Types of Welded Steel Pipes

Welded steel pipe meaning: Welded steel pipes & tubes refer to steel pipes with seams on the surface that are formed by bending steel strips or steel plates into round, square and other shapes and then welding them. The blanks used for welded steel pipes are steel plates or strips. Its core feature is the presence of one or more longitudinal or spiral welds, which is different from the overall rolling structure of seamless pipes.

What is a carbon steel welded pipe?

Carbon steel welded pipes are steel pipes made of carbon steel as the main material through welding processes. Its carbon content is usually ≤0.25% (low carbon steel), with the characteristics of low cost, moderate strength and easy processing. It is the most widely used type of welded pipe in the industrial field.

Types of welded steel pipes:

Carbon steel welded pipes can be divided into straight seam welded pipes (ERW/LSAW) and spiral welded pipes (SSAW) according to the shape of the welds.

Straight seam welded steel pipes (ERW/LSAW):
According to different production processes, they are divided into ERW pipes and LSAW pipes. Straight seam welded steel pipe is a steel pipe made by welding the edges of hot-rolled or cold-rolled steel plates or strip coils in a straight line on welding equipment (named because the weld of the steel pipe is in a straight line). This kind of steel pipe has a simple production process, high finished product efficiency, good strength and low cost, but the strength is slightly lower than the spiral welded steel pipe of the same specification.

What is ERW steel pipe?

ERW steel pipe (Electric Resistance Welded Pipe) is a longitudinal welded steel pipe manufactured by high-frequency resistance welding process. It is widely used in the fields of oil and natural gas transportation, building structure, urban pipeline network, etc. ERW steel pipe uses the skin effect and proximity effect generated by high-frequency current to instantly heat the edge of the tube blank to a molten state, and then forms a continuous weld by extrusion roller crimping to achieve production.

The Electric Resistance Welding process has the characteristics of high efficiency, low cost, material saving and easy automation. It is widely used in aviation, aerospace, energy, electronics, automobile, light industry and other industrial sectors, and is an important link in the welding process.

What is LSAW steel pipe?

LSAW steel pipe (Longitudinal submerged arc steel pipe) is a steel pipe with a weld parallel to the length of the steel pipe. It is made of a single medium and thick plate as raw material. The steel plate is pressed (rolled) into a pipe blank in a mold or a forming machine, and the pipe is produced by double-sided submerged arc welding and expansion. The finished product specifications of LSAW steel pipe are wide, the toughness, plasticity, uniformity and density of the weld are good, and it has the advantages of large pipe diameter, thick pipe wall, high pressure resistance, low temperature resistance and strong corrosion resistance.

When building high-strength, high-quality and long-distance oil and gas pipelines, most of the required steel pipes are large-diameter thick-walled straight seam submerged arc welded pipes. According to API standards, in large-scale oil and gas transmission pipelines, when passing through Class 1 and Class 2 areas such as high-cold areas, seabeds, and densely populated urban areas, straight seam submerged arc welded pipes are the only designated applicable pipe type. LSAW steel pipes are widely used in water supply projects, petrochemicals, chemical industry, power industry, agricultural irrigation, urban construction, etc.

Spiral welded pipe (SSAW):

SSAW steel pipe (spiral welded steel pipe) is a steel pipe manufactured by spiral welding process, which is widely used in oil and gas transportation, construction and chemical industry.
The strength of spiral welded pipe is generally higher than that of straight seam welded pipe. It can produce welded pipes with larger diameters with narrower billets, and can also produce welded pipes with different diameters with billets of the same width. However, compared with straight seam pipes of the same length, the weld length increases by 30~100%, and the production speed is lower. Therefore, smaller diameter welded pipes are mostly straight seam welded, while large diameter welded pipes are mostly spiral welded.

Application fields of welded steel pipes:

Welded steel pipes are widely used in many fields due to their advantages such as low cost, flexible specifications and mature technology. The main application scenarios are as follows:

1. Construction and municipal engineering ‌

Building structure ‌:
Used for load-bearing components such as columns, beams and stair handrails of steel structure buildings.
As a supporting member in the frame of super high-rise buildings, it replaces some seamless steel pipes to reduce costs.

Water supply and drainage system: 

Low-pressure fluid transportation (water, gas, heating), such as indoor heating mains, fire sprinkler systems (DN80 is common). 

Municipal water supply and drainage network, galvanized welded pipes are used for non-drinking water pipelines. 

2. Energy and industrial fields 

Oil and gas: 

Spiral welded pipes are used for long-distance oil and gas pipelines, and large-diameter design improves transportation efficiency. 

Low-pressure gathering and transportation pipelines (such as internal pipelines in oil fields) use straight seam welded pipes. 

Chemical and electric power: 

Welded pipes after anti-corrosion treatment (such as 3PE coating) are used for chemical medium transportation. Cable protection sleeves (galvanized or plastic-coated) ensure the safety of power lines. 

3. Agriculture and infrastructure 

Agricultural irrigation: 

Plastic-coated welded pipes (DN25-DN200) are used for farmland water conservancy, corrosion-resistant and have a service life of 30 years. 

Transportation facilities: 

As bridge piers and arch rib components in bridge engineering (high-frequency welded pipes have high strength). Spiral welded pipes for subway tunnel support.

4. Mechanical manufacturing and light industry

Mechanical equipment:
Special welded pipes such as transformer heat dissipation pipes and automobile exhaust pipes.

Furniture and decoration:
Welded thin-walled pipes are used for lamps and furniture frames, and stainless steel welded pipes are used for high-end decoration.

5. Special purposes

Steelmaking oxygen blowing: small-diameter oxygen blowing welded pipes (3/8-2 inches).
Conveyor rollers: Special roller pipes (diameter 63.5-219mm).

Note: High-pressure and high-temperature scenes (such as boiler tubes) require seamless steel pipes.

FAQ:

Q1: Will carbon steel welded pipes rust?
It will definitely rust! Unprotected Q235B will rust in 1-2 years in a humid environment and needs to be galvanized or coated for corrosion protection.

Q2: Can it replace seamless pipes?
It can be replaced under the following conditions:
Pressure ≤16MPa (ERW) or ≤70MPa (LSAW)
Pass 100% non-destructive testing.

Q3: How to identify inferior welded pipes?

a. Check whether the weld is straight and burr-free
b. Check whether the wall thickness is uniform (caliper measurement)
c. Check whether there are cracks/slag inclusions on the surface
d. Measure the thickness of the zinc layer

Conclusion:

Carbon steel welded pipes occupy more than 70% of the global welded pipe market due to their low cost, easy processing, and reliable strength. When selecting a model, it is necessary to comprehensively consider the medium pressure (select ERW/LSAW/SSAW), the corrosive environment (matching galvanizing/3PE anti-corrosion), and the standard compliance (GB, ASTM or API certification).

Read more: Types of Seamless Carbon Steel Pipes or Seamless vs ERW Pipe Cost