Answers

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  Are threaded pipes and spiral pipes the same thing?

  Spiral steel pipes are completely called spiral welded steel pipes. It is a spiral steel pipe that uses automatic double-wire submerged arc welding technology, with strip steel coils as raw materials, often using warm extrusion molding and double-wire double-sided automatic submerged arc welding technology, with spiral welds on the surface, called spiral welded pipes.
  Threaded steel pipe refers to the outer surface of the steel pipe pressed by embossing equipment. Threaded pipes, also known as low-rib pipes, mainly rely on external rib pipes (rib coefficient is 2-3) to expand the heat exchange area and are usually used when the heat transfer coefficient inside the pipe is more than 1 times higher than that outside the pipe.
  
  Threaded steel pipes have good connectivity and sealing properties, so they are widely used in pipeline systems in industries such as petroleum, chemical industry, and natural gas, as well as in connection and fixing parts in fields such as construction and machinery.
  The spiral pipe, due to its unique spiral structure, plays an important role in drainage, sewage, ventilation, and other occasions that require flexible connection and bending performance.

  
  
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  What are the types of cold cracks?

  Cold cracks are cracks formed during the cooling stage of the welded joint during welding. The thermal stress generated during welding will remain in the joint after the weld pool solidifies. As the joint cools, the thermal stress will gradually release. When the thermal stress exceeds the tensile strength of the material, cracks will occur.
  Cold cracks are mainly divided into the following three categories:
  1. Intergranular cracks: Intergranular cracks mainly occur in certain alloy materials, such as stainless steel, nickel alloys, etc. This type of crack occurs between grains because the welding thermal cycle and changes in material composition lead to intergranular corrosion and brittleness.
  2. Penetration cracks: Penetration cracks occur in the weld pool of the weld, usually due to excessive heat input during welding, resulting in excessive amounts of dissolved metal, causing the weld pool to solidify excessively, thus forming cracks.
  3. Heat-affected zone cracks: Heat-affected zone cracks occur in the weld heat-affected zone, that is, the area around the weld joint. The heat input during welding changes the structure and properties of the material, resulting in increased brittleness in these areas, thus forming cracks.

  
  
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  What is the hardness of NM400?

  NM400 is a high-strength wear-resistant steel plate. NM400 wear-resistant steel plate has an excellent surface hardness, usually reaching the range of 360~450HB, which makes it exhibit extremely high wear resistance in various applications.
  
  

  
  

  NM400 is a kind of wear-resistant steel plate. NM400 has a very high mechanical strength; its mechanical properties are 3 to 5 times that of ordinary low-alloy steel plates; it can significantly improve the wear resistance of mechanical-related parts; thus increasing the service life of the machinery; and reducing production costs. The surface hardness of this product usually reaches 360~450HB.