Brief introduction to fluoroplastic-lined pipe manufacturing processes: loose lining, tight lining, molding, isostatic pressing, and winding processes

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Introduction to several manufacturing processes for fluorinated lining pipes: The first process is the loose-lining method, in which the outer diameter of the PTFE pipe is slightly smaller than the inner diameter of the steel pipe; the PTFE pipe is then pulled into the steel pipe and flanged into shape. This process is not suitable for use in negative-pressure pipelines, as its resistance to negative pressure is poor. It is recommended to use a temperature range of -29 to 150°C, a pressure of 0.01 to 1.0 Mpa, and a diameter of DN25 to 200. Second, the difference between the tight-lining process and the loose-lining process is that the outer diameter of the PTFE tube used in tight lining is slightly larger than the inner diameter of the steel pipe. The advantage of tight lining is that the PTFE tube fits closely against the steel pipe, resulting in little air inside the pipe wall; hence, it has better resistance to negative pressures. We believe that tight-lined pipes can be used in pipelines with low negative pressures, small diameters, and low temperatures. However, they are not recommended for use in negative-pressure pipelines where the temperature exceeds 120 degrees or the diameter is greater than DN100. The largest diameter currently available domestically is DN500. Third, the powder molding process involves using a set of rubber molds to fill the tetrafluoro compound powder into these molds, followed by compression and sintering to achieve the desired shape. This production method requires high pressure; the resulting tetrafluoro compounds have a relatively high density as well as excellent temperature and pressure resistance. It is currently one of the most common production methods in China, and both pipes and pipe fittings can be manufactured using this molding process. It has good temperature and pressure resistance. The pipe diameter range is DN25–700; the operating temperature ranges from -30 to 180°C, while the operating pressure ranges from -0.09 to 1.6 Mpa (these values can vary depending on temperature, pressure, and diameter). Fourthly, in this process, a steel mesh is added as an inner lining. The fluoroplastic-lined pipes produced using this method have a relatively thick inner lining, with a layer of high-strength steel mesh inserted between the fluoroplastic layers to enhance their resistance to negative pressures. The diameter range for these pipes is DN80–700. Fifthly, the isostatic pressing process is used to produce pipes that meet the requirements of the American standard F1545. These are among the highest-standard fluoroplastic-lined pipes available today. However, using isostatic pressing to manufacture pipe fittings requires expensive isostatic presses. The operating temperature range is from -29 to 260°C, and the operating pressure range is from -0.096 to 1.6 Mpa. Sixthly, the winding process is less commonly used for producing fluoroplastic-lined pipes these days. The reason is that it takes longer to produce them and the cost is high. In practice, there isn’t much difference between pipes produced by this method and those made by molding, so they are generally replaced by molded pipes. The winding process is now more often used for manufacturing equipment, storage tanks, and large-diameter components. While molding is difficult for such applications, the winding process works well. Moreover, the fluoroplastic layer in pipes produced by this method is integral, allowing them to withstand temperatures up to 180°C and negative pressures up to -0.05 Mpa. There are currently many companies in China that produce fluorinated lining pipes, and each company has its own specific production processes. There are also various factors that influence the quality of these pipes. If there are any discrepancies, please feel free to point them out.