Types of welded steel pipes

Welded steel pipe is a steel pipe welded with steel plates or steel strips. Welded steel pipes have the advantages of simple production process, high production efficiency, many varieties, and low equipment costs, but their overall strength is lower than seamless pipes.

Welded steel pipes can be divided into straight seam welded pipes (LSAW and ERW Pipe) and spiral welded pipes (SSAW Pipe). The straight seam welded pipe process is simple, has high production efficiency, low cost and is developing rapidly. The strength of spiral welded pipes is generally higher than that of straight welded pipes, and welded pipes of different diameters can be produced with the same billet width. However, compared with straight seam pipes of the same length, the weld lengths are increased by 30% and 100% respectively, and the production speed is lower. Therefore, most small diameter straight seam welded pipes are mostly spiral welded. This article will introduce the types of welded steel pipes.

1. Welded steel pipes can be used for low-pressure fluid transportation, also known as ordinary welded pipes, commonly known as black pipes. Used to transport low-pressure liquid water, air, gas, oil, steam heating, etc. Steel pipes for connection are divided into ordinary steel pipes and thickened steel pipes according to wall thickness. According to wall thickness, they are divided into unthreaded steel pipes (smooth steel pipes) and threaded steel pipes. Steel pipe specifications are expressed in nominal diameter (mm), which is an approximate value of the inner diameter. It is customary to use inches, such as 11 inches, 2 inches, etc. Welded steel pipes are used for low-pressure fluids. They are not only used to directly transport fluids, but can also be used as raw materials for low-pressure galvanized welded steel pipes.

2. Galvanized welded steel pipes can be used to transport low-pressure working fluids, also known as galvanized welded steel pipes, commonly known as white pipes. It is used to transport water, gas, gas, oil and other general low-pressure fluids, such as heating steam, warm water or other hot-dip galvanized welded steel pipes (electric furnace welding or electric welding). Steel pipe walls are divided into ordinary galvanized steel pipes and galvanized thick steel pipes, galvanized steel pipes and threaded galvanized steel plates without threads. Steel pipe specifications are expressed in nominal diameter (mm), which is an approximate value of the inner diameter. Usually inches are used, such as 11x2, etc.

3. Ordinary carbon steel casing is a protective casing for industrial and civil buildings, installation of wire machinery and other equipment, and electrical equipment.

4. Straight seam welded steel pipe is a parallel steel pipe studied along the longitudinal direction of the steel pipe. It can usually be divided into metric welding process steel pipes, welding material thin-walled steel pipes, transformer cooling pipes, etc.

5. Spiral submerged arc welded steel pipe is a spiral welded steel pipe formed from hot rolled strip steel and often formed at high temperature. Double-sided submerged arc welding is used for pressure fluid transfer. Steel pipes have strong load-bearing capacity and good weldability. After various rigorous scientific and technical inspections and experiments, it is reliable in use. Mainly used for pipeline transportation of oil and natural gas.

6. Spiral seam high-frequency welded steel pipes for pressure fluid transportation are spiral seam high-frequency welded steel pipes, which are welded by high-frequency lap jointing methods. Hot rolled steel strip coils are often used as tube blanks. Strong bearing steel and plastic are easy to weld and process. After various rigorous scientific inspections and tests, it is reliable in use and is mainly used for the laying of oil and natural gas pipelines.

7. The spiral submerged arc welded steel pipe for low-pressure transportation uses hot-rolled strip steel as the blank, the spiral submerged arc welded steel pipe is a normal-temperature spiral low-pressure transportation steel pipe, and the hot-rolled strip steel is a normal-temperature spiral low-pressure transportation steel pipe. Rolled steel strip is a kind of tube blank. Used for general water, gas, steam and other low-pressure fluid transportation.

8. Generally, spiral seam high-frequency welded steel pipes for low-pressure fluid transportation mainly use hot-rolled strip steel as the tube blank and are formed at room temperature. The high-frequency lap joint method is used to weld spiral welded high-frequency welded steel pipes. Generally used for low pressure fluid transportation.

Welded Steel Pipe VS Seamless Steel Pipe

Method for identification of seamless and welded steel pipes:
 
Common steel pipe mainly has two forms of seamless steel pipe and welded steel pipe. In the process of engineering construction, appropriate steel pipes will be selected according to the specific construction situation, and the cost will be the primary factor.
 

1) Manufacturing process
Seamless steel pipe is mainly a solid tube billet or steel ingot for perforation, made of wool tube, and through hot rolling, cold rolling, cold drawing and other processing, and then formed seamless steel pipe. Since seamless steel tubes contain a members section, this hollow section can be used as a conduit for transporting fluids.
 
 A Welded steel pipe is generally a steel strip or steel plate under the action of external force, make it into a round or square, and then weld the surface joints, thus forming a welded steel pipe. The commonly used processes are arc welding, high or low frequency, cold rolling and so on, but the use of these processes for welding will lead to welded steel pipes. At present, according to the shape of welding seam can be divided into straight seam and spiral welded steel pipe, but the two use different technology. 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, mainly based on the principle of electromagnetic induction, due to the ac charge in the conductor will occur adjacent and turbine heat effect, can achieve the welding edge of steel to melt state, the final completion of welding.
 

2) Appearance difference
In appearance, the difference between seamless steel pipe and welded steel pipe is that the inner wall of the welded pipe has welding ribs, while seamless steel pipe does not. Seamless steel pipe pressure is higher, welded pipe is generally about 10 MPa. Seamless steel tube is formed once in rolling. Welded steel pipes need to be rolled and welded, generally spiral welding and direct welding. Performance seamless tube is better. Of course, the price is higher.

3) Wall thickness
The precision of seamless steel pipes is low and the wall thickness is relatively thick. The steel pipe of welded steel pipe has high precision and the wall thickness is usually thin.

4) Price
Seamless steel pipes are more expensive than welded steel pipes because the production process of seamless steel pipes is more complex and their costs are higher.

5) Performance characteristics
Seamless steel pipe: Because there are no welded joints, seamless steel pipe generally performs better in high temperature, high pressure, and corrosive environments. They are suitable for applications requiring high strength and high corrosion resistance, such as oil and gas transmission, chemical industry and high-pressure boilers. 

Welded steel pipe: The performance of welded steel pipe often depends on the quality of the weld. Although they can be used in many applications, welded joints can become a potential source of corrosion and weakness. However, with proper welding techniques and corrosion protection, the risk of these problems can be reduced. In terms of corrosion resistance, pressure bearing, high temperature resistance and other properties, seamless steel pipes are better than welded steel pipes.

6) Applicable fields
Seamless steel pipe: Due to their high-performance characteristics, seamless steel pipes are often used in applications that require a high degree of reliability and safety, such as nuclear power plants, high-temperature and high-pressure vessels, and chemical equipment.
Welded steel pipe: Welded steel pipe is suitable for some general engineering and low pressure applications such as building structures, hydraulic transmission and general piping systems. They are usually more affordable.

Seamless steel pipes and welded steel pipes each have advantages in different application areas. When selecting pipe materials, engineering needs, performance requirements, and cost factors need to be considered to determine which type of steel pipe is more suitable for a specific project.

Tips: ASTM A53 covers seamless and welded steel pipe with nominal wall thickness. The surface condition is usually black and hot-dipped galvanized. ASTM A53 is produced mainly for pressure and mechanical applications, and is also used for transport of steam, water, gas line pipes.