Thickness Measurement for LNG Carriers and Gas Ships at Ras Laffan

Inspection services for ships at Ras Laffan

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

Where LNG carrier hull gauging is done at Ras Laffan

Most full programmes take place at the Erhama Bin Jaber Al Jalahma Shipyard, where ships are in dry dock or at repair berths with staging and gas-free certificates in place. The yard's sequence drives the work: ballast tanks are opened, cleaned and ventilated in groups, so we take readings tank by tank as they are released and pass suspect results to the superintendent each day. On membrane ships, readings on the inner hull are taken from the ballast side only, and nothing is done inside the cargo containment system.

Outside the yard, opportunities are limited but real. LPG carriers, condensate tankers and product tankers sometimes have idle periods at anchorage or lay-by, when deck plating, accessible ballast tanks and piping can be measured. Port service craft, the tugs, mooring launches and pilot boats that work the LNG berths, also need gauging at their renewal surveys. Because every visit to the industrial city depends on security passes, we try to group these smaller scopes with a docking already planned at the yard, so the permits and travel serve more than one vessel.

• Erhama Bin Jaber Al Jalahma Shipyard — renewal and docking-survey gauging on LNG carriers, LPG carriers and tankers in dry dock, with confirmation readings after steel renewal
• Shipyard repair berths — afloat gauging of ballast tanks, cofferdams and piping on gas carriers before the ship enters dock or after it floats out
• Ras Laffan anchorage — deck, ballast tank and piping checks on LPG carriers and product tankers waiting for loading slots, by launch through the agent
• Condensate and product berths — limited pipe and deck gauging on tankers lying idle at the berth, subject to the terminal's own permit
• Port service craft berths — renewal-survey gauging of the tugs, mooring launches and pilot boats that handle the LNG fleet

Gas-carrier rules, port state control and the LNG expansion

Ras Laffan is a Qatari port and so is covered by the Riyadh MoU port state control regime, though the LNG fleet calling here also faces demanding charterer and terminal vetting. Gas carriers are inspected under OCIMF's SIRE programme like oil and chemical tankers, and terminal acceptance depends on a clean record. No emission control area applies in Qatari waters. LNG carriers burn boil-off gas for much of their propulsion, so scrubber piping is rarely the issue here, but large seawater systems are, particularly on steam-turbine ships with big main condenser circuits drawing warm Gulf water.

QatarEnergy's North Field expansion is adding liquefaction capacity at Ras Laffan and has brought a large new fleet of LNG carriers into service, with more to follow. For new ships, an owner-specified baseline of readings at an early docking gives every later survey a reference. At the other end of the age range, steam-turbine LNG carriers built for the early Qatari contracts are reaching the point where owners choose between further trading, conversion to floating storage or regasification units, or sale, and each option calls for a clear picture of the hull's remaining margins. Warm, saline ballast water and high deck temperatures work against the coatings in wing and double-bottom tanks on all of them.

Wherever a ship is outside a sulphur emission control area, the global 0.50% sulphur cap applies, and many of the ships calling at Ras Laffan meet it with an exhaust gas cleaning system rather than compliant fuel. Scrubber wash-water piping, the overboard discharge and the hull penetration around it corrode quickly in service, especially on open-loop systems, and are worth adding to the gauging scope.

How a thickness measurement job runs at Ras Laffan

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

Hamad International Airport (DOH) is the arrival point, served directly from many Indian cities, and from there the team drives north to Ras Laffan Industrial City. Entry to the industrial city and the port is tightly controlled: every person needs a security pass applied for in advance, sponsored through the yard or the ship's agent, and the portable gauging equipment may also need to be declared. Entry formalities for Qatar are handled ahead of travel, which is why we want the docking date as early as possible and start the pass applications alongside them.

• 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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