Contact: Cheng Huiqiang
Address：No. 333, Jinxian Road, Jinjiaba, FENHU Town, Wujiang District, Suzhou City, Jiangsu Province
Selection and distribution test method of carbon black in polyethylene anticorrosive coating
Anticorrosion of pipelines in China ’s natural gas and petroleum transmission and distribution systems, urban municipal construction of water supply, gas supply, and thermal pipelines. Corrosion protection of various types of pipelines, tanks, and bridges in hydropower systems has developed rapidly. Practice has also proven that the polyethylene anticorrosion process has Since its introduction in the late 1950s, it has been widely used. However, as the outer protective layer of polyethylene, the first layer must not be damaged to ensure the integrity of the other layers, thereby ensuring the safe operation of the entire piping system. The owner and the anti-corrosion installation engineering company hope that after the steel pipeline and other metal objects pass the anti-corrosion, the quality is safe and reliable, and the service life is long. Under severe geological and climatic conditions, the performance of the pipeline is still excellent and reliable after decades of buried.
一分彩A steel pipe or metal component generally requires a service life of 20 to 50 years. To ensure the quality of its outer layer and internal performance, it must have a high-quality protective layer. The polyethylene anticorrosive layer has sufficient mechanical strength and weather resistance. Anti-aging, environmental cracking and other properties. To improve and ensure the performance of polyethylene anticorrosive materials, it is necessary to have higher technical requirements for raw materials.
2 Main factors affecting the quality of polyethylene antiseptics
Polyethylene anticorrosive material is based on polyethylene resin, and is added by carbon black, antioxidants, other modifiers and additives through melt blending and granulation. Polyethylene anticorrosive material is the protective material of the outer layer of the pipeline, and its internal performance must ensure that the pipeline has a service life of more than 20 years or even 50 years. The pipeline mainly has three processes of stacking, transportation and burial. During the stacking and transportation process, steel pipelines are subject to the sun, rain and cold and hot weather. The light resistance of polyethylene materials must be considered. At the same time, the polyethylene protective layer will also undergo oxidation reactions. The pipelines are laid underground, The composition of the underground soil medium is complex. Electrochemical corrosion and surfactants make the polyethylene protective layer to accelerate damage under the effect of environmental stress.
一分彩Based on the above, to ensure that the steel pipeline reaches the design service life, the polyethylene anticorrosive material must have the following properties:
一分彩1) Excellent light resistance and mechanical strength;
2) Excellent resistance to environmental stress cracking;
3) Excellent electrical performance;
Anti-corrosion installation companies and most owners consider that the smooth, shiny, and black surface of the pipeline is a good polyethylene anti-corrosion material when measuring the pros and cons of steel pipes. The above analysis proves that this view is obviously not comprehensive enough.
一分彩We have collected polyethylene anticorrosive materials from some production plants and found that the carbon black had poor dispersion in individual batches. If carbon black is not well dispersed, it will not be able to effectively block ultraviolet rays from sunlight and easily cause degradation of polymer materials. Therefore, anticorrosive materials with poor carbon black dispersibility may have cracks on the surface of pipes after several years. It is not easy to detect in a short time. Anticorrosion pipeline companies must pay attention to the selection of anticorrosive materials in order to ensure the quality of their products and protect the interests of the owners.
2.1 Focus on light resistance
一分彩In order to block the attack of sunlight and ultraviolet rays, anti-corrosive materials generally use a light-resistant additive-carbon black. Carbon black plays a light shielding role in polyethylene, preventing light waves from passing through the carbon black layer, thereby protecting the polyethylene from ultraviolet rays. The resistance to photoelectricity and cracking depends on the type of carbon black, the content of carbon black (2 to 2.4%), and the dispersion of carbon black in plastics. These are the three major factors that affect the performance of polyethylene anticorrosive materials. The particle size of carbon black is required to be very small (less than 25nm). After aging experiments, it is proved that as the particle size increases, its light resistance will deteriorate. The smaller the carbon black particles, the greater the cohesion between the particles and the more difficult it is to disperse. Carbon black must meet the requirements of GB / T23257-2009 standard and be evenly dispersed in plastic, which is one of the elements to ensure the quality of anticorrosive materials. Therefore, by testing the dispersion of carbon black in anticorrosive materials, we can see the quality level and basic performance of polyethylene anticorrosive materials.
