Discharged Large Diameter Pipeline for coal fired generation plant by PE-sGF in Japan
In 2020, a PE-sGF discharged pipeline with a diameter of DN/ID1800mm and approximately 2 km length was completely installed for a coal fired power plant in Japan. In this paper, the characteristics, designation and construction of large diameter PS-sGF pipelines are presented.
Plastic pipes must be designated in two directions - circumferential and longitudinal - when laid on construction site. Basically, thermoplastic pipes have been designed with the same values, yet PE-sGF pipes with different properties can be specified for these directions. PE-sGF pipes provided with a spiral cross-wound method of PE100, short glass fibers and a coupling agent have two times tensile strength in the circumferential direction than PE100, but the same strength in the longitudinal direction as the flexibility of the axes. According to the statistics of the Ministry of Economy, Trade and Industry, there are 142 thermal power plants in Japan in June 2020, and taking into account the energy supply and demand as well as the environmental assessment, 17 thermal power plants are planned to be newly built or renovated. In thermal power generation, a large amount of water is required to cool the steam with the condenser and ascites treatment system, so it is still common to use seawater as cooling water.
Previously, iron pipes were mainly used for pipelines to pull up seawater, but there were problems such as corrosion due to salt damage and blockage due to biofouling.
Corrosion resistant and resistant to biofouling
Therefore, the use of plastic pipes that are corrosion resistant and resistant to biofouling is being invetigated for seawater use worldwide. Andrew Wedgner et al. (2016) summarized the results of laying a PE100 pipeline for geothermal power generation facilities in Java, Indonesia, in 2012 to deal with the problem of corrosion of existing iron pipes (PPXVIII 18th Plastic Pipes Conference 2016, Berlin).
Oka et al. (2020) installed for the first time a PE80 pipeline with a very large diameter of DN/ID3000mm manufactured by the spiral winding method in Japan in the construction of water intake and discharge pipelines for a thermal power plant, and clarified the validity of its design and biofouling characteristics (Electric Power Civil Engineering, 2020 No.407 pp 60-76).
Furthermore, Tokiyoshi et al. (2018) laid PE-sGF pipes on soft ground and conducted an analysis of long-term burial behavior in terms of circumferential stiffness and longitudinal flexibility to verify the circumferential pressure tolerance and the longitudinal tracking capability (PPXVIII 18th Plastic Pipes Conference 2018, Las Vegas Nevada USA).
This paper shows an example of the design, demonstrating testing, and installation of a discharge pipeline for a thermal power plant using similar pipe and joint types as above. Based on an example of the design, construction and demonstration tests of a discharge pipeline using PE-sGF pipes and joints for a thermal power plant, the following findings were obtained:
- Using PE-sGF pipes and joints manufactured by the spiral-wound method, a discharge pipeline with an DN/ID1825 mm, a pipe wall thickness of 51 mm, and an expansion distance of 1844 m was laid for a thermal power plant.
- An electrofusion joint and a butt fusion joint were selected, and their safety was confirmed at actual scale.
- It was found that the stresses in the electrofusion joints were about 40% lower than in straight pipes, with no local stress concentration.
- Under the same conditions, the circumferential thickness for PE pipe is 70 mm.
- A stress of 5,645 kN/m2 is generated in the PE pipe, depending on the range of operating temperature change of the liquid in the pipe. The permissible change due to the Poisson effect resulting from the permissible longitudinal stress limit (5,920 kN/m2) shall not exceed 275 kN/m2. When used under conditions where both ends are restrained, a thickness of 116 mm is required, considering the Poisson effect resulting from the pipe wall thickness. On the other hand, PE-sGF pipes have been shown to have a lower coefficient of linear expansion, which is about 40% of that of PE pipes, so that the pipe wall thickness of 51 mm achieved in the circumferential direction is sufficient to show good behavior in the longitudinal direction as well.
C.I. Takiron Corporation