Why Use Seamless Pipe instead of ERW Pipe?

Why use Seamless Pipe instead of ERW Pipe?

There are two benefits to using seamless pipes. First of all, the working pressure capacity of seamless pipe is 20% higher than that of ERW steel pipe, and applying higher pressure levels will not cause the pipe to fail or burst. Another, more common reason for choosing seamless pipes is that they are less susceptible to intergranular corrosion. Unlike seamless pipes, the seam lines of welded pipes, especially the heat-affected zone or heat-affected weld zone, are affected at the grain boundaries due to sensitization. This promotes intergranular corrosion, which weakens the ERW pipe.

Cost difference between seamless pipe and ERW pipe:

Since the manufacturing process of seamless pipes is longer and involves more processes, the cost of seamless pipes is always higher compared to welded pipes. ERW pipe uses cold-formed sheets that are then joined together by high-frequency welding, a relatively simple process that costs a fraction of the cost of seamless varieties.

Why does the oil and gas industry choose seamless pipes?

The use of seamless pipes is suitable for all high pressure operations. In the oil and gas industry, media flowing through the system exerts strong forces on the pipes, especially at higher temperatures. This powerful force combined with the increase in temperature creates high stresses on the pipes. In the case of seamless pipes, their pressure-bearing capacity is almost 20% higher, making them ideal for use in the oil and gas industry.

ERW pipe manufacturing process:

Electric resistance welded pipe, or ERW pipe for short, can be produced by cold forming steel plate into a cylindrical shape. After cold forming, an electric current is passed between the two edges of the steel. The electric current heats the cold-formed steel plate to such an extent that the edges are simultaneously stressed to form a bond. The bond formed during this welding process is achieved without the use of weld filler material. To achieve the highest quality welds, the high-frequency ERW process is considered the most commercially viable option.

Seamless pipe manufacturing process:

Unlike welded pipes, the procedure to manufacture Seamless pipes is longer and more intensive. This process uses heat and several other operations to achieve the final product. Raw steel is first heated and cast into solid billets. These solid billets mold the raw steel alloy into the shape of a cylinder. Upon achieving the cylindrical shape, the raw steel pipe is then rolled until a stretched and hollowed product is created. This newly created product has a center that is irregularly shaped. To get a more even surface and uniform shaped hollow, a bullet-shaped piercer point is rammed through the center of the billet even as the billet is being rolled.

How to identify stainless steel seamless pipe or ERW pipe?

Pipes are produced in various specifications. However, if ASTM A53 specifications are used in its construction, the pipe will be marked through a template.  If the stencil print mentions Type S, the pipe has a seamless construction. On the other hand, if Type E has been stenciled onto the pipe, it indicates that the construction is an Electric resistance welded kind. Another way to confirm welded pipe is to use UV inspection. Under UV light irradiation, the grain structure of the pipe weld area will show obvious differences. Today, welds can still be inspected via UV inspection, despite surface treatments to minimize them.