Ultrasonic Thickness Gauging for Tankers at the Sullom Voe Terminal

Inspection services for ships at Sullom Voe

Each service has its own page with the method, the class requirements and what the report contains.

Where gauging fits at Sullom Voe

The jetties are the terminal's working berths, and any inspection there runs under its permit system. External UT on deck plating, deck piping, air and vent pipes and hatch coamings is usually the most that can be done during cargo operations, because the cargo deck is a hazardous area and tank entry is not normally allowed while cargo is being worked. Instruments taken onto the deck must also satisfy the terminal's rules for equipment in hazardous areas. That limited scope is still valuable: a superintendent can confirm the condition of deck lines, or of a suspect area noted at the last survey, without diverting the ship. A ship held off the berth by weather or cargo timing is a different case, and there gas-free tanks can be entered under the ship's own permits if the master and the owner agree.

There is no drydock or repair yard at Sullom Voe, and tankers trading here take their dockings at yards elsewhere in Europe or further afield. When a tug or launch is withdrawn from service for maintenance, it lies alongside without the time pressure of a loading tanker, and that period suits hull, deck and piping work. For shuttle tankers, the most useful Sullom Voe job is often a focused set of readings that feeds the steel estimate for the next docking, taken while the ship is already in Shetland waters and passed to the yard before she arrives.

• Terminal jetties — external UT on deck plating, deck cargo and ballast lines, air pipes and coamings, under the terminal's permit system and hazardous-area rules.
• Waiting time off the berth — ballast tank and void-space gauging on gas-free spaces of ships delayed by weather or cargo timing.
• Tug and launch berths — hull, towing-gear foundation and sea-water piping checks on harbour craft during maintenance periods.
• Shuttle tankers between liftings — targeted ballast tank and piping gauging planned with the operator to feed the next docking's steel estimate.

Terminal rules, tanker vetting and the UK regime

Port state control at Sullom Voe is carried out by the Maritime and Coastguard Agency under the Paris MoU, and tankers attract particular attention in the regime's risk-based targeting. For tankers, though, the more frequent scrutiny comes from oil-major vetting under OCIMF's SIRE programme and from terminal acceptance checks, both of which look closely at deck condition, piping and the records behind them. Visible corrosion on deck lines or air pipes draws observations that can complicate the next fixture. A set of recent, well-documented readings lets a technical manager answer those questions with measurements, and close an observation before the next inspection rather than after it.

Shuttle tankers add their own engineering. Many are dynamically positioned and fitted with bow loading systems, so the bow loading area, the hawser and hose handling structure and the thruster rooms see loads and vibration that ordinary tankers do not, and fatigue cracking at welded details is a known concern alongside corrosion in ballast tanks. As double-hull tankers age, their extensive ballast spaces receive more close-up survey under the ESP Code at each renewal. Combining thickness readings with magnetic particle or dye penetrant testing at the highly stressed details gives the owner a fuller picture than either method alone.

Ships trading to Sullom Voe are inside a sulphur emission control area, where fuel must not exceed 0.10% sulphur unless an exhaust gas cleaning system (scrubber) is fitted. Scrubber wash-water piping, the overboard discharge and the hull penetration around it are among the fastest-corroding parts of a modern ship, so they belong in the gauging scope at every docking and, on open-loop systems, between dockings.

How a thickness measurement job runs at Sullom Voe

Most of the work on a Sullom Voe job happens before the team boards: scope, plan and access are settled first, so the time on board goes on measurement.

Sumburgh Airport, at the southern end of Mainland Shetland, receives Loganair flights from Aberdeen, Edinburgh and Glasgow, and the terminal lies at the opposite end of Mainland, reached by road, so the team stays nearby for the duration of the job. The overnight ferry from Aberdeen to Lerwick is an alternative when flights are cancelled. Our technicians come from India on UK visas, and the terminal's own access arrangements, including inductions and passes for its secure site, are made through the ship's agent and the terminal operator before arrival.

• Send the vessel name or IMO number, ship type, class society, the survey due (annual, intermediate, renewal survey number, CAP or owner's condition survey), the port and dates, and the scope you expect.
• We confirm the scope against the class rules for that survey, prepare the thickness measurement plan with frame and section references, and say whether the measurement will be credited to a class survey.
• Mobilisation is planned around visa lead times and the vessel's schedule; the ship's agent arranges port access, and the yard or ship arranges staging, lighting, ventilation and gas-free certificates.
• Gauging with calibrated ultrasonic thickness gauges: through sound coatings only where the gauge's through-coating mode has been verified on a coated reference, otherwise on cleaned bare steel, with every reading tied to its frame, strake and location on the sketch.
• Readings are compared with original thicknesses as work proceeds; substantial and excessive corrosion and any cracks are reported to the attending surveyor and the superintendent the same day.
• The final report is issued on the class thickness-measurement formats with sketches, a summary of locations exceeding the allowable margins, piping tables where piping was in scope, and the gauge calibration and technician certificates.

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