Underwater and marine inspection

What is underwater and marine inspection?

Underwater and marine inspection checks the physical condition of structures that stand in, on, or under water. The objects of work include ship hulls, offshore pipelines and subsea equipment, dams, quay walls, piers, bridge supports, and port structures both above and below the waterline. The job is to look over the whole surface that matters and record what is found: cracks, corrosion, dents, marine growth, gaps in pipeline burial, leaks, or missing protection coatings.

A finished inspection produces a record that an engineer can use to judge the structure's condition and plan repairs. This record usually combines video or still images with sonar data, each tied to a location on the structure so a defect can be found again later. For pipelines, the record often includes a profile of the pipe's shape and burial depth along its length. For ship hulls, it can include the amount and type of buildup removed as well as the hull's remaining condition. The record must cover the structure completely enough that no section is missed, and any defect found must be sized and located well enough to support a repair decision.

Until recently, divers carried out most of this work, swimming along the structure with a camera or hand tools and writing up what they saw. This is slow, limited by how far a diver can see and reach, and risky in strong currents, low visibility, or deep water. Robots now take over much of this direct observation, letting people review the recorded images and sonar data from the surface instead of entering the water themselves.

Who relies on underwater and marine inspection?

Port and harbor authorities: They own quay walls, piers, breakwaters, and bridges that sit partly in the water, and they commission inspections to check that these structures are still sound enough for ships and vehicles to use safely.

Water utilities and dam operators: They own dams, intake structures, and other water-retaining infrastructure, and they need regular inspection records to meet safety rules and catch deterioration before it threatens the structure.

Oil and gas operators: They own offshore pipelines and subsea equipment and commission inspections to find gaps in burial, damaged protection systems, and leaks before they cause a spill or a costly shutdown.

Shipping companies: They own the vessels whose hulls need regular inspection and cleaning to keep fuel use down, meet port and environmental rules, and catch hull damage early.

Underwater inspection service providers: These are contractors who do not own the structures or vessels themselves. They sell inspection work to port authorities, utilities, oil and gas operators, and shipping companies, and they are the ones who operate the robots described in this article.

Coast guards and other maritime security agencies: They own piers, vessels, and other waterside infrastructure and need fast inspection after storms or accidents to assess damage, along with underwater checks for security threats such as hidden mines or unauthorized objects on a hull.

How underwater and marine inspection robots work

Several kinds of robot carry out this work, each suited to a different setting.

Tethered underwater vehicles are piloted by a person from the surface through a cable that also supplies power. The pilot steers the robot's camera and lights along a hull, pier, or pipe, watching live video to spot damage; some of these robots also carry sonar for water too murky for a camera to see through, and can mount a manipulator arm to clear debris or take a sample. The tether lets them keep working in strong currents where a battery-powered robot might struggle.

Autonomous underwater vehicles follow a pre-set path without a tether, carrying sonar and cameras to survey a pipeline route or a stretch of seafloor. They store the data on board and send it back after the mission or during it, and some travel in coordinated groups to cover ground faster.

Some robots hold a fixed position in the water using multiple thrusters, which keeps their sonar or camera steady while they examine a hull, dam face, or bridge support in detail, including the section just above the waterline.

One type of robot combines cleaning with inspection: it attaches to a ship's hull while the vessel is underway, scrapes off buildup, and records the hull's condition as it goes.

Small, slim robots designed to fit inside pipes and culverts carry sonar through confined spaces to profile the inside of a pipe without needing their own onboard battery.

For work close to shore, a small uncrewed boat can carry or deploy a separate underwater vehicle; two operators on shore direct the boat's path and the underwater vehicle's camera and sonar together.