Advantages and Disadvantages of Straight Seam Steel Pipe

Straight seam steel pipe is a steel pipe whose weld seam is parallel to the longitudinal direction of the steel pipe. The production process of straight seam steel pipe is simple, with high production efficiency, low cost and rapid development. The strength of spiral welded pipes is generally higher than that of straight seam welded pipes. A narrower blank can be used to produce steel pipes with larger pipe diameters. The same width of blanks can also be used to produce welded pipes with different pipe diameters. But compared with the straight seam pipe of the same length, the weld length is increased by 30-100%, and the production speed is lower.

Straight seam steel pipes can be divided into ERW steel pipe and submerged arc welded straight seam steel pipes (LSAW) according to the production process. Submerged arc welded straight seam steel pipes are divided into UOE, RBE, JCOE steel pipes, etc. according to their different forming methods.

The length of the straight seam steel pipe is usually 300 mm-1200 mm, and the perforation temperature of the straight seam steel pipe billet varies with different raw materials.

Most of the heat-expanded straight seam steel pipes are around 1200°C. The higher the carbon content and other alloying elements, the lower the temperature. The key to the heating operation of the straight seam steel pipe is to minimize the amount of oxide scale, especially during heat treatment.

In the production process of straight seam steel pipes, since the primary processing is performed under heating, the heating operation is a very important process for determining the product. Furnaces for heating straight seam steel pipes are divided into heating furnaces and reheating furnaces according to their effects; the former is used to heat the blank from room temperature to processing temperature;the latter is used to reheat the blank to the necessary processing temperature during processing.

Improper heating of straight seam steel pipes will cause cracks on the inner or outer surface of the billet.

There are many ways to heat a straight seam steel pipe, but the first one is a suspension furnace. This kind of heating furnace has an annular furnace bottom, which can be slowly changed. The billet is loaded from the inlet along the diameter of the bottom. When the outlet is used, it can be heated evenly to the normal temperature. The key to this heating operation is to evenly heat the billet to be suitable for processing. temperature.

Since perforation has a great influence on perforation, that is to say, the temperature of perforation processing is an important condition, so it is generally necessary to control the temperature of the blank during perforation processing.

Disadvantages of hot-rolled straight seam steel pipe:

1.Residual stress caused by uneven cooling. Residual stress is the internal self-balanced stress without external force. Hot-rolled steel sections of various sections have such residual stresses. Generally, the larger the section size of the steel section, the larger the residual stress. Although the residual stress is self-balanced, it still has a certain influence on the performance of steel components under external force. For example, it may have adverse effects on deformation, stability, fatigue resistance, etc.;

2.After welding, the non-metallic inclusions inside the straight seam steel pipe are pressed into thin slices, and delamination occurs. The delamination greatly deteriorates the tensile properties of the straight seam steel pipe in the thickness direction, and it is possible that the interlayer tear occurs when the weld shrinks. The local strain induced by weld shrinkage often reaches several times the yield point strain, which is much larger than the strain caused by the load.

Advantages of submerged arc welding longitudinal seam steel pipe:

It can destroy the cast structure of the steel ingot, refine the grain of the steel, and eliminate the defects of the microstructure, so that the steel structure is dense and the mechanical properties are improved. This improvement is mainly reflected in the rolling direction, so that the straight seam steel pipe is no longer isotropic to a certain extent; the bubbles, cracks and looseness formed during casting can also be welded under the action of high temperature and pressure.