Nitrogen is a kind of inert gas that accounts for about 78% in the earth’s atmosphere, chemically stable and not easy to react with other substances. It is colorless, odorless, non-flammable and non-toxic. Under standard atmospheric pressure, its boiling point is -195.8°C. Through air separation techniques, such as low-temperature distillation or pressure-variable adsorption, nitrogen can be separated from air and made into nitrogen suitable for industrial use.
In welding applications, nitrogen purity is critical. Generally speaking, the purity of nitrogen used for welding needs to be 99.9% or more to ensure that it plays its full role in the welding process. Different welding processes and metal materials have different requirements for nitrogen purity. Strict adherence to relevant industry standards is the basis for safeguarding welding quality.
In the welding process, the welding area is very susceptible to the influence of oxygen, water vapor and other impurities in the air, resulting in oxidation, porosity and other defects in the weld. Nitrogen, as a protective gas, can form a layer of stable gas curtain on the surface of the welding molten pool, effectively isolating the air from the molten pool.
Due to the isolation of oxygen, metal oxidation is greatly inhibited, and the strength and toughness of the weld metal can be improved. For example, when welding stainless steel, nitrogen protection prevents oxidation of chromium and maintains the corrosion resistance of stainless steel. At the same time, nitrogen protection can also significantly reduce welding spatter and porosity, so that the weld surface is flatter and smoother, to achieve a higher standard of beauty and quality.
Nitrogen is particularly suitable for welding stainless steel, aluminum and aluminum alloys, copper alloys and other metals. In gas shielded arc welding (GMAW) and tungsten gas shielded arc welding (GTAW) and other processes, the rational use of nitrogen as a shielding gas can greatly improve the welding efficiency and quality.
When welding pipes, fittings and other closed structures, the residual air inside will have a serious impact on the welding quality. Nitrogen purging process is before welding, high-purity nitrogen gas into the pipeline, the air and other impurities completely discharged.
Through the nitrogen purge, can effectively avoid the welding process due to oxygen and water vapor caused by porosity, cracks and other defects, and at the same time to prevent oxidation phenomenon in the weld area, to ensure that the sealing of the welded joints and corrosion resistance. In the welding of pipelines in the chemical, petroleum, natural gas and other industries, nitrogen purging is an indispensable and critical step, which is directly related to the safe operation of the entire pipeline system.
In the high temperature welding process, the metal surface is very easy to oxidize with the oxygen in the air, resulting in a decline in metal properties. In addition, for carbon-containing metal materials, carbon will be combined with oxygen at high temperatures, decarburization occurs, affecting the strength and hardness of the material.
Nitrogen, by virtue of its chemical inertness, can effectively inhibit the occurrence of oxidation and decarburization reactions when welding. In welding carbon steel, alloy steel and other materials, the use of nitrogen protection or blowing, can reduce the generation of metal surface oxides, to maintain the stability of the carbon content, so as to ensure the mechanical properties of welded joints.
Post-weld heat treatment is an important part of improving the organization and properties of welded joints. In the annealing, stress relief and other heat treatment processes, nitrogen can be used to control the atmosphere of the treatment environment.
By charging nitrogen into the heat treatment furnace, can avoid metal oxidation at high temperatures in contact with oxygen, while helping to uniformly control the furnace temperature and atmosphere, reduce the residual stress of welded joints, improve their dimensional stability and comprehensive mechanical properties. In automobile manufacturing, machining and other industries in the post-welding treatment of parts, nitrogen is widely used.
Oxygen has flammability, and is mainly used in welding for gas welding, gas cutting and other fields, but in welding protection, it will exacerbate metal oxidation and can not be used as a protective gas. Argon is also commonly used welding protective gas, compared with nitrogen, argon is more inert, in welding some active metal protection effect is better.
However, the price of nitrogen is relatively low, and in some welding scenarios where the requirements for shielding gas are not extremely high, the use of nitrogen can significantly reduce costs. Enterprises can choose welding gases reasonably according to welding materials, process requirements and cost budget.
High-pressure cylinder gas supply is a more common way of nitrogen supply, its advantages are high flexibility, easy transportation and storage, suitable for small welding enterprises or small nitrogen usage scenarios. However, the storage capacity of cylinders is limited, and frequent replacement of cylinders will increase the transportation and management costs, and there are certain safety risks during transportation and use.
For large-scale welding operations, liquid nitrogen tanker gas supply can provide a more adequate and stable supply of nitrogen. The large storage capacity of liquid nitrogen reduces the frequency of container replacement and can meet the demand for long-time continuous welding. However, this method requires high storage and transportation conditions, and it needs to be equipped with special low-temperature storage equipment and transportation vehicles.
The on-site nitrogen production system directly produces nitrogen from air through pressure change adsorption or membrane separation and other technologies. This method does not need to rely on external gas supply, can be flexibly adjusted according to the actual demand for nitrogen production, long-term use of low cost, and high safety, easy maintenance, especially for large-scale welding production enterprises.
Although nitrogen is non-toxic, a large amount of nitrogen gathered in a confined space will lead to a decrease in oxygen content, triggering the danger of asphyxiation. In places where nitrogen is used, good ventilation must be ensured and oxygen concentration monitoring equipment must be equipped. Operators should strictly follow the safety regulations and wear appropriate protective equipment to avoid safety accidents caused by nitrogen leakage.
In the process of use, the flow rate and purity of nitrogen should be precisely adjusted according to the welding process and material characteristics. Too high or too low flow rate will affect the protective effect, and unsuitable purity may also lead to welding defects. At the same time, the gas supply equipment should be inspected and maintained regularly to ensure a stable and reliable supply of nitrogen to obtain the best welding results.
The various applications of nitrogen in the field of welding provide an effective means to improve welding quality and ensure production safety. With the continuous development of industrial technology, the application of nitrogen in welding will also be more extensive and in-depth, for the high-quality development of the manufacturing industry to continue to help. Enterprises should fully understand the characteristics and application advantages of nitrogen, combined with their own needs to choose the appropriate nitrogen supply and use of the program, in order to improve production efficiency at the same time, reduce costs and enhance product competitiveness.
