The development of powder coating for oil casing

Abstract:
based on SY/T6717-2016 "Technical Conditions for Coatings in Oil Pipes and Casings", combined with SY/T0315-2013 "Steel Pipe Melting Ring" By exploring the effects of epoxy resin, curing agent, resin content, filler and additive on coating performance, the relevant testing methods of the technical specification of oxygen powder coating have been developed to withstand high temperature, high pressure and all performance indicators are in line with the standard requirements of powder coating.
foreword
Epoxy resin has excellent water resistance, chemical resistance and excellent mechanical properties, is the main film-forming substances of heavy anti-corrosion powder coatings. Among them, epoxy resin molecules contain hydroxyl, so the metal substrate adhesion is good, the molecule contains ether bonds, so the coating film flexibility and chemical resistance performance is excellent, the molecule contains a large number of benzene rings, so the coating film hardness is high, good scratch resistance, excellent heat resistance .
fused epoxy powder coating has become the standard material of global pipeline corrosion resistance by virtue of its VOC-free, fast coating, fast curing speed, good mechanical performance and excellent chemical corrosion resistance. In order to ensure the long-term smooth and safe operation of the pipe, the glass transition temperature (Tg) of the general coating should be slightly higher than the operating temperature. When the operating temperature exceeds Tg, the coating gradually changes from a hard and brittle solid state to a soft and tough high-bounce state, and the rate at which oxygen, moisture, and other ions penetrate through the coating to the substrate increases significantly, resulting in a fractured coating structure that ultimately affects the adhesion of the coating and substrate. With the exploration and development of deep-water oil fields, the temperature of oil or natural gas extracted is usually above 80 degrees C, while the glass transition temperature of ordinary pipe antiseptic powder coating is less than 100 degrees C, in order to meet SY/T6717-2016 "T-tube and casing coating technical conditions" 148 degrees C, 70MPa high temperature performance indicators, it is necessary to develop coating glass transformation temperature higher than 148 degrees C.
This paper, based on SY/T6717-2016 "Technical Conditions for Coatings in Oil Pipes and Casings", develops high temperature and high pressure powder coatings for oil casings in terms of epoxy resin, curing agent, resin content, filler and adhesion promoter addition.
Experimental Part
1.1 Raw Materials
Epoxy 903H, Industrial Grade, Guangzhou Hongchang Electronics; Epoxy Amanda 1160, Industrial Grade, Daqing Lurun Technology; Epoxy RESIN DER672U, Industrial Grade, Dow Chemical; Curing Agent HB310, Industrial Grade, Huangshan Xinjia Fine Materials; Solidion HyH251CG01, Industrial Grade, Anhui Far new materials; leveling agent KC758, industrial grade, Anhui Jingcheng new material; mica powder, industrial grade, Jiangxi; precipitation sulfuric acid, industrial grade, Shenzhen; Xiashi powder, industrial grade, Guangzhou; high-gloss calcium carbonate, industrial grade, Shanghai; adhesive promoter W-1007, industrial grade, Patner; Sabbath 404, industrial grade, Changzhou; carbon black P279, industrial grade, Tianjin.
1.2 Main instruments and equipment
differential scan volume heat meter DSC8231, Japanese Science; high temperature autoclave WHFS-5, Weihai self-controlled reactor; twin screw extruder SFJ-32N Yantai Yuanfeng machinery; multi-functional shredder YB-700, Yongkang City fast-forward industry and trade; high-voltage electrostectronic spray gun CQ-SJ5, Shenzhen Chengcheng Xin Technology; electric blowing drying box WGL-125B, Tianjin Tester instrument. Other tools: blade, translucent pressure-sensitive tape.
1.3 Experimental conditions
the raw materials are weighed according to the formula in Table 1.
fully premixed with extruder melt extrusion, extruder host speed 50 Hz, I. zone temperature 85 to 95 degrees C, II. zone temperature 110 to 120 degrees C, the sheet material after initial crushing with multi-functional crusher broken, more than 100 hands sieve powder coating.
experimental work parts in advance after blasting rust treatment into the oven preheated, preheated 30 min, waiting for the work parts temperature reached 220 to 230 degrees C, the powder coating with electrostature spray gun quickly sprayed to the surface of the work piece, coating thickness of 150 to 200 m, due to the laboratory work pieces small, limited heat storage capacity, so after spraying back to the oven solidified 3min, cooling to be checked.
1.4 Performance Detection
The differential scanning volume heat meter (DSC) for the finished powder coating will be made in accordance with SY/T0315-2013 Appendix B of the Technical Specification for the External Coating of Steel Pipe Melted Epoxy Powders to measure the glass transition temperature. The cooled work parts will be in accordance with SY/T6717-2016 "oil pipe and casing coating technical conditions" Appendix B and Appendix C respectively to detect coating adhesion and resistance to high temperature, high pressure performance. The specific requirements are shown in Table 2.
results and discussion
2.1 epoxy resin selection
epoxy resin structure is the main factor that determines the performance of epoxy powder coating and coating, epoxy resin molecules contain hydroxyl determines the powder coating on the metal substrate adhesion. The glass transition temperature of the coating formed by different epoxy resins is not the same, in order to pass the high temperature and high pressure detection, first of all, the glass transformation temperature of the coating must be higher than the experimental temperature, so here choose 3 different epoxy epoxy resins 903H, Amanda 1160, DER672U for experiments, specific indicators and test results as shown in Table 3.
From the experimental results, it can be seen that epoxy 903H coating glass transition temperature is the lowest, only 99.3 degrees C, epoxy Amanda 1160 coating glass transformation temperature is the highest, reaching 121.4 degrees C, and epoxy DE672U coating glass transformation temperature between the two, 108.7 degrees C. The adhesion of the 3 formulations has reached the 5A optimal grade, but the high temperature and high pressure performance are not qualified. The comparison found that the smaller the epoxy equivalent of epoxy resin, the higher the glass transition temperature of the coating. This is because the smaller the epoxy equivalent, the more epoxy groups involved in the reaction, the greater the crosslink density of the coating, so the higher the glass transition temperature of the coating. Although the above 3 formulations of high temperature resistance, high pressure performance is not qualified, but it can be seen that epoxy resin Amanda 1160 than epoxy resin 903H and epoxy resin DER672U coating glass transformation temperature is much higher, so the selection of epoxy resin Amanda 1160 to continue the experiment.
2.2 Choice of curing agent type and resin content
Curing agent as one of the film-forming substances of powder coating, is also a major factor affecting the properties of powder coating and coating properties, different curing agents due to different types and the number of reaction groups, the resulting coating properties are not exactly the same. In order to improve the glass transition temperature of the coating, two different curing agents, HB310 and HYH251CG01, were selected for the experiment. However, the smaller the hydroxyl equivalent of the curing agent, the greater the crosslink density of the coating, the greater the brittleness, according to SY/T6717-2016 test adhesion may be degraded. Therefore, at the same time increase the resin content for experiments, specific indicators and test results as shown in Table 4.
When the curing agent is selected HB310, the resin content is 60% (mass fraction, the same after) and 68%, the glass transition temperature of the coating is 120.9 degrees C and 122.0 degrees C, respectively, the change is not significant, the coating adhesion is 5A, 107 degrees C, 35MPa and 148 degrees C, 70MPa conditions of high temperature resistance, high pressure performance is not passed. When the curing agent was replaced with HYH251CG01 with a resin content of 60% and 68%, the glass transition temperature of the coating was 155.8 degrees C and 156.6 degrees C, respectively. By comparison, it is found that the glass transition temperature of the coating using the curing agent HYH251CG01 is significantly higher than that of the curing agent HB310, because the curing agent HYH251CG01 hydroxyl equivalent is relatively small, and the hydroxyl group involved in the reaction is more, which makes the crosslink density of the coating relatively large. Therefore, HYH251CG01 was selected as the curing agent of amanda1160, epoxy resin.
2.3 Filler Selection
Filler, as one of the main components of powder coatings, directly affects the physical and mechanical properties of the coating, while also reducing the cost of the product. Four kinds of fillers - mica powder, precipitated sulphate powder, xiashi powder and high-gloss calcium carbonate - were selected for research, and the specific indicators and test results were shown in Table 5.
can be seen from the experimental data of Table 5, the high temperature and high pressure properties of mica powder and xiashi powder are qualified under two temperature pressures. The high temperature and high pressure properties of precipitated sulphate are passed under the conditions of 107 degrees C and 35MPa, but the coating foams and the adhesion is degraded in the high temperature and high pressure properties under the conditions of 148 degrees C and 70MPa. High-gloss calcium carbonate at both temperature pressure of high temperature, high pressure performance is not qualified, the coating foaming, adhesion degradation. This is because different fillers on the corrosive media shielding and barrier effect is not the same, mica powder and xiashi powder itself structure can be a good shield from the outside corrosive medium penetration into the coating and thus damage the coating, and the use of precipitation of radon sulfate and high-gloss calcium carbonate coating due to differences in the structure in the harsh environment of the protective media shielding effect basically failed. In addition, considering that the price of xiashi powder is relatively expensive, so mica powder is the ideal system filler.
2.4 Adhesion Promoter Addition Options
powder coatings are available in a wide variety of additives and need to be added selectively depending on the type and purpose. According to past experience, adhesion promoter has a very important influence on the high temperature water resistance of the coating, and the long-term water resistance of products without adhesion promoter is very poor. Therefore, the experiment studied the different additions of adhesion promoter W-1007, and the specific indicators and test results were shown in Table 6.
From Table 6, it can be seen that the coating film resistance is not qualified when the adhesion promoter W-1007 addition is 0.5%, and the high temperature and high pressure performance is qualified when the addition is 1.0% and 1.5%, but considering the cost, the addition of adhesive promoter is determined to be 1.0%.
Conclusion
(1) When used in conjunction with the modified epoxy resin Amanda1160 with low oxycodone dosing agent HYH251CG01, the glass transition temperature of the coating can reach about 155 degrees C, which can meet the most basic requirements for high temperature and high pressure performance.
(2) in addition to high Tg resins and curing agents, increasing the resin content can also improve the adhesion of the coating, but the glass transition temperature of the coating does not increase much. The temperature determinants of the glass transformation of the coating are mainly epoxy resins and curing agents.
(3) mica powder and xiashi powder have a strong shielding effect on corrosive media, they can effectively improve the mechanical strength and performance of the coating. Because the price of xiashi powder is relatively expensive, so the experiment used mica powder as a system filler.
(4) adhesion promoter W-1007 contributes to the long-term service life of the coating film, the larger the effect is the best. When the mass score is 1.0%, the coating performance meets the standard requirements.
(5) epoxy resin selection Amanda1160, curing agent selection HYH251CG01, filler selection of mica powder, resin content of 68% (mass fraction, the latest same), adhesion promoter addition of 1.0%, the powder coating produced in line with the standard SY/T6717-2016 "oil pipe and casing coating technical conditions" indicators.
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