ERW vs. LSAW vs. SSAW: Key Differences and How to Choose

ERW, LSAW, SSAW Welded Pipes: How to Choose?

In the fields of oil and gas transportation and structural piping, ERW, LSAW, and SSAW are the three most widely used welded steel pipes. ERW stands for Electric Resistance Welding, LSAW for Straight Seam Submerged Arc Welding, and SSAW for Spiral Submerged Arc Welding. Behind these three abbreviations lie completely different process routes, quality levels, and cost logics. Choosing the wrong one can either waste money or create safety hazards.

The most fundamental difference between the three types of pipes: weld seam and diameter.

ERW is a straight seam high-frequency weld, relying on resistance heat to fuse the two sides of the steel strip together without adding any filler. LSAW is also a straight seam, but it uses submerged arc welding, requiring the addition of welding wire and flux, and is a double-sided weld. SSAW is a spiral seam, also submerged arc welding, but the weld seam runs around the pipe.

Comparison of the core differences between the three types of welded pipes

Which one to choose depends on the project specifications and operating conditions. The table below lists key specifications such as caliber, weld seam, precision, and regional restrictions, making it easy for you to quickly filter based on your project requirements.

Comparison Items	ERW	LSAW	SSAW
Weld Seam	Straight seam, no filler metal	Straight seam, double-sided submerged arc welding	Spiral seam, double-sided submerged arc welding
Diameter Range	Maximum 24 inches (610mm)	16~60 inches (and above)	Up to 120 inches (3048mm) and above
Wall Thickness	≤25mm (mainly thin-walled)	Thicker, up to approximately 175mm	Medium, usually ≤25mm
Geometric Accuracy	Highest (uniform wall thickness, low ellipticity)	Good	Relatively weaker than straight seam pipes (higher ellipticity)
Quality Grade	Medium (depends on factory testing capabilities)	Highest (can be 100% RT tested)	Medium (long weld seam, high defect probability)
Applicable Regions	Unlimited (non-high-voltage trunk lines)	Applicable to Class 1/2/3/4 regions	Only applicable to Class 3/4 regions
Cost	Lowest	Highest	Relatively Low
Typical Scenarios	Gas, water transmission, building structures	Long-distance oil and gas trunk lines, submarine pipelines	Large-diameter water transmission, low-pressure gas transmission, pile foundations

The data in the table presents the conclusions; below, we'll discuss the reasons. The reason for such significant differences in diameter, precision, and applicable regions among the three types of pipes lies in their completely different forming and welding processes. Below, we'll break down how ERW, LSAW, and SSAW are manufactured, their advantages, and their disadvantages.

● ERW Welded Pipe: The Most Cost-Effective Choice for Small and Medium Diameters

ERW's raw material is hot-rolled steel strip, continuously cold-bent, and high-frequency welded, without filler metal.

Its biggest advantages are high dimensional accuracy, uniform wall thickness, and a smooth surface. The outer diameter tolerance can be within ±0.5%, which is very convenient during engineering installation—quick alignment, and welders are more willing to do it. In terms of price, ERW is the lowest among the three types of welded pipes.

However, it has significant disadvantages: it can only be made up to 24 inches (610mm) or less, and the wall thickness cannot be thickened. Furthermore, if parameters are not properly controlled during welding, defects such as gray spots and lack of fusion may occur—these are not detectable by every factory.

I've seen an ERW pipe on-site; it looked fine externally, but ultrasonic testing revealed lack of fusion in the weld. Therefore, when choosing ERW, the manufacturer's qualifications and testing capabilities are more important than price. ERW weld quality is reliable, provided the factory has complete non-destructive testing capabilities—even with the same standards, the actual quality of products from different manufacturers can vary significantly.

When to choose ERW?

For medium- and low-pressure scenarios such as city gas, water supply, and building structures, ERW is perfectly adequate and offers the best cost-performance ratio. If someone on a project says, "ERW pipes are fine," they usually mean this type of application.

● LSAW Welded Pipe: A Reliable Choice for High-Pressure Trunk Lines

LSAW uses a single medium-thick steel plate, pressed into a U-shape or O-shape in a mold, and then double-sided submerged arc welding. This is the most reliable welded steel pipe process. Understanding the core differences between ERW and LSAW is the first step in selecting the right type.

The weld is straight, fully penetrated on both sides, and there is also a diameter expansion process. Its toughness, plasticity, and uniformity are close to those of seamless pipes. More importantly, the weld seam can be 100% radiographically inspected—meaning you can accurately know the weld quality, giving you peace of mind.

However, there's a trade-off: it's expensive. LSAW production efficiency is much lower than ERW and SSAW, and material utilization is also lower, making it the most expensive of the three welded pipe types.

I participated in a branch line project of the West-East Gas Pipeline, designed for a pressure of 10 MPa, passing through a densely populated area. At the pipe selection meeting, someone suggested using SSAW, but it was rejected by the design institute on the grounds that "according to design specifications, only straight seam pipes can be used in this area." In the end, LSAW was used. In critical sections with high pressure and high requirements, LSAW is usually the only choice.

When to choose LSAW?

Large-diameter, high-pressure, long-distance trunk lines, submarine pipelines, high-altitude and cold regions, and densely populated Class I and Class II areas. In these places, it's not a question of whether you want to use LSAW; the design specifications require you to use it.

● SSAW Welded Pipe: A Low-Cost, Large-Diameter Option, But with Strict Limitations

SSAW pipe is formed by spirally rolling steel strips and welding simultaneously. Because the forming angle can be adjusted, the same width of steel strip can be used to roll pipes of different diameters, which is its greatest flexibility.

In terms of cost, SSAW is significantly lower than LSAW, and it can be made in very large diameters—over 3 meters. If we compare the costs of ERW and SSAW, ERW is cheaper for diameters below 24 inches, but the advantage of SSAW becomes apparent for diameters exceeding this. However, it has several unavoidable problems:

First, geometric dimensional control is not as good as with straight seam pipes, resulting in greater ovality. This makes on-site butt welding more challenging, requiring welders to spend considerable time adjusting. 

Second, the weld length is 1.2 to 1.5 times the pipe length, naturally increasing the probability of defects. 

Third, the stress on the weld is more complex, making stress concentration issues more pronounced than with straight seam pipes.

Crucially, design specifications strictly limit the use of SSAW. According to regulations for long-distance oil and gas pipelines, SSAW can only be used in Class 3 and Class 4 areas—simply put, areas that are not extremely cold, not subsea, and not densely populated. The US, Japan, and Germany