Quality issues encountered in the PE pipe production process and their solutions

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Unexpected quality issues often arise during the production of E-tubes, usually due to problems with the equipment or raw materials. Below, based on years of experience in PE pipe production, the common quality issues associated with PE pipes, as well as the causes of these issues and the solutions for them, will be discussed one by one. Waves on the surface of the pipe: Causes: 1. Insufficient cooling; 2. Inappropriate size of the sealing ring, resulting in vibration. Solution: Increase the water flow into the sizing sleeve or increase the distance between the die and the sizing sleeve. Check whether the size of the seal ring in the vacuum tank is too small; if so, replace it or appropriately reduce the vacuum level in the first section of the vacuum tank while increasing the vacuum level in the second section. Surface pitting (mainly on the inner wall): Causes: (1) Impurities present in the raw materials; (2) Inadequate cleaning of the inner wall between the mouth die and the core die; (3) Excessively high local temperatures, leading to aging. Solutions: (1) Check the raw materials. (2) Clean them thoroughly or wait for a while. (3) Check the temperature sensor. Surface pits: Causes: (1) Moist raw materials and bursting bubbles; (2) Uneven water supply in the sizing sleeve. Solution: (1) Dry the raw materials; (2) Adjust the water amount or replace the sizing die. Bright spots on the surface: Cause: Insufficient water amount in the sizing die. Solution: Increase the water volume in the sizing sleeve or replace it with one that uses more water. Axial roughness on the inner and outer walls: Cause: Excess moisture content in the raw material. Solution: Dry the raw materials. Poor surface finish: Cause: Inappropriate melt temperature or problems with the raw materials. Solution: Adjust the melt temperature or replace the raw materials. Scratches on the outer surface: Cause: Sand or debris attached to the sizing sleeve, support plate, or seal ring. Solution: Clean the sizing sleeve, support plate, or seal ring. Water marks on the outer surface: Cause: Blockage in some of the water holes in the sizing sleeve, resulting in excessive water flow in those holes. Solution: Clean the grooves on the inner wall of the sizing sleeve (this issue occurs frequently in pipes with thick walls). Reason: The excessive wall thickness makes it difficult for the melt to cool, resulting in flow. Solution: Try using a center cooling system to lower the temperature of the mouth mold and core mold. Uneven wall thickness of the pipe: Causes: (1) Loose bolts on the mouth mold or core mold, or improper adjustment of the gap in the mouth mold. (2) Uneven temperature at the mouth or core touch, resulting in inconsistent material flow. (3) Misalignment of the sizing sleeve and die, or blockage of the spiral shunt shuttle or screen. Solutions: (1) Tighten the bolts or adjust the die gap. (2) Check the heating coil and temperature sensor. (3) Adjust the alignment of the sizing sleeve and die, as well as the shunt shuttle or screen. Low elongation at break: Reasons: (1) Poor plasticization of the raw material; (2) Increased orientation and improved cleanliness. Solutions: (1) Adjust the process temperature to enhance plasticization; (2) Increase the distance between the die and the sizing die. High ellipticity: Cause: Gravity. Solution: Install correction devices. PE pipe manufacturers must establish strict evaluation procedures for raw material suppliers, select appropriate raw materials, and take appropriate actions based on the test results of those materials. The production of high-quality polyethylene pressure pipes relies heavily on the overall performance of the equipment used. Pipe manufacturers must conduct thorough research and evaluation when selecting equipment in order to choose those that offer the best cost-performance ratio. Pipe manufacturers should establish strict operating and process procedures, as well as enhance monitoring and control measures, in order to ensure both the control of pipe quality and the reasonable reduction of production costs. The process setup for pressure pipes, as well as the resolution of quality issues during production, require extensive production experience. This necessitates that manufacturers accumulate a large amount of raw data, analyze and summarize it, and use this information to guide production in order to achieve a steady improvement in product quality.