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Influence of corrosive environment on explosion-proof light and electrical equipment

CESP Ex Wiki Thursday, 09 June 2022 07:29

 Tab: explosion proof electrical equipment, anti-corrosive lighting, marine lighting, corrosion resistant Lighting, influence of corrosive environment


The manufacture of any electrical equipment is inseparable from the materials and the use of any electrical equipment is also inseparable from the environment. Under the action of the surrounding environment, the performance of materials will decline, the state will change, and it will be damaged and deteriorated. This is corrosion. The corrosion behavior of materials is closely related to environmental conditions. Where there is a considerable concentration of chemically corrosive gases or vapors, especially when condensation occurs due to moisture, various forms of corrosion are provided for the occurrence and development of environmental conditions to accelerate materials (especially Corrosion of metal materials) leads to performance degradation or early failure of electrical equipment or components.

Part 1. Types of corrosion

In terms of corrosion, according to the corrosive environment, it can be divided into atmospheric corrosion, water corrosion, soil corrosion and chemical medium corrosion.

In general, atmospheric corrosion can also be classified into three categories: atmospheric industrial atmosphere, marine atmosphere, and rural atmosphere; the main influencing factors are humidity, industrial pollution, and salt content.

Water corrosion is mostly water that exists in nature, such as seawater, river water, rainwater, groundwater, etc. Most of these waters are near-neutral media, and the depolarizers in the corrosion process are mainly dissolved oxygen, some polluted water. There may be hydrogen depolarization.

Soil corrosion is generally electrochemical corrosion, and its main influencing factors are moisture, pH value, salt content, oxygen content, water permeability and air permeability, etc., as well as stray current and bacterial activity. Generally, soil corrosion resistivity is commonly used. As an indicator of corrosiveness, the smaller the resistivity, the greater the corrosiveness.

Chemical medium corrosion includes acid, alkali, salt, oxidant, non-electrolyte and melt and other corrosive media. Due to the wide variety and complex conditions, this type of corrosion has become the most complex and difficult to control corrosion problem.

Here, it is mainly aimed at different types (mainly related to flameproof type, increased safety type), different flameproof structures (plane type, stop type, cylindrical type, threaded type), different materials (stainless steel, carbon steel, aluminum, copper And plastic, rubber, coating, etc.) explosion-proof electrical products in the marine salt spray and sulfur dioxide corrosion environment artificial simulation accelerated test to obtain the material corrosion resistance and corrosion environment on the characteristics of explosion-proof structure damage and the impact on electrical explosion-proof safety performance .

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Part 2 Analysis of material corrosion characteristics

In order to ensure the reliable and long-term operation of explosion-proof electrical equipment, it is very important to closely combine the work of reasonable material selection, correct design, careful manufacture and good maintenance. Reasonable selection of materials is the first and foremost part, and environmental factors must be considered when selecting materials. We know that no material is omnipotent, and their applications are conditional. The so-called corrosion resistance is also relative, so we must look at the performance of each material in two. Material selection should be based on specific analysis of the corrosive environment. In order to facilitate the analysis, we selected the most representative (marine atmosphere) salt spray environment and (industrial atmosphere) sulfur dioxide corrosion environment as the simulated environmental conditions for material corrosion characteristics analysis, and analyzed its corrosion characteristics through material corrosion tests. Influence of explosion-proof performance of equipment.

The materials used in explosion-proof electrical equipment usually involve two categories, namely metal materials and non-metal materials. Commonly used metal materials include carbon steel and cast iron, stainless steel, aluminum and aluminum alloys, copper and copper alloys, etc.; non-metallic materials (only organic materials are considered here) There are plastic, rubber, glass fiber reinforced plastic, coating, etc. The corrosion mechanisms of metallic materials and non-metallic materials are different, and the corrosion characterization is also different. The corrosion of metal materials is generally electrochemical corrosion and is easily eroded by chemically corrosive media such as acids, alkalis, and salts; the corrosion of non-metallic materials is purely chemical or physical. ) and radiation to cause material swelling, degradation, deterioration, aging and other damage. The common corrosion forms of metallic materials are mostly manifested by surface features such as uniform corrosion, galvanic corrosion, crevice corrosion and pitting corrosion; non-metallic materials are corroded by changes in physical and mechanical properties (such as strength reduction, softening or hardening, etc.) or appearance. Damage (such as surface blistering, roughening or discoloration, etc.). Understanding the corrosion characteristics and corrosion resistance of materials under different environmental conditions can truly make the best use of materials.

