Research Of Large-diameter Polyethylene Pipes With High-strength For Nuclear Power Plants

Due to richness and high cooling efficiency of sea water resource,coastal nuclear power plants usually use sea water as the refrigerant to bring out heat.However,the corrosion and erosion of seawater system is a common problem in coastal power plants.At present,the traditional pipes consumed in nuclear power plants at home and overseas,to a certain extent,are easily corroded and eroded which seriously and directly impair the safety and reliability of the system.The HDPE pipeline has distinctive seawater corrosion resistance,erosion resistance and aging resistance.In the meantime,its has advantages of small flow resistance,high strength,good toughness and long life.It has been developed and applied in Europe and America widely.They are gradually applied to the safety level system of nuclear power plants.In the future,the application of HDPE pipe in seawater cooling system of nuclear power plants should be an inevitable trend.In China,the manufacture and application of HDPE pipelines with large diameter and thick wall is initial.The domestic production is still blank,which can not meet the requirements of nuclear power construction.This thesis systematically studies the selection of raw materials for large-diameter and thick-walled HDPE pipes,the production process,and the aging resistance of the pipeline,and solves the problems of large-diameter,high-wall-thickness,high-pressure resistance,and high-temperature resistance,HDPE pipes.Gel Permeation Chromatography(GPC)is used to determine the molecular weight and molecular weight distribution of 5 HDPE samples.The HDPE grade HE3490 LSH produced by Borouge Chemical has a weight average molecular weight(Mw)of 470,800 and a molecular weight distribution(Mw/Mn)of 21.4.The crystallinity of five kinds of polyethylene materials is analyzed by differential scanning calorimetry.The melting point of HE3490 LSH is 134.5℃ and the crystallinity is 70.14%.Mcr301 rotary rheometer is used to investigate the zero shear viscosity of five kinds of raw materials.The results show that the melt viscosity of HE3490 LSH is about 1249 k Pa·s under 747 Pa shear force.Above test results show that HE3490 LSH HDPE raw material has the best performance in five test samples,and is the best material for preparing large diameter and thick wall pipe.By testing the wall thickness deviation,melt strength,oxidation induction time and tensile properties of the products,the effects of screw speed,process temperature,die design,cooling water flow rate and cooling water temperature on the properties of the products are studied.The optimum technological scheme of extruding large diameter and thick wall pipe,which can not only reduce the material "sag",but also ensure the mechanical properties of the product,is determined as follows: the screw speed range of the extruder is 70-80 The process temperature is 180℃;the straight section of the extruder die is lengthened to 2 times of the die gap,the draw ratio is reduced to 1.2,the oil cooling device is installed in the die core,and the inner diameter of the vacuum sizing sleeve is reduced to 1.08 times of the die gap;the original nozzles are all renewed to 2.5 mm straight nozzle,the cooling water flow is increased,and the cooling water temperature is reduced to 15℃.The results show that the process not only reduces the "sag" of the material,but also ensures the mechanical properties of the product.Successfully manufacture the 36 inch SDR9 pipe.The aging mechanism,long-term life,and migration and consumption of HDPE pipe stabilizers are studied for large-diameter thick-walled HDPE pipes.The results of tensile property data,HDPE pipe long cycle loop test and HDPE pipe stabilizer migration consumption test demonstrate that the extruded HDPE pipe has remarkable aging resistance,Under the actual maximum service temperature of 55℃,HDPE pipeline has a service life of 124 years,which meets the design service life requirements;research has obtained the migration and consumption law of HDPE pipe stabilizer,and the aging behavior and influencing factors of HDPE pipe during actual engineering service.The aging behavior of HDPE pipelines under actual oxidative service conditions is mastered.Many problems encountered in the domestic production and engineering application of large diameter and high wall thickness HDPE pipes for nuclear power plants have been comprehensively solved,Break the foreign technology monopoly and fill the domestic gap.