Pipeline internal lacquer coating technology Cui Tao's Song Xuqiang (China Petroleum Pipeline Company Beijing Petroleum Office) (China National Petroleum Pipeline Bureau Oil and Gas Company) Qian Chengwen Liu Guangwen (China Petroleum Pipeline Company Pipeline Technology Research Center) Cui Tao Song Xuqiang: Pipeline Internal Coating Layer coating technology, oil and gas storage and transportation, 2000, 19 (12) caliber pipeline derusting and spraying plant prefabrication process technology used, pointing out the gap with the foreign internal coating technology, aimed at accelerating the domestic long-distance The research process of the coating technology in the natural gas pipeline has improved the manufacturing level of domestic coating construction machinery, and promoted the promotion and application of the drag reduction technology of the internal coating of the natural gas pipeline in China.
Subject terms: Pipeline inner coating coating construction technology At present, the natural gas pipeline inner coating drag reduction technology has been widely used in developed countries in the European and American pipeline industry. Epoxy coating to reduce friction during gas transportation. In order for the internal coating drag reduction technology to reflect its excellent characteristics in the actual operation of the pipeline, it is necessary to pay attention to the internal coating of the pipeline, because the internal coating of the pipeline is a key technology in the entire internal coating construction. The quality will directly affect the technical performance and service life of the inner coating. Only by adopting advanced and reliable technology can high-quality pipeline inner coating be obtained, which can effectively extend the service life of the pipeline and greatly improve the operational benefits after the pipeline is put into production.
The research on the internal coating technology of the pipeline started late in China, especially in the long-distance, large-caliber natural gas pipeline project, there is no application example, and it is urgent to strengthen the research in this area. With the construction of long-distance natural gas pipelines such as Seininglan, Zhongwu, West-to-East Gas Pipeline, the drag reduction technology of inner coating will be vigorously promoted. Therefore, we must carefully study and master the coating technology of inner coating and strictly control the The quality of the coating process promotes the application of inner coating technology in China.
1. Development level of internal coating technology at home and abroad The pipeline coating technology and equipment are continuously developed with the development and application of various internal anti-corrosion coatings. Tennessee Gas Pipeline Company (TennesseeGasPipelineCompany) put the internal coating pipeline into practical application for the first time in 1955. After decades of development, various new processes and new technologies with practical value continue to appear. Many well-known foreign pipe manufacturing plants and pipeline construction engineering companies have accumulated quite rich practical experience, such as Mannesmann in Germany, NKK in Japan, Selmers in the Netherlands, NOVA in Canada, CRC in the United States, and BrederoPrice in Singapore, etc. All have complete sets of surface pretreatment and spraying lines suitable for different pipe diameters and pipe lengths, and have many years of construction experience and good performance. In general, the technical level of the internal coating operation line of foreign companies is higher than that of domestic ones. Its equipment has a high degree of automation, a low failure rate, a long time without failure, a wide range of applicable pipe diameters, and a reliable overall coating quality. Flow chart of the inner coating of Japanese Steel Pipe (NKK).
Although China started late in the coating of pipeline internal coatings, in recent years, various oilfields have successively set up a technical team for pipeline internal coating research, which has carried out deep research on the coatings used for internal coatings, internal surface pretreatment and spraying equipment, etc. People have made many gratifying achievements, such as the one-time film forming technology developed by the Daqing Oil Construction Technology Research Institute for medium and small diameter pipelines, which can improve work efficiency by 34 times; developed by China National Petroleum Corporation Construction Technology Research Institute The successful powder electrostatic spraying technology on the inner surface of the steel pipe guarantees the quality and safe production of the spraying inside the pipeline; the steel pipe inner coating repairing machine and coating inspection repairing coater successfully developed in Zhongyuan Oilfield and Shengli Oilfield can realize the repair The integration of inspection, coating and coating has filled the gap of coating repair technology in domestic pipelines. Recently, Shengli Oil Construction Pipeline Prefabrication Plant introduced a set of liquid epoxy inner coating application line from CRC in the United States, which can complete the inner coating operation of 60 920mm pipe diameter. These research results have greatly shortened the gap with developed countries, and promoted the promotion and application of oil and gas pipeline inner coating technology in China.
Second, the internal coating construction process of the pipeline The internal coating process of the pipeline can generally be divided into two types, namely the factory coating method and the on-site coating method. The former is used for the construction of new pipelines, and the latter is used for the repair of old pipelines in active service. When repairing the old pipeline, first use the scraper cleaner and wire brush cleaner to clean the pipe, and then use the rubber isolation ball to carry the chemical agent for multiple cleanings to make the inner surface quality of the pipe meet the coating requirements, and then use the double The pig squeezes the paint to apply it. During coating, the liquid paint is clamped between the two pigs. The one in the front is called the pilot pig and the one in the back is called the coating pig, which acts as a squeeze. For the Ninglan and West-East Gas Pipeline The characteristics of the project, etc., mainly introduce the factory prefabricated coating process of the new pipeline.
