Classification, structure and installation of explosion proof flexible pipes and how to judge whether to install them or not

Explosion-proof flexible pipe with flame retardant, corrosion resistance, aging resistance and other performance advantages, often used in large quantities in petrochemical and other explosive hazardous places, it can not only effectively prevent the occurrence of explosions and fires, but also protect the safety of equipment and personnel.

I. Classification of explosion-proof flexible tube

1. According to the explosion-proof type, the explosion-proof flexible pipe is usually divided into explosion-proof type and safety-enhancing type, respectively, with explosion-proof equipment and safety-enhancing equipment, as a flexible connection for conduit wiring. Field installation should be matched with the explosion-proof electrical equipment explosion-proof type.
 2. According to the material, performance and use of the scene can be divided into the following two categories:

①Stainless steel, corrosion resistance and aging resistance, mainly installed in the outdoors

②Rubber material, strong corrosion resistance aging resistance in general, mainly installed in the indoor

II. explosion-proof flexible pipe structure requirements

1. Explosion-proof flexible pipe consists of pipe joints and connecting pipes at both ends, and the connecting pipes are composed of inner pipes and sheaths;

2. The external connection thread of the pipe joint of the explosion-proof flexible pipe can be made into metric thread, cylindrical pipe thread or conical pipe thread structure;
3. explosion-proof flexible pipe joints shall be made of rolled metal materials that are not susceptible to corrosion or plating treatment, and shall not be made of light metal materials, with a thread accuracy of not less than 6g/6H, a pitch of not less than 0.75mm and not more than 3mm; the number of engagement buttons is not less than 5 buttons, and the length of the engagement is not less than 8mm;
4. The inner pipe of the explosion-proof flexible pipe shall be made of corrugated metal pipe, metal hose or metal snake skin pipe, and the inner pipe shall be made of stainless steel or electroplated metal material;
5. explosion-proof flexible pipe sheath can be made of metal mesh braided sheath, rubber sheath, plastic sheath and other structures, plastic or rubber sheath thickness of not less than 0.8mm;
6. explosion-proof flexible pipe applicable ambient temperature should be consistent with the provisions of the following table:

   Metal mesh braided sheath flexible tube applicable to the ambient temperature does not limit the

   Rubber sheathed flexible hose applicable to the ambient temperature is generally -20 ~ +60 ° C

   Plastic sheath casting tube applicable to the ambient temperature is generally +5 ~ +40 ° C

Note: The use of high-quality rubber or plastic sheath flexible pipe, in other ambient temperature range, when the test is qualified, can also be appropriate.

Expanding the ambient temperature range in which it can be used.

7. Flame-proof flexible pipes can be made of seamless copper or stainless steel bellows covered with copper, brass or stainless steel wire braid;
8. for the inner diameter of 20mm and below the flameproof flexible pipe can be used in accordance with YB / T 5306 galvanized metal hose, covered with non-combustible or flame-retardant rubber or plastic sheath made;
9. The safety-enhancing flexible pipe can be made of galvanized metal hose in accordance with YB/T 5306, covered with copper, brass or stainless steel braid or non-flammable or flame-retardant rubber or plastic sheath.

III.Installation of explosion-proof flexible pipe

1. Explosion-proof flexible pipe installation application prerequisites

① explosion-proof equipment is equipped with the introduction of the introduction of the device; ② introduction of the device contains a seal; ③ sealing ring size and the size of the outer diameter of the cable (non-armored) to match the size.
 Based on the above premise, explosion-proof flexible pipe in the field of installation and application must pay attention to the following two situations:
 (1) explosion-proof flexible pipe and the introduction of the mouth of the transition between the installation of compression elements
 Application: The non-axial compression length of the sealing ring is limited and is not sufficient to ensure that the explosion-proof flexible tube is pressed against the sealing ring in the introduction device. Installation plan: between the explosion-proof flexible tube and the introduction of the mouth must be installed transition compression element, to achieve the purpose of the first compression of the sealing ring to hold the cable tight, and then connect the explosion-proof flexible tube.
 (2) Explosion-proof flexible pipe and the introduction of direct connection between the port
 Application: non-axial compression of the sealing ring length to ensure that the explosion-proof flexible tube compression introduced into the device within the sealing ring. Installation: Direct connection between the explosion-proof flexible tube and the inlet, using the front connector of the explosion-proof flexible tube to compress the sealing ring and hold the cable tightly.
 

2. Special instructions:

Special attention should be paid to the fact that if the armored cable wiring method is applicable, the armored cable introduction device must be installed at the introduction port of the explosion-proof electrical equipment before connecting the flexible tube.

VI. Application Scenarios of Explosion-proof Flexible Tube

Explosion-proof flexible tubing is part of steel pipe wiring In order to avoid stress damage, explosion-proof flexible tubing should be used with steel pipe wiring and in the following three scenarios.

1. Motor inlet;

2. Where there is difficulty in connecting conduit to electrical equipment;

3. Where conduit passes through expansion joints and settlement joints in buildings.

V. Is it necessary to install the explosion-proof flexible pipe

1. Advantages and disadvantages of explosion-proof flexible pipes

Explosion-proof flexible connecting pipe has the advantages of flame-resistant, corrosion-resistant, water-resistant, aging-resistant, solid structure, etc. In addition, the explosion-proof flexible pipe can protect the cable from being harmed. However, due to the explosion-proof flexible tube in the instrument junction is not sealed, its biggest drawback is the instrument into the water, the instrument into the water is light instrument damage, heavy instrument control failure, resulting in safety accidents. This is the main reason why the explosion-proof flexible tube is not welcomed by the instrument maintenance personnel. 2.
 

2. From the point of view of the specification must be equipped with explosion-proof flexible tube

Mention of explosion-proof flexible pipe specification, only new, modified (expansion) construction of oil and gas pipeline instrumentation engineering instrumentation should be equipped with explosion-proof flexible pipe, and other instrumentation specifications, there is no specification requirements for the instrumentation with explosion-proof flexible pipe, explosion-proof flexible pipe and cable explosion-proof clamping and sealing joints meet the requirements.

3. Choose whether or not to install an explosion-proof flexible pipe according to the specific situation.

① For intrinsically safe circuit instruments, there is no need to dwell on whether or not to equip with explosion-proof flexible pipes. Intrinsically safe instrumentation due to the energy limitations of the safety grid, even if the circuit is short-circuited, the maximum current generally does not exceed 50mA, the energy is not enough to ignite flammable gases, that is to say, there is no point in discussing whether or not to add the explosion-proof flexure tube.
 ② For explosion-proof instrumentation, solenoid valves, combustible and toxic gas alarms, etc., can be used explosion-proof flexible pipe, can also be used explosion-proof cable clamping sealing connector. These two configurations are in line with the specification requirements.
 ③ For some other special requirements, such as “hazardous chemicals major sources of risk tank site safety monitoring equipment setup specifications” 4.2.5 said in the tank area constitutes a major source of risk and oil and gas pipelines, in accordance with the norms of the implementation of the standard operation.
 ④ From the safety point of view, the blanket use of steel pipe wiring can better prevent mechanical damage and can fulfill the requirements of the code across the board.
 ⑤ From the owner’s point of view, explosion-proof flexible pipes can protect cables more effectively, prolong the aging time of the cable sheath, and also cope with inspections.
     In any case, the design should be legally compliant first and reasonable second. When cables are used for power cables, flexible pipes can be dispensed with in plants and installations, but for some harsh environments, such as for the prevention of mechanical injuries and easy aging of the cable sheath, it is more reasonable to use flexible pipes.