LNG Carrier

Overview

A modern 174,000 m³ membrane LNG carrier is among the most part-dense ships afloat: shipbuilders describe the complete vessel as roughly 1.2 million discrete parts. The unusual share sits in the cargo containment. Where a crude tanker's tanks are bare steel, each of the four Mark III Cargo Tanks here is lined with GTT's Mark III system, thousands of corrugated stainless sheets over thousands of insulation panels, each panel levelled, anchored and sealed individually, so a single tank carries close to 98,000 components before any cargo machinery is counted.

The ship exists to move natural gas as a liquid at −163 °C, 1/600th of its gaseous volume. Everything unusual about the design follows from that temperature: the flexible membrane that shrinks without cracking, the insulation that keeps daily boil-off near 0.085 %, and the dual-fuel engines that burn the boil-off instead of venting it.

Hull and construction

The hull is a conventional double-hull structure erected from about 90 Hull Grand Blocks, each a pre-outfitted grand block of up to ~300 t. A block is itself a few thousand parts: sixty-odd Hull Plates, hundreds of Hull Stiffeners and Structural Brackets, and, dominating the count, as in every large welded structure, around 5,800 tracked Weld Seams. Across 90 blocks the hull alone passes half a million parts. Penetrations for pipe and cable runs are individually detailed Penetration Piece pieces, since every hole in the inner hull borders the cargo insulation space.

Cargo containment

The Mark III system is the reason this article's part count has six digits. Each tank's inner hull is lined first with Insulation Panels, reinforced-polyurethane-foam and plywood sandwiches about 400 mm thick carrying the bonded Triplex secondary membrane, set on Wedge / Shims and epoxy beds that take up hull fabrication tolerance, and pulled down by Coupler Studs threaded onto studs welded to the inner hull. A single tank uses on the order of 60,000 studs and couplers and over 20,000 wedges and shims.

Over the panels goes the primary barrier: 1.2 mm Corrugated Membrane Sheet sheets of 304L stainless steel, pressed with two-way corrugations and lap-welded to Anchoring Strips. The corrugations act as expansion joints, flexing as the membrane contracts several centimetres per tank length on cooldown. The membrane carries no structural load; cargo weight passes through the insulation into the ship's structure.

Each tank is served from a single Cargo Pump Tower hung from the liquid dome, a tripod of stainless Tower Pipe Sections carrying two main Submerged Cargo Pumps and a Spray / Stripping Pump to the tank floor, braced by Tower Clamps against sloshing loads. There are no other tank penetrations below the dome.

Cargo handling

The Cargo Handling Plant loads and discharges 174,000 m³ in around 12–14 hours through the port and starboard Cargo Manifolds. Boil-off gas is drawn off by four Boil-Off Gas Compressors, two high-duty for cargo operations, two low-duty feeding the engines, with Cargo Heaters warming vapour for tank gas-up and warm-up. Surplus boil-off can be recondensed and returned to the tanks by a Reliquefaction Unit, and an Emergency Shutdown System can halt transfer in seconds. The deck lines run through roughly 850 Cryogenic Valves and 2,400 insulated Pipe Spools on 3,800 Cryogenic Pipe Supports, joined by some 17,000 Flange Bolt Set Items.

Propulsion

Two 5-cylinder Dual-Fuel Two-Stroke Engines of the ME-GI type drive twin Fixed-Pitch Propellers through short Propeller Shaft Section lines in a twin-skeg afterbody. Each engine delivers about 12.4 MW at 66 rpm, injecting natural gas at 300 bar with a small pilot-oil charge; a low-speed engine of this bore is a several-thousand-part machine built up from five Cylinder Units on a Engine Bedplate, a Crankshaft clamped by Engine Tie Rods, twin Turbochargers and the double-walled Double-Wall Gas Pipe runs of its gas-injection system. Three High-Pressure LNG Pumps raise LNG to injection pressure, each engine takes gas through its own Gas Valve Unit, and a Gas Combustion Unit burns whatever boil-off the plant cannot use, keeping tank pressure in band without venting methane.

Ship systems

Electrical power comes from four dual-fuel Dual-Fuel Generator Sets feeding 6.6 kV Main Switchboards. The installation runs about 450 km of cable in 17,000 Cable Runs, restrained by 26,000 Cable Cleats and terminated through 9,000 Connectors, cabling alone is a five-figure part population. The Ballast & Machinery Piping group adds 6,000 Pipe Spools and 18,000 Flange Bolt Set Items across ballast, cooling and fuel systems, with three 3,000 m³/h Ballast Pumps managing the 50,000-odd tonnes of ballast water a light passage requires.

The crew of about 30 lives in the aft Deckhouse & Accommodation, outfitted from 38 prefabricated Cabin Modules and held together by some 29,000 Joiner Screw / Pins and pins. On deck, six Mooring Winches with 64 t brake loads hold the ship at the terminal while the manifolds are connected, and two enclosed Enclosed Lifeboats cover the full complement.