How is 316 stainless steel pipe produced?

316 stainless steel pipe has good corrosion resistance and high-temperature resistance and is often used in chemical, food, light industry, mechanical instrumentation, and other industrial transportation pipelines and mechanical structural components. Do you know how 316 stainless steel pipes are produced? Let’s find out together.

1. Material selection

The cold-rolled stainless steel strip is used as the raw material, and the surface state is BA grade. Before the steel strip is used in the factory, a detailed inspection of the steel strip must be carried out. Inspection items include thickness, width, edge quality status, appearance, and physical performance inspection. When necessary, the grain size of the raw material should be checked, and it can be used for production after passing the inspection.

2. Unwind

Before the steel strip enters the welded pipe unit, it needs to use the steel strip uncoiler to unwind the steel strip. For the steel strip after comparison, it is necessary to add a leveling mechanism to level the steel strip to ensure that the steel strip enters the welded pipe unit in a straight state. The forming part of the steel strip is successfully completed.

3. Tube blank forming

Using continuous roll forming equipment, the steel strip is continuously rolled and deformed to form an open tube blank. The steel strip needs to pass the joint action of several functional modules including the import module, the rough rolling module, and the closing module of the welded pipe unit. Bend to form an open tube blank, ready to be welded into a 304 stainless steel tube.

4. Continuous welding

After the steel strip passes through the continuous roll forming unit, it is made into an open tube blank. Using TIG welding equipment, continuous welding is performed to make round tubes. Argon is used as a protective gas during the welding process to prevent the weld from being oxidized in contact with oxygen before it solidifies and cools. Argon gas is introduced into the tube to protect the internal welding seam, and the argon gas introduced into the welding torch is used to protect the tungsten electrode. A protective layer of argon gas is formed around the molten pool to protect the molten pool and weld from oxidation.

5. Weld leveling

Due to the impact of the welding current and the influence of gravity, the internal weld of the 316 stainless steel pipe will be protruded, and the external weld will also be depressed. If these problems are used in an ordinary low-pressure fluid environment, they will not have an impact. If it is used in a high temperature, high pressure, high-speed fluid environment, it will cause problems in use. This defect must be eliminated with dedicated weld leveling equipment.

6. Online heat treatment

During the roll-bending process of the steel strip, work hardening will occur, which is not conducive to the post-processing of the pipe, especially the bending of the pipe. During the welding process, there will be welding stress at the welding seam, which will cause a hidden danger of cracking in the later use process, which requires heat treatment.

At present, the commonly used heat treatment process is bright solution treatment in a hydrogen protective atmosphere. The 304 stainless steel pipe is heated to above 1050°. After a period of heat preservation, the internal structure and morphology are transformed to form a uniform austenite structure. Under the protection of the atmosphere, no oxidation occurs.

7. Sizing and finishing

The outer diameter of the welded pipe will be deformed during the welding and heat treatment process, causing the outer diameter to fail to meet the requirements of use, and it needs to be sized and finished. The commonly used sizing and finishing unit consist of 4 sets of flat rolls and 4 sets of side rolls. The flat rolls are designed to be flat oval (or round), and the side rolls are designed to be oval (or round). The amount of sizing depends on the outer diameter and wall thickness of the pipe, generally within the range of 0.20 to 0.50 mm. After sizing and finishing, the outer diameter tolerance of the tube can be controlled within ±0.05mm, which can fully meet the requirements of use accuracy.

8. Online flaw detection

Due to the certain pressure and the need for certain reliability, it is difficult to detect the internal defects of the weld by only relying on pressure testing. Online eddy current testing or ultrasonic testing can be used to conduct 100% real-time online testing. The welding state can be corrected at any time according to the alarm information to reduce the production of unqualified products.

9. Cut to length

Using online fixed-length cutting equipment, according to the length required by the customer, the fixed-length cutting can be performed by rotary cutting (chipless) technology. Deburring of ports.

10. Straightening

The straightness of the welded pipes produced by the roll-forming unit cannot meet the requirements of use. Generally, the straightness of such welded pipes needs to be controlled at 0.10/100mm. It is necessary to use a straightening machine to straighten the welded pipe to meet the required production requirements.

11. Stress test

Using an automatic static hydraulic testing machine, the 304 stainless steel pipe is subjected to a pressure resistance test. The feeding, flushing, pressure testing, and unloading are all completed automatically. After maintaining the pressure for a certain period of time, the unqualified welded pipes are sorted by the differential pressure method.

12. Wash and dry

After the welded pipe is mechanically processed, the final cleaning and drying are required to remove the coolant, oil, and other contaminants remaining on the inner or outer wall of the pipe, and then use hot air for drying to prevent rust during transportation and storage. Finally, the finished product inspection and packaging of the stainless steel welded pipe can be carried out.

The above is the production process of 316 stainless steel pipe manufacturers. The production process includes a series of processes such as material selection, uncoiling, tube blank forming, continuous welding, and welding seam leveling.