What are the welding processes for 304 stainless steel pipes

When producing stainless steel pipes, a flat steel strip is first formed and then shaped into a round tube shape. Once formed, the pipe's seams must be welded together. This weld greatly affects the formability of the part. Therefore, it is extremely important to select the appropriate welding technology to obtain a welding profile that can meet the stringent testing requirements in the manufacturing industry. 304 stainless steel pipe welding is an important step in stainless steel pipe processing. The welding process can be roughly divided into three types.

High-frequency arc pulse of 304 stainless steel pipes

In recent years, GTAW welding power sources, also known as high-speed switches, enable arc pulses exceeding 10,000Hz. Customers of steel pipe processing plants are the first to benefit from this new technology. The high-frequency arc pulse transmission causes the arc downward pressure to be five times greater than that of traditional GTAW. Typical features of improvements include increased burst strength, faster welding line speeds, and less scrap. Customers of steel pipe mills quickly discovered that the weld seam profile obtained with this welding process needed to be reduced. In addition, the welding speed is still relatively slow.

Brazing of 304 stainless steel pipes

The main issues that we need to consider in air brazing are that the brazing time needs to be as short as possible, the brazing temperature needs to be as low as possible, and the heat input into the social working environment must be balanced so that the temperature of the joint part will not be too high. As for brazing in a reducing atmosphere, this is in response to the automotive industry's requirements for stainless steel fuel rails and systems. In this application, chemical reduction of surface oxides relies on providing an oxide-free surface, which is required to allow wetting and flow of molten filler material. Precisely for the reason of our problem, brazing is usually performed in a continuous conveyor furnace, which is an arrangement of heat-resistant alloys, so that the enterprise can pass through the containing atmosphere. In furnaces where brazing is performed with a reduced ambient atmosphere, it is important to carefully analyze the control system hydrogen, oxygen, and water vapor levels. Usually, copper or copper-based alloy is used as filler material in reducing atmosphere furnace brazing, which means that the brazing temperature usually exceeds 1085°C.

Moving on to vacuum brazing, in most applications where stainless steel is brazed in a vacuum, high-temperature brazing metal is used. Vacuum brazing temperatures are usually "high", that is, over 1000°C. This provides the opportunity for some heat treatment as part of the brazing operation cycle. As part of the process, the furnace can be "filled" with an inert gas to help "flush" any residual air out of the capillary path of the parts to be brazed. The gas is removed before the brazing operation begins. Inert gases can be used by the company to accelerate cooling after the filler solidifies.

Laser welding of 304 stainless steel pipes

In all seamless pipe welding applications, the edges of the steel strip are melted and solidified when the edges of the seamless pipe are squeezed together using clamping brackets. However, the characteristic property of laser welding is its high energy beam density. The laser beam not only melts the surface layer of the material but also creates small holes that narrow the weld. Power densities below 1 MW/cm, such as GTAW technology, cannot produce sufficient energy density to create keyholes. In this way, the keyholeless process results in a wide and shallow weld profile.

The high precision of laser welding results in more efficient penetration, which reduces grain growth and results in better metallographic quality. On the other hand, the higher heat input and slower cooling process of GTAW results in a rough welded structure. Generally speaking, it is believed that the laser welding process is faster than GTAW, they have the same scrap rate, and the former brings better metallographic properties, which brings higher blast strength and higher formability. Compared with high-frequency welding, laser-processed materials do not oxidize, have lower scrap rates, and have higher formability.

The above is the brazing process of 304 stainless steel pipe. The high-frequency arc pulse welding speed is relatively slow. Brazing requires the brazing time to be as short as possible and the brazing temperature to be low; the brazing temperature in the reducing atmosphere furnace usually exceeds 1085°C; the vacuum brazing temperature is, over 1000℃. Laser welding processes have lower scrap rates.