When liquid natural gas (LNG) tankers go in for scheduled maintenance, it is an immense undertaking. In its largest coordinated project to date, Atlas Copco Gas and Process Aftermarket Services is playing a key role in the overhaul of a fleet of Q-Flex LNG carriers, helping ensure the tankers remain active on the high seas and deliver their cargo to markets around the world.
Ascending 164 steps aboard the 315-meter-long Al Thumama LNG tanker, Atlas Copco engineer Thomas Engels surveyed an impressive scene: An immense dry-dock installation, a state-of-the-art shipyard on the outer edge of the largest LNG export facility on the planet.Here, at the N-KOM facilities of the Erhama Bin Jaber Al Jalahma Shipyard north of Doha, Qatar, Engels joined a team of Atlas Copco Aftermarket service specialists. Their mission: Assist with the overhaul of 31 of the world’s top LNG carriers, the Q-Flex line.In a span of just seven months in 2012, the team saw 15 Q-Flex vessels come through the shipyard. Engels and his fellow employees overhauled the Atlas Copco companders and compressors at the heart of these ships’ on-board reliquefaction plants. Activities started up once again in April 2013, with 11 tankers in the Q-Flex fleet scheduled for servicing before the end of the year.With a carrying capacity of 216 000 m3, these Q-Flex ships are some of the largest ships on the ocean. They carry a unique on-board reliquefaction plant that allows them to deliver nearly all of their liquid natural gas cargo to its destination – without losing many tons of so-called boil-off gas (BOG) along the way. This technology is powered by Atlas Copco Gas and Process companders and compressors.
Despite the overwhelming scale and complexity of the project, the Atlas Copco Aftermarket team has delivered excellent technical results that impressed both the dry-dock operators and the ships’ owners. “We’ve had a good interaction with Atlas Copco. Overall, this has been a good operation, especially from the technical point of view,” says Dahmane Belloum, technical superintendent at N-KOM’s co-owner Nakilat.The Quatar shipyard is quickly becoming a major hub for gas carrier maintenance. At each of N-KOM’s two high-tech dry-docks, some 2 000 people might be busy at work. Atlas Copco specialists focus on the interior of Q-Flex tankers, their reliquefaction systems, performing crucial work for which only few technicians in the world are trained.
Long before the first Q-Flex ship entered the yard in 2012, the Atlas Copco team was already hard at work with preparations. They arranged for transportation of the specialized tools and countless spare parts vital to the project’s success. Due to long transportation times and often unpredictable schedules, many of the parts needed to be ordered up to one-and-a-half years ahead of servicing. At N-KOM, the LNG vessels have a short window of only 20 days to enter a dry-dock, undergo an engine overhaul and a complete hull inspection and instrumentation check. Then it’s back out to sea to make room for the next ship in line. Atlas Copco technicians have to dismantle, service, and then reassemble a vessel’s reliquefaction system, inspecting not only the main compander and compressor but also a reserve pair.
When it came to servicing 15 Q-Flex vessels within a span of seven months, Atlas Copco’s global presence has proved to be an invaluable asset.Now, roughly two-thirds of the way through the overhaul operations, the team has a lot to be proud of. The project is by far the largest servicing operation the unit has organized, and its smooth execution required extensive coordination of parts, equipment and personnel.Atlas Copco successfully met all of the operation’s exacting deadlines and received extremely positive feedback from the LNG vessels’ owners and operators. The coordinated work ensures that Q-Flex vessels will continue to deliver top performance for years to come. “There are a limited number of people in the field who can service, repair, and recalibrate these machines to the very highest standards” says Ahmed Nour, Atlas Copco Aftermarket Sales Consultant in Dubai. “Thanks to a talented and diverse team of Aftermarket specialists we have been able to deliver terrific results on this project.”
At the heart of a Q-Flex ships’ reliquefaction system is an Atlas Copco compander, which compresses nitrogen from about 10 to 44 bar across three stages. The nitrogen is then expanded to 11.2 bar, causing it to chill BOG to icy temperatures. This gas is simultaneously compressed to approximately 8 bar in a three-stage, integrally-geared centrifugal compressor made by Atlas Copco, which enables it to return to a liquid state.