Primary Production Processes for Hot-Rolled Seamless Steel Pipes

The production process of hot-rolled seamless steel pipes can be divided into the following three main steps:

Step 1: Preparation Work—Material Preparation and Heating

It all begins with a circular solid pipe billet, which can be a continuous cast billet, a rolled billet, or a forged billet. Before entering the formal rolling process, the billet must be uniformly heated to a specified high temperature in a heating furnace. This ensures it possesses good plasticity, preparing it for subsequent deformation.

Step 2: Core Deformation—Three Major Processes

This is the key to forming hot-rolled seamless steel pipes, encompassing three primary deformation processes:

Piercing—Solid to Hollow

The heated billet is fed into the piercing machine. Under the action of rollers and a piercing tool, the solid billet is pierced into a thick-walled hollow blank. This is the most distinctive step in seamless steel pipe production and the origin of the term “seamless.” Essentially, this step “sets the shape” of the pipe, defining its hollow circular cross-section.

Rolling and Drawing — Wall Thickness Reduction

The drawn blank has thick walls and short length. It is then sent to a rolling mill for drawing. Through rolling with mandrels, the blank's wall thickness is significantly reduced while its length increases, transforming it into a rough tube closer to the finished product. The primary task here is “wall thickness control,” precisely regulating the uniformity of the steel tube's wall thickness.

Sizing (Reducing) — Final Forming

At this stage, the blank pipe's outer diameter and wall thickness still fall short of final specifications. The concluding deformation process occurs on the sizing (reducing) mill. Through continuous multi-stand rolling, the blank pipe's outer diameter is precisely reduced to standard dimensions while further enhancing the pipe's surface finish and roundness. This step achieves “sizing,” ensuring the pipe's dimensions meet final requirements.

Step 3: Finishing and Inspection

After deformation, steel tubes undergo a series of processes to become final products:

Cooling and Straightening: Rolled tubes are cooled in a cooling zone, then straightened using a straightening machine to correct any bending that may have occurred during rolling.

Inspection: Each steel pipe undergoes rigorous quality control, primarily involving hydrostatic testing or various non-destructive testing methods to ensure no internal or external defects exist and that it can withstand specified pressure.

Marking and Storage: Finally, qualified steel pipes are marked and stored in the warehouse, awaiting shipment.

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