“Double-resistant” heavy-duty anti-corrosion powder coating for mine pipelines
Abstract: In actual industrial production, situations that require continuous elimination of static electricity are often encountered, such as: coal mine gas exhaust pipes, vents, water pumping pipes, gas storage cabinets, gas pipes, inner and outer wall anti-corrosion of oil and gas storage tanks, etc. . The anti-corrosion coatings of these devices need to have good electrical conductivity to ensure timely elimination of static electricity and minimize the possibility of explosions. For this purpose, the coating must be both anti-corrosive and conductive. When the environmental medium is flammable and explosive, it is very necessary for the coating to have excellent conductivity, which can quickly eliminate static sparks, guide lightning, shield high-energy rays (welding arc, high-frequency particle flow), etc., to ensure the safety of property and personnel. . The coating must pass the inspection by the Safety Standards Office of the Ministry of Coal and pass expert argumentation. It has been widely used in the anti-corrosion of coal mine pipelines and supporting equipment. Such as: Shanxi Coal Group, Lianghuai Coalfield, Donghong Pipe Industry, Tianjin Chengwang Pipe Industry, Dalian Shiwang Pipe Manufacturing Company, etc.
Keywords: static conductive, flame retardant, epoxy heavy-duty anti-corrosion, brominated bisphenol A epoxy resin, conductive trans polyacetylene black, conductive polyaniline, composite flame retardant, phenolic resin curing agent, ablative agent, dehydration agent, char-forming agent
Introduction:
Coal mine pipelines and supporting equipment have been exposed to harsh working conditions such as moisture, salt, and alkali for a long time, coupled with the gas environment. It is required to not only protect the pipelines from corrosion, but also conduct static electricity, and prevent static electricity from forming on the surface of the pipeline coating. build up. Once encountering open flame or high temperature, it can prevent combustion and achieve the purpose of anti-static, anti-burning and anti-corrosion. Early mine pipes mostly used plastic PE pipes or cloth air ducts. Once a fire broke out, they would fuse and lose their ventilation and gas extraction functions, causing inconvenience and even disaster to rescue and personnel lives. In recent years, the Ministry of Coal has required all thick-walled steel pipes to be used as main ventilation ducts (high strength, ablation resistance, and no bending and deformation). The anti-corrosion of the steel pipe itself is the primary consideration. To this end, coatings that are conductive, flame retardant, and anti-corrosive have been developed to better serve this application field. The energy-saving, environmentally friendly and environment-friendly fused epoxy powder coating (FBE) system can well meet this requirement, with low cost, convenient construction and wide source of materials. Our coatings are developed based on this background.
1 Overview and technical characteristics, technical parameters, research plan
Appearance: Ultra-fine powder, mainly black; stable in storage; also conductive in itself, applied to the inner and outer walls of the pipe by electrostatic spraying or other coating methods, then heated and melted, maintaining the temperature at 180 degrees for 10-15 minutes to form The continuous and dense coating film covers the surface of the pipe, wrapping the pipe and isolating the direct contact between the metal and the external medium.
Parameters:
Particle size: 30-45um
Density: 1.4-1.5g/cm3
Curing conditions: 1800C*15min
Research plan:
First of all, it must meet the anti-corrosion performance requirements and pass the CJ/T-120-2008 standard test;
Secondly, it must be conductive, with surface resistance ≦106 ohms;
Third, it must be flame retardant. It must be able to pass the Ministry of Coal Industry standard MT-181 and MT-113 testing. New unified standards are being developed.
In order to achieve the above goals, we first decided to use a sintered epoxy resin system; secondly, the conductive material was a doped conductive material, which is affordable, has excellent conductive properties, has good miscibility with the epoxy system, and the resulting coating is dense; thirdly, From the resin system to the flame retardant additives, fire retardant materials with special functions are selected, reaching the domestic advanced level.
We applied carbon nano-conductive fibers to mine conductive powder coating systems for the first time; at the same time, we introduced brominated bisphenol A epoxy resin into flame-retardant powder coating systems, and invented the “double-resistant” anti-corrosion mine pipeline special powder coating, which is different from previous such pipelines. Compared with liquid paint, the conductivity value is significantly improved, the flame retardant performance is significantly enhanced, the coating density is high, the hardness and wear resistance are improved to a new level, and the comprehensive performance of the coating reaches the advanced level of similar coatings. Then organic phosphorus, carbon-forming agents, foaming agents, magnesium aluminum hydroxide and other composite flame retardants are applied to this coating system to achieve a very good flame retardant effect.
2 Research directions on solving heavy anti-corrosion problems
At present, the mainstream of heavy-duty anti-corrosion of steel pipelines is to use sintered epoxy as the main film-forming resin, a body-type phenolic hydroxyl curing agent, a certain amount of linear phenolic hydroxyl curing agent, and an imidazole catalytic system. The epoxy system itself has excellent anti-corrosion properties, excellent flexibility and adhesion, and the coating is dense and does not leak. Excellent resistance to acid, alkali, salt and chemical corrosion, and good resistance to chloride penetration. It is the first choice to solve the anti-corrosion problem of mine pipelines, but considering the flame retardancy, we chose epoxy resin with modified flame retardant function as the main film-forming material, so that the performance of all aspects of the coating can be taken into account.
