Common situations encountered during welding of refrigeration equipment

Welding in refrigeration systems generally uses non-ferrous metal materials such as copper and aluminum. In the manufacturing, installation, and maintenance processes, pipeline welding is a key link that directly affects the effectiveness, service life, and after-sales of equipment operation. Therefore, this article is specially issued in the hope of attracting the attention of industry practitioners. Let's take a look together, what are the effects of poor welding? How to avoid welding hazards?
1. What are the effects of poor welding?
Firstly, welding issues: Poor welding may result in leakage points
The original function of welding is to connect refrigeration equipment, so as to connect the inner and outer units and form a closed system between them. The refrigerant can circulate and flow inside the inner and outer units. Generally, the large pipe passes gaseous refrigerant, and the small pipe passes liquid refrigerant. What is the use of refrigerant?

Refrigerant, also known as refrigerant, refrigerant, or refrigerant, is a medium substance used in refrigeration systems to complete energy conversion. Simply put, it means absorbing heat at the indoor unit, releasing heat at the outdoor unit, and transferring indoor heat to the outside through it. If the welding of the refrigeration system is not good, the refrigeration equipment will leak, and over time, not only will there be no refrigeration effect, but it is also more likely to damage the refrigeration compressor.
Secondly, welding issue: the formation of an oxide layer inside the copper tube
During the welding process, there was no standardized operation, resulting in the formation of black oxide scale on the inner wall of the copper tube. However, according to the proper operation shown in the lower right picture, the copper tube at the welding site was as bright as new, mainly due to the absence of oxide scale inside the tube.
It should be understood that if the oxide scale deposits on the indoor unit side, the refrigerant flow rate of the indoor unit may be greatly affected, and the refrigeration effect may not achieve the expected effect. If the oxide skin enters the compressor, it will increase compressor wear (reduce service life), and even directly cause compressor damage.
Always, no matter what kind of after-sales problems arise, it takes a lot of time and effort, so we should avoid such situations when installing and constructing refrigeration systems.
2. How to avoid welding hazards?
Firstly, the operation of nitrogen filling welding
How to prevent the formation of oxide scale inside copper pipes during welding? Just need to perform nitrogen filling welding! So why can nitrogen filled welding prevent the formation of oxide scale?
Because the chemical properties of nitrogen are very stable, nitrogen filled welding can prevent the formation of oxide scale on the inner wall of copper pipes at high temperatures. The air contains oxygen, and when welding copper pipes, oxidation reactions occur, producing oxides.
It should be noted that after welding, nitrogen gas should be continuously supplied for 3 to 5 minutes until oxidation no longer occurs. It is strictly prohibited to cool the surface of the copper tube with cold water. Additionally, it is emphasized that the protective gas for nitrogen filling must be nitrogen, and the use of oxygen is prohibited to avoid explosion hazards! During welding, the nitrogen pressure should be controlled at around 0.2-0.3kgf/cm2 and should not be too high.

Secondly, airtightness testing
After nitrogen filling welding is completed, it does not mean that the welding is good. If there are sand holes or bubbles in the welding, it needs to be re welded. Because airtightness testing is required. After the welding is completed, a pressure test must be conducted on the copper tube. Nitrogen gas at a certain pressure is filled into the copper tube to maintain pressure. Nitrogen gas is slowly injected from the low-pressure process port. If there is a liquid circuit solenoid valve in the system, the solenoid valve should be powered on first, and a positive pressure gauge should be hung at the high-pressure process port to detect the pressure.
R410A refrigerant needs to maintain a pipe pressure of 40 kilograms, while R22 refrigerant needs to maintain a pipe pressure of 20 kilograms. The holding time is 24 hours. The change in ambient temperature can cause a change in nitrogen pressure. For every ± 1 ℃ temperature difference in ambient temperature, there will be a pressure difference of ± 0.1 kgf/cm2.
Attention: It is still strictly prohibited to use oxygen for pressure maintenance. Oxygen can come into contact with the refrigeration oil in the refrigeration system, which can easily cause explosions!
3. Summary
Welding is a crucial step in the installation and construction process of refrigeration equipment. Improper welding may result in leakage points at the welding site; Oxidation scale is generated inside the copper tube during the welding process. The best way to prevent internal oxidation of copper pipes during the welding process is through nitrogen filling welding; A pressure holding test must be conducted to ensure that there are no leakage points at the welding point.