Pipe is a kind of hollow steel, which can be divided into seamless aluminium tube and welded pipe according to the production process. Compared with seamless aluminium tubes, they also have different properties and applications. A skilled engineer used his eyes to clarify the difference between seamless and welded pipes. Do you know where and how to see it? End or surface? Is there any quick way? Today we will give you a detailed instruction on how to judge whether the aluminium tube is welded or seamless with the naked eye.

1. welding type

Generally speaking, there are two welding methods: seam welding and spiral welding. For seamless aluminium tubes without surface coating, if the weld can be clearly seen, there must be welded pipes. There are two common types of resistance welding and submerged arc welding, and the general resistance welding (RW, ERW or HFW).

But for high frequency welded pipe with high requirements for straight seam, it is necessary to remove the inner and outer cage after welding. Generally, it will protrude obviously, but there will be some bending bulge (insufficient deburring) or groove (too much deburring) in many or less. Some scaffolding welded pipes are usually provided with burr supply due to their low requirements and small size. As shown in the figure below, large-scale high frequency welded pipe with burr is undoubtedly welded pipe.

If ERW pipe breaks and is treated with internal and external corrosion protection, it is difficult to see if there is weld on the surface. Direct seam submerged arc welding (UOE, JCOE, etc.) involves the welding wire supply to the welding process, so there is obvious impact in the weld, even after coating, the weld can be found.

SRW pipe, commonly used in large welded pipe, is spiral curve along the length of pipe and is wound on the surface of pipe. There will be some obvious dents in the weld on the inner and outer surfaces. The welding arms can be seen even after coating. Sometimes spiral welded pipe also has ring welding blunt welding, there may be several circles of peripheral weld, generally there are convex welds on the inner and outer walls.

2. color and needle strip

Due to the high temperature heating and drainage treatment, the welding seam of high frequency welding pier and heat treatment area is blue, the color is obviously deeper than the surrounding, and it is distributed in strip shape, the width is roughly the same, and the depth has no obvious change. Seamless steel usually does not have a continuous groove of that length, sometimes rolling makes defects that look like strip steel urgent, but it is difficult to continue to distribute.

3. Accuracy and ovality of wall thickness

Seamless seamless aluminium tube is produced by rolling the sheet steel directly through the tube, which is complex deformation in three dimensions, and the precision of wall thickness is difficult to control. Generally speaking, the tolerance level of seamless aluminium tube wall thickness is about 12.5%, and the higher level can be achieved ± 8% to 10%, even ± 5%, most of these pipes are thick wall pipes.

The welded pipe is made of hot rolled / thick plate welded directly by steel plate or coil. The wall thickness depends on the thickness control accuracy of steel plate, which can usually be achieved ± Within 0.10 mm. Therefore, it is easier to weld pipes with high thickness and precision. At the same time, ERW welding pipe and UOE pipe have good roundness due to the increase of production process and diameter, and the ovality level can also be used as the basis for evaluating whether to weld. Low ovality tubes can be used for welding pipes.