ERW Pipe VS Seamless Pipe: What's the Difference?

When we purchase steel pipes, we often come into contact with two products, ERW steel pipes and seamless steel pipes, which are widely used in our lives. So, what's the difference between the two? How to choose?

There are differences between ERW steel pipes and seamless steel pipes in production processes, physical properties ，application scenarios and so on. Below we will introduce the differences between ERW steel pipes and seamless steel pipes from these three aspects.

1. Production process
The biggest difference between ERW steel pipes and seamless steel pipes is that ERW has a weld seam, which is also the key to the quality of ERW steel pipes. The production process of ERW steel pipes generally adopts the resistance welding process. ERW welded steel pipes are made by bending steel strips or steel plates into the required shape, and then going through processes such as welding, heat treatment and mechanical processing.

ERW stands for resistance welding. Resistance welding has the characteristics of high production efficiency, low cost, material saving, and easy automation. Therefore, it is widely used in various industrial sectors such as aviation, aerospace, energy, electronics, automobiles, and light industry. It is one of the important welding processes. one.

Seamless steel pipes generally use perforation and rolling processes. Seamless steel pipes are characterized by no welds in the pipe and have high strength, toughness and corrosion resistance.

2. Physical properties
There are also differences in the physical properties of ERW steel pipes and seamless steel pipes. The strength, toughness, corrosion resistance and high pressure resistance of seamless steel pipes are better than those of welded steel pipes (ERW steel pipes). Therefore, seamless steel pipes are widely used in pipelines and equipment under high pressure, high temperature and special environments.

ERW steel pipes have good toughness and reliability and are suitable for transporting low-pressure liquids and gases such as oil and natural gas. ERW steel pipes are also widely used in manufacturing machines, constructing buildings, etc.

3.  Wall thickness tolerance
ERW steel pipe: using hot-rolled strip as the raw material, the thickness tolerance of modern hot-rolled strips can be controlled within 0.05mm, and seamless steel pipes are produced by round steel perforation, with large wall thickness deviations. The subsequent hot rolling can partially eliminate the wall thickness. Thickness non-uniformity, but currently the most advanced units can only be controlled within + 5 ~ 10% t, corresponding to steel tubes with a thickness of 8.94mm.
Seamless steel pipe: The limit of wall thickness control accuracy is 0.9mm.

4. Ovality

ERW steel pipe: cold-formed, so the outer diameter is controlled accurately and the fluctuation range is small.

Seamless steel pipe: The hot-rolled forming process is used. The raw material composition, cooling conditions, and cooling conditions of the rolls have a large impact on the outer diameter of the steel pipe. Therefore, it is difficult to control the outer diameter accurately and the fluctuation range is large.

5. Tensile test
The tensile properties of seamless steel pipes and ERW steel pipes meet API standards, but the strength of seamless steel pipes is generally at the upper limit and the plasticity is at the lower limit. In comparison, the strength of ERW steel pipes is at its best and the plasticity index is 33.3% higher than the standard. The reason is that the performance of the raw material and hot-rolled strip of ERW steel pipe is guaranteed by means of micro-alloying smelting, refining outside the furnace, and controlled cold and controlled rolling; seamless steel pipes mainly rely on means of increasing carbon content, which is difficult to ensure strength and plastic Reasonable match.

6. Appearance
The defects on the outer surface of the billet used in the seamless steel tube cannot be eliminated by the hot rolling process, and the defects can only be polished after the finished product is completed; the spiral channel left after the perforation can only be partially eliminated during the wall reduction process. 
ERW steel pipe uses hot rolled coil as the raw material. The surface quality of the coil is the surface quality of the ERW steel pipe. The surface quality of the hot rolled coil is easy to control and the quality is high. Therefore, the surface quality of the ERW steel pipe is far better than that of the seamless steel pipe. 

ERW steel pipe VS Seamless steel pipe: Different application scenarios.

There are also differences in the application scenarios of ERW steel pipes and seamless steel pipes.

1. Application scenarios of ERW steel pipes
ERW steel pipes are mainly used to transport low-pressure liquids and gases, such as tap water, gas, air conditioning water pipes, etc. ERW steel pipes are also widely used in construction materials, machinery manufacturing, power chemical industry and other fields. Compared with seamless steel pipes, ERW steel pipes are more affordable and suitable for some economically limited occasions.

2. Application scenarios of seamless steel pipes

Seamless steel pipes are mainly used in transportation pipelines and equipment under high pressure, high temperature and special environments. Specifically, seamless steel pipes are widely used in petroleum, natural gas, chemical industry, electric power, aerospace, pharmaceutical and other fields. In some special industries, such as the nuclear energy industry, seamless steel pipes are an indispensable material.

Tips: ERW welded pipe is formed by rolling strip and welding the seam, with tighter dimensional tolerances and less weight. The weld seam is heat treated after welding that no untempered martensite remains, and the weld flash can be removed from both inner and outer surfaces. ASTM A53 ERW steel pipe is a typical carbon steel pipe. It is largely used to convey fluids at low / medium pressures such as oil, gas, steam, water, air and also for mechanical applications.

Advantages and disadvantages:

The pros and cons of seamless pipe:
Seamless pipes are manufactured out of a solid block of steel and do not have any weld seam, which may represent a weak area (subject to corrosion, erosion and, general failure)
Seamless pipes have more predictable and precise shapes, in terms of roundness and ovality, compared to welded pipes.
The main disadvantage of seamless pipes is that their cost per ton is higher than the cost of ERW pipes of the same size and grade (Seamless vs ERW pipe compete in the range 2 to 20 inches)
Delivery times may be longer, as there are fewer manufacturers of seamless pipes than welded pipes (lower entry barriers exists for weldedpipes vs. seamless pipes)

Seamless pipes may have an inconsistent wall thickness across their length, indeed the general tolerance is +/- 12.5%

The pros and cons of ERW pipe:
Welded pipes are cheaper than seamless (ERW HFI type), as they are manufactured using steel coils as feedstock in less complex manufacturing plants.
Welded pipes have shorter lead times than seamless pipes, as the manufacturing base is larger.
Welded pipes have a consistent wall thickness, as they are manufactured using coils (ERW) or plates (LSAW), both subject to tight tolerance control.

The major "defect" attributed to welded pipes is that the presence of a weld seam constitutes a weakness factor. Whereas this may have been true in the past, this is becoming less and less true with the advances of the welding technologies in the last ten years.