In many scenarios of industrial production, such as petroleum, chemical, coal mining and other industries, the production, transportation and storage links are often accompanied by flammable and explosive substances, which puts forward explosion-proof requirements for the instrument devices used on site. Explosion-proof instruments can work normally in flammable and explosive environments to avoid accidents caused by electrical sparks or high temperatures, thereby ensuring production safety. In order to ensure the effectiveness and safety of explosion-proof instruments, countries have formulated corresponding standards. my country’s current national explosion-proof standard is GB/T 3836-2021. Instruments that meet this standard will obtain an “Explosion-proof Certificate” and be marked with explosion-proof signs and explosion-proof certificate numbers. At the same time, the standard also has clear provisions for the installation, use and maintenance of instruments.
Faced with many explosion-proof instruments on the market, how to judge whether they are really explosion-proof? Taking fixed gas detectors as an example, the following methods can be used: Check product identification and certificates
- **Explosion-proof mark**: There is generally an explosion-proof mark in a conspicuous position on the shell of the explosion-proof instrument, such as Ex d IIB T4 Gb, or Ex db IIB T4 Gb (in accordance with GB/T3836.1-2021 standard). Among them, “Ex” stands for explosion-proof, “d” or “db” means flameproof type, “IIB” is the gas group, “T4” is the temperature group, and “Gb” is the equipment protection level. We can check whether the mark is standardized and complete by comparing it with the relevant standards, and then combine the explosion-proof mark and the actual structure of the product to make a preliminary judgment on the authenticity of the instrument explosion-proof.
- **Explosion-proof certificate**: Regular explosion-proof instruments have explosion-proof certificates. We can log in to the official website of the issuing agency, enter the certificate number, and check whether the certificate information is consistent with the information certified by the official website, and at the same time confirm whether the product’s factory date is within the validity period of the certificate.
- **Other certification marks**: In addition to the explosion-proof certificate, some instruments may also have other relevant certifications. For example, explosion-proof products in the CCC catalog must have the CCC certificate of the product.
Check the appearance and structure of the product
By observing the appearance of the instrument, you can also preliminarily judge whether it meets the explosion-proof requirements:
- **Shell material and process**: Taking the explosion-proof instrument as an example, its shell is usually made of high-strength, flame-retardant, and impact-resistant materials, such as aluminum alloy, stainless steel, castings, etc. We need to check whether the shell has cracks, sand holes, pores and other defects, whether the surface is smooth, and whether the connection parts are tight. Instruments with fine craftsmanship and flawless are more likely to be real explosion-proof products, but they still need to be comprehensively judged in combination with the explosion-proof mark in the explosion-proof certificate.
- **Sealing structure**: Good sealing is the key to explosion-proof. Check whether the instrument’s line inlet, junction box, observation window and other parts have reliable sealing measures, such as whether there are sealing rings, sealing pads, or explosion-proof glands, etc. At the same time, observe whether the installation is in place and whether the seal has aging, deformation and other problems that affect the sealing performance.
- **Grounding device**: Explosion-proof instruments with metal shells generally have perfect grounding devices. Check whether the shell of the instrument has obvious grounding marks and grounding bolts, whether the grounding bolts are firm, whether the grounding wire meets the standard requirements, and whether the grounding is good.
Carry out technical inspection
The core technology of explosion-proof instruments is reflected in the design and manufacture of their shells. Flameproof instruments are one of the common explosion-proof instruments. Their shells must be able to withstand the explosion pressure of the internal explosive gas mixture and prevent the internal explosion from spreading to the explosive mixture around the shell. Therefore, when inspecting the instrument, you can identify whether the instrument meets the explosion-proof requirements based on the basic definition of flameproof from the shell size and structure.
According to the requirements of the industrial instrument flameproof standard, the basic definition of flameproof is as follows:
(1) Gap explosion-proof technology, relying on gap and meshing length to achieve cooling and flameout effects.
(2) Allowing dangerous gases to enter the flameproof shell, which may cause explosions inside the shell. However, the shell must have sufficient strength; and each shell joint surface must have a sufficiently long meshing length and a sufficiently small gap to ensure that the internal explosion will not pass through the flameproof joint surface and cause an explosion in the external environment.
(3) An electrical equipment housing that can withstand the explosion pressure of an explosive gas mixture inside and prevent the internal explosion from spreading to the explosive mixture around the housing.
Understand the product source and manufacturer reputation
- **Purchase channel**: Purchasing instruments through formal and qualified channels, such as the manufacturer’s official website, authorized dealers, etc., can reduce the risk of buying counterfeit and inferior products. Avoid purchasing from informal channels or unknown sources to prevent buying counterfeit or non-explosion-proof instruments.
- **Manufacturer qualifications and reputation**: Understand the manufacturer’s qualifications and reputation, check whether the manufacturer has the qualifications to produce explosion-proof instruments, whether it has a good reputation in the industry, and whether it has a bad record or violations. The quality of instruments produced by manufacturers with strength and reputation is more guaranteed.
Conduct actual tests (if conditions permit)
- **Gas environment test**: Under the premise of complying with safety regulations, place the instrument in an environment containing a certain concentration of explosive gas for actual testing to determine whether its explosion-proof performance is good. However, this method is dangerous and belongs to a destructive test, which requires professionals to conduct in professional places.
- **Electrical performance test**: Use professional instruments to test the electrical parameters of the instrument, such as insulation resistance, ground resistance, etc., to see if they meet the corresponding requirements of the explosion-proof standards. If the electrical performance does not meet the standards, it may affect the explosion-proof performance. Generally speaking, through the above methods, it is easy to identify whether the industrial instrument meets the explosion-proof requirements.
Daily maintenance methods for explosion-proof instruments
- Explosion-proof instruments should be inspected and maintained regularly. During the inspection, check the appearance, environment (temperature, humidity, dust, corrosion), vibration, and whether the installation is firm.
- When maintaining explosion-proof instruments under power, the junction box and observation window must not be opened. When the cover needs to be opened for maintenance, the power must be cut off first. It is never allowed to open the cover for maintenance with power on.
- Sparks must not be generated during maintenance. The test instrument used should be explosion-proof or intrinsically safe to avoid the test instrument causing induced sparks or directing excessive voltage to inappropriate parts.
- When disassembling, attention should be paid to protecting the flameproof threads and flameproof planes, and no damage or scratches should be made, especially no longitudinal scratches are allowed on the flameproof planes.
- When disassembling rubber sealing elements, sharp instruments should not be used to pry or smash them, and no longitudinal scratches should be made on their sealing surfaces.
- When assembling, the assembly sequence should be followed, and no anti-loosening parts or fasteners should be missed.
- Rusted and damaged components should be replaced in time, and aging, damaged and non-sealing rubber sealing components should also be replaced in time.
- After regular maintenance of the instrument, it must be confirmed that the explosion-proof performance has been restored before it can be put back into use.
Installing explosion-proof instruments in explosive environments has important significance and positive effects, such as ensuring the safety of personnel, protecting production equipment and facilities, complying with regulatory requirements and industry standards, enhancing corporate image and brand value, and promoting technological innovation and development. Therefore, users should master the relevant knowledge and judgment methods of explosion-proof to ensure the safety and reliability of the instrument.
