Answers

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  What's the difference between a material certificate and a certificate of conformity when purchasing steel. are both necessary?

  When purchasing steel, a material certificate and a certificate of conformity are two different documents, but usually both are required as they are crucial documents for ensuring steel quality.
  The certificate of conformity is relatively simple, mainly containing basic information such as product name, model, specifications, batch number, quantity, and a "qualified" mark. Steel certificates of conformity are sometimes colloquially referred to as quality certificates.
  In addition to basic information, the material certificate details key data such as the steel's chemical composition and mechanical properties (e.g., yield strength, tensile strength). It is an important basis for understanding the steel's performance.
  The material certificate provides detailed performance data for the steel, forming the foundation for quality traceability and technical verification. For export trade, a material certificate conforming to international standards (such as EN 10204) is a core document.

  
  
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  Do fire-fighting steel pipes need to be galvanized?

  Using ordinary black pipes for fire-fighting systems in an attempt to reduce procurement costs can lead to failure in final acceptance testing and create potential safety hazards.
  Fire protection pipe networks are kept closed and circulated with water for a long time, and are most susceptible to rust, scale buildup, and blockage. Ordinary black pipes are prone to oxidation and rust. Rust flakes off and accumulates on the pipe walls. With long-term use, the inner diameter of the pipe decreases, the nozzles become clogged, and the valves become stuck. In the event of a fire, the water output and water pressure are insufficient, which directly affects the effectiveness of fire rescue and poses a great safety hazard. The zinc coating on the galvanized pipe protects the pipe wall, making it less prone to rust and scaling, ensuring clean water quality, and guaranteeing smooth water flow and stable operation of the fire protection system.
  Galvanized pipes are corrosion-resistant, moisture-resistant, and suitable for complex building environments. Fire protection pipes are often embedded in ceilings, shafts, and damp underground areas, which are dark and damp all year round. Ordinary black pipes will corrode extensively within a few months, resulting in a very short service life and making later maintenance and replacement extremely difficult. Hot-dip galvanized pipes have strong anti-corrosion properties, are resistant to moisture, oxidation, and aging, and will not rust even after years of use. They are suitable for long-term concealed construction conditions, requiring no maintenance and minimal repairs.

  
  
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  Besides thickness, what other methods are there for judging the quality of galvanized pipes?

  Judging the quality of galvanized pipes is a comprehensive evaluation process. In addition to checking the thickness, key data such as adhesion and salt spray test results should also be considered.
  Uniformity: A high-quality galvanized layer should be uniform and continuous, without defects such as incomplete coating or black spots. This can be tested by immersion in a copper sulfate solution; if it does not turn red (no copper color) after five consecutive immersions, it is considered合格 (qualified).
  Adhesion: The zinc layer should be firmly bonded to the steel pipe substrate. This can be checked by a bending test (e.g., bending 90° or 180°); a qualified galvanized layer should not peel off or crack.
  Surface Quality: Visually inspect the surface; it should be smooth, without severe defects such as zinc nodules, peeling, or bubbles.
  Chemical Composition Analysis: Test the content of elements such as carbon, manganese, silicon, sulfur, and phosphorus in the steel pipe substrate to ensure that the material meets standards.
  Mechanical Property Testing: This includes tensile tests (tensile strength, yield strength) and impact tests (toughness) to ensure that the pipe has sufficient strength and toughness.
  
  When purchasing galvanized steel pipes, a reliable method is to request the supplier to provide an authoritative testing report.