8 Metal Enclosures and Metal Enclosure Components

8.1 Material Composition

The material of the enclosure or enclosure component shall be specified in the documents required in Chapter 24.

Note 1: The documents do not require experimental verification of the chemical composition of the material.

Note 2: Paint or coatings applied to metal enclosures are non-metallic components of the enclosure, and the requirements of GB/T 3836.7.4 "Electrostatic charges on external non-metallic materials" shall apply.

Note 3: Zinc and zinc alloys containing 80% or more zinc tend to deteriorate rapidly (especially in terms of tensile strength), especially in warm and humid air. Zinc is also considered more active than other metals. Some explosion-proof types do not allow the use of zinc for enclosures.

8.2 Class I Equipment

For the material of enclosures manufacturing Class I equipment with EPL Ma or Mb, the total content (mass fraction) shall not exceed:

15% aluminum, magnesium, titanium and zirconium, of which magnesium, titanium and zirconium shall not exceed 7.5%.

The above requirements do not apply to Class I portable measuring equipment, but the equipment shall be marked with the symbol "X" in accordance with the requirements of 29.3e), and special precautions during storage, transportation and use shall be specified in the special operating conditions.

8.3 Class II Equipment

For the material of enclosures manufacturing Class II equipment for different equipment protection levels, the total content (mass fraction) shall not exceed:

For EPL Ga: 10% aluminum, magnesium, titanium and zirconium, of which magnesium, titanium and zirconium shall not exceed 7.5%;

For EPL Gb: 7.5% magnesium, titanium and zirconium;

For EPL Gc: No other requirements except that fans, fan shrouds and vent baffles shall comply with the requirements for EPL Gb.

If the material composition limits for EPL Ga or Gb equipment specified above are exceeded, the equipment shall be marked with "X" in accordance with the provisions of 29.3e), and the special operating conditions shall contain sufficient information to ensure that the user can determine whether the equipment is suitable for use under specific conditions, for example, preventing ignition risks caused by impact or friction.

8.4 Class III Equipment

For the material of enclosures manufacturing Class III equipment for different equipment protection levels, the total content (mass fraction) shall not exceed:

For EPL Da: 7.5% magnesium, titanium and zirconium;

For EPL Db: 7.5% magnesium, titanium and zirconium;

For EPL Dc: No other requirements except that fans, fan shrouds and vent baffles shall comply with the requirements for EPL Db.

If the material composition limits for EPL Da or Db equipment specified above are exceeded, the equipment shall be marked with "X" in accordance with the provisions of 29.3e), and the special operating conditions shall contain sufficient information to ensure that the user can determine whether the equipment is suitable for use under specific conditions, for example, preventing ignition risks caused by impact or friction.

8.5 Copper Alloys

If intended for use in acetylene-containing environments, equipment enclosures and Ex component enclosures used for external installation, if made of copper or copper alloys, shall comply with the following requirements:

Be coated with zinc, nickel or other coatings; or

The maximum copper content in the alloy shall not exceed 65%.

Cable glands, seals, threaded pipe joints and insulating sleeves specified in Annex A are not considered as enclosure surfaces requiring coating or copper content limits.

Note: The restriction on the use of copper in acetylene environments is due to the possible formation of acetylides on the outer surface that can be ignited by friction or impact.

From the provisions in the standard, we can summarize the following:

1. For Class I equipment with EPL Ma and EPL Mb, there are clear requirements on the aluminum content of the metal material used for the enclosure. In addition, equipment with enclosures containing aluminum shall be marked with the symbol "X" in accordance with the requirements of 29.3e), and special precautions during storage, transportation and use shall be specified in the special operating conditions.

2. For Class II equipment with EPL Ga, there are clear requirements on the aluminum content of the metal material used for the enclosure. Generally, we do not recommend the use of aluminum alloy enclosures. If the customer's product adopts an aluminum alloy enclosure, a material report of the metal enclosure must be provided to specify the aluminum content. If the aluminum content exceeds the specified limit, there are usually two solutions:

(1) The equipment shall be marked with the symbol "X" in accordance with the requirements of 29.3e), and the special operating conditions shall contain sufficient information to ensure that the user can determine whether the equipment is suitable for use under specific conditions, for example, preventing ignition risks caused by impact or friction.

(2) Reduce the equipment protection level, for example, change the explosion-proof marking from Ex ia IIC T4 Ga to Ex ia IIC T4 Gb.

3. For Class II equipment with EPL Gc and Class III equipment with EPL Dc, material requirements are only imposed on certain metal components of the enclosure, and no requirements are imposed on others.

4. Requirements for the use of copper or copper alloys in acetylene-containing environments. Both GB/T 3836.1-2021 and GB/T 3836.2-2021 have put forward specific requirements for metal enclosures and metal components of enclosures for equipment used in acetylene environments. However, according to the principle that special standards take precedence over general standards, the copper content in the alloy shall not exceed 60%.

Reproduction and reprinting on any platform are prohibited!