一分彩The inspection of carbon black dispersion is easy for pipeline anticorrosion companies, with low cost, simple operation and easy operation. It is very intuitive to use standard picture comparison. Establish this test method to ensure that the content and particle size of the carbon black of the polyethylene antiseptic are within the specified values, and its aging resistance, mechanical and electrical properties are more reliably guaranteed.
2.1.1 Selection of carbon black
The main raw materials for experiments
一分彩LDPE: 7042N, Lanhua; HDPE: 5000S, Lanhua;
HDPE: 6098, Qilu Petrochemical POE: 8150, LG
Carbon black: N220, N330, N234, Zigong;
一分彩Zinc stearate, polyethylene wax, commercially available
2.1.2 Main instruments and equipment for experiments
一分彩Twin screw extruder: SHJ35, Coperion Company;
High-speed mixer: SHR50, Zhangjiagang Yili Machinery;
Hydraulic flat vulcanizing machine: XLB-25JPH50, Jiangdu Jingyi Experimental Machinery Co., Ltd .;
Microcomputer-controlled electronic universal testing machine: CMT6104Z, Meters Industrial Systems (China) Co., Ltd .;
Punching machine test machine: TH-7010, Jiangdu Tianhui Test Machinery Co., Ltd .;
一分彩Blades with sharp edges: double-sided shavers;
Biological microscope capable of 100 times magnification: biological microscope for general chemical laboratory;
0.8 ~ 1.5mm thick glass slides: can be purchased in medical instrument shops or glass instrument shops;
一分彩Desktop electric heating constant temperature drying oven: 202-00, Tianjin Taisite Instrument Co., Ltd.
2.1.3 Sample preparation
一分彩LLDPE7042 is mixed with carbon black and additives in a certain proportion, and then extruded on a twin-screw extruder, pelletized to obtain a one-step master batch. The carbon black master batch was vacuum dried at 105 ° C for 2 hours. LLDPE, POE, HDPE, masterbatch and additives are mixed uniformly in a certain proportion, and then extruded on a twin-screw extruder and pelletized to obtain a polyethylene anticorrosive material. The extruder temperature was 190 ° C, 200 ° C, 215 ° C, 215 ° C, 215 ° C, 215 ° C, 215 ° C, 210 ° C, 210 ° C, and 215 ° C; the screw revolutions were 65 r / min. The granules were dried in a vacuum oven at 105 ° C. for 2 hours, and then pressed and cut into standard samples.
Table-1 Effect of carbon black grades on mechanical properties and processing properties of blended polyethylene anticorrosive materials
一分彩Carbon black grade Tensile strength Elongation at break Yield strength Notched impact strength Melt index
/ MPa /% / MPa / KJ / m2 g / 10min
N330 22.2 625 19.3 45 0. 29
N220 24.5 654 22 NB 0.34
N234 25.3 700 24 NB 0.38
2.1.2 Simple test method of carbon black dispersion
一分彩1) On the prepared standard samples or particles, use a blade to cut a small slice at least 6 or more places (note that it must be thin and weigh about 0.2mg)
2) Put the cut small pieces on a piece of glass (the surface of the glass is wiped clean in advance), with a certain interval between each small piece, and then cover the small piece with another clean glass cover. On the slide, two slides are clamped with a strong folder (at least two);
3) Put the slides with the clips together in an oven at a temperature of 200 ~ 210 ° C and heat for about 3 minutes. As long as the small flakes added in the film melt and the small black spots become translucent, you can take them out. Cool in a cool place to room temperature. The slide should look translucent brown when facing bright light. If the dots are not transparent, it means that the observation slide is not ready. The sample sheet is too thick, the heating time is not enough, the temperature is low, or the clamping force of the clamp is insufficient, and it must be redone.
