Winding tube knowledge sharing
Thread Content
It can be seen from various specifications that there is no requirement to use flexible tubing between the galvanized wire conduit and the instrument during installation. In terms of practical use, flexible pipes have now been eliminated in most cases. There are two main reasons for this. 1 Flexible pipes are prone to water ingress; once water gets inside them, it is difficult to remove. Therefore, regulations repeatedly emphasize the need for drainage measures when using flexible pipes. 2 The construction is difficult; for flexible pipes, it is hard to verify whether the sealing joint between the explosion-proof cable and the instruments, as well as between the cable itself, is properly sealed during installation. Installation is a matter of integrity; not all construction companies have a strong sense of responsibility. If the sealing is not proper, there is a risk of explosion. If it is an intrinsically safe instrument, there are no explosion-proof requirements for the field instrument; the cable entry point only needs to be waterproof and dustproof, and plastic sealing joints can even be used. Explosion-proof instruments can completely do without flexible tubes; their explosion protection relies entirely on explosion-proof sealing joints, which tightly connect the instrument cables and provide a secure seal. Even when using flexible pipes, explosion protection is achieved through the sealed joints of the explosion-proof cables. Only Article 7.3.4 of SY/T 4129-2014 \"Technical Specifications for the Construction of Automation Instrumentation Projects in Oil and Gas Pipelines\" states that when unarmored cables or wires are installed inside the protective conduit, galvanized pipes should be used throughout the length starting from the instrument enclosure; explosion-proof flexible hoses should be used to protect the connections between the instruments and the junction boxes ； When armored cables are laid inside the protective tube, the bending radius of the protective tube at turns should be greater than 10 times the diameter of the protective tube. 1.0.2 These specifications apply to the construction of instrumentation projects for newly built, renovated (or expanded) oil and gas pipelines. In short, when installing instruments in chemical plants, there is no mandatory requirement to use flexible tubes between the galvanized wire conduits and the instruments. I believe that it is better to not use flexible tubes, as this prevents water from entering the instruments and makes it easier to check whether the sealing joints of the explosion-proof cables are in good condition.
Experts say it’s blast-proof, but what about fire resistance?
Agreed, but I recall that relevant documents from the Emergency Management Bureau require the use of explosion-proof flexible hoses for instruments in tank areas with major hazard sources.
Some experts are complete nonsense. For example, I have equipment here that uses armored cables; however, after coming out of the cable tray, they pass through tubes, but no flexible tubes are used up to the equipment itself. The experts said it is non-compliant. He believes that explosion-proof flexible tubing must be used when threading pipes. According to his explanation, we are using armored cables, but he doesn’t care about that and insists that we make corrections. Expert nonsense!
The flexible tube itself is easier to install due to its flexibility. Currently, at natural gas stations (the West-East Gas Pipeline and the China-Russia pipeline), it has been observed that the outlet connections for all instruments use flexible pipes, elbow boxes, and galvanized pipes. Some design or engineering firms also use installation legends for flexible pipes in their design documents. Everyone shares their opinions to make progress together