Concentrated Seawater Pipelines
A project saves 13 million cubic meters of fresh water, 600,000 tons of raw salt, and gains an annual profit of 120 million RMB, effectively solving the problem of shortage of raw salt supply and water. The concentrated seawater in the project comes from the process wastewater of a seawater desalination company, and its Cl- content can reach 45 to 55mg/l, which is 80% to 100% higher than that of ordinary seawater. The concentrated seawater is sent to the concentrated seawater transmission pump station through the underground pipeline, and after being pressurized, it is transported to the concentrated seawater buffer tank in the production unit area through the pipeline. The effective utilization of the concentrated seawater is about 1200m3/h. With the implementation and operation of the project, the load of the production system is reduced, and the pollution to the surrounding environment has caused great economic losses to the enterprise due to the leakage of the pipeline during the transportation and recycling of concentrated seawater. Therefore, designing an effective corrosion detection method for the pipeline, establishing a set of effective anti-corrosion technology for the pipeline to enhance its corrosion resistance, delaying the corrosion rate of the pipeline, and prolonging the service life of the pipeline has significant economic and social benefits.
The current situation of buried concentrated seawater pipelines
The concentrated seawater pipeline has two parts: pipelines inside the plant and pipelines outside the plant. The pipeline in the plant was put into use in 2012 and 2014. It is made of Q235B spiral carbon steel. The pipelines were mainly divided into two parts: the water supply pipe and the return pipe of the circulating seawater cooling tower. The water supply pipe of circulating seawater cooling tower with DN800 has a length of 500m.
The temperature of circulating concentrated seawater in the pipeline is 24 to 38℃; circulating seawater cooling tower's return pipe has a size of DN900 and length 600m, and the circulating concentrated seawater temperature in the pipeline is 35 to 45ºC. Two pipelines were laid underground with a depth of 1.5 m, and the inner wall of the pipeline is sprayed with non-toxic solvent-free epoxy ceramic coating with 0.6mm by one-time molding for anti-corrosion. Part of the pipeline outside the plant was put into use in 2012. The whole length is about 54km. The carbon steel pipe with DN800 from Shougang to Caofeidian Pumping Station is 5.1km. There are five parts from Caofeidian Pumping Station to the plant within 49km: 14.44km of DN1000 carbon steel pipes from Caofeidian Pumping Station to the discharge port of Yanchang Bridge, 4.5km DN900 SDR17 PE pipes from Yanchang Bridge to Dazhiqu, 3.5km DN800 carbon steel pipes from Dazhiqu to Caofeidian Wetland exit, 21km DN900 SDR21 PE pipes from Caofeidian exit to Nanbao Development Zone Substation, and the glass steel pipe with DN800 and 4km from Nanbao Development Zone Substation to the brine clarification tank in the factory area.
Carbon steel pipes are made of Q235B spiral carbon steel, and the main body has a wall thickness of 12mm. A wall thickness of 14mm was adopted for the crossing section with 3km. The inner wall of the pipeline was sprayed with non-toxic and solvent-free epoxy ceramic coatings with a thickness of 0.6mm by one-time molding. The outer wall of the pipeline adopts solvent-free epoxy coal asphalt and glass fiber cloth; the overall thickness of the anti-corrosion layer was not less than 0.6mm. Meanwhile, sacrificial anodes were provided for enhanced protection. The laying environment of the pipe section outside the plant was complex; there were other pipes and underground cables laid in parallel.
Research on the detection of anticorrosive coatings in the non-crossing section of buried pipelines
PCM (Pipeline Current mapper) technology is mainly to detect the pipeline's current decay gradient. The condition of the outer anti-corrosion coating is usually evaluated based on its distribution of damage points, resistivity, and current decay rates. The working principles of this method are as follows: set up a test pile; get a current signal, and an electromagnetic field will be formed around the test pile. The equivalent current will be converted according to the principle of the magnetic field of the current-carrying wire. There is a proportional relationship between the pipeline's current value and the equivalent current. The signal current value can be measured by the magnetic field component at the receiving end. If the anti-corrosion layer is not damaged, the magnetic field around the pipeline is relatively stable. In the process of increasing the distance of the damage point, the signal of the effective current will decrease accordingly, and the attenuation will change smoothly according to the exponential law, that is, I being Io-eax. A represents the attenuation coefficient. If the anti-corrosion layer is damaged, the current at the damaged point will be transmitted to the soil, resulting in abnormal current in the pipeline and obvious attenuation. If you want to evaluate the condition of the anti-corrosion layer, you can continuously measure and analyze the current decay law. Meanwhile, locate the damage point according to the frame.
This method does not need to excavate the pipeline, and has the characteristics of outstanding reliability, good accuracy, simple operation and rapid detection, and can obtain intuitive detection results in combination with the data processing system. However, the effect of this method is not ideal in the frozen soil season, and the test distance is limited. This method cannot detect the peeling of the anti-corrosion layer. GIPS detection technology can effectively evaluate the application effect of the cathodic protection system. The detection principle is to use a cable to connect the collector and the test pile, and the other end of the collector is connected to the reference electrode; the distance between the pipeline potential measurement and collection is about 2m.
