Answers

• 
  What standards does S690QL steel plate comply with?

  S690QL is a high-strength alloy structural steel plate that belongs to the European standard (EN 10025-6) special alloy structural steel with excellent mechanical properties and a wide range of applications. The chemical composition of S690QL is carefully formulated to meet its high strength and toughness requirements.
  
  The main element contents (maximum %) include:
  C: ≤0.20%; Si: ≤0.80%; Mn: ≤1.70%; P: ≤0.020%; S: ≤0.010%; Cr: ≤1.50%; Ni: ≤2.00%; Mo: ≤0.70%; Cu: ≤0.50%; V: ≤0.12%; Nb≤0.06%,
  The content and ratio of these elements are crucial to ensuring the overall performance of the steel plate.
  
  Mechanical Properties of S690QL:
  Yield Strength: σ0.2 ≥ 690 MPa (Some sources indicate a yield strength range of 690-890 MPa, but the lower limit of EN 10025-6 is generally followed).
  Tensile Strength: σb 770-940 MPa
  Elongation: ≥ 14%
  Low-Temperature Impact Resistance: Longitudinal V-shaped impact energy ≥ 30J at -40°C
  These mechanical properties enable S690QL steel to withstand high-intensity and heavy-load environments while maintaining excellent toughness and impact resistance.
  
  S690QL steel plate offers the following performance advantages:
  Ultra-high strength: Yield strength ≥ 690 MPa, tensile strength up to 940 MPa, enabling lightweight structures.
  Excellent low-temperature toughness: -40℃ impact energy ≥30J, suitable for extremely cold areas or low-temperature impact conditions.
  Good welding performance: low-temperature impact energy of weld and fusion line> 60J, supporting arc welding, submerged arc welding and other processes. Strong fatigue resistance: low crack growth rate under dynamic load, extending equipment life.
  Corrosion resistance: Surface treatment (such as hot-dip galvanizing and spraying anti-corrosion paint) can further improve corrosion resistance.

  
  
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  What are the main aspects of rebar testing?

  1. Chemical Composition Testing: Detects the content of various elements in rebar, such as carbon, silicon, manganese, phosphorus, and sulfur.
  
  2. Mechanical Properties Testing: Test items assessing the mechanical properties of rebar include tensile testing (tensile strength, yield strength, and elongation) and bend testing (single and reverse bend).
  
  Bending performance: After being bent 180 degrees according to the specified bending diameter, no cracks shall appear on the surface of the bent part of the steel bar.
  Reverse bending performance: According to the requirements of the purchaser, the steel bars can be subjected to reverse bending performance tests. The bending center diameter of the reverse bending test is one steel bar diameter larger than that of the bending test. First bend forward 90 degrees, then bend backward 20 degrees. After the reverse bending test, no cracks shall occur on the surface of the bent part of the steel bar.
  
  3. Dimensional and Appearance Inspection: Measure the diameter, length, thread parameters, and other dimensional indicators of the rebar, and inspect its appearance for defects, cracks, and other issues.
  
  4. Surface Quality Inspection: Detect defects such as oxide layers, rust, and scratches on the rebar surface.

  
  
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  What is the difference between large-diameter welded steel pipe and spiral welded pipe?

  Welded Steel Pipe
  
  Forming Process: Welded steel pipe is formed by directly rolling steel plates or strips through a forming machine into the shape of a straight seam steel pipe. Generally, the flat steel is first edge-processed, such as beveling, and then bent into a cylindrical shape by a press or roller, so that the two sides of the steel plate are aligned to form a straight seam.
  
  Welding method: When welding straight seams, high-frequency straight seam welding (ERW) or submerged arc welding (SAW) is often used. High-frequency straight seam welding uses the resistance heat generated by high-frequency current on the edge of the steel plate to melt the edge and weld it together under pressure. Submerged arc welding is achieved by covering the welding area with flux, allowing the welding wire and steel plate to melt and fuse under the action of the arc. The flux protects the molten pool and participates in metallurgical reactions.
  
  Weld characteristics: A straight weld runs along the longitudinal direction of the steel pipe, resulting in a regular, simple weld shape. High-frequency straight welds result in a relatively small heat-affected zone and a smooth, neat weld appearance. However, since the weld is linear, the stress distribution at the weld is relatively concentrated when subjected to internal pressure, especially in the case of large diameter and high pressure, which places extremely high demands on the weld quality.
  
  Spiral Welded Pipe
  
  Forming Process: Spiral welded pipe is made from a coiled steel strip. At room temperature, the coiled steel strip is formed into a tube blank using a spiral forming machine at a specific angle (helix angle). As the strip steel moves forward continuously, it is curled and welded at the same time, ultimately forming a steel pipe with a spiral weld.
  
  Welding method: The welding mainly employs double-wire double-sided submerged arc welding. Two welding wires are welded on both sides of the steel pipe at the same time. This method can improve welding speed and welding quality. During welding, the arc, under the protection of the flux, melts and combines the welding wire and the edge of the strip to form a continuous spiral weld.
  
  Weld characteristics: Spiral welds are spirally distributed along the steel pipe. Compared to straight seam steel pipe, the stress concentration at the spiral weld is lower under the same pressure. However, the shape of spiral welds is more complex, and it is slightly more difficult to detect and control the quality than straight welds.