1. The process flow of the factory prefabricated coating method See the typical process flow of the pipeline inner wall coating in the factory.
The coating process in the pipeline in the plant and the main process steps of internal coating (1) The pretreatment process of the inner surface of the steel pipe The inner surface pretreatment of the steel pipe is the most important link in the coating technology of the inner wall of the pipe, and the quality of the surface pretreatment is guaranteed One of the most important conditions for coating quality is that the derusting of the inner surface of the steel pipe will directly affect the adhesion between the coating and the surface of the pipe body. Commonly used pretreatments for the inner wall of steel pipes include chemical cleaning and mechanical rust removal.
Chemical cleaning is an early method. It is necessary to immerse the tube in a hot acid solution (usually sulfuric acid), hot water, and phosphoric acid solution in a large washing tank, and then rinse with hot water. This method has low efficiency and high cost. If a small amount of acid remains in the treated pipe wall, the curing agent in the coating will fail, and it is difficult to ensure that a certain depth of anchor lines is formed on the inner surface of the steel pipe (generally coated internal coating The depth of the anchor line after the inner surface treatment of the steel pipe layer should be 3060fxmM), therefore, the chemical cleaning method is not suitable for large-scale steel pipe derusting construction operations.
Mechanical rust removal is a widely used pretreatment method for the inner surface of steel pipes. It includes mechanical wire brush rust removal and spraying and shot blasting (sand) rust removal. In the past, steel pipes used for oil and gas transportation mostly used steel wire brushes to remove rust, but the effect was far inferior to sand blasting (shot) rust removal. It was difficult to achieve the rust removal level of Sa2 / 2 specified by GB8923, which affected the coating and The bonding quality of the tube body. In addition, the power consumed by mechanical wire brushes for rust removal is also higher than the sandblasting (shot) method, which is not suitable for the technical development of new coatings and cannot meet the requirements of the construction schedule.
Shot blasting and shot blasting (sand) rust removal are currently commonly used steel pipe surface pretreatment technology at home and abroad. There are two main methods of removing rust on the inner surface of the steel pipe. One is to use compressed high-pressure air to accelerate the abrasive of a certain shape onto the wall of the pipe; the other is to use the high-speed rotation of the centrifugal impeller to drive the abrasive to the surface of the steel pipe. See the device for the two methods. The steel pipe can be rotated or fixed as needed, while the nozzle moves along the direction of the pipe axis (horizontal or vertical).
According to foreign construction experience, sand blasting is usually used for small diameter steel pipes, and internal shot blasting is generally used for large diameter steel pipes.
The internal shot blasting derusting method has high abrasive utilization rate, fast derusting speed and low cost.
Centrifugal impeller shot blasting device 1-centrifugal impeller blasting head; 2-steel pipe; 3-rotating steel pipe roller (2) steel pipe inner surface pretreatment effect test As early as the 1950s, the United States first formulated a steel surface treatment specification ( SSPC), proposed five kinds of sandblasting treatment standards, since then, Britain, Japan, Sweden and other countries have successively formulated their own steel surface treatment specifications. For steel pipes for internal coating construction, the internal surface pretreatment effect is not the same as the inspection standards adopted by various countries, but the rust removal quality level is required to reach Sa2y2 level.
China also stipulates some corresponding standards and specifications for pretreatment of steel surfaces before painting. In order to ensure the quality and technical performance of the coating. The pretreatment method for the inner surface of oil and gas pipelines should meet the requirements of SY / T040797, and the rust removal level should reach Sa2 / 2 level specified in GB8923-88, and the inspection should be compared with the photos or standard test pieces in GB8923. After sandblasting (shot) the inner wall of the steel pipe, the depth of the anchor lines should be around 3060um, which is selected by design.
The inner wall of the pipe should be sprayed immediately after sandblasting, derusting, cleaning and drying.
At present, air spraying devices have been basically eliminated abroad, replaced by new processes such as high-pressure airless spraying, electrostatic powder spraying, and high-temperature ion spraying, of which high-pressure airless spraying accounts for more than 80%.
