The stainless steel welded pipe processing process is a continuous, precise, and modern industrial process. Its core is to transform stainless steel strip/sheet into pipe through forming and welding, and then further process it to achieve the required performance.

Detailed Steps

Phase 1: Raw Material Preparation
Uncoiling and Leveling:

The stainless steel coil is unwound and passed through a leveler to eliminate curling stress and flatten it.

Shearing and Butt Welding:

Irregularities at the beginning and end of the strip are trimmed. To ensure continuous production, the end of the previous coil is welded to the beginning of the next coil.

Looping:

This creates a buffer area to store a certain length of steel strip, ensuring that subsequent processes can continue during coil change and butt welding without disrupting production.

Phase 2: Forming and Welding (Core Process)
Forming:

The flat steel strip passes through a series of forming rollers, gradually bending it from a “C” shape to an “O” shape, ultimately forming a closed round tube.

Common Forming Technologies:

Roll Forming: The most commonly used process, using multiple roll passes to gradually form the pipe, offering wide versatility.

Spiral Forming: Used to produce large-diameter spiral welded pipe.

Welding:

This is the heart of welded pipe manufacturing. The closed pipe is welded together by welding equipment, fusing the joints.

Main Welding Methods:

Tungsten Inert Gas (TIG): Uses a tungsten electrode and inert gas shielding. It produces high-quality, aesthetically pleasing welds and is suitable for thin-walled pipes, precision pipes, and food-grade pipes. It is the most commonly used method for high-end pipe welding.

Plasma Arc Welding (PAW): Plasma arc welding offers more concentrated energy, faster welding speeds, and greater penetration, making it suitable for thick-walled pipes.

High-Frequency (HF) Welding: High-frequency welding offers extremely high efficiency and low cost, but weld quality is slightly inferior to TIG and is primarily used for structural and decorative pipes.

Laser Welding: Laser welding offers extremely high precision and a minimal heat-affected zone, making it an emerging high-end technology.

Submerged Arc Welding (SAW): Used for thick-walled, large-diameter steel pipes.

Stage 3: Finishing and Processing
Removing Internal and External Weld Bursts:

Excess weld burrs will form on the inside and outside of the pipe during welding. These must be immediately removed with a scraper or roller to create smooth internal and external surfaces.

Cooling and Sizing:

The welded pipe enters the cooling section. It then passes through a sizing mill, which gently compresses the pipe to ensure the outer diameter meets precise tolerances and improves roundness.

Straightening:

A straightening mill removes bends in the pipe and ensures its straightness.

Eddy Current Testing/Ultrasonic Testing:

In-line non-destructive testing. 100% weld inspection is performed to detect defects such as porosity, slag inclusions, and incomplete penetration. This is a critical step in ensuring weld quality.

Cutting:

The continuous run of pipe is cut into lengths according to order specifications.

Heat Treatment (Solution Treatment):

Purpose: Heat treatment is required for pipes used in critical applications (such as pressure pipes).

Relieves welding stresses.

Restores corrosion resistance in the weld and heat-affected zone (prevents intergranular corrosion caused by chromium carbide precipitation).

Produces uniform microstructure throughout the pipe.

Process: The pipe is heated to approximately 1040-1150°C and then rapidly cooled (quenched).

Pickling and Passivation:

Purpose: Removes the oxide scale on the pipe surface after heat treatment and rebuilds the passive film. This is a necessary step to restore and maintain the corrosion resistance of stainless steel.

Process: Typically, a nitric acid-hydrofluoric acid mixture is used for immersion or brushing, followed by thorough rinsing.

Stage 4: Final Inspection and Packaging
Final Inspection:

Hydraulic Pressure Test: A water pressure exceeding the operating pressure is applied to the pipe to check its strength and leak tightness.

Air Tightness Test: Compressed air or nitrogen is used to test the pipe’s leak tightness.

Appearance Inspection: Check surface finish and scratches.

Dimensional Inspection: Verify outer diameter, wall thickness, length, etc.

Material Analysis: Verify material certificates.

Marking and Packaging:

Spray or label the tube with information such as specifications, material, standard, and batch number.

Finally, bundle and package the tube to prevent damage during transportation.

Cherry
Website: www.jinyoumetal.com
Email: Cherry@jinyoumetal.com
WhatsApp/WeChat: +86 13373795593

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