Material _1: Stainless steel

Three grades of stainless steel, 321, 302 and 316L, were selected for the corrosion test. Although their corrosion in the humid SO2 and salt spray environment is electrochemical corrosion, the corrosion form in the humid SO2 environment is mainly uniform corrosion, while The form of corrosion in the salt spray environment is mainly localized corrosion. For example, the explosion-proof junction box made of 321 stainless steel has uniform corrosion on the surface of the sample after the SO2 corrosion test, but basically no corrosion on the surface of the sample after the salt spray test. Corrosion patterns in corrosive media are different.

Influence of SO2 corrosive environment on stainless steel

Different grades of stainless steel have different corrosion resistance in the same environment. Comparing 316L, 321 and 302 grades of stainless steel from the surface corrosion of the samples, exposed to SO2 gas corrosion environment, the corrosion resistance of 316L is obviously better than that of 321 and 302, while the surfaces of 321 and 302 samples show obvious corrosion. This means that they are not resistant to moisture SO2 corrosion.

 The same grade of stainless steel has different corrosion resistance due to different protective conditions. For example, the shell of the explosion-proof anti-corrosion lamp with the grade of 321 has different corrosion conditions on the inner and outer surfaces due to the direct exposure and the protection conditions of the rubber sealing ring. After the corrosion test, the inner surface of the lamp shell is bright as new, indicating that The rubber sealing ring between the lamp body and the lampshade effectively blocks the immersion of SO2 corrosive gas, while the directly exposed outer surface of the lamp has rust in pieces.

 Under the same environmental conditions, the same grade of stainless steel has different corrosion resistance due to different surface conditions. 316L is a stainless steel material with excellent corrosion resistance, but for example, the explosion-proof control button with the same grade of 316L and the F027 sample have large corrosion differences due to different surface conditions. The surface of the explosion-proof control button sample has a silver-white coating. The coating is thin and the surface state of the sample is not uniform due to the existence of local peeling defects, thereby promoting the occurrence and development of corrosion. Stainless steel generally has good corrosion resistance, and its surface is not suitable for coating when used as a structural material.

Influence of salt spray corrosion environment on stainless steel

Stainless steel is originally a material with good corrosion resistance, but in the salt spray environment, the passivation film on the surface of the stainless steel tends to be destroyed due to the presence of a large amount of Cl-, and the destroyed passivation film in the salt spray environment The ability to repair is reduced, which is the root cause of localized corrosion of stainless steel in the salt spray environment. The common local corrosion forms of stainless steel in salt spray environment include galvanic corrosion, crevice corrosion and pitting corrosion.

 In the salt spray corrosion environment, the surface of the stainless steel sample basically did not undergo large-scale uniform corrosion, but the corrosion rust formed along the bolts was clearly visible, and the corrosion of all fastening bolts, washers and external grounding was relatively serious. Differences between the material of the bolts, washers, and external grounding and the material of the sample. In a corrosive environment, the contact of dissimilar metals with different potentials will generate a potential difference to form a galvanic couple, thereby accelerating the corrosion of the negative potential metal (anode), that is, galvanic corrosion. Therefore, the fasteners and grounding of the stainless steel shell should be made of the same material to avoid the occurrence of galvanic corrosion. In the design of explosion-proof electrical structure, the contact of dissimilar metals should be avoided as much as possible to cause galvanic corrosion. If it must be used, insulating pads (such as rubber and plastic) should be used to separate dissimilar metals. In addition, for explosion-proof electrical equipment made of stainless steel, the gap between the nameplate and the surface of the shell and the gap between the plane explosion-proof joints create conditions for crevice corrosion. Generally, crevice corrosion is most likely to occur in environments containing Cl-. The oxygen-deficient area is in an occluded state. With the occurrence and development of corrosion, the Cl- concentration in the crack increases, the pH value decreases, and the corrosion is accelerated. Although the crevice is the main design defect that causes corrosion, the crevice between the flameproof joint surfaces is unavoidable in the design, and grease with corrosion inhibitor can be applied to prevent crevice corrosion.

