The Problem
A pipeline with nothing underneath it
A nearshore section of a 3.5-inch MEG pipeline at a coastal site had lost the seabed beneath it. The operator needed a subsea pipeline inspection that established how long the freespan was, how high the pipe sat above the bed, what condition the pipe was in and whether anything on the surrounding seabed added to the risk.
A freespan is a pipeline under load it was not designed for. Currents and waves work on the unsupported length and over time that means fatigue, deformation or, in the worst case, a rupture and a leak into the marine environment. Operators are expected to inspect known weak points like this and show they are managing them.
Planning a fix needs accurate numbers. Without the span length, the span height and a clear picture of the seabed, the remediation design is guesswork.
The Inspection
Condition, dimensions and the seabed around it
The pipe itself
A high-definition video survey along the freespan, checking for damage, deformation and leaks and recording marine growth coverage. The ROV's internal navigation kept the survey positioned throughout.
Length and height by sonar
Multibeam sonar measured the unsupported length at 28.14 metres, with the gap under the pipe ranging from half to one and a half times the pipe diameter. Burial locations and touchdown points were fixed by GPS and internal navigation.
40 by 30 metres around the span
A seabed survey around the pipeline looked for debris, trawl scars and anything else that could affect the span or get in the way of the repair.
Our Solution
A Defender with sonar and navigation
The team deployed a VideoRay Mission Specialist Defender ROV fitted with a high-definition camera, multibeam sonar and a navigation system. The Defender is small enough to mobilise nearshore without a large vessel and stable enough to hold a survey line along the pipe in current.
Sonar did the measuring. Video did the condition check. Navigation tied every observation to a position, so the burial points, touchdown points and the span itself can be found again on the next survey.
The Scope
What was inspected and measured
Pipeline condition
Checked by HD video along the freespan for damage, deformation and leaks.
Marine growth
Coverage recorded: hard growth over 75 to 100 percent of the surface, soft growth over 25 to 50 percent.
Freespan length
Measured by multibeam sonar at 28.14 metres.
Span height
Gap beneath the pipe from 0.5 to 1.5 times the pipe diameter along the span.
Burial and touchdown points
Positioned by GPS and internal navigation at each transition between buried and exposed pipe.
Seabed survey
A 40 by 30 metre area around the span checked for debris and trawling activity.
From the ROV
The Result
The numbers the remediation design needed
The pipeline showed no visible damage, deformation or leaks, which took the immediate pressure off and let the operator plan the repair as a scheduled job rather than an emergency.
The span was measured at 28.14 metres with a height of 0.5 to 1.5 times the pipe diameter, and the seabed survey found no debris and no sign of trawler damage. Together with the positioned burial and touchdown points, that gave the operator a clean baseline for designing supports and for monitoring the span over time.
Delivered to the client
- High-definition video of the freespan and the pipe condition
- Multibeam sonar measurement of span length and height
- Burial and touchdown points fixed by GPS and navigation
- Marine growth coverage record
- 40 by 30 metre seabed survey with debris and trawling check
- A report built for remediation planning
A freespan is only as manageable as the data behind it. A subsea freespan pipeline inspection that measures it once, properly, it becomes a planned support installation instead of an open risk.
Why Atlantas Marine
What made the difference
Compact system
A Defender mobilised nearshore without a survey vessel or a large spread.
Sonar measurement
Multibeam sonar gave span length and height as numbers, not estimates from video.
Positioned data
Burial and touchdown points fixed by GPS and internal navigation, so the next survey starts from the same baseline.
Operational experience
The team runs pipeline and structure surveys in current and poor visibility, and plans the dive so the sonar and video both come back clean.
One span. Measured, positioned, reported. Save time. No dive. No risk.
Need a pipeline or freespan surveyed?
Talk to a team that measures spans by sonar, fixes positions by navigation and hands over data the remediation design can use.
How can we help?
Tell us about your inspection campaign
Send the ROV operations team a few details about the asset, the location and the timing, and we will come back to you with how we would approach it.