Thread Content
1 Structure and characteristics of traditional insulating flanges: The traditional Type I insulating flange consists of insulating gaskets placed between two butt-welded flat flanges, along with insulating sleeves fitted over the fastening bolts and insulating bolt gaskets. Its structural assembly diagram is shown in Figure 1, and the materials for its flange insulation gaskets are made from oil-resistant rubber asbestos boards, neoprene boards, fabric-based neoprene boards, polytetrafluoroethylene, and other similar materials. Insulated bolt sleeves and bolt insulating washers are made from high-strength phenolic laminated cloth boards and cloth-pressure tubes. Its features are: high stiffness, stable insulation performance, the need for a dedicated installation location, and high cost. 2 Development of new insulating flanges: We made appropriate improvements to the structure of the traditional insulating flanges. In urban gas transmission and distribution projects, improvements are made in light of the low pressure characteristics of such projects (PN≤2.5MPa) as well as the pressure in the pipeline network (PN≤0.4MPa). In pipeline distribution projects, steel face flanges are used in place of butt-welded face flanges. The insulating gaskets for the flanges are made from materials such as polytetrafluoroethylene, oil-resistant rubber and asbestos sheets, and neoprene. The insulating sleeves for the fastening bolts and the insulating gaskets are combined into one unit, with the insulating sleeve being shortened by half to form an integrated, high-strength insulating sleeve gasket. As shown in Figure 2, enlarge the bolt holes of the flange fitted with insulating gaskets so that the insulating gaskets can pass through ； This ensures that the inner diameter of the gasket meets the requirements of the bolts used in the original steel flange, thereby creating a steel flange with special functions; once assembled, it becomes a new type of insulated flange, whose structural arrangement is shown in Figures 3 and 4. It can be installed separately or together with the connecting valve ； It saves both project costs and on-site installation space; it is a simple and practical new type of insulating flange with particularly low costs. 3 Insulation Principle and Performance The working principle of an insulating flange is to utilize the electrical insulation properties of the insulating gaskets and high-strength insulating sleeves contained within it in order to provide electrical isolation between the two sides of the flange. Based on the actual engineering conditions, we tested the insulation performance of this insulated flange in accordance with the relevant requirements specified in the \"Technical Specifications for the Design of Insulated Flanges\" (SY/T0516–1997) as well as the relevant methods outlined in the \"Test Methods for Cathodic Protection Parameters of Buried Steel Pipelines\" (SYJ23—86). The test results showed that the resistance values between the insulating gaskets and the insulating sleeves of the fastening bolts on the insulating surfaces met the requirements set by the standards. 4 Application: This type of insulated flange is used at building valves in cathodically protected water supply and distribution networks, as well as in buried pipe valve chambers where potential zoning is required. Segmenting (zoning) the buried distribution pipelines allows for a clearer understanding of the cathodic protection status of each segment (zone) of the pipeline network ； Evaluate the cathodic protection sections (areas) and take appropriate actions based on the different cathodic protection conditions ； When the protection potentials of adjacent sheets (areas) are the same (or similar) and meet the requirements for such protection potentials, cross bars can be used to connect both sides of the insulating flange in order to provide unified protection ； When there is a large difference in the protection potentials of adjacent cells (areas), and some cells (areas) fail to meet the required protection potential, those cells (areas) that do not meet the standards can be given special treatment until they satisfy the requirements, after which they can be connected and operated together. 5 Strong applicability: The insulating flanges produced by this method are also suitable for use in long-distance pipelines and stations in oil and gas fields where the pressure is PN≥2.5 MPa. All that is needed is to replace the flange with a special flange of the appropriate grade; the method of use remains exactly the same. 6 Conclusions (1) This new type of insulating flange features a novel design, strong applicability, and low cost. (2) It is applicable not only to electrical insulation isolation in urban gas distribution projects ； It is also applicable to long-distance pipelines, gas gathering and transmission pipelines, as well as distribution stations and other locations that require electrical insulation. References: Construction and Quality Inspection of Gas Pipeline Networks, Hubei Scientific Research Achievements Technology Press; Technical Specifications for Insulated Flanges (SY/T0516—1997), Petroleum Industry Press; Testing Methods for Cathodic Protection Parameters of Buried Steel Pipelines (SYJ23—86), Petroleum Industry Press. Author: Jiang Kailan, Zhao Xianqin, Foshan Gas Corporation