Is a drain tee provided for instrument piping in chemical plants?
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This post was last edited by louhoo on 2019-3-27 08:33. During the initial inspections by the work safety supervision agency, it was stated that in areas with explosion hazards (the actual area was classified as Zone II), drain tees are not allowed to be used; such connections must be completely sealed. After checking the relevant standards, I believe the difference arises from the distinct approaches adopted in formulating these two standards. Chemical engineering design mostly follows the \"Code for Design of Instrumentation and Piping in Petrochemical Industries\" (SH/T 3019-2016). The said code states that… Meanwhile, the \"Explosive Environments – Part 15: Design, Selection, and Installation of Electrical Equipment\" (GB/T 3836.15-2017) specifies that, according to the standards for chemical engineering, it is permissible for liquid to enter but it must be removed; whereas the standards for explosive environments require that everything be properly sealed, so as to prevent gases and liquids from flowing inside the protective enclosures. The safety supervision agency still primarily relies on the standards for explosive environments. Are these two specifications contradictory in this regard, or have I misunderstood? I would appreciate guidance from the experts. The original documents of the above two standards are attached; those who need them can download them, and they are all in high-definition format.
My understanding is that if it’s an explosion-proof area, the second option should definitely be used; if it’s not an explosion-proof area, the first option can be used.
Thank you. The regulations in the chemical industry do not make a distinction between explosion-proof and non-explosion-proof environments; therefore, chemical engineering design firms design according to these standards. As a result, the local safety supervision agencies may have experts in electrical systems who also handle instrumentation and control tasks, but they are not very familiar with the regulations related to the chemical industry. Hence, they simply classify such situations as potential safety hazards without further consideration~
Uh... I’m not quite sure. Do you mean that for explosion-proof areas, the first one is the one that can be used? Do we still have to follow the second method? After all, these two methods of installing hoses are contradictory, and only one can be chosen. . .
Now, design institutes all use the first design method, such as SEI
I’ve been working on a project recently and have been struggling with this issue as well. At my previous company, different people who came to inspect the work had different requirements: some wanted it to be airtight, while others wanted proper drainage; as a result, those working on it had to keep making changes
You are indeed right in understanding. It’s just that this is the current situation of our country. Safety inspectors don’t know anything. Amateurs trying to manage experts.
The first specification is the instrumentation design specification, and the second is the electrical design specification. Not to mention different industries, even within the same field there are differences; clearly, the design and construction of instrumentation systems cannot be forced to comply with electrical specifications. Therefore, it is possible to strive to maintain the current design status. It is also possible to ask a design firm to reply on your behalf, which will yield better results.
A drain tee should be installed, and it can be sealed off with explosion-proof putty for security inspections. ;P
Generally, a drain tee can be added, and a sealing plug can be used; it can be unscrewed when draining water
As “cable wiring,” field instrument cables are usually laid in raceways, trays, or steel pipes. However, for the short section of cable located near the outside of the cable inlet in various types of field instruments or junction boxes, there are significant differences in the methods used for its protection and handling across different projects. This section is divided into the following two categories based on the different methods of cable protection: 4.2.1 Continuous type: The cable is fully protected inside steel pipes or flexible tubes, with no exposed parts and thus less susceptible to mechanical damage. There are two implementation methods for this type of installation: “Steel pipe type”: The steel pipes and associated components are directly connected to the instrument (or junction box) itself ； “\"Flexible tube type\": The cable passes through a steel tube and a flexible tube to be connected to the instrument (or junction box) itself. 4.2.2 Discontinuous type: Over a short distance after the cable emerges from the field instrument or junction box, the protective tube is disconnected, and the cable remains exposed with no protection. The aforementioned connection method is used in projects both domestically and internationally. Since effective isolation and sealing are implemented at the cable entry points of the components where dangerous sparks may be generated, it meets the requirements for explosion protection and safety. Considering the current practices in cable installation and the need to align with foreign engineering standards, this catalog recommends four types of connection methods: cable sealing joint + bus duct (discontinuous protection connection), cable sealing joint + steel pipe (discontinuous protection connection), cable sealing joint + steel pipe (continuous protection connection), and cable sealing joint flexible tube + steel pipe (continuous protection connection).