In the crane industry, the explosion-proof grade, to put it simply, is to see whether the equipment can work safely in those flammable and explosive environments. Just think about it. In places like chemical workshops or oil and gas depots, there might be flammable gases, vapors or dust floating in the air. If a crane starts running and sparks fly or the temperature gets too high, the consequences could be very serious. Therefore, the explosion-proof grade is to set a "safety standard" for these devices to see if they can prevent the explosion risks they may cause.
To understand the explosion-proof grade, one must first grasp these core matters
The explosion-proof grade cannot be clearly stated in one sentence. It needs to be comprehensively evaluated in combination with the degree of environmental hazard, the explosion-proof technology used by the equipment, and the maximum temperature it can withstand.
First, look at how dangerous the working environment is
The explosion risks vary from place to place and need to be clearly distinguished first. According to domestic and international standards (such as IEC 60079, GB 3836), they can be roughly classified into the following categories:
Gas or vapor environment
In underground coal mines, methane is the main component, which is classified as Class I. Other places, such as chemical plants, may have propane, hydrogen and the like, which are classified as Class II. In Class II, further subdivision is needed. According to the degree to which gases are easily ignited, they are classified into IIA, IIB, and IIC. IIC is the most dangerous, such as hydrogen, which can catch fire at the slightest provocation.
There are also certain considerations regarding the area:
- Zone 0 refers to places where explosive gases are present throughout the year or at all times.
- Zone 1 may occur occasionally;
- Zone 2 is very rare. Even if it exists, it disappears very quickly.
Dust environment
Places like flour mills and aluminium powder workshops, where there is a lot of combustible dust, are classified as Class III. Regional division is similar to the gas environment:
- In Zone 20, there is always dust floating around;
- In Zone 21, it is occasional;
- In Zone 22, it is rarely seen.
2. What explosion-proof measures were used for the equipment
For cranes to be explosion-proof, specific technical measures must be taken. The common ones are as follows:
Flameproof type (d)
In simple terms, it's about adding a "sturdy shell" to the electrified components. Even if the shell really explosively bursts inside, it can withstand the pressure and prevent the flames and hot air from escaping into the dangerous environment outside. For instance, the motors and control boxes of cranes often use this type.
Increased safety type (e)
This approach reduces risks from the source. For instance, by improving the insulation of the circuit and allowing the current to travel further away, it is less likely to generate sparks or arcs during normal operation, and the temperature will not be too high. For explosion-proof junction boxes, this method is often used.
Intrinsically safe type (i)
The main issue is that the energy, voltage and current in the control circuit are all limited very low. Whether it is normal operation or a minor malfunction, the sparks or heat generated are not enough to ignite those flammable and explosive substances. This is commonly used for weak current components such as control circuits and sensors.
Positive pressure type (p)
Pass some clean air or nitrogen into the equipment casing to make the pressure inside higher than that outside. In this way, explosive gases from outside cannot enter. This type may be used in large control cabinets and control rooms of cranes.
Encapsulation type (m)
Seal the electrified small components with materials like epoxy resin to completely isolate them from the dangerous environment outside, such as some small explosion-proof sensors.
3. The temperature should not be too high; otherwise, accidents are likely to occur
When the equipment is in operation, if the surface temperature is too high, even if there is no spark, it may ignite the flammable and explosive substances around. So there is a term called "temperature group". For gas environments T1 to T6, the corresponding maximum allowable temperatures are different:
T1 does not exceed 450℃, T2 does not exceed 300℃, T3 does not exceed 200℃, T4 does not exceed 135℃, T5 does not exceed 100℃, and T6 is the strictest, not exceeding 85℃. For instance, if there is acetylene in the environment, which is highly flammable, then the temperature class of the equipment must be T6.
4. To what extent can the equipment be protected (EPL)
This refers to whether the equipment can work in different hazardous areas.
- In a gas environment, Ga can be used for Zone 0, Gb for Zone 1, and Gc for Zone 2.
- In a dusty environment, Da is used for Zone 20, Db for Zone 21, and Dc for Zone 22.
For instance, the flameproof type "d" can generally reach the Gb level, and there will be no problem when used in Zone 1.
II. How to Determine the Explosion-proof grade? There are certain considerations when marking.
The explosion-proof components or the entire machine on the crane will have a label, such as "Ex d IIB T3 Gb", where each letter and number has a meaning:
- "Ex" is the symbol of explosion-proof.
- "d" indicates that it is flameproof type.
- "IIB" indicates that it is applicable to Class II, Grade B gas environments, such as ethylene and propylene.
- "T3" indicates that the maximum surface temperature does not exceed 200℃.
- "Gb" means it can be used in Zone 1.
For example, the label "Ex tD A21 IP65 T80℃ Db" in a dust environment means: "tD" is a dust explosion-proof enclosure protection type, suitable for non-conductive dust areas in Zone 21. It has a protection level of IP65 (dust-proof and water-proof), with a maximum surface temperature of 80℃, and can be used in Zone 21 areas.
Third, explosion-proofing of cranes is not something that can be done casually
Cranes are large equipment and need to be moved. Explosion-proof design must take into account all aspects:
- The power system, such as the motor, must be of flameproof or increased safety type, the cables must be flame-retardant, and the joints must also be explosion-proof.
- For control systems such as buttons and limit switches, either intrinsically safe types or flameproof types should be used.
- The transmission system and hydraulic components must avoid generating sparks due to friction. The gearbox must be well sealed to prevent dust from entering.
- For metal structures, copper alloys may be used in some areas to prevent sparks from occurring upon collision.
Moreover, the entire machine must be certified for explosion-proof by authoritative institutions, such as ATEX and IECEx. It's not just about putting together a few explosion-proof components.
In general, the explosion-proof grade is the "safety certificate" for cranes in hazardous environments. It should be comprehensively judged based on the specific degree of danger of the environment, the explosion-proof technology used by the equipment, and the maximum temperature it can withstand. To be in this line of work, one must understand these things clearly so that they can have a clear idea when choosing, installing and maintaining equipment. It's not the case that the higher the grade, the better; it must be suitable for the actual working conditions.If you have any related needs, please feel free to contact us at any time. CATET will provide you with professional consultation and support.
