After the cable of the explosion-proof instrument passes through the steel pipe, it is connected to the instrument using an explosion-proof flexible tube; is an explosion-proof sealing joint still required...
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After the cable of the explosion-proof instrument passes through the steel pipe, it is connected to the instrument using an explosion-proof flexible tube; is it still necessary to use an explosion-proof sealing joint as well? It turns out that the old installations did not have explosion-proof sealing joints from the start, and it is quite troublesome to make corrections now. Since the length of the cables is insufficient, adding explosion-proof sealing joints would require cutting a section of the steel pipe; this could lead to the cables being damaged during installation, as they are buried directly in the cable trenches, making replacement inconvenient as well. Is there anyone with a solution? Thank you!
A flexible tube can be considered an explosion-proof sealing joint… there’s no need to install a separate explosion-proof sealing joint. Cable tray - wire conduit - flexible tube - instruments; this connection is fine.
According to clause 7.3.6 of the specification for the design of instrument piping and wiring, HG/T 20512-2000, a flexible connection tube should be used to link the protective tube with the sensing elements or field instruments. Appropriate explosion-proof sealing measures shall be taken at the cable entrances of explosion-proof field instruments and wiring boxes. How should this sentence be understood? Is installing an explosion-proof sealing joint a requirement specified by the standards? When experts came to inspect the site, they determined that failing to install explosion-proof sealing joints meant we were not in compliance with the standards, which resulted in points being deducted. But I looked for it; it’s mentioned in these design specifications. Are there any other regulations that mention it as well? Thank you!
SH/T 3521-2013 Technical Specifications for the Construction of Petrochemical Instrumentation Projects > 8 Installation of Instrument Circuits > 8.4.7 When connecting the protective tube to components such as local control panels, instrument boxes, junction boxes, and wire ducts, sealing measures shall be taken, and the tube shall be fixed firmly. The outlet of the protective tube should be about 250 mm below the inlet for the instrument equipment. A flexible tube is recommended for connecting it to the sensing elements or local instruments; if a flexible tube is not used, the end of the tube should be shaped like a flare or equipped with a cable guard. When the protective pipe is laid from top to bottom, a drainage tee should be installed at the lowest point. The inlet ports for instruments and instrument equipment should be sealed using cable sealing joints, as shown in Figure 8.4.7. SH/T 3019-2016 Specification for the Design of Instrumentation Piping in Petrochemical Industries > 7 Installation of Cables > 7.3.6 When a flexible pipe is used to connect the protective tube to the sensing elements or field instruments, the opening of the protective tube should be approximately 250 mm below the instrument’s inlet. When the protective tube is laid from top to bottom toward the instrument, a drainage tee should be installed at the end of the tube. When a flexible tube is not used to connect the protective tube to the instrument, the end of the tube should be fitted with a cable guard or shaped into a flared end. HG/T 20512-2014 Code for Design of Instrument Piping and Wiring > 8 Cable Laying > 8.1.13 For the protection of the cables at the entrances and exits of field instruments, junction boxes, and local instrument panels/cabinets, one of the following two methods is recommended: 1 Continuous type: The cable sealing joint flexible tube is connected to the galvanized welded steel pipe. 2 Discontinuous type: cable sealing joint plus cable tray, or cable sealing joint plus galvanized welded steel pipe. GB 50093-2013 Code for Construction and Quality Acceptance of Automation Instrumentation Projects > 7 Installation of Instrumentation Circuits > 7.4.8 Flexible pipes should be used to connect cable conduits to sensing elements or field instruments, and waterproof bends shall be provided. When connecting to field instrument boxes, junction boxes, wiring boxes, etc., it must be sealed and firmly fixed. GB 50093-2013 Code for Construction and Quality Acceptance of Automation Instrumentation Projects > Explanations of Provisions > 7 Installation of Instrument Circuits > 7.4.8 To prevent dust, water, or other liquids from entering the sensing elements or field instruments, flexible pipes can be used for connection; in some projects, cable conduits are used with a disconnected connection to the sensing elements or field instruments, and seals are employed when the cables enter these elements or instruments. From this perspective, national standards do stipulate that seals must be used to connect instruments, but this requirement is rather pointless – if seals are used, then what’s the need for flexible hoses? Just use a direct Golan connector plus a conduit... Given this situation, it is recommended that you either replace the flexible tube by using a sealed flexible tube (which is likely not available), or opt for a gland seal plus bare cable plus an insulation cover, thereby eliminating the need for a flexible tube.
As I understand it, explosion-proof flexible hoses are equivalent to sealing devices... but this is not explicitly stated in the national standards……
Um, let me ask the experts at SEI and CEI to see what they have to say……
There are no additional flexible tubes needed now; a flameproof gland seal can be used directly. Flexible tubes don’t offer much benefit other than for irrigation.
Installation can be done via continuous or discontinuous connections, but in both cases sealed joints are necessary. For discontinuous connections, explosion-proof gland connections are used, while for continuous connections, a Y-shaped explosion-proof isolation seal joint or an explosion-proof seal joint for flexible pipes must be installed at one end of the flexible pipe. All of these measures serve the purpose of providing explosion-proof sealing, which is why sealing devices are essential
In principle, there is no problem with using steel pipes combined with flexible tubes to connect intrinsically safe instruments to them； But if it is an explosion-proof instrument, a sealed joint should be used.
Our institute generally regards flexible hoses as a form of protection at the end of cables, while explosion protection is achieved through sealed gaskets
Firstly, flexible pipes are generally designed to have explosion-proof sealing joints; these sealing joints serve the purpose of providing sealing and explosion protection. What you refer to as an explosion-proof sealing joint is commonly known as an explosion-proof gland or explosion-proof sealing fitting. Generally, cables are not protected mechanically with galvanized pipes; instead, armored cables are used to enter the panel directly through small trunking, with a portion of the cable remaining exposed outside. So I don’t understand what you mean over there.