The main advantage of this method is that it can effectively detect the cathodic protection potential of the pipeline, and then accurately evaluate the cathodic protection effect. The method can also accurately locate the potential corrosion part, and determine whether the damaged point needs to be repaired. The disadvantage is that in the process of urban construction and the continuous movement of the geomagnetic field, some stray currents will be generated, which will have a certain impact on the detection accuracy. If the cathodic protection is unconditionally disconnected, the power-off potential cannot be tested.
The current situation of buried concentrated seawater pipelines
The concentrated seawater pipeline has two parts: pipelines inside the plant and pipelines outside the plant. The pipeline in the plant was put into use in 2012 and 2014. It is made of Q235B spiral carbon steel. The pipelines were mainly divided into two parts: the water supply pipe and the return pipe of the circulating seawater cooling tower. The water supply pipe of circulating seawater cooling tower with DN800 has a length of 500m.
The temperature of circulating concentrated seawater in the pipeline is 24 to 38℃; circulating seawater cooling tower's return pipe has a size of DN900 and length 600m, and the circulating concentrated seawater temperature in the pipeline is 35 to 45ºC. Two pipelines were laid underground with a depth of 1.5 m, and the inner wall of the pipeline is sprayed with non-toxic solvent-free epoxy ceramic coating with 0.6mm by one-time molding for anti-corrosion. Part of the pipeline outside the plant was put into use in 2012. The whole length is about 54km. The carbon steel pipe with DN800 from Shougang to Caofeidian Pumping Station is 5.1km. There are five parts from Caofeidian Pumping Station to the plant within 49km: 14.44km of DN1000 carbon steel pipes from Caofeidian Pumping Station to the discharge port of Yanchang Bridge, 4.5km DN900 SDR17 PE pipes from Yanchang Bridge to Dazhiqu, 3.5km DN800 carbon steel pipes from Dazhiqu to Caofeidian Wetland exit, 21km DN900 SDR21 PE pipes from Caofeidian exit to Nanbao Development Zone Substation, and the glass steel pipe with DN800 and 4km from Nanbao Development Zone Substation to the brine clarification tank in the factory area.
Carbon steel pipes are made of Q235B spiral carbon steel, and the main body has a wall thickness of 12mm. A wall thickness of 14mm was adopted for the crossing section with 3km. The inner wall of the pipeline was sprayed with non-toxic and solvent-free epoxy ceramic coatings with a thickness of 0.6mm by one-time molding. The outer wall of the pipeline adopts solvent-free epoxy coal asphalt and glass fiber cloth; the overall thickness of the anti-corrosion layer was not less than 0.6mm. Meanwhile, sacrificial anodes were provided for enhanced protection. The laying environment of the pipe section outside the plant was complex; there were other pipes and underground cables laid in parallel.
Research on the detection of anticorrosive coatings in the non-crossing section of buried pipelines
PCM (Pipeline Current mapper) technology is mainly to detect the pipeline's current decay gradient. The condition of the outer anti-corrosion coating is usually evaluated based on its distribution of damage points, resistivity, and current decay rates. The working principles of this method are as follows: set up a test pile; get a current signal, and an electromagnetic field will be formed around the test pile. The equivalent current will be converted according to the principle of the magnetic field of the current-carrying wire. There is a proportional relationship between the pipeline's current value and the equivalent current. The signal current value can be measured by the magnetic field component at the receiving end. If the anti-corrosion layer is not damaged, the magnetic field around the pipeline is relatively stable. In the process of increasing the distance of the damage point, the signal of the effective current will decrease accordingly, and the attenuation will change smoothly according to the exponential law, that is, I being Io-eax. A represents the attenuation coefficient. If the anti-corrosion layer is damaged, the current at the damaged point will be transmitted to the soil, resulting in abnormal current in the pipeline and obvious attenuation. If you want to evaluate the condition of the anti-corrosion layer, you can continuously measure and analyze the current decay law. Meanwhile, locate the damage point according to the frame.
This method does not need to excavate the pipeline, and has the characteristics of outstanding reliability, good accuracy, simple operation and rapid detection, and can obtain intuitive detection results in combination with the data processing system. However, the effect of this method is not ideal in the frozen soil season, and the test distance is limited. This method cannot detect the peeling of the anti-corrosion layer. GIPS detection technology can effectively evaluate the application effect of the cathodic protection system. The detection principle is to use a cable to connect the collector and the test pile, and the other end of the collector is connected to the reference electrode; the distance between the pipeline potential measurement and collection is about 2m.
The main advantage of this method is that it can effectively detect the cathodic protection potential of the pipeline, and then accurately evaluate the cathodic protection effect. The method can also accurately locate the potential corrosion part, and determine whether the damaged point needs to be repaired. The disadvantage is that in the process of urban construction and the continuous movement of the geomagnetic field, some stray currents will be generated, which will have a certain impact on the detection accuracy. If the cathodic protection is unconditionally disconnected, the power-off potential cannot be tested.
