ENTERPRISE FUTURE
Project to construct one of the world’s largest LNG storage tank

Challenging task not yet achieved in the world

  Looming large on your right after driving south from downtown Osaka on the bayshore Route 4 of the Hanshin Expressway is a huge cylindrical structure. This is the No. 5 liquefied natural gas (LNG) tank set up at the Osaka Gas Senboku Terminal Ⅰ. The tank, with an outer diameter of about 91 meters and height of about 60 meters, is so large in area that it could house a facility equal to two castle towers of Osaka Castle.

  An LNG strage tank is a huge container whose purpose is to store LNG, kept in its liquid state at the very low temperature of minus 160 degrees Celsius. The No. 5 LNG tank is capable of storing 230,000 cubic meters of LNG, and was the world’s largest aboveground LNG tank when it was constructed. The project to construct the No. 5 tank at Senboku Terminal was launched in 2011. It marked another challenging project for Osaka Gas, which constructed an LNG strage tank with a storage capacity of 180,000 cubic meters in 2000, the world’s largest when it was built.

  Osaka Gas has tried to build a larger-capacity LNG tank as part of its efforts to reduce construction costs. Building one 230,000-cubic-meter tank would cost less than building two 115,000-cubic-meter tanks, for example. In addition ,if construction time can be shortened, construction costs would be cut further.

  Constructing an LNG strage tank as large as the No. 5 tank was an unprecedented challenge for engineers involved in the project. It required the achievement of aspects usually considered incompatible—enlarging a tank while shortening construction time. Given that nobody in the world had constructed such a huge structure for LNG storage, the project members, as engineers, could not conceal their excitement when assigned to the project.

「Actual video of No. 5 LNG tank construction by slip forming method」

Development of a new material, the first of its kind in the world, defying tightly held industry beliefs of the previous 50 years

  When the project to construct an 180,000-cubic-meter tank was under way in 2000, Maki Yamashita, as a junior member of the project, was engaged in front-line tasks. In the 2011 project, as project manager, Yamashita led its front-line operations. Before the project was launched, he studied the possibility of changing the materials used for the inner tank of an LNG strage tank. An iron-nickel alloy, a type of specialty steel, is used for the inner tank material. The alloy is necessary for the wall’s material because it can enhance the wall’s low-temperature resistance. When Yamashita was assigned to the project, it was said the best mix of nickel in the alloy is 9%, a ratio that for 50 years had been considered the best. To maintain a certain degree of low-temperature resistance while cutting material costs to a certain level, setting the content ratio of nickel, a high-priced rare-earth metal, to 9% was considered the best at that time.

  But to build a tank as large as 230,000 cubic meters, the cost of the nickel needed would be enormous. Under these circumstances, Osaka Gas decided to develop a new material in cooperation with a steelmaker and a construction company. The decision was seen as an attempt to challenge 50 years of common sense belief in the gas industry. What his team finally came up with was a new alloy with a nickel content of 7%. Low-temperature resistance of the new alloy was found to be the same or stronger than that of the conventional 9% nickel steel. The development was a spectacular achievement for the industry, marking the first time in the world that 7% nickel steel was used for the material of the inner tank of the tank.

  The development of the alloy immediately led to negotiations with authorities for obtaining approval for its use in the material of an LNG strage tank. In talks with regulators, Yamashita’s team was asked to explain—from various angles—why the use of 7% nickel steel in an LNG tank, the first time in the world, would be better. Yamashita did not give up undertaking the tough task. He remembered that Osaka Gas had taken an initiative in developing the world’s largest LNG strage tank and actualized the initiative. Yamashita was determined to do all he could to commercialize the new technology—with pride and a strong sense of mission backed by Osaka Gas’s position as the industry leader. With his heart brimming with determination, he visited authorities time after time while carrying various experimental data. The effort was finally rewarded when authorities gave approval to the new material.

Innovative constructionmethod that can shorten construction time of the outer tank to 10% of what it once was.

  In addition to enlarging the LNG strage tank and developing a new material, another big challenge for Osaka Gas was employing a new construction method. What the company adopted was a slip forming method, which was used in constructing the concrete outer wall that forms the outer part of the LNG strage tank. The wall serves as a outer tank. The use of this construction method was the first for a domestic LNG strage tank. In this construction method, concrete is poured around the clock into a formwork, enabling production of a seamless concrete wall. Using this method, constructing a outer tank takes only 20 days, down sharply from nine months using the conventional construction method. Product quality, however, should not be compromised in exchange for shorter construction time. If that happens, it is like putting the cart before the horse. Osaka Gas decided to adopt the new construction method after it was convinced through repeated studies that the requested product quality could be guaranteed.

