The stainless steel pipes for air conditioners have a long period from procurement to end use, especially for indoor unit pipes and indoor and outdoor unit connection pipes. The cycle is longer, even more than one year. In order to ensure the normal use of bent pipes, stainless steel pipes are required to have no obvious aging phenomenon.
A high work hardening index n facilitates deep drawing and the material has a higher elongation. However, when used in the air-conditioning industry, the stainless steel tube hardens too quickly when repeatedly bent, which will eventually cause the bend to become unusable. Therefore, the work hardening index n value of the stainless steel pipe for air conditioning should be as small as possible, but the smaller the n value, the lower the elongation of the material. Therefore, a reasonable choice is needed.
Tensile strength Rm: The original standard Rm≥290mpa is not much different from the air-conditioning industry≥270mpa.
Yield strength rel: According to the original standard, rel≥180mpa; For the air-conditioning industry, it is hoped that the lower the rel value, the better and easy to deform. Now requires rel≤180mpa, rel≤140mpa;
Elongation after breaking a: The original standard stipulated that a≥25%; the air-conditioning industry hopes to reach the copper pipe index, which requires a≥38%, and the most ideal is a≥40%.
The selection of the outer surface anticorrosive layer of the original standard is determined by both the supplier and the buyer through consultation. After the galvanized anticorrosive layer is passivated, the neutral salt spray test (NSS) can be divided into five levels of A, B, C, D, and E. The longest corrosion resistance of the E level is 200h. The requirements are much higher than the requirements of this standard, and the anticorrosive coating of its outer coating must meet the following four conditions at the same time:
(1) Corrosion resistance: Since the outdoor unit of the air conditioner has been exposed for many years, the use conditions are quite harsh, mainly due to the condensation on the outer surface of the pipe during the operation of the air conditioner, and the corrosion resistance of the outer coating is very high. The corrosion resistance time of the neutral salt spray test must be greater than 500h, and some users even require the corrosion resistance time to be greater than 1000h.
(2) High temperature resistance: In the production of air conditioners, the connection between various components is completed by mutual welding. The solder temperature is about 800 ° C, but the torch flame temperature is higher. At this high temperature, the outer coating of the pipe cannot fail and melt.
(3) Ductility: After the anti-corrosion treatment of the air-conditioning tube, the air-conditioning tube is expanded and contracted and bent to form. At this time, the outer coating cannot fail or fall off, and it is required that the outer coating has good ductility.
(4) Weldability: The outer coating must be weldable to the copper pipe. The above conditions greatly limit the choice of outer coatings for stainless steel pipes of air conditioners, and also increase the technical difficulty.