Material_2: carbon steel

Both carbon steel and cast iron are iron-carbon alloys, which are inexpensive and have good mechanical and technological properties, especially carbon steel, which is widely used in structural materials for explosion-proof electrical products. In terms of corrosion resistance, its chemical stability is low. In practical applications, corrosion-resistant metal coatings or anti-corrosion measures such as paint protection are used to improve its corrosion resistance. The corrosion test is made of Q235A carbon steel.

Q235A is ordinary carbon steel, and its surface should be coated with a protective coating when used in a corrosive environment. After the SO2 corrosion test and the salt spray corrosion test, the surface coating of the sample is basically intact, but the surface corrosion of the nameplate, fastening bolts and washers is not well-coated or not protected. The plane or port-type flameproof joint of flameproof explosion-proof electrical equipment is bounded by the "O-type" rubber sealing ring. The outer part is corroded, and the inner part is not corroded. In addition, the flameproof joint after salt spray corrosion The surface corrosion is relatively light, while the corrosion of the flameproof joint surface after SO2 corrosion is more serious, which shows that the Q235A carbon steel has better resistance to salt spray corrosion than SO2 corrosion resistance.

Material_3: Aluminum and aluminum alloys

The industrial application of aluminum alloy is second only to steel materials, and it is one of the most commonly used structural materials for the manufacture of explosion-proof electrical equipment. This is not only because of its light weight and low price, but also because of its surface The alumina protective film becomes a good protective barrier layer. The standard potential of aluminum is very negative, and it is a thermodynamically active metal. If it is used in a chemically corrosive environment, it is definitely not corrosion-resistant. Therefore, when using aluminum explosion-proof electrical equipment in a chemically corrosive environment, the surface must be designed with an anti-corrosion layer. For the corrosion test, aluminum materials with grades ZL102 and YL104 were selected.

The corrosion resistance of aluminum depends to a large extent on the surrounding environment and the stability of the surface oxide film in the medium. Moist SO2 can accelerate the corrosion of aluminum, but compared with Fe and Cu under the same conditions, aluminum is still corrosion resistant. The corrosion resistance of aluminum electrical equipment in SO2 corrosive environment mainly depends on the properties of its surface protective coating. After the SO2 gas corrosion test, the surface coating of the sample did not corrode significantly, and the underlying metal aluminum did not corrode, indicating that the coating Played the due protective effect.

In the marine salt spray environment, aluminum is not resistant to corrosion in the salt spray environment containing Cl- because Cl- can destroy its passivation film and is prone to pitting corrosion. The radius of Cl- is small, and its ability to penetrate and diffuse into the interior through the micropores of the coating is relatively strong. At the same time, Cl- is extremely corrosive to metal aluminum. Therefore, after corroding the surface coating, it continues to corrode the base metal. The product is loose and expands in volume, which further promotes cracking, peeling and peeling of the surface coating. After salt spray test, almost all aluminum explosion-proof electrical equipment not only has quality defects such as serious bubbling, warping, peeling, and falling off on the outer surface coating/plating, but also the bottom metal aluminum is also severely corroded. The damage starts from the corners, which fully illustrates the corner effect of the coating, that is, the corners are the weakest and most prone to quality defects of the coating.

Metal aluminum is very sensitive to chloride ions. After corrosion, a layer of white powdery corrosion products is formed on the surface, which has a great impact on the threaded structure. The threads of the aluminum alloys cannot be opened due to severe corrosion, and the fasteners (such as bolts, nuts) and threaded parts of all aluminum samples in the salt spray environment are blocked by corrosion products, which brings great inconvenience to the disassembly of all threaded structures. Due to the presence of a large amount of Cl- in the salt spray environment, Al is severely corroded, so aluminum explosion-proof electrical equipment is not suitable for use in the salt spray environment.

