Application Of Stainless Steel Pipe In Air Conditioning Field

Prospects Of Air Conditioning Industry
Since China’s reform and opening up, after decades of efforts by air conditioners, a large number of stainless steel pipes are used in air conditioners, which can be roughly divided into two categories: one is to participate in heat exchange, such as stainless steel tubes for condenser and evaporator; another type is not involved in the heat exchanger, such as indoor machine with stainless steel pipe, outdoor machine pipe and connecting pipe. The latter does not need heat transfer, which provides the possibility for the stainless steel tube to replace the copper tube (the thermal conductivity of steel is 1/8.5 of copper, theoretically speaking, the use of stainless steel tube is more heat preservation, energy saving, electricity saving). 
At first, it is estimated that the consumption of each air conditioner is about 1.5kg, among which the consumption of each air conditioner outdoor unit piping is about 0.5kg, and the consumption of each air conditioner indoor and outdoor unit connecting pipe is about 1.0kg. According to the 2011 national air conditioner output to calculate, the annual market theoretical demand is about 200,000 t if can be replaced successfully, will bring great development opportunities for the double coil welding stainless steel pipe and related industries, but also can save a lot of copper resources for the country. 
Air Conditioning With Double Stainless Steel Pipe Main Performance Characteristics

 Air Conditioning With Double Stainless Steel Pipe Main Performance Characteristics

  • No Aging Phenomenon
    Stainless steel pipes for air conditioning, from procurement to use, the cycle is very long, especially the indoor machine piping and indoor and outdoor machine connecting pipe, the cycle is longer, even more than one year, in order to ensure the normal bending use, the stainless steel pipes can not have obvious aging phenomenon.
  • Work Hardening Index
    Work hardening index n value is large, conducive to deep drawing, high elongation of the material, but applied to the air conditioning industry, stainless steel pipe in repeated bending hardening too fast, will lead to bending immovable and can not be used, so the stainless steel pipe with air conditioning hope that the work hardening index n value as small as possible. But when n value is small, the elongation of the material will decrease. Therefore, a reasonable choice is needed.
  • Mechanical properties
    Tensile strength Rm: The original standard Rm 290Mpa min. air conditioning industry 270Mpa min. the difference is not very big.
    Yield strength Rel: Rel 180Mpa min. as specified in the original standard; For the air conditioning industry, it is hoped that the lower the Rel value, the better, easy deformation, Rel180Mpa max. as far as possible Rel140Mpa max.
    Elongation after fracture A: A25% min according to the original standard, the air conditioning industry hopes to achieve the index of copper pipe, requiring A38% min, the ideal is A40% min.
  • Chemical composition
    Due to the particularity of performance requirements, the chemical composition of steel is more inclined to carbon steel, where C0.04% max, and the original standard chemcial composition stipulated C=0.02%-0.08%
  • Bending Test
    The original standard stipulates: for stainless steel pipe with outer diameter less than 8.00mm, the bending core diameter is 3 times of outer diameter; If the outside diameter is greater than 8.00mm, the bending core diameter is 6 times of the outside diameter. But air conditioning due to space restrictions, various specifications of the bending core diameter are within 3 times.
  • Flatness
    The bending ratio e<1.15 after bending for air conditioning pipe, the higher requirement e<1.23. (Flatness e refers to: after the connecting pipe is bent by coil tooling, the cross section of the bending pipe will change from a circle before bending to an oval, and the ratio of the long diameter A to the short diameter b of the oval).
  • Corrosion resistance of the outer coating
    In the original standard, the selection of the outer surface corrosion protection layer is determined by the negotiation between the supply and demand parties. After passivation treatment, the corrosion resistance level of galvanized corrosion protection layer can be divided into A,B,C,D and E after neutral salt spray test (NSS), among which grade E with the longest corrosion resistance is 200h. But the air conditioning industry requirements are much higher than this standard, their outer coating corrosion resistance protective layer must simultaneously meet the following four conditions:
    1. Corrosion resistance: Because the outdoor unit of air conditioning has been exposed to the outdoors for many years, the use conditions are quite harsh. More importantly, the outer surface of the pipe will condensation in the operation of air conditioning. The corrosion resistance of the external coating is very high.
    2.High temperature resistance: In the production of air conditioning, the connection between the components is completed by mutual welding. The solder temperature is about 800 degrees, but the flame temperature of the welding gun is higher. The outer coating of the pipe cannot fail and cannot be melted at this high temperature.
    3. Ductility: the air conditioner
    Tube is to do anti-corrosion treatment and then expand mouth, bending molding and other processing, at this time the external coating can not fail more can not fall off, so the external coating has the corresponding good ductility.
    4. Weldability: the outer coating
    Must be weldable with copper pipe. The above conditions greatly limit the optioanl solution of the outer coating of stainless steel pipe with air conditioning, and also improve the technical difficulty.
  • Pipe Cleanliness
    The original standard stipulates that the residue of inner surface cleanliness of double-layer coil welded steel pipe is not more than 0.16g/m2, the air conditioning industry requires that the residue is not more than 38mg/m2, and the lowest requirement is not more than 25mg/m2.

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