There are two main forms of common steel pipes, namely seamless and welded pipe. Because the cost of welded steel pipes is significantly lower than that of seamless steel pipes, some merchants process welded steel pipes in order to obtain more economic benefits, and then pretend to be seamless steel pipes, and then sell them into the market, causing market confusion. The processed welded steel pipe cannot be effectively distinguished from the appearance. Once in the process of engineering construction, welded steel pipes are used instead of seamless steel pipes, which will cause gas or liquid leakage, and in severe cases, it is easy to cause an explosion. Therefore, it is necessary to distinguish welded steel pipes from seamless steel pipes to ensure the quality of the project.
Welded steel pipes are generally formed by deforming steel strips or steel plates into round or square shapes under the action of external force, and then welding the seams on the surface to form welded steel pipes. Commonly used processes include arc welding, high frequency or low frequency, cold rolling, etc., but welding with these processes will result in welded seams in steel pipes. At present, according to the shape of the weld, it can be divided into straight seam and spiral welded steel pipe, but the processes used by the two are different. The spiral steel pipe is welded by submerged arc welding, which has the advantages of high welding efficiency and less dust. For high-frequency or low-frequency welding, it is mainly based on the principle of electromagnetic induction. Since the AC charge will cause proximity and turbine heating effects in the conductor, it can achieve the melting of the steel at the edge of the weld and finally complete the welding.
The seamless steel pipe is mainly to perforate a solid tube billet or steel ingot to make a capillary pipe, and then process it through hot rolling, cold rolling, cold drawing, etc., and then form a seamless steel pipe. Since the seamless steel pipe contains a hollow section, this hollow section can be used as a pipe for conveying fluid.
1. Distinguish welded steel pipes and seamless steel pipes according to the process
In the process of distinguishing welded steel pipes and seamless steel pipes according to the process, welded steel pipes are welded according to cold rolling, extrusion and other processes. In addition, when steel pipes are welded by high-frequency, low-frequency arc welded pipes and resistance welded pipe processes, spiral pipe welding and straight seam pipe welding will be formed. Round steel pipes, square steel pipes, oval steel pipes, triangular steel pipes, hexagonal steel pipes, rhombus steel pipes, octagonal steel pipes, and even more complex steel pipes will be formed. In short, different processes will form steel pipes of different shapes, so that welded steel pipes and seamless steel pipes can be clearly distinguished. However, in the process of identifying seamless steel pipes according to the process, it is mainly based on hot-rolled and cold-rolled treatment methods, and there are mainly two forms of seamless steel pipes, namely hot-rolled seamless steel pipes and cold drawn seamless tubing. Hot-rolled seamless steel pipes are formed by piercing, rolling and other processes, especially large-diameter and thick seamless steel pipes are welded by this process. The cold-drawn tube is formed by cold-drawing the tube blank. The strength of the material is lower, but its outer and inner control surfaces are smooth.
2. Classify welded steel pipes and seamless steel pipes by use
Welded steel pipes have higher bending and torsional strength, and more load-bearing capacity, so they are generally widely used in the manufacture of mechanical parts. For example, oil drill pipes, automobile drive shafts, bicycle frames, and steel scaffolding used in building construction are all made of welded steel pipes. However, seamless steel pipes can be used as pipes for conveying fluids because they have hollow sections and long strips of steel without seams around them. For example, it can be used as a pipeline for transporting oil, natural gas, gas, water, etc. In addition, the bending strength of seamless steel pipe is relatively small, so it is generally widely used in superheated steam pipes for low and medium pressure boilers, boiling water pipes and superheated steam pipes for locomotive boilers. In short, through the classification of uses, welded steel pipes and seamless steel pipes can be clearly distinguished.
In order to ensure a higher quality of engineering construction, it is necessary to distinguish welded steel pipes and seamless steel pipes, and then use suitable steel pipes for construction. In the process of distinguishing welded steel pipes and seamless steel pipes, metallographic and corrosion methods can be used to inspect the welds by observing the structure and welds, and finally accurately identify them. At the same time, the two types of steel pipes can also be distinguished according to their properties and uses, and then a reasonable steel pipe can be selected for construction.
When that project involves any type of piping, someone will have to make a decision between welded and seamless pipes.
That decision is not always a straightforward as it appears.For example, there are many regulations regarding the use of welded pipes.
This based on the materials traveling through the pipe and the pressure those materials will travel under.
Despite improvements in welding technology, a welded pipe can handle a maximum pressure 20% less than that of a seamless pipe.
A seamless pipe does not require any weld integrity testing and, in most cases, a heat treatment.
Meanwhile, a welded pipe cannot take the place of a seamless pipe due to strong regulations.
