1, preface
Internationally, fiber winding technology began in the 1940s, and obtained 65438-0946 patents in the United States. It has been more than 40 years since it began to make FRP pipes in the early 1950s. At present, the world FRP pipeline industry is developing rapidly and the annual output is increasing day by day. In the United States, for example, the annual usage of FRP pipes is 10000km, and it is increasing by 5% ~ 10% every year.
China's filament winding technology began in 1958, which was mainly used for the national defense construction of "two bombs and one machine". The earliest FRP pipes used for civil use were mainly hand-paste and cloth tape winding. The pipe produced in this way has poor anti-seepage performance and unstable quality. Although it has been tested many times, it has not been widely used. At the end of 1980s, China first introduced the winding equipment of FRP pipes. Since then, China's FRP pipeline industry has really started to develop. Up to 1997, there are 133 FRP pipeline fiber winding production lines. 43 of them are imported production lines [1], and some internationally renowned companies have set up joint ventures or wholly-owned companies in China. The quality of FRP pipes produced by some domestic manufacturers can be comparable to that of international products, and the products have been exported many times. The FRP pipeline industry is in a period of great development in China.
Nevertheless, compared with the huge pipeline market in China. The occupancy rate of FRP pipes is still very low, the key reason is that many users have not fully understood the excellent performance of winding FRP pipes, the application status of FRP pipes in China, and are still hesitant to choose FRP pipes. Therefore, this paper makes a detailed analysis of the performance of the winding FRP pipeline and summarizes its application status in China, with a view to further promoting the development of the FRP pipeline industry in China.
2. Special features
2. 1 has good corrosion resistance.
The structure of fiber-wound FRP pipeline is divided into three parts: inner lining, structural layer and outer protective layer. Among them, the resin content of the inner liner is relatively high, generally above 70%, and the resin content of the resin-rich layer on its inner surface is as high as 95%. By selecting the resin used in the lining, FRP pipes can have different corrosion resistance when transporting liquids, thus meeting different work needs; For occasions where external corrosion protection is needed, different external corrosion protection purposes can be achieved by carefully selecting external protective layer resin.
According to different corrosive environments, different anticorrosive resins can be selected, mainly including m-benzene unsaturated polyester resin, vinyl resin, bisphenol A resin, epoxy resin, furan resin and so on. , according to the specific situation, respectively: for acidic environment, choose bisphenol A resin and furan resin; For alkaline environment, choose vinyl resin, epoxy resin or furan resin; For solvent-based use environment, furan and other resins are selected; When the corrosion of acid, salt and solvent is not very serious, meta-benzene resin [2] with relatively low price can be selected. By selecting different lining resins, FRP pipes can be widely used in acid, alkali, salt, solvent and other working environments, showing good corrosion resistance.
2.2 Excellent hydraulic performance
The inner surface of the winding FRP pipe is smooth, and the absolute roughness of the inner wall is only 0.0 1mm, which is much smaller than that of steel pipe and cast iron pipe. See table 1 [3], which belongs to hydraulic smooth pipe.
Table 1 Absolute Roughness of Inner Wall of Different Pipes
Type of pipeline: new steel pipe, semi-new steel pipe, old steel pipe, cast iron pipe, glass steel pipe roughness/mm 0./~ 0.20.2 ~ 0.30.5 ~ 0.80.6 ~1.00.01
According to Hassan-Williams formula:
HF =〔42.7 q/(c×d 2.63〕 1.852( 1)
The calculation comparison between the wrapped FRP pipeline and the new carbon steel pipeline shows that the head loss caused by the wrapped FRP pipeline is only 0.856 times that of the new carbon steel pipeline with the same diameter [4].
The calculation results show that the hydraulic performance of fiber-wound FRP pipes is better than that of steel pipes or cast iron pipes.
2.3 Light weight and convenient installation and transportation.
The specific gravity of FRP pipes is about 1.6, which is only 1/4 ~ 1/5 of that of steel pipes or cast iron pipes. The practical application shows that under the same internal pressure, the weight of FRP pipes with the same diameter and length is about 30% of that of steel pipes. Therefore, FRP pipes can be transported in complete sets during transportation, saving fuel consumption and other expenses; When installing, the medium and small diameter FRP pipes generally do not need heavy machinery, and some can even be carried manually, which improves the installation speed.
2.4 High specific strength and reasonable mechanical properties.
The axial tensile strength of wrapped FRP pipes is 160 ~ 320 MPa, which is close to that of steel pipes and has higher specific strength. In structural design, the dead weight of the pipeline can be greatly reduced and the installation is very easy. See Table 2 for comparison.
Table 2 Strength and specific strength of FRP pipes and steel pipes
Specific gravity tensile strength of materials /MPa specific strength /MPa advanced alloy steel 8 1280 160 A3 steel 7.85 400 50 cast iron 7.4 240 32-clad FRP1.6160 ~ 320100 ~ 200.
2.5 Low thermal conductivity and small thermal stress.
See Table 3 for the comparison of thermal performance data between FRP pipes and steel pipes. Table 3 Comparison of Thermal Performance Parameters between FRP Pipe and Steel Pipe
Performance parameters: thermal conductivity of FRP pipe /W * (cm *℃)- 1.27 62.8 thermal expansion coefficient/k-1.1.2×10-51.23×/kloc.