4) Remove the clamp from the cooled sample and place it in a biological microscope for observation. The magnification should be 100 times, but it should not exceed 200 times (eyepiece multiplied by the objective lens). , Apply standard magnification comparison.
一分彩5) Adjust the focus to clearly see the edges of the test sample, move the test piece back and forth, and take the difference (see the illustration)
1) Under the microscope: Fig. 1 shows that the carbon black has a good dispersion, and the rest are second, and Fig. 7 is poor; Fig. 8 shows the appearance of stains and streaks that are allowed to appear in the tablet.
2) Bid counting method: Compare the dispersion of carbon black in the difference part of the observation point with the standard photo, record 1 similar to the case in Figure 1, and record 6 in the case of Figure 6, and take 6 test points to compare with the standard photo. Make a note of 6 numbers, take the average value and take an integer. When the average value is less than 5, it means that the carbon black dispersion is acceptable. When the average value is more than 5, it means that it is unqualified. The smaller the number, the better the dispersion of carbon black.
一分彩3) Due to the strength of the clip or the high temperature residence time, the operation is not careful when taking out, and there may be streaks or stains in the film. If it is worse than Figure 8, it should be re-produced.
This experimental method is effective for the internal control quality of pipeline anticorrosive companies, and it is effective to compare the dispersion of the carbon black of the polyethylene anticorrosive material from the anticorrosive material manufacturers of various manufacturers. Of course, for companies and owners purchasing polyethylene anticorrosive materials, the acceptance standards should also be implemented in accordance with the current technical specification documents, that is, GB / T23257-2009 standards.
2.2 Resistance to environmental stress cracking
Environmental stress cracking resistance is another very important performance requirement for polyethylene preservatives. Polyethylene anti-corrosion material is very sensitive to environmental stress. 3PE anti-corrosion with polyethylene should be buried in the soil for a long time, and some sections should be immersed in wetland and sewage for a long time. Common polyethylene materials are prone to cracking. Therefore, the polyethylene used as the anticorrosive material for steel pipelines must use a specific category, a special model, and polyethylene with excellent resistance to environmental stress cracking, and blend with high-efficiency additives to modify it. However, this polyethylene anticorrosive material manufacturing technology with excellent environmental stress cracking resistance has not yet been mastered by all anticorrosive material manufacturers. The environmental stress crack resistance test takes a long time, often the anticorrosion project has been completed, and the test data is not yet available. If the pipeline anticorrosion installation company can check the environmental stress crack resistance performance test itself, the quality risk is reduced.
一分彩The mechanical properties and processing properties of polyethylene anticorrosive materials are shown in Table-1. It can be seen that the choice of carbon black grades has an impact on the mechanical properties of the blended materials. With the addition of N234, N220, and N330, the mechanical properties decrease in order. N234 in carbon black is a high-tech ultra-wear-resistant carbon black with a new process. Compared with N220, N234 has an iodine absorption value and a DBP absorption value that are 10% -20% higher. Compared with N330 carbon black, it contains N220 carbon black rubber. The abrasion resistance of the material should be 10% ~ 20 higher, which can give the rubber material higher tensile strength and tear resistance.
一分彩Through the melting index test, the data characterizes the same carbon black content. Under the premise of excellent mechanical properties, the carbon black with narrow particle size distribution, high structure and finer fineness is selected. Reasonable processing ensures its dispersion effect and its processing flow. Better performance. Under the premise of ensuring material properties, properly increasing fluidity is conducive to increasing the amount of glue and appearance. Based on the foregoing descriptions, for materials manufacturers and pipeline anticorrosion companies, in addition to materials and anticorrosive coatings that meet the standards, if special attention is paid to the choice of carbon black and the two above-mentioned experiments are solved by themselves, the carbon black dispersion test and environmental stress cracking resistance Tests, under normal circumstances, can produce high-quality anticorrosive materials to ensure the quality of the anticorrosive outer layer
Contact: Cheng Huiqiang
|Contact : Li Cong|
|Address: No. 333, Jinxian Road, Jinjiaba, Wujiang District, Suzhou, Jiangsu|