Material_4: Copper and Copper Alloys

Under atmospheric conditions, copper is relatively stable; in humid SO2, the corrosion of copper is intensified. At this time, a film of CuSO4 3Cu(OH)2 alkaline copper sulfate is formed on the surface of copper. This film has no Protective effect; in the marine atmosphere, in addition to the formation of alkaline copper sulfate CuSO4 3Cu(OH)2 on the surface of copper, there is also alkaline copper chloride CuCl2 3Cu(OH)2. Widely used in practice are copper alloys—brass, bronze, and especially bronze, often used as corrosion-resistant structural materials. For the corrosion test, ordinary brass H59 was selected, and the test showed that it is not resistant to corrosion by salt spray and humid SO2 medium. The material of the explosion-proof junction box is H59. After the corrosion test, the surface coating of the junction box does not change significantly, but the surface of the copper nameplate is also corroded even after the coating treatment. In the salt spray environment, it corrodes and turns white; the junction box flameproof joint surface shows obvious corrosion whether in the SO2 environment or in the salt spray environment, and the corrosion occurs outside the "O-type" rubber sealing ring. The plane part, while the cylindrical part inside the "O-type" rubber sealing ring has no corrosion, which means that the "O-type" rubber sealing ring blocks the channel for the inward diffusion of corrosive gas and plays a protective role. In addition, the surface of the copper sealing stuffing box of the explosion-proof junction box has not been subjected to any protective treatment, and is directly exposed to the corrosive environment. In the SO2 environment, the corrosion is black, while in the salt spray environment, patina corrosion products appear. From the above analysis, it is not difficult to see that copper and copper alloys should not be directly exposed to corrosive environments, that is to say, copper explosion-proof electrical appliances should be surface protected when used in corrosive environments, and their corrosion resistance depends on the properties of the surface coating and paint quality.

Material_5: Plastic

Plastic is a type of polymer material that is mainly composed of resin, and can be plasticized and formed during processing with appropriate additives. Therefore, it can also be said that plastic is a polymer product dominated by resin. Plastic materials are widely used in the manufacture of explosion-proof electrical equipment due to their excellent processing properties, corrosion resistance and electrical insulation properties. For electrical insulating materials, their dielectric properties, heat resistance and flame retardancy must exceed the specified index by an appropriate range to increase their safety factor to prevent local heating or breakdown caused by excessive voltage and current, resulting in fire, explosion accident. On the other hand, plastics have good electrical insulation properties and are prone to electrostatic accumulation. Measures should be taken to ensure their safety when used in flammable and explosive environments.

 The test selected several plastic materials commonly used in explosion-proof electrical equipment, such as polyhexamethylene adipamide (polyamide-66), polyvinyl chloride plastic (PVC), acrylonitrile-butadiene-styrene copolymer (ABS engineering Plastics), polycarbonate plastics (PC), unsaturated polyester sheet molding compounds (SMC), unsaturated polyester bulk molding compounds (DMC), etc., which show better performance in SO2 and salt spray corrosion environments Therefore, under the premise of meeting the technical requirements of explosion-proof, plastic materials can be used as structural materials for explosion-proof electrical equipment in corrosive environments.

 After the corrosion test, the plastic shell of the sample is basically free of corrosion, but all the metal parts (fasteners, nameplates, etc.) in the sample show obvious corrosion; Corrosion of metal parts) indicates that corrosive media has entered the interior, so the corrosion of internal components depends on the protection performance of the sample. In addition, some samples of unsaturated polyester molding compounds (SMC, DMC) have discoloration and roughening on the surface after SO2 corrosion test, but there is no change after salt spray corrosion test, which shows that SMC and DMC materials are resistant to salt spray. The performance is better than that of SO2 corrosion resistance.

 Although plastic materials have many advantages and good comprehensive performance, they often cannot or should not be used under certain conditions. Plastics cannot be used when the material strength is particularly high. The use temperature range of plastic materials is narrow, and plastics should not be used when the use temperature is too high or too low. This is because plastic is a viscoelastic material that is extremely sensitive to temperature changes. Generally, the mechanical properties, electrical properties and corrosion resistance of plastic materials decrease with the increase of temperature, and when the temperature is too low, the plastic material will become hard, brittle, easy to crack, and even lose its performance. In addition to ambient temperature, humidity and medium conditions, the selection of plastic materials should also consider environmental factors such as light, oxygen, and radiation. Under the environment of light, oxygen and radiation, plastic products will cause plastic degradation reaction (ie aging), resulting in the decline of the performance of plastic products, thus greatly shortening their service life. Therefore, explosion-proof electrical equipment made of plastic materials should not be exposed to outdoor use for a long time. 

