Installation of blind flanges on process pipelines
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1. Classification and selection of blind plates: Blind plates are primarily used to completely isolate the production medium, preventing disruptions in production due to imperfect closure of the shut-off valves, which could even 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 mutual blind connections). Blind plates should be installed at the locations where separation (shutting off) is required, such as at the equipment connection ports, in front of and behind the shut-off valve, or between two flanges. It is generally recommended to use 8-character blind flanges ； Plug plates can also be used for one-time-use parts such as suppression and purging. 2. Locations where blind flanges 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 flanges must be installed at the connections between the equipment and the pipelines. 2.2 For various process material pipelines that connect outside the boundary zone to inside it, when the plant is shut down, if such pipelines are still in operation, a blind flange shall be installed at the isolation valve. 2.3 When the unit consists of multiple series, the main pipeline coming from outside the boundary area is divided into several branch pipelines that feed each series, and blind plates are installed at the isolation valves of each branch pipeline. 2.4 When the device requires regular maintenance, inspection, or mutual switching, and the associated equipment needs to be completely isolated, a blind flange should 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 materials that are non-toxic, do not pose a health hazard, and are not explosive. 2.8 When the installation is constructed in phases, blind plates are installed at the isolation valves for interconnected pipelines to facilitate subsequent construction work. 2.9 For some auxiliary pipelines that need to be completely shut off during normal operation of the device, blind flanges should generally also be installed. 2.10 Other situations where blind plates are required due to process requirements. 3. Examples of blind plate installation 3.1 The graphical representation of blind plates on P&ID diagrams follows the industry standard \"Graphic Symbols for Piping and Fittings in Piping and Instrumentation Diagrams\" (HG 20559.3-93). The 8-character symbol for blind plates is used in these regulations. 4. Precautions for blind plate installation 4.1 Where possible, install as few blind plates as necessary, provided that the process requirements are met. 4.2 The blind plates installed must indicate whether they are to be opened normally or closed normally. 4.3 Whether the blind plate should be installed upstream or downstream of the isolation valve shall be determined based on the isolation effectiveness, safety requirements, and process requirements. The information in this article comes from HGT 20570.23-1995 \"Installation of Blind Flanges\".
The installation of blind flanges in process pipelines includes the following aspects: 1. Classification and selection of blind flanges: Blind flanges are primarily used to completely isolate the process medium, thereby preventing problems or accidents that may arise from inadequate sealing of the shut-off valves. Common pipe blind plates can be divided into three types: 8-shaped blind plates, plug blind plates, and gasketed blind plates. Blind plates are generally installed at the locations where separation or isolation is required, such as at the equipment connections, in front of and behind isolation valves, or between two flanges. It is generally recommended to use 8-character blind plates, while plug plates can be used for one-time applications such as pressurization and purging. 2. Locations where blind flanges need to be installed: – Blind flanges should be installed at the connections between equipment and pipes, especially during the initial startup phase when conducting tests on the strength or tightness of the pipes. - For process material pipes that connect outside the boundary zone to inside it, a blind flange is installed at the shut-off valve when the plant is shut down but the pipes are still in operation. - The main pipeline of multi-series installations is divided into several branch pipelines; upon entering each series, blind plates are installed at the isolation valves of these branch pipelines. - During regular maintenance, inspection, or replacement of the device, the associated equipment must be completely isolated, with a blind flange installed at the shut-off valve. - When the pressurization pipeline and the displacement gas pipeline are connected to the equipment, a blind flange is installed at the shut-off valve. - At the low-point drain points of equipment and pipelines, if centralized collection is required, a blind flange should be installed after the isolation valve. - Blind plates or plug valves should be installed behind the valves for exhaust pipes, liquid discharge pipes, and sampling pipes, except for those containing non-hazardous materials. - When constructing the device in phases, blind plates are installed at the isolation valves for the intersecting pipes to facilitate construction. - Blind plates should generally also be installed on the auxiliary pipelines that need to be shut off during normal production. - For applications with other process requirements. 3. The representation of blind flanges on the process diagram (P&ID) is carried out in accordance with the standards specified in \"Graphic Symbols for Piping and Fittings in Piping and Instrumentation Diagrams\" (HG 20559.3-93). 4. Precautions for installing blind plates: – Minimize the use of blind plates as much as possible, provided that the process requirements are met. - The normal open or closed state of the blind plate should be clearly indicated. - The blind plate is installed upstream or downstream of the isolation valve, and its location should be determined based on the isolation efficiency, safety considerations, and process requirements. The above content is based on HGT 20570.23-1995 \"Installation of Blind Flanges\". .