It is not mandatory to use, the regulation is "suitable for use". In cases where explosion-proof flexible connecting pipes can be used, it is best to use explosion-proof flexible connecting pipes.

According to Article 7.4.8 of GB 50093-2013 "Code for Construction and Quality Acceptance of Automation Instrumentation Engineering", flexible pipes should be used to connect cable conduits with detection components or field instruments, and waterproof bends should be provided. When connecting with on-site instrument boxes, junction boxes, junction boxes, etc., they should be sealed and firmly fixed.

The article states that in order to prevent dust, water, or other liquids from entering the detection element or field instrument, flexible pipes can be used for connection. Some projects also have cable conduits that are disconnected from the detection element or field instrument, and seals are used when cables enter the detection element or field instrument.

Article 8.4.7 of SH/T3521-2013 "Technical Regulations for Construction of Petrochemical Instrumentation Engineering" states that when connecting protective pipes to local instrument panels, instrument boxes, junction boxes, wiring boxes and other components, sealing measures should be taken and the pipes should be firmly fixed. The protective pipe mouth should be about 250mm lower than the instrument equipment inlet, and flexible pipes should be used to connect with the detection element or local instrument. When explosion-proof flexible connecting pipes are not used for connection, the pipe end should be processed into a horn mouth or equipped with a protective wire cap. When the protective pipe is laid from top to bottom, a drainage tee should be added at the low point. The inlet of instruments and instrument equipment should be sealed with cable sealing joints.

Article 7.3.6 of SH/T3019-2016 "Design Specification for Instrumentation and Piping in Petrochemical Industry": When using explosion-proof flexible connecting pipes to connect protective pipes with detection components or field instruments, the protective pipe mouth should be about 250mm lower than the instrument inlet. When the protective pipe is laid from top to bottom to the instrument, a drainage tee should be added at the end of the pipe. When flexible pipes are not used to connect the protective tube and the instrument, the end of the tube should be equipped with a wire protection cap (protective mouth) or processed into a horn mouth.

HG/T20512-2014 "Design Specification for Instrument Piping and Wiring", Article 8 one Article 13: For the protection of cables at the inlet and outlet of on-site instruments, junction boxes, and local instrument panels (cabinets), the following two methods should be adopted:

(1) Continuous type: The explosion-proof flexible connecting pipe of the cable sealing joint is connected to the galvanized welded steel pipe.

(2) Non continuous: cable sealing joint with cable tray or cable sealing joint with galvanized welded steel pipe.