Brominated bisphenol A type epoxy resin
Structural formula of body-type phenolic hydroxyl resin curing agent
Regarding the relevant knowledge of anti-corrosion, previous articles have explained too much, so I won’t go into details at this time.
3 Research directions for solving electrical conduction problems
There are two main methods commonly used to make coatings conductive, one is doping conductivity, and the other is intrinsic conductivity. The main film-forming material of the doped conductive coating itself has no conductivity. It uses an insulating polymer as the main film-forming material and mixes the conductive material into it to form a coating. Its conductivity is achieved by incorporating conductive particles, which provide free electron carriers. The incorporated conductive materials here mainly use conductive acetylene or conductive graphite. These materials are blended into the polymer to make The polymer becomes a semiconductor. As the amount of conductive material added increases, the conductivity becomes better and the resistivity becomes lower. This method is currently the most commonly used practical application method. It is low cost, easy to obtain materials, and the conductive properties are durable and stable after doping. , the conductivity value is easy to adjust. As the concentration of conductive filler particles increases, the surface resistivity of the powder coating gradually decreases. When the concentration of the conductive filler reaches a certain critical value, the surface resistivity of the powder coating decreases sharply, and a sudden change in properties occurs from insulation to conductivity. . This critical value is called the percolation threshold. There are many factors that affect the percolation threshold, including the type, structure and form of the conductive filler, the interaction between the powder coating matrix and the conductive filler, processing conditions, etc. The following figure shows the structural formulas of two conductive materials:
Intrinsically conductive materials are difficult to obtain and expensive, making it difficult to be widely used in general industry, so we will not discuss them in detail here. Conductive polyaniline is used here to dope, mainly to take advantage of its excellent self-healing function. Once the coating is slightly damaged during construction, the special function of polyaniline will be exerted, and the anti-corrosion conductive function of leaking points can be quickly and automatically repaired.
4 Research directions on solving flame retardant problems
Flame retardancy must target the three elements of combustion: (combustible substances, combustion-supporting oxygen, and temperature to maintain combustion). If any one of these links is cut off, the purpose of flame retardancy can be achieved. For the formula design of powder coatings, we can start from three aspects at the same time.
(1) Reduce heat release, accelerate heat dissipation, cool down, reduce pyrolysis and combustible gas generation, and inhibit gas phase combustion.
(2) Release non-combustible gases, such as N2, CO2, H2O; promote carbonization, dilute and isolate oxygen, and weaken heat and mass transfer.
(3) Capture free radicals and terminate chain oxidation and depolymerization reactions. Cover the combustible material with an ablative molten shell to block combustion.
Ammonium polyphosphate is a foaming agent, a flame retardant and a catalyst; pentaerythritol is a carbon-forming agent; ammonium melamine is a foaming agent and a flame retardant. The main function of silicone coupling agents is to increase the dispersion and wettability of various materials, improve the fire resistance time of the coating, and act as a flame retardant. Quasi-spherical silica powder and mica powder are originally the first choice for temperature-resistant materials, which can reduce costs and increase solid content. It is best to choose heat-resistant pigments, such as: manganese black, iron black, iron red, iron yellow, chrome yellow, chrome green, chrome red, cobalt blue, iron blue, graphite, etc. There are also many types of other additives, such as microencapsulated red phosphorus, aluminum hydroxide, magnesium hydroxide, antimony or bromine organic compounds, zinc borate, barium metaborate, etc., which are all good flame retardants. After being burned at high temperature, the coating expands into a loose and porous structure to isolate the heat source.
In actual production, we use solid components such as titanium dioxide, silica powder, barium sulfate, and composite flame retardants to be first moistened with a coupling agent for film treatment, then matured for a period of time, and then mixed with other components such as resin. Refined powder. The resulting powder coating has good surface leveling, excellent electrical conductivity, ideal gloss, and excellent adhesion to the substrate. It is an ideal anti-corrosion conductive and flame-retardant material.
5 Conclusion
The current main research direction of conductive and flame-resistant heavy-duty anti-corrosion powder coatings is to develop a series of new systems with high conductivity, low cost and high thermal efficiency. It is believed that with the increasing demand for powder coatings in various fields and the development of powder coatings themselves, conductive Flame retardant powder coatings will make great progress. At present, the testing standards for this type of powder coating coating are comprehensively derived from MT181, MT113, and CJ/T120. However, since these standards are testing standards for polymer and plastic pipelines, they are not specifically for mining pipelines and natural gas. Designed for pipelines, some aspects cannot fully meet the safety requirements of mine pipelines. At present, the industry partially adopts the methods in these three standards to form the current pipeline inspection standards. Now the “Safety Standards Office of the Ministry of Coal” is taking the lead in formulating the “New Standard for Mine Pipe Coatings”. Preliminary training is in progress, and the standard draft and inspection methods are under discussion. We look forward to the early implementation of the new standards.
Become the current pipeline inspection standard. Now the “Safety Standards Office of the Ministry of Coal” is taking the lead in formulating the “New Standard for Mine Pipe Coatings”. Preliminary training is in progress, and the standard draft and inspection methods are under discussion. We look forward to the early implementation of the new standards.
