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Differences Between Seamless Steel Pipe and Welded Steel Pipe

Seamless steel pipe is manufactured by the round steel billet, through hot rolling, cold rolling, or cold drawn processes, with no seam on the pipe body.
Welded steel pipe is manufactured by a flat steel plate, with a welding seam on the pipe body. Including ERW pipe, LSAW pipe, SSAW pipe.

Octal tells you the differences between seamless pipe and welded pipe on raw material, manufacturing processes, performances, appearances, sizes, applications, cost prices, etc.

How is Seamless steel pipe made.

API 5L and ASTM Seamless steel pipe adopts steel ingot or solid tube as raw material through the perforated tube, then can be formed by hot rolled, cold rolled or cold drew. Hot-rolled seamless steel pipe is formed by billet forging, perforation, rolling, shaping, and other processes. For large diameter pipe, and thick-walled seamless pipe is usually made in this way. Cold drawn seamless pipe used cold-drawn forming technology. The material strength is relatively low, the appearance and internal control surface are smooth. Small diameter and thin wall seamless pipe usually made in this way. The seamless steel pipes are rolled by carbon structural steel, low alloy structure steel or alloy structure steel, and stainless steel. Seamless steel pipes applied in different industries: Line pipe for pipelines, thermal services, mechanical industries, chemicals, etc.

How is Welded steel pipe made

API 5L or ASTM welded steel pipe includes LSAW pipe, SSAW pipe, and ERW steel pipe. These pipes are made with steel strips or steel plates. The manufacturing processes first bending the steel plate, then welded into circular, square, and other shapes. Welded steel pipe has the characteristics of high production efficiency, low cost, and saving material. It has been widely applied to aviation, aerospace, energy, electronics, automobile, light industry, and other industries. With strong corrosion resistance in the acidic environment.

Why Should You Prefer To Buy Seamless Steel Pipes?

The reason why most people prefer seamless steel pipe over welded steel pipe is that seamless pipes can withstand extremely high pressure without cracking. But the seam or welded pipes cannot do the same as the welded points are vulnerable to cracking up under high pressure. Furthermore, it is very easy to accurately calculate the pressure of seamless pipes. Seamless pipes are also thinner and lighter than welded ones, and they also have uniformity of shape as they are made up of uniform extrusion of an alloy. If you are looking to buy the best quality of seamless steel pipes, you should use Octal Steel API 5L and ASTM seamless steel pipes.

Seamless vs welded steel pipe differences summary

API 5L / ASTM Seamless steel pipe and ERW welded steel pipe have some differences as below:

1. Appearance difference

Seamless steel pipe used steel billet as raw material. The outer surface defects of the billet cannot be eliminated by the hot rolling process, it is only polished after the product is finished. In the process of wall reduction, the defect can only get partially eliminated.

Welded steel pipe made by the hot-rolled coil as raw material, the surface quality of coil is just the pipe’s surface quality, and easy to control. The surface of the hot-rolled coil has high quality.

So Welded steel pipe surface quality is much better than the seamless steel pipe.

2. Molding process differences

Seamless steel pipe can be formed one time in the rolling process.
Welded steel pipe is manufacturing with steel strip or steel plate, through bending and different welding processes.

3. Performance and Usage

Seamless steel pipe has better pressure capacity, strength is higher than ERW welded steel pipe. So it is widely applied in high-pressure equipment, and thermal, boiler industries.
Generally, the welding seam of the welded steel pipe is the weak point, the quality affects overall performance.

In general, welded steel pipes can withhold 20% less working pressure than seamless ones. This reliability is the prime factor why people go for seamless steel pipes. As a matter of fact, all the industrial pipelines are done with seamless pipes only because the pipes undergo extreme thermal, chemical, and mechanical workloads. Welded pipes are more preferred in aerospace, automobile, and electronics industries where the budget is comparatively low, and so is the work pressure put on the pipes.

4. Available Sizes differences

For most seamless steel pipe manufacturers in China, they produce original seamless pipe sizes maximum OD in 20 inches, 508 mm. Where usually is smaller than 16 inches, 406.4 mm, because of the equipment limits. And if the client would like to purchase the seamless steel pipe more than the above sizes, then hot expanding machining shall be used. But usually, this kind of hot expanded seamless steel pipe quality could not compare with the original seamless steel pipe.
On the contrary, welded steel pipes don’t have these limitations, sizes available from 1-1/2 inch 48.3mm to 100 inches 2540 mm.

5. Cost and prices

Usually, the seamless steel pipe cost is higher than welded steel pipes, because of the raw material, manufacturing equipment, and processes. But sometimes by the market pressure, the welded pipe is more expensive, so if you met this situation, don’t hesitate to purchase the seamless steel pipe for the same dimensions.

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