Material_6: "Coating, plating" used for anti-corrosion

The coating generally refers to the non-metallic coating (including organic coatings and inorganic coatings) covering the metal surface; and the coating refers to the metal covering such as electroplating, hot dip plating, and electroless plating on the metal surface. That is, the metal/alloy or coating with strong corrosion resistance is used to cover the metal with weak corrosion resistance to achieve the purpose of anti-corrosion. Coating and plating combine the excellent properties of both the protective layer and the protected layer, such as the corrosion resistance, wear resistance and oxidation resistance of the protective layer, and the strength and stiffness of the protected layer. Compared with the non-metallic protective layer, the metal protective layer has the advantages of high strength and good heat resistance, and the non-metallic protective layer has the advantages of convenient construction and good corrosion resistance. The coatings and coatings on the metal surface are generally porous films. Although they cannot completely isolate the metal from the corrosive medium, the existence of the coating and the coating can increase the diffusion resistance and solution resistance of the corrosive medium through the pores, so that the corrosion current can be reduced. down thereby slowing the corrosion of the underlying metal.

 The coating and plating on the surface of explosion-proof electrical products is an important protection method used to isolate the base material and the surrounding environment. In the design of coating and coating, materials with good corrosion resistance should be selected according to environmental conditions. At the same time, the coating quality of coating and coating is also directly related to its corrosion resistance and service life. Only those well-coated and coated surfaces can play a role. Due to the protective effect, coatings and coatings with defects such as cracks, mechanical scratches, and local shedding not only have no protective effect, but also accelerate corrosion. In addition, the service life of the coating and plating layer is related to the strong and weak corrosiveness of the environmental medium in the installation site of explosion-proof electrical products. During the service life of explosion-proof electrical equipment, recoating protection can be planned according to the surrounding environmental medium conditions to prolong the explosion-proof electrical equipment. service life.

Material_7: Rubber

Rubber is a highly elastic material that can be deformed under the action of external force and can be restored after the external force is removed. Therefore, it is a main sealing structure material. The essence of the rubber seal is to seal the gap between the two contact surfaces by plugging the rubber, that is, the contact surface seal. Rubber is usually used as a seal in explosion-proof electrical equipment. If the seal is permanently deformed under the action of external force, the sealing effect is not good or the sealing performance is lost. Therefore, the permanent deformation of the seal material should be small, the elasticity should be high, the resilience should be strong, and it should have appropriate hardness; the rubber material has certain When the temperature is higher than the limit temperature, the elasticity will be lost due to aging; when the temperature is lower than the limit temperature, the high elastic deformation will be suppressed and the rigidity will be enhanced. Therefore, if the temperature exceeds the operating temperature range, the rubber seal will lose its sealing performance; in addition, it should be noted that Under the action of pressure, temperature and medium, the vulcanized rubber itself will age after a certain period of time, resulting in irreversible deformation and damage to the sealing performance. When it is lost, it should be replaced in time.

Natural rubber is easy to age under the action of oxygen, so natural rubber is rarely used as a seal, and synthetic rubber is usually used as a seal, such as nitrile rubber, neoprene, ethylene propylene rubber, butyl rubber, butadiene rubber, Silicone rubber and fluorine rubber, etc. Different types of rubber seals have different sealing properties. When selecting materials, various properties such as tensile strength, permanent deformation, hardness, temperature resistance, medium resistance, and permeability should be considered, and selected according to actual working conditions. , in order to improve the sealing effect. Nitrile rubber is a copolymer of butadiene and acrylonitrile. It has excellent oil resistance. It also has the mechanical strength and wear resistance required as a sealing material. It is widely used in various seals; neoprene is a kind of The polarity is second only to the self-reinforcing elastomer of nitrile rubber. It is the best kind of general-purpose rubber, and it is a flame-retardant rubber. Ethylene-propylene rubber is a copolymer of ethylene and propylene. Halo performance is very outstanding, and the price is cheap; Butyl rubber is made of isobutylene and isoprene copolymerization, the most prominent feature is low air permeability, is the best air tightness rubber, can be used for vacuum sealing; Rubber is a general-purpose synthetic rubber polymerized from butadiene as raw material. The glass transition temperature of high cis-butadiene rubber is as low as -105 °C, so it has good low temperature resistance and is an excellent material for making sealing products in low-cold areas. Good flexibility, especially suitable for sealing needs to withstand multiple deformations; silicone rubber has a wide operating temperature range (-100 ° C ~ +350 ° C), good air permeability, but its shortcomings are low strength and high price; fluorine rubber The biggest feature is high corrosion resistance, its high temperature resistance is comparable to that of silicone rubber, and it has excellent high vacuum resistance.

