A brief introduction to the practical advantages and diameter expansion technology of straight seam steel pipes

Straight seam steel pipes are welded by a welding method parallel to the longitudinal direction of the steel pipes and are widely used. With the same diameter and length, the welding length of the straight seam steel pipe is much less, while the welding length of the spiral steel pipe may increase by more than 30%. Due to the process of welding, the efficiency is relatively low, and the output is also quite low. However, for the same blank, generally, spiral welded pipes can obtain products of various diameters. In contrast, straight seam steel pipes cannot achieve this welding effect.

During the steel pipe production process, the core pumping machine had some technical problems, such as uneven wall thickness of the produced products, jamming, inner straightness, outer diameter out-of-tolerance, etc. How to improve the steel pipe and accelerate the production speed is an important issue in front of us. Laboratory experiments cannot solve production problems, and on-site experiments in the workshop are too costly and cannot last long. It is just that the conclusion of one or two experiments is unreliable. Therefore, it is very important to use numerical simulation methods to study the rolling process of straight seam steel pipes. At present, in our industry, the research object is the rolling speed and the key factor affecting the 5-stand MPM continuous rolling product—the roll gap value and the numerical simulation plan is established by using the relative equal load description method to study the key adjustable parameters (roll gap value and rolling speed) on the continuous rolling force and metal stacking, through the MARC platform, a finite element model of the rolling process of straight seam steel pipes was established to study its influence on the rolling force and wall thickness during the rolling process.

In my country, there is a demand for straight seam steel pipes in the petrochemical industry, water supply engineering industry, urban construction, power engineering, etc. The diameter expansion of straight seam welded pipe is a pressure processing process that uses hydraulic or mechanical means to apply force from the inner wall of the steel pipe to expand the steel pipe radially outward. Compared with the hydraulic method, the mechanical method has simpler equipment and higher efficiency. The expansion process of several large-diameter straight seam welded pipe pipelines in the world has been adopted.

The mechanical diameter expansion of the straight seam steel pipe uses the fan-shaped block at the end of the diameter expander to expand radially, so that the tube blank is stepped along the length direction, and the process of realizing the plastic deformation of the whole pipe length is segmented. Divided into 5 stages:

1. Initial full circle stage. The fan-shaped blocks are opened until all fan-shaped blocks touch the inner wall of the steel pipe. At this time, the radii of all points in the inner circular pipe of the steel pipe within the step range are almost the same, and the steel pipe obtains a preliminary full circle.

2. Nominal inner diameter stage. The fan-shaped block starts to reduce the moving speed from the front position until it reaches the required position, which is the required position of the inner circumference of the finished tube.

3. Springback compensation stage. The fan-shaped block starts to lower the speed at the position of the second stage until it reaches the required position, which is the position of the inner circumference of the steel pipe before spring back is required by the process design.

4. Stable pressure holding stage. The fan-shaped block remains stationary for some time at the inner circumference of the steel pipe before springing back, which is the pressure-holding and stable stage required by the equipment and diameter-expanding process.

5. Unloading and regression stage. The fan-shaped block retracts rapidly from the inner circumference of the steel pipe before springing back, until it reaches the initial diameter expansion position, which is the smaller shrinkage diameter of the fan-shaped block required by the diameter expansion process.