Cable and pipeline inspection reports are highly structured documents that follow industry or client-specific formats. The ROV team is responsible for delivering the raw data — video, photographs, event logs, positioning data, and anomaly records — in a format that supports the final engineering report. Accurate, well-organized field data is the foundation of a credible inspection report. ThrusterLog helps ensure that the dive-level records are complete and properly structured for integration into the final deliverables.