The corrosion test uses nitrile rubber. After the corrosion test of the sample, the surface of the sample has no corrosion characteristics such as delamination, brittle cracking, deformation and stickiness. The hardness change rate of the rubber sample before and after the test in the SO2 environment is 4.4%. The hardness change rate of the rubber samples before and after the test in the environment is 4.1%, which meets the requirements of relevant standards, indicating that the nitrile rubber has excellent corrosion resistance in SO2 and salt spray environments. Material corrosion test results show that non-metallic materials have better corrosion resistance than metal materials in chemically corrosive environments. As far as metal materials are concerned, Fe corrodes more seriously than Al in SO2 environment, while Al corrodes more seriously than Fe in salt spray environment; stainless steel corrodes more seriously in SO2 environment than in salt spray environment; copper and copper alloys corrode more in SO2 environment. Corrosion was evident in both the copper and the salt spray environment, the copper surface corroded and turned black in the SO2 environment, and patina appeared in the salt spray environment. The surface of ordinary metal materials (such as carbon steel, aluminum, copper, etc.) used in corrosive environments should be designed with protective coatings, and attention should also be paid to strengthening the sealing protection of the casing structure to avoid the intrusion of corrosive media.

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Part.3: Influence of Corrosion on Explosion-Proof Performance of Electrical Equipment


The effect of corrosion on flameproof jointsof explosion proof electrical equipment

The standard GB3836.2-2010 stipulates that "the average surface roughness Ra of the joint surface shall not exceed 6.3μm". After the corrosion test, the flameproof joint surface of some flameproof explosion-proof electrical equipment is corroded, and the average surface roughness far exceeds the standard value and cannot meet the explosion-proof requirements.

 Tests show that among several different types of flameproof joints, the corrosion of the flat flameproof joint is the most serious, while the corrosion of the cylindrical, spigot and threaded flameproof joints is relatively light. The corrosion of explosion-proof joints is related to the ease with which corrosive gases come into contact with explosion-proof joints. From the structural point of view of the flameproof joint surface, the path for corrosive gas to enter the flameproof cavity through the plane and cylindrical joint surfaces is linear; the path through the port type is "L" shape; the path through the threaded type For the zigzag line, it is obvious that the corrosive medium is the easiest to pass through the flat and cylindrical joint surfaces, followed by the spigot type, and the threaded type is the most difficult. In addition, whether it is a plane type or a spigot type flameproof joint, the plane part outside the "O-type" rubber seal is severely corroded, while the part inside the "O-type" rubber seal has no corrosion. The test results show that, If an "O" ring is set on the flameproof joint surface, it can block the passage of the corrosive medium from diffusing into the flameproof cavity. Corrosive medium entering the cavity affects the performance and life of the internal electrical components.

The explosion-proof joint surface of explosion-proof explosion-proof electrical equipment is not allowed to be painted, only grease is allowed. Grease will lose its anti-corrosion effect when used in a corrosive environment for a long time. Therefore, explosion-proof electrical equipment should be regularly cleaned during its service life. The flameproof joint surface shall be oiled and maintained.

Influence of Corrosion on Strength of Explosion-Proof Electrical Enclosures

After the salt spray corrosion test, the surface coating of aluminum explosion-proof electrical equipment is severely peeled and peeled off. After the coating is peeled off, the salt spray further corrodes the underlying metal, which will lead to changes in the strength and mechanical properties of the shell over time. For example, after some aluminum electrical equipment is subjected to the salt spray test, and then the impact test specified in GB3836.1-2010 and the explosion test specified in GB3836.2-2010, the sample ruptures and does not meet the requirements of explosion-proof performance.

