Seamless Pipe vs. EFW Pipe

In the petroleum, chemical, power, construction, and high-end manufacturing industries, the choice of steel pipe type directly affects system safety, service life, and overall cost. Among the many types of steel pipes, seamless pipe and electric fusion welded pipe (EFW pipe full form) are the two most frequently compared.

This article will provide a systematic comparative analysis of the two from the perspectives of definition, manufacturing process, mechanical properties, corrosion resistance, standards, application scenarios, and cost to help you make a more reasonable selection.

What is Seamless Pipe?

Seamless pipe is made from a single piece of metal. The metal is heated and formed into a pipe. Seamless steel pipes are stronger than arc-welded steel pipes and can withstand higher pressures. Seamless steel pipes are available in various sizes, but cannot be customized like arc-welded steel pipes.

1. Characteristics of Seamless Pipes

No weld seams, continuous structure;

High pressure resistance; dense structure, uniform mechanical properties;

More suitable for high-pressure, high-temperature, and high-risk working conditions.

2. Common Seamless Pipe Standards

ASTM A106 / ASTM A53 / A179 / A192

ASTM A312 (Stainless Steel)

EN 10216

GB/T 8162 / 8163

What is EFW in Pipe?

EFW (Electric Fusion Welded) pipe is made of welded steel plate. The steel plate is rolled and then welded. As a type of seam pipe, it is typically used to transport high-pressure fluids or gases. EFW pipes are available in various sizes and can be customized according to customer needs.

1. Characteristics of EFW Pipe

Made from steel plate/strip;

Welding method: electrofusion welding (non-resistance welding);

Commonly found in medium to large diameter, stainless steel or alloy steel pipes;

Welds require non-destructive testing such as RT/UT/PT.

2. EFW ≠ ERW

ERW: Resistance welding, does not melt metal

EFW: Electrofusion welding, weld metal is completely fused (common in stainless steel)

3. Common EFW Standards

ASTM A358 (Austenitic stainless steel EFW)

ASTM A672 / A691 (Carbon steel / Alloy steel EFW)

EN 10217 / EN 10216 (partial European system)

Seamless Pipe vs. Seam Pipe

1. Seamless Pipe Symbols

Seamless steel pipes refer to steel pipes produced without welds through rolling, extrusion, or forging. Their symbols generally consist of the following parts:

Pipe Cross-Sectional Shape Symbol

Round: Φ

Square: ◇

Rectangular: []

Seamless Pipe Material Symbol

Carbon steel: A

Carbon-manganese steel: B

Carbon-chromium steel: C

Chromium-molybdenum steel: D

Chromium-chromium-molybdenum steel: E

Stainless steel: F

Manufacturing Process Symbol

Hot-rolled: R

Cold-drawn: B

Hot-drawn: S

For example: Φ89×6mm A R indicates a seamless pipe with a diameter of 89mm and a wall thickness of 6mm, hot-rolled from carbon steel.

2. Seam Pipe Symbols

Seam pipes are pipes manufactured by welding. Their symbols generally consist of the following parts:

Pipe Cross-Section Shape Symbols

Circular: Φ

Square: □

Rectangular: []

Seam Pipe Material Symbols (same as above)

Manufacturing Process Symbols

Resistance welding: ERW

Arc welding: EFW

Electrofusion welding: EFW

For example: Φ89×6mm A ERW indicates a welded pipe with a diameter of 89mm and a wall thickness of 6mm, made of carbon steel by resistance welding.

Seamless Pipe VS. EFW Pipe

1. Manufacturing Process

Seamless Pipe: Formed in one piece without weld joints, resulting in more even stress distribution and higher reliability.

EFW Pipe: Welded from steel plates, the microstructure of the weld area differs from the base material. Under high stress or extreme conditions, the weld may become a potential weak point.

2. Strength and Durability

Seamless Pipe: Seamless steel pipes have high strength and good durability because they have no weld seams. Their design allows them to withstand higher pressures and temperatures, making them ideal for harsh applications.

For example, seamless pipes are often the preferred choice in high-temperature steam pipelines and chemical reaction units.

EFW Pipes: EFW pipes also exhibit good mechanical properties in low- and medium-pressure systems, especially when using low-carbon or low-sulfur, low-phosphorus stainless steel materials (such as 304L and 316L), where their overall performance meets most industrial requirements.

3. Corrosion Resistance

Seamless Pipes: Due to the absence of welds, seamless pipes have a more uniform surface, generally exhibiting superior corrosion resistance in harsh environments.

For example, 304L stainless steel seamless pipes are ideal for environments with extremely high corrosion resistance requirements, such as chemical plants or marine environments.

EFW Pipes: While EFW pipes possess a certain degree of corrosion resistance, the weld seams can be more susceptible to localized corrosion if not properly treated.

The weld area of EFW pipes is more prone to localized corrosion in extremely corrosive environments, but with post-weld heat treatment and rigorous weld inspection, its service life can still meet the requirements of most industrial applications.

4. Cost

Seamless Pipe Price: Due to its complex manufacturing process, seamless pipe is more expensive. Although the cost per ton is higher, its reliability and service life in high-risk, high-load conditions often reduce long-term maintenance costs.

EFW Pipe Price: Due to its simpler manufacturing process, EFW pipe is less expensive than seamless pipe. This makes it an ideal choice for industries where cost considerations are important and requirements are not stringent.

5. Size Flexibility

EFW pipe has a significant advantage in terms of size and customization capabilities. The welding process allows for greater flexibility in large diameters, non-standard sizes, and standard lengths, and also makes it easier to control delivery cycles.

In contrast, the production of seamless steel pipe is limited by billet specifications and equipment capabilities, resulting in a relatively standardized size range, but it has advantages in thick-walled and high-performance requirements.

6. Welded Joints

Seamless Pipe: Seamless pipe requires no welding during manufacturing, therefore it has no welded joints or seams along its length. This characteristic improves reliability and strength, and reduces the risk of leaks or failures at joints.

EFW Pipe: EFW pipes have welded joints along their length because they are made by fusing two separate sheets or coils of material. These welded joints may have slightly different properties than the base material and are prone to potential defects or corrosion.

7. Wall Thickness

Seamless Pipe Thickness: Seamless pipes typically have thicker walls, making them suitable for high-pressure applications requiring extremely high strength and durability. Due to their uniform structure, seamless pipes can withstand higher internal pressures.

EFW Pipe Thickness: EFW pipes can be manufactured in various wall thicknesses. However, they are generally used in applications where pressure ratings are not as high as for seamless pipes.

8. Typical Applications

Preferred Applications for Seamless Pipes: High-pressure steam lines, oil and gas transportation, chemical plants, boiler and heat exchanger systems.

Preferred Applications for EFW Pipes: Building structures, water supply and drainage systems, medium and low-pressure fluid transportation, large-diameter stainless steel piping projects.

FAQ

1. Are EFW pipes and ERW pipes the same?

No.

ERW stands for resistance welding, while EFW stands for electrofusion welding. Both are commonly used for stainless steel and thick-plate welded pipes.

2. Are seamless pipes always better than welded pipes?

No.

Seamless pipes offer superior performance but are more expensive. The choice should be made based on the specific operating conditions.