Answers

• 
  How to distinguish between round steel and rebar?

  1. Different shapes:
  Round steel has a smooth outer surface.
  Rebar has spiral ribs on its outer surface.

  
  2. Different production standards:
  In current standards, round steel refers to HPB235 grade rebar, and its production standard is "Hot-rolled plain steel bars for reinforced concrete" (GB13013).
  Rebar generally refers to HRB335 and HRB400 grade rebar, and its production standard is "Hot-rolled ribbed steel bars for reinforced concrete" (GB1499).
  
  3. Strength Differences:
  The design strength of round steel (HPB235) is 210 MPa.
  Rebar has higher strength than round steel. The design strength of HRB335 is 300 MPa, and the design strength of HRB400 is 360 MPa.
  
  4. Different steel grades (chemical compositions):
  Round steel (HPB235) is a carbon steel, grade Q235.
  Rebar is a low-alloy steel. HRB335 grade rebar is 20MnSi (20 manganese silicon); HRB400 grade rebar is 20MnSiV, 20MnSiNb, or 20MnTi, etc. 5. Different physical and mechanical properties:
  Due to differences in the chemical composition and strength of steel bars, their physical and mechanical properties vary. Round steel has better cold bending performance and can be made into 180-degree hooks, while rebar can only be made into 90-degree straight hooks. Round steel has better weldability and can be made with ordinary carbon welding rods, while rebar must use low-alloy welding rods; rebar has better toughness and fatigue resistance than round steel.

  
  
• 
  What are the advantages of the special-shaped pipe compared to the round pipe?

  Special-shaped seamless steel pipes refer collectively to seamless steel pipes with cross-sectional shapes other than circular. These pipes are widely used in various structural components, tools, and mechanical parts. Compared to circular pipes, special-shaped pipes generally possess larger moment of inertia and section modulus, offering greater resistance to bending and torsion. They better accommodate the specific demands of usage conditions, significantly reducing structural weight, conserving steel resources, and enhancing labor productivity in component manufacturing.

  
  
• 
  What are the methods for steel pipe corrosion protection?

  1.Coating Anticorrosion
  Coating anticorrosion is a widely used method for steel pipe corrosion protection. Common coating materials include epoxy resin, polyethylene, and polyurethane. They effectively prevent corrosive media from penetrating the steel pipe surface, providing long-term protection. Epoxy coatings also have excellent insulation properties, making them suitable for applications requiring high electrical performance.
  
  Polyethylene coating: Polyethylene coating offers excellent water resistance, low-temperature resistance, and impact resistance. It can maintain good protection effect under harsh environmental conditions and is especially suitable for steel pipes such as buried pipelines that are exposed to moist soil for a long time.
  
  Polyurethane coating: Polyurethane coating offers advantages such as high hardness, good wear resistance, and excellent flexibility. It can adapt to the deformation and vibration of steel pipes during use while providing good corrosion protection.
  
  2. Galvanized anti-corrosion
  Galvanizing is a process where steel pipes are immersed in molten zinc to form a zinc coating on the surface. The advantage of galvanizing for corrosion protection is that the electrochemical activity of zinc is higher than that of iron. When the zinc coating on the surface of the steel pipe is locally damaged, the zinc will be corroded first as an anode, thereby protecting the steel pipe substrate from corrosion. In addition, the galvanized layer also has good decorative appearance and certain wear resistance.
  
  3. Cathodic Protection
  Cathode protection inhibits corrosion by applying an impressed current or sacrificial anodes to the steel pipe, turning it into a cathode.
  
  Impressed Current Cathodic Protection (ICCP)
  This method allows precise control of the magnitude and distribution of the protective current as needed, making it suitable for large steel pipe structures and long-distance pipeline systems.
  
  Sacrificial Anode Cathodic Protection
  Sacrificial anodes are typically made of active metals such as magnesium and zinc. These metals dissolve preferentially during corrosion, providing protection for the steel pipe. The sacrificial anode cathodic protection system is easy to install and has low maintenance costs.
  
  4. Composite Anticorrosion
  Combined anticorrosion methods combine two or more of the aforementioned anticorrosion methods to achieve a better anticorrosion effect.