Effects of Corrosion on Explosion-Proof Electrical Fasteners

The strength of fasteners is particularly important for the explosion-proof performance of flameproof electrical equipment. Clause 11 of the standard GB3836.2-2010 (equivalent to IEC60079-1:2007) specifies that the minimum yield stress of fasteners is 240N/mm2. After the corrosion test, most fasteners are corroded to varying degrees, and the yield stress of the corroded fasteners must change, which is likely to fail to meet this requirement. Therefore, the material of the fasteners of explosion-proof electrical equipment used in corrosive environments must also be resistant to corrosion.

Influence on the internal wiring terminals of explosion-proof electrical equipment

GB3836.3-2010 stipulates that the temperature of electrical equipment components does not exceed the maximum surface temperature specified in GB3836.1-2010. Corrosion of the terminals will inevitably cause the contact resistance to increase, resulting in an increase in temperature, so that the terminals that originally meet the temperature group exceed the specified maximum surface temperature and fail to achieve the original explosion-proof performance. An effective way to prevent corrosion of internal terminals is to enhance the sealing performance of the protective structure of the housing to achieve IP54 or IP55 protection level.

The effect of corrosion on explosion-proof electrical nameplates

GB3836.3-2010 stipulates that the temperature of electrical equipment components does not exceed the maximum surface temperature specified in GB3836.1-2010. Corrosion of the terminals will inevitably cause the contact resistance to increase, resulting in an increase in temperature, so that the terminals that originally meet the temperature group exceed the specified maximum surface temperature and fail to achieve the original explosion-proof performance. An effective way to prevent corrosion of internal terminals is to enhance the sealing performance of the protective structure of the housing to achieve IP54 or IP55 protection level.


Part.4: Determination and detection methods of different anti-corrosion grades


Corrosive environmental conditions and their test standards

GB4796 is the classification of environmental parameters of electrical and electronic products and the grading standard of severity. GB4797 and GB4798 series of standards are the environmental conditions and application environmental conditions of electrical and electronic products respectively. Most of these standards are equivalent or modified to adopt the IEC60721 series of the International Electrotechnical Commission Standard; GB2423 series standards are environmental test series standards for electrical and electronic products in my country. Most of this series of standards are equivalent or modified to adopt IEC60068 series standards of the International Electrotechnical Commission. method; in addition, there are a series of JB standards that can be used with reference.

Test methods for different anti-corrosion grades

Explosion-proof electrical equipment is used under different environmental conditions such as chemical corrosion and will be affected by environmental corrosion. Therefore, on the basis of reasonable selection of materials, correct design, and careful manufacture, explosion-proof electrical products should pass relevant explosion-proof type tests and corresponding environmental tests according to the expected environmental conditions to verify their reliability scientifically, and based on the corrosion results obtained by artificial simulated environmental tests Trends and approximate results, scientifically guide the development, manufacture, selection and use of explosion-proof electrical products. The environmental tests involved in different anti-corrosion levels usually include damp heat test, chemical gas corrosion test and comprehensive test of different combinations of environmental factors.

 The reliability of explosion-proof and light-corrosion-proof electrical products that are fixed in places without climate protection can usually be verified by damp heat test. Generally speaking, the corrosion rate increases as the relative humidity increases. The test method of the damp heat test can be carried out according to the provisions of GB/T2423.4. The severity level of the damp heat test is determined by the combination of high temperature (55°C or 40°C) and different test cycles, which can be appropriately selected according to the product use environment. Before the test, during the test and after the test, the samples should be visually inspected and performance tested according to the relevant requirements, so as to determine the environmental adaptability, electrical and mechanical properties of the explosion-proof and light-corrosion-proof electrical products that are used in non-climate protected places. changes.

 Explosion-proof and medium-corrosion-proof electrical products that are used in non-climate protection places and places with climate protection should at least pass 2 cycles of sulfur dioxide gas corrosion test to verify their reliability; Strongly corrosive electrical products should at least pass a 10-cycle sulfur dioxide gas corrosion test to verify their reliability. The test method of the corrosion test can be carried out according to the provisions of GB2423.33. Before the test, during the test and after the test, the appearance inspection and performance test of the sample should be carried out according to the relevant requirements. If the appearance or function of the sample has been damaged due to corrosion during the test process , the test can be terminated, and it can be determined that the test sample is not suitable for chemical corrosion environment.

