[History of the Ocean-Sichuan Pipeline] The first polar oil pipeline full of technological content
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In 1968, the United States discovered the Prudhoe Bay oil field in the Arctic Circle on the north slope of Alaska. It was not until November 1973, due to the first energy crisis, that the U.S. Congress approved the construction of the Trans-Alaska Oil Pipeline. It starts from the Prudhoe Bay oil field and ends at Valdez Port in southern Alaska. It has a total length of 1,287 kilometers, a pipe diameter of 1,220 millimeters, and a daily oil delivery capacity of approximately 80,000 cubic meters. It was not completed until 1977. The total investment is as high as 8.8 billion US dollars, which can be described as "the largest in the world". Its technical difficulty lies in crossing permafrost and earthquake-prone areas. A large number of scientific experiments were carried out for this purpose, and the overhead laying method was adopted in an original way.
In the past, oil was extracted in tropical or temperate areas. The experience of oil extraction in cold zones is extremely limited, and it is unprecedented in the Arctic Circle. The development of the Alaska oil fields located within the Arctic Circle is truly the greatest challenge in the history of petroleum. The project of building an oil pipeline across Alaska is already huge. Coupled with the cold weather and many unexpected natural phenomena, such as the tundra climate, uneven groundwater, and seawater freezing in winter and thawing in summer, the engineers who laid the oil pipeline have suffered a lot. Tundra is soil that contains a lot of water and becomes as hard as stone in winter when temperatures drop below freezing ； When the sun shines in the summer, the underground ice melts and turns into mud, making it difficult for even people to stand on it. In some places, even in the summer, only a thin 30 centimeters of topsoil on the tundra melts, while the underground remains near the freezing point. Therefore, as long as the temperature rises by 1°C, the permafrost will melt into a large mud pool. The tundra is so sensitive to temperature changes, causing many facilities to have problems due to seasonal changes. The bridge in Figure 3 is an example. Therefore, unless the project is designed very carefully in advance, it will definitely not last for a year. The temperature in Alaska is below freezing for most of the year, so it is difficult for organisms to survive. The organic nutrients in the soil are only in a thin surface layer. Due to the lack of appropriate plants to protect water and soil, once the frozen soil underground is exposed in summer, the new layer of topsoil is easily washed away by snow and water. This kind of topographic and geological destruction has been ongoing for a long time. Gold prospectors in the early 20th century excavated and destroyed these tundras at will, and they still cannot restore their old appearance. Therefore the United States * * There are strict specifications for the laying of oil pipes to protect the integrity of the natural environment.
Groundwater is unevenly distributed due to the influence of geology and topography, which is another headache in the tundra area. The pressure generated by the freezing and expansion of groundwater in winter is very uneven, which often deforms ground facilities and crushes or twists underground equipment. On the other hand, the crude oil in the oil pipeline must be at a temperature above 50°C to maintain smooth flow. No matter how well it is insulated, some of this heat will always be conducted to the outside. ； Therefore, if the oil pipe is buried underground, sooner or later heat will be released and the frozen soil will thaw, and the oil pipe will inevitably collapse. After various considerations, the project leader decided to erect the oil pipe high off the ground. The temperature difference between winter and summer in the Arctic is as high as 80°C. Various engineering facilities must first prevent damage caused by thermal expansion and contraction. Take building a house for example. It looks good when it is built in the winter, but in the summer the ground swells and seals the door, making it impossible to get out. In order to prevent the oil pipe from breaking due to thermal expansion and contraction, the engineers designed a zigzag laying method. (See masthead picture) However, the oil pipe is elevated above the ground in a zigzag shape. The problem has not been completely solved. The support piles used for the elevated structure are still in trouble. In summer, when the ground temperature is higher than underground, the heat absorbed by the top of the support pile is transferred to the ground, melting the underground ice in the surrounding frozen soil, and the support pile loses its attachment and slides down. In winter, especially early winter, the underground temperature is higher than the ground temperature. The groundwater close to the support pile flows from top to bottom and freezes along the outer wall of the support pile. The ice becomes tight on the support pile wall. When it continues to expand, the support pile is pushed upward. If the support piles are moved up and down like this, it will not take long for the oil pipe to bend or even break.
[History of Haichuan Pipeline] Summary post is constantly being updated to understand the development process of various pipelines https://bbs.hcbbs.com/thread-3068575-1-1.html (Source: Ocean and River Currents-Ocean Chemical Forum)
It is not difficult to solve the problem of supporting piles. Engineers made two designs, and finally adopted the design of fixed temperature pipes. First drive the hollow steel pile into the ground, and then insert a sealed steel pipe containing 50 grams of liquid ammonia. In summer, liquid ammonia absorbs the heat transmitted from top to bottom, evaporates into ammonia gas, and rises to the top of the tube. Due to continuous evaporation, the pressure increases, compressing the ammonia gas at the upper end of the tube into liquid ammonia. The heat released is transferred to the atmosphere by the air-cooled exchanger, and the condensed liquid ammonia flows down to the bottom of the tube. Such repeated evaporation and condensation can maintain a low and uniform temperature in the underground part of the pile. In winter, the whole process is reversed. Ammonia gas goes from bottom to top, exchanging heat with liquid ammonia from top to bottom. The ammonia gas that has not yet been liquefied continues to rise, and finally exchanges heat with the outside world at the top to liquefy. The entire design is to use the volatilization and condensation of ammonia to transfer heat from hot places to cold places and maintain a uniform temperature within the tube. As long as the temperature in the lower half of the pile remains uniform and below freezing, allowing the surrounding frozen soil to freeze all year round without thawing, the pile can be fixed.
In severely cold Alaska, to keep the crude oil in the pipe above 50°C, heating stations must be set up along the way. There are small refineries and heating equipment at the heating station. The refinery extracts a portion of the crude oil in the oil pipe for refining and separation. The resulting fuel oil is separated and sent to the boiler for combustion to maintain the temperature of the oil pipe. The remaining part is returned to the oil pipe to be mixed with the crude oil for continued transportation. Because most of the areas where oil pipelines pass through are extremely cold and desolate ice fields, it is not easy to hire people to station in the factory, so the heating stations are all fully automated equipment. After overcoming many difficulties, an elevated oil pipeline was finally built. It starts from Brujo Bay and runs through Alaska to Valdez on the south coast. It has a total length of 1,300 kilometers and a pipe diameter of 1.2 meters. At the Port of Valdez, engineers used the same support piles to build a pier to allow tankers to dock and transport the oil back to the United States. Unexpectedly, the pier was built at a huge cost and was reimbursed within a year of completion. It turns out that in winter, a large ice pick is frozen on the top of the dock support pile. When the sea temperature rises in spring, the support pile carries the heat upwards. The part where the ice pick meets the support pile melts, and it becomes loosely attached to the support pile, sliding up and down with the tide or waves. In the Port of Valdez, this ice pick slides up and down as high as 7 meters. When summer comes, all these ice picks rush upward and tear down the entire pier.
Those pipe supports inserted into the permafrost zone are called "temperature fixing rods", which prevent the permafrost from thawing and settling when the temperature rises in summer, and always keep the permafrost zone as a large ice belt. In the 1990s, China used "fixed temperature rod technology" to solve the railway subgrade problem of the Qinghai-Tibet Railway.