The ratio of thermal strain to thermal stress in the table is derived under the assumption that the length of FRP pipe and steel pipe is the same and the temperature difference between the media at both ends of the pipe is the same. As can be seen from the data in the table, the thermal conductivity of FRP pipe is low, only 0.4% of that of steel pipe, so it has good thermal insulation performance, which can reduce the heat loss when conveying media; In addition, it can be seen from Table 3 that when both ends of FRP pipe and steel pipe have the same thermal temperature difference, the linear expansion coefficient of FRP pipe is slightly larger than that of steel pipe, resulting in larger thermal strain. However, since the axial tensile modulus of FRP pipe is about 1 1.2GPa and the modulus of steel pipe is 2 10GPa, the thermal stress caused by temperature difference on FRP pipe is only about/kloc-. The thermal expansion coefficient of FRP pipes makes them have good heat and cold resistance, and can be used in various harsh environments such as ground, underground, overhead, seabed, desert, freezing and humidity.
2.6 Less joints and flexible connection.
The length of a single winding FRP pipe is 6 ~ 12m, or even longer. When installing long-distance pipelines, fewer joints are needed, which not only reduces the resistance of running water, but also reduces the construction cost. At the same time, because there are many joints, the possibility of pipeline leakage is greatly reduced than that of steel pipe. In addition, there are many connection methods for winding FRP pipes, mainly including: socket gluing, butt joint with flat ends, flange connection (looper), O-ring connection (with locking device) and threaded connection. The joint mode can be flexibly selected according to the specific construction conditions to improve the reliability of the project.
2.7 Good electrical insulation performance
Steel pipes and cast iron pipes are good conductors of electricity. FRP pipes are insulators, with breakdown voltage 12 ~ 16kV/mm and volume resistivity1014Ω. Cm, surface resistivity: ~ 10 1 1ω, excellent insulation performance, and can be safely applied to areas with dense transmission and telecommunication lines and minefields.
2.8 no rust
During the storage and use of steel pipes and cast iron pipes, due to the chemical and electrochemical effects, local battery reactions will occur, and the surfaces are easy to rust, which often pollutes the conveying medium. Therefore, it is often necessary to carry out special rust prevention and derusting treatment on their surfaces. Fiber-wound FRP pipes are made of nonmetallic materials, with high electrode potential, no oxidation and rust on the surface, no treatment and no pollution to water quality.
2.9 Pollution prevention and moth prevention
The inner wall of glass steel pipe is clean and smooth, and it is not easy to be polluted and eaten by microorganisms such as shellfish and fungi in seawater or sewage. However, the inner surface of steel pipe, cast iron pipe or reinforced concrete pipe is easy to breed shellfish and oysters, and it is extremely difficult to remove them, which makes the roughness increase, the effective pipe diameter decrease, the flow resistance increase and the cross-sectional area decrease.
2. 10 has strong designability.
According to the specific usage, the specific performance and shape of the pipeline can be designed:
① The winding angle can be designed to make the pipeline have different longitudinal/circumferential strength distribution;
② The wall thickness of the pipeline can be designed so that the pipeline can bear different internal and external pressures;
③ Materials can be designed for different purposes of corrosion resistance, flame retardant and dielectric.
④ The joint mode can be designed to adapt to different installation conditions and improve the installation speed;
⑤ Product shapes can be designed to meet specific shape requirements.
3, should use
3. 1 Oilfield
(1) High-pressure pipelines The high-pressure pipelines used in oil fields mainly include water injection pipes and oil well pipes, with smaller diameters, mostly in the range of DN50~200mm, and higher pressures, generally in the range of 5 ~ 30mpa. For FRP, the conditions are harsh, and the performance of domestic FRP products is difficult to meet the requirements. The glass fiber needed to produce this kind of pipeline needs to be imported from abroad. At present, only Harbin Smith FRP Products Co., Ltd., a Sino-foreign joint venture, produces this kind of pipeline in China, and it has been used in oil fields since 1994. It has provided dozens of kilometers of high-pressure FRP pipelines for anniversary Oilfield, Jilin Oilfield, Shengli Oilfield, Changqing Oilfield and Liaohe Oilfield.
(2) Among a large number of pipelines used in low-pressure FRP pipelines in oilfield production, 80% pipelines are used to transport high water-cut crude oil, oil-gas mixed transportation and oilfield produced water. Due to the harsh conditions of oilfield sewage media, such as the sewage produced in Shengli Oilfield, the salt content can reach 5.7× 104 mg/L, the chlorine content can reach 3× 104mg/L, and corrosive substances such as dissolved oxygen, CO2, sulfide and sulfate-reducing bacteria exist, so the corrosion of metal pipelines is quite serious. The selected steel pipe will be perforated as soon as 3 months after production [6], and it is common to scrap it in one year. Therefore, in 1983, Shengli Oilfield began to try to use FRP pipes with good corrosion resistance as steel pipe substitutes. In the late 1980s and early 1990s, China produced a large number of fiber-wound FRP pipes, which were quickly welcomed by oil fields. Several large oilfields in China, such as Shengli Oilfield, Liaohe Oilfield, Zhongyuan Oilfield, Daqing Oilfield, Karamay Oilfield and Jianghan Oilfield, have adopted a large number of medium and low pressure wound FRP pipelines. In Yunsi Oilfield in Qinghai, Jiangdu Oilfield in Jiangsu, Huabei Oilfield in Hebei and Golmud Oilfield in Qinghai, etc. Medium and low pressure winding FRP pipes are also used in different degrees. Only 20km was used in Yunsi Oilfield in Qinghai during 1990, and only 30km〔7〕 was used in Shengli Oilfield during 199 1 ~ 1992 [7]. Therefore, in the past few years, oil fields have become a very important application market for FRP pipelines. At present, the medium and low pressure FRP pipeline used in the oilfield is nearly 1000 km, and the pipe diameter is mostly between DN50 and 700 mm. The maximum temperature of the conveying medium is about 78℃, and the pressure is generally 0. 1 ~ 1.6 MPa.
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