 The reliability of explosion-proof electrical products used in the marine salt spray environment shall be verified through the corresponding salt spray test. The test method of the salt spray test can be carried out according to the provisions of GB/T2423.17 (Test Ka) or GB/T2423.18 (Test Kb). The test Ka is used to divide the severity level by the duration of continuous salt spray. This test method is suitable for assessing the ability of materials, protective layers and products to resist salt spray corrosion, but it should not be used as a general corrosion test method; test Kb is composed of two Or two or more different environmental stages are combined to form different severity levels, which can more effectively simulate the effect of natural salt spray environment. In addition to showing the corrosion effect of salt spray, it can also show the degree of deterioration of some non-metallic materials due to absorption of salt. , and can also be used as a general corrosion test method.

 After the artificial simulated accelerated corrosion test, relevant tests on electrical performance should be carried out according to the technical requirements of the product. For example, in the electrical insulation performance test, it is required that the insulation resistance value between the outer casing of the electrical appliance and the conductive parts and between the conductive parts that are insulated from each other is not less than 2MΩ, and the dielectric properties meet the relevant regulations of the technical standard; After the test, the action and operation performance of the electrical appliance should be flexible and reliable, and the conductive/magnetic conductive elements, metal structural parts and fasteners on the outer casing should not show obvious corrosion (such as patina and rust); the paint layer on the surface of the casing should not appear loose, Obvious bubbling, peeling, peeling and bottom metal corrosion, etc.; plastic casings and plastic parts on the casing shall not be blistered, deformed or brittle; rubber parts shall not be corroded, delaminated, brittle, deformed and sticky, sealing rings and seals The hardness change value of the gasket shall not be greater than 20% of that before the test; the nameplate shall not corrode, lift or fall off, and the writing on the nameplate shall be clear; the flameproof surface of the flameproof electrical appliance shall not be corroded; the conductive parts and fasteners in the junction box shall not be corroded. There must be no visible corrosion.

Other Corrosion environment test

 In addition to the above-mentioned different anti-corrosion grade judgment tests, there are many other environmental tests, such as temperature test (including low temperature test, high temperature test and temperature change test), low pressure test radiation test (mainly solar radiation and thermal radiation), mold test , Vibration test, tilt and swing test, impact test, noise test, electromagnetic compatibility test, etc., can be appropriately selected according to different places of use. It is important to point out that non-metallic materials are very sensitive to temperature and sunlight. Especially when the working environment is close to the limit temperature of the material, or when the product generates heat during use, or when there is a temperature change, the temperature test cannot be ignored. when it is used under sunlight (ultraviolet) irradiation conditions, the light test cannot be ignored.

Part.5: CESP Explosion proof lights and explosion proof electrical equipment for the corrosion environment

CESP anti-corrosion led lights and electronics equipment are made of Material _1: Stainless steel, Material_3: Aluminum and aluminum alloys and Material_6: "Coating, plating" used for anti-corrosion, then the the products throught electrophoresis technology, are coated with a non-metallic paint-like coating on the surface of the housing, which makes the appearance of the lamp flat, smooth, corrosion-resistant and impact-resistant. Then, apply multiple coats of marine anti-corrosion paint to enhance corrosion resistance. That can protect the lamps and equipment from long-term harsh salt water and atmospheric corrosion in the marine environment.

 These items can applied to the marine environment, such as the Offshore Engineering, Offshore Facilities, Offshore Oil Platforms and seagoing vessel. In additional, it suitable for some chemical plants, sewage treatment plants are relatively harsh and corrosive environments.

 Product Category of CESP Hazardous Area Lighting



Corrosion starts from the deterioration of material properties, which in turn affects the explosion-proof performance of electrical equipment. Environmental testing is an important means to ensure the quality of explosion-proof electrical products. It can discover potential quality hazards of explosion-proof electrical products and improve the safety and reliability of explosion-proof electrical products.