  Tomonari Niimura was a freshman when he joined the team in charge of introducing this construction method. When he was assigned to the job, he did not know anything about what he was supposed to do. So, he turned to senior colleagues for support. Slip forming was a fantastic dream for him and other team members because if it was established, the construction period could be shortened to one-tenth the time using the conventional method. Many hurdles, however, stood in the way of implementing the new method. Questions that crossed his mind included whether or not the outer tank’s quality could reach the requested level and if it was possible to make a tank with an outer diameter of 91 meters a perfect circle. He also thought about the speed for setting up reinforcing bars, the number of workers to be deployed for construction work, and where each of them was to be positioned. Once concrete is poured into the formwork, it would be impossible to stop it midway. Before starting construction work where a second attempt was not an option, Niimura repeatedly conducted simulations.

  Finally, the construction started, and concrete was poured into the formwork of the outer tank. The wall grew by two meters a day—which visually was the best part of the construction. Twenty days later, the huge wall was completed, standing 40 meters high, at which Niimura looked up, full of emotion. He felt relief from the pressure that had been building since he was first assigned to the job as a freshman.

Air pressure used to lift a 2,400-ton domed roof

  After the outer tank was completed, construction of the tank’s roof began. Employed for this work was an air-raising method, under which the roof is constructed at ground level inside the tank, and upon completion raised 60 meters to its final anchoring place due to an increase in air pressure. Assigned to this job was Hiroshi Nishigami. Air is infused into the inside of the domed structure that acts as a roof through the outer wall of the tank, and air pressure generated inside the dome through the infusion works to lift the roof. The mechanism of the air-raising method is simple. But it is extremely difficult to lift a roof—90 meters in diameter, weighing 2,400 tons—to the anchoring point without it contacting the wall of the outer tank, a task whose maximum allowable margin of error in slope is only several centimeters. Nishigami’s team adjusted the lifting balance based on prior simulations. In constructing huge structures like this LNG strage tank, even a few centimeters of construction error would later result in a significant configuration discrepancy. For the final adjustment, Nishigami repeated the test lifting—raising the roof only about 10 centimeters from the ground.

  On the day of lifting the roof, Nishigami supervised engineers of the construction company mobilized for the work, and instructed them to raise the roof cautiously. Lifting was initially smooth. As the roof was raised toward the highest position, however, some deflection occurred due to a change in the center of balance—something Nishigami had not thought about during the test lifting. Under these circumstances, adjusting the degree of slope was difficult for him. But he had to do it with great accuracy. He was thus determined to do all he could to complete the mission, which he felt must be accomplished since he was assigned to it. He mobilized all his knowledge and expertise based on simulations and test data, and adjusted the roof’s balance. Finally, the roof was raised to a point as high as the top of the outer tank—40 meters above the ground—to cap the tank. Project manager Yamashita, observing the entire lifting process from in back, tapped Nishigami’s shoulder in encouragement.

“You did it,” he told Nishigami.

「Actual video of No.5 LNG tank construction by air-raising method」

Osaka Gas to outrival itself by developing new technology that is also the first of its kind in the world

  The entire process of constructing the No. 5 LNG tank was completed. After that, LNG was infused into the enclosed tank. The temperature inside the tank was cooled to minus 160 degrees Celsius over five days. Nothing irregular or abnormal was detected inside the tank, which effectively marked the project’s completion—39 months after construction started. Osaka Gas’s attempt to construct an LNG strage tank the world had never seen before ended in success. Project members including manager Yamashita felt fulfilled following the project’s completion, which marked another step forward in the evolution of LNG strage tanks.

  But now is not the time for Osaka Gas to stop moving. It’s not what Osaka Gas is supposed to do. Having constructed the 230,000-cubic-meter tank was not a final goal for Osaka Gas. Osaka Gas is prepared to outrival itself by developing new technology that is also the first of its kind in the world. This is what the company is supposed to do. The door for the next challenging mission may have already opened.

Profiles
  • [Project Manager]
    Osaka Gas Engineering Co., Ltd
    General Manager of Plant Engineering Work Dept., Plant Business Div.
    Maki Yamashita
    (joined the company in 1997)
    Position at the time:
    Osaka Gas Co., Ltd.
    Manager of LNG Tank Construction Project Team, Senboku LNG Terminal
  • [Machine technology field]
    Osaka Gas Co., Ltd.
    Plant Technology Team,
    Engineering Dept.
    Hiroshi Nishigami
    (joined the company in 2005)
    Position at the time:
    Osaka Gas Co., Ltd.
    Plant Technology Team, Engineering Dept.
    LNG Tank Construction Project Team, Senboku LNG Terminal
    (concurrent positions)
  • [Civil engineering technology field]
    Osaka Gas Co., Ltd.
    Civil Engineering Team,
    Engineering Dept.
    Tomonari Niimura
    (joined the company in 2010)
    Position at the time:
    Osaka Gas Co., Ltd.
    Civil Engineering Team
    LNG Tank Construction Project Team, Senboku LNG Terminal
    (concurrent positions)

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