Blind flanges for process pipelines

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Basic Knowledge of Blind Flanges in Process Pipelines 1. Classification and Selection of Blind Flanges Blind flanges are primarily used to completely isolate the process medium, preventing disruptions in production due to imperfect closure of shut-off valves, which could otherwise lead to accidents. In terms of appearance, the commonly used pipe blind plates can be divided into 8-shaped blind plates, plug plates, and gaskets (plug plates and gaskets serve as mutually blind openings). Blind flanges should be installed at locations where separation (isolation) is required, such as at equipment nozzles, before and after shut-off valves, or between two flanges. Generally, it is recommended to use 8-shaped blind flanges ； Plugs can also be used for one-time-use parts such as dampening and purging sections. 2. Locations where blind plates need to be installed 2.1 During the initial startup preparation phase, when conducting strength tests or integrity tests on pipelines, and it is not possible to carry out these tests simultaneously with the connected equipment (such as turbines, compressors, gasifiers, reactors, etc.), blind plates must be installed at the connections between the equipment and the pipelines. 2.2 For pipelines transporting various process materials from outside the battery limit to within it, when the plant is shut down and such pipelines remain in operation, blind flanges shall be installed at the shut-off valves. 2.3 When the unit consists of multiple trains, the main pipe coming from outside the battery limits is divided into several branch pipes leading to each train; blind flanges are installed at the shut-off valves of each branch pipe. 2.4 When devices need to be regularly maintained, inspected, or switched with each other, and the involved equipment must be completely isolated, a blind flange shall be installed at the shut-off valve. 2.5 When pressurization pipelines and purging pipelines (such as nitrogen pipelines and compressed air pipelines), which are process pipelines, are connected to equipment, a blind flange is installed at the isolation valve. 2.6 Drain all low points in equipment and pipelines. If the process media need to be collected into a unified collection system, install blind flanges after the shut-off valves. 2.7 Blind plates or plug valves should be installed behind the valves on the exhaust pipes, drain pipes, and sampling pipes of equipment and pipelines. Except for non-toxic materials that pose no health hazards or explosion risks. 2.8 When the facility is constructed in phases, blind flanges shall be installed on interconnected pipelines at shut-off valves to facilitate subsequent construction work. 2.9 When the equipment is in normal operation, blind flanges should generally be installed on certain auxiliary pipelines that need to be completely isolated. 2.10 Situations where blind flanges are required due to other process requirements. 3. Examples of blind flange installation
3.1 The graphical representation of blind flanges on P&ID diagrams shall be in accordance with the industry standard “Graphical Symbols for Pipes and Fittings in Piping and Instrumentation Diagrams” (HG 20559.3-93). The figure showing the figure-eight-shaped blind flange used in these regulations is shown below. 3.2 When the unit is used for multi-series production, the blind flange setup is as shown in the figure. 3.3 The setting of blind flanges for the pressurization and purging pipelines is shown in the figure. 3.4 The installation of blind flanges for draining the lowest points of equipment pipelines is shown in the figure. 3.5 When the device is constructed in phases, the placement of blind flanges is as shown in the diagram. 4. Precautions for blind flange installation
4.1 On the premise of meeting process requirements, use as few blind flanges as possible. 4.2 The blind plates installed must indicate whether they are to be opened or closed in normal operation. 4.3 Whether the blind plate should be installed upstream or downstream of the isolation valve should be determined based on the isolation efficiency, safety requirements, and process needs. 5. Management requirements for blind flanges
5.1 The facility shall designate a specific person to be responsible for the management of blind flanges; a diagram of the blind flanges must be drawn up, and each blind flange should be labeled with a number. 5.2 A register for blind plates should be established, with detailed records kept for reference. 5.3 The fabrication of blind flanges shall be based on steel plates and must have sufficient strength; no other materials may be used as a substitute. Their thickness shall not be less than the wall thickness of the equipment or piping. 5.4 Blind flanges should be installed at the flanges located behind valves from which materials originate; gaskets must be placed on both sides of the blind flange to prevent damage to the flanges. 5.5 Issue a work permit when removing or installing blind flanges, and take necessary safety measures. 5.6 After use, blind flanges shall be collected and stored for future use.