US standard API5L2 non-corrosive gas pipeline internal coating recommended practices and British natural gas engineering enterprise standard GBE / CM1 both require (best) to use airless spray equipment for internal coating operations. For the spraying of liquid epoxy paint on the inner wall of large-diameter gas pipelines, the high-pressure airless pressure-applying paint method is mainly used. The principle of this spraying method is that after the compressed air is injected into the jet, the pressure of the paint chamber is raised to a certain level (78 MPa) using the piston principle. After the paint is molecularly cracked under high pressure, it is polymerized again to produce an interpenetrating network cross-chain reaction. After the paint injection is filtered, the high-pressure spray gun is pushed to the spray head by the spiral feeder, and the ball is formed to face the pipe wall for spraying. See its working principle.
High-pressure airless spraying schematic diagram-compressor f2-piston; 3-paint room; 4 one spray gun; 5-screw feeder high-pressure airless spraying Compared with air spraying, the paint film after spraying has good quality and uniform coating 1. No pinholes, can reduce the pollution of paint and solvent mist to the atmosphere. There are two types of high-pressure airless spraying devices: traction type and cantilever type. Traction type is to install the spray head on a traction trolley with rollers. The trolley moves axially along the inner wall of the tube. The spray head rotates at a certain speed for spraying. The tube is fixed. See the device. In the cantilever type, several spray heads are installed on the beam of the cantilever spray gun. The beam drives the spray gun to move along the axial direction of the pipe, and the pipe rotates. See the device.
Traction type internal spraying device For epoxy powder coatings, the commonly used method abroad is electrostatic spraying. The coating utilization rate of this method is 80% 95%. The basic principle is high-voltage electrostatic induction adsorption, that is, the spray gun head and the high-voltage electric negative electrode Connection, the tube is grounded as a positive electrode, so that a strong electrostatic field is formed between the spray gun head and the tube. When the paint is sprayed from the spray gun mouth, due to the corona discharge generated by the sharp edge of the gun head, the powder particles are negatively charged and adsorbed to the inner surface of the pipe under the action of the electrostatic force of the electric field. As the pipe rotates and heats, the paint Melt evenly, and then cool and solidify the coating.
Cantilever spraying device 1 paint storage tank; 2 spray gun carriage; 3 spray gun; 4 spray head; 5 inlet tube; 6-rotary fixture At present, many countries and companies have formulated standards for pipeline coating, such as the American Petroleum Institute (API) ) Recommended guidelines for APIRP5L2 gas pipeline internal coating, British Gas Council (GasCauncil) standard GIS / CMI-1968 French standard R03 and 20S50, Dutch standard CS1N, and Canadian Alberta main pipe company standard C-1 1 etc. . The domestic standards mainly include the petroleum industry standard SY / T0442-97 steel pipe sintered epoxy powder coating technical standard and the SY / T4057-93 liquid epoxy coating internal anti-corrosion coating steel pipe technical conditions.
For pipelines coated with liquid two-component epoxy coating, the quality inspection of the inner coating can refer to the relevant provisions of SY / T4057-93 technical conditions of anti-corrosion coating steel pipe in liquid epoxy coating. The standard pointed out in its preparation instructions that the provisions of ordinary grade anti-corrosion coatings are applicable to pipelines with drag reduction and less corrosive transmission media. The pipelines with imported coatings can be accepted according to the technical information provided by the manufacturer. Generally, BS (British Standard) and ASTM Standard (American Material Standard) are mainly adopted. The owner can refer to the provisions of foreign internal coating construction standards (such as API5L2, GBE / CM1 and GBE / CM2), and jointly agree with the coating manufacturer on the quality test methods and evaluation criteria of epoxy resin coatings. Table 1 gives the quality index of the internal coating of the drag reduction type natural gas pipeline.
It should be noted that the inner coating of general steel pipes is divided into two types of drag reduction type and anti-corrosion type according to the purpose of use. Since the natural gas that has been purified by dehydration and desulfurization has little corrosion to the pipeline during transportation, the role of its inner coating is mainly to improve the internal surface condition of the steel pipeline, reduce the consumption of transmission power, and reduce the transportation cost. Resistance type inner coating. According to foreign sources, the original roughness of steel pipes is usually below 40 (20um in the US and 30 / xm in the former Soviet Union). For the purpose of drag reduction, the thickness of the inner coating should be greater than the original roughness of the steel pipe. The US API-RP5L2 non-corrosive pipeline inner coating recommended method stipulates that the dry film thickness of the steel pipeline inner coating is 50.8 ± 5.08 / nm, and the thickness of the drag reduction type inner coating specified in SY / T0442-97 is 50um This kind of thickness can not only achieve the purpose of drag reduction, but also leave a more economical coating thickness margin.
Table 1 Inner coating quality index items Quality standard test method Appearance surface smooth, smooth, no bubble visual inspection (or endoscopy) Number of pinholes 50pm (or according to design requirements) Qualified adhesion Appendix 1 Hardness 12H pencil) No scratch Trace steel pipes shall be repaired and overcoated in accordance with the provisions specified in the standard. The steel pipe after overcoating fails the quality inspection and can only be used separately, not for the third coating.
3. The joint construction process of inner and outer coatings of pipelines Because the long-distance natural gas pipelines also involve an external anti-corrosion problem in actual construction, therefore, in the process of factory prefabrication, the coating process connection of inner and outer coatings should be fully considered Problems, so that the construction progress of the coating inside and outside the pipe can be synchronized as much as possible, which can save investment and speed up the construction progress. It is the flow chart of the joint construction process of the inner and outer coating of the pipeline "first in and then out". The "outside first" technique is the same as the "inside first" technique, but in reverse order.
For the structure of external anti-corrosion using fused epoxy powder (FBE) or three-layer PE, and the internal coating using liquid epoxy coating (drag reduction type), the process of "first inside then outside" or "first outside then inside" is adopted The process is technically feasible. A survey of several major foreign coating equipment manufacturers found that more "inner then outer" processes are used. For example, British BG has at least several thousand kilometers of natural gas pipelines that are coated with "inner then outer" process Yes, it has worked well so far. The so-called "inner first then outer" process, that is, after the inner coating is done, protective covers are added at both ends of the pipe, and then the construction of the outer anti-corrosion layer is carried out. It should be particularly noted that when a foreign company performs medium-frequency heating on a steel pipe body, how to control the power supply frequency during medium-frequency heating is a key technology, because the heating is only a certain depth on the outer surface of the pipe, and the outer surface is not deep when the inner surface is not deep. It is over, so it will not cause damage to the inner coating, and can fully guarantee the overall quality of the inner and outer coatings.
Process flow chart of prefabricated joint construction of pipeline inner and outer coating plants At present, the domestic units with medium and large-diameter pipeline inner coating application lines are mainly Shengli Oilfield No. 1 Company and Daqing Oilfield No. 1 Company. The construction progress of the internal coating operation line introduced by the United States CRC company in Shengli Oilfield Oil Construction Company No. 1 is calculated at 8h per shift, and for pipes with lengths of 11, 12m, the average coating can be 081 5km per shift. The construction progress of the operation line is that for 0711 pipes, the inner coating can be applied for 2.4km per shift, and the outer coating can be applied for 3.65km per shift, both of which are finished pipes.
Because the curing time of the inner coating is longer, the other is similar to the outer coating progress. Therefore, in flow operation, a certain number of inner coating tubes are usually applied first, and then the joint construction of the inner and outer coatings is carried out.
4. Existing problems and suggestions China Petroleum Pipeline Company Pipeline Technology Research Center Natural Gas Pipeline Internal Coating Drag Reduction Technology Research Group has conducted extensive research on domestic and foreign well-known internal coating construction companies (units), and has conducted on-site inspections of victory Oilfield Oil Jianyi Company recently introduced the internal coating operation line from American CRC Company, and found the following problems through investigation.
At present, except for a few oilfield construction companies in Daqing, Shengli and other oilfields that can undertake the internal coating construction of medium and small caliber pipelines, no unit has ever performed the internal coating construction of long-distance and large-caliber natural gas pipelines. It is a joint construction operation combined with external corrosion protection.
For the design, manufacture and layout structure of the blasting (or sandblasting) blasting line and spraying line on the inner wall of the pipeline, it is a problem that needs to be researched and solved. Some key equipment, such as sand blasting mechanism, spray head (including sand blasting and spraying), hydraulic drive motor of spray gun and pipe, air compressor, sand tank, paint mixing tank, automatic control mechanism of spray gun rotation and paint spray volume, etc. All need to cooperate with foreign units to develop or import.
According to the schedule of the implementation of the West-East Gas Pipeline Project and the current gap between the domestic and foreign internal coating construction equipment design and manufacturing technology level, only relying on the current domestic technical strength and equipment, it is necessary to reach the foreign technical level in a short time. Great difficulties and risks.
In order to ensure the quality and construction progress of the West-to-East Gas Pipeline project and save investment, it is recommended that Baoji, Qingxian, Liaoyang, Ziyang and other pipe factories first import key equipment from several operation lines from abroad, and after manufacturing a number of forming operation lines Then digest, absorb, and develop several production lines on their own. It can also be done in cooperation with foreign parties. This will not only train the team, accumulate on-site construction experience, but also purchase foreign equipment with less capital after the project is completed. The West-East Gas Pipeline project is about to begin, and the manufacturing technology and construction technology of the inner coating construction line should be mastered as soon as possible to meet the needs of the project.
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