Answers

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  Causes of Common Production Problems in Q235 Spiral Pipes

  Common Defects and Causes of Spiral Steel Pipes: Loosening, bubbles, shrinkage cavities, residues, non-metallic inclusions, segregation, white spots, cracks, and various abnormal fracture defects in spiral steel pipes.

  Causes of Segregation in Q235 Spiral Pipes: During casting and solidification, selective crystallization and diffusion can cause the aggregation of certain elements, leading to uneven chemical composition. Depending on the distribution location, this can be classified as ingot segregation, center segregation, and point segregation.

  Causes of porosity in Q235 spiral tubes: During hot working, gaps are created by the solidification shrinkage of low-melting-point materials and the release of gas, preventing the steel from being welded. Based on their basic distribution, porosity can be divided into two types: centrally located type and generally loose type.

  
  
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  Can galvanized pipes be painted?

  You can paint them, but not directly.

  Since galvanized pipes have a smooth surface and a highly reactive zinc coating, they must first be cleaned and sanded, then coated with a specialized primer (such as epoxy zinc yellow primer or zinc phosphate primer), followed by a compatible topcoat (such as epoxy paint, polyurethane paint, or water-based acrylic paint). At the same time, avoid using ordinary latex paint, paints containing copper pigments, and alkyd paints, as these can cause peeling, flaking, or accelerated corrosion.

  
  
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  What are the common coating processes for anti-corrosive spiral steel pipes?

  The corrosion protection method for anti-corrosion spiral steel pipes is generally to use coating anti-corrosion, and increasingly, composite materials or composite structures are being adopted. These materials and structures must possess good dielectric properties, physical properties, stable chemical properties, and a wide temperature adaptability range.

  1. External anti-corrosion coating: Types of coating materials and application conditions for the external wall of spiral steel pipes.

  Inner wall anti-corrosion coating: A thin film applied to the inner wall of the pipe to prevent internal corrosion, reduce frictional resistance, and increase flow rate. Commonly used coatings include amine-cured epoxy resin and polyamide epoxy resin, with a coating thickness of 0.038–0.2 mm. To ensure a strong bond between the coating and the pipe wall, the inner wall of the pipe must be surface-treated. Since the 1970s, there has been a trend to use the same material for the coating of the inner and outer walls of pipes, so that the coating of the inner and outer walls can be carried out at the same time.

  2. Anti-corrosion and heat-insulating coating: On medium and small diameter pipelines for transporting hot crude oil or fuel oil, in order to reduce heat loss from the pipeline to the soil, a composite layer of heat insulation and anti-corrosion is added to the outside of the pipeline. The commonly used insulation material is rigid polyurethane foam, which is suitable for temperatures ranging from -185 to 95°C. This material is soft in texture. To improve its strength, a layer of high-density polyethylene is applied to the outside of the insulation layer to form a composite material structure, which prevents groundwater from seeping into the insulation layer.

  
  

  The coating scheme for anti-corrosive spiral steel pipes is determined by the operating environment.

  The three-layer polyethylene (3PE) coating system combines epoxy powder, an adhesive layer, and a polyethylene layer to form a structurally stable protective barrier.

  Epoxy coal tar coating involves the alternating application of epoxy coal tar paint and glass fiber cloth, creating a water- and corrosion-resistant coating system. Internal cement mortar lining forms a smooth inner surface on the pipe wall, helping to reduce flow resistance.

  Epoxy powder coating utilizes high-density polyethylene as a base material, balancing mechanical strength with corrosion resistance. Each process has its own specific advantages; the appropriate method should be selected based on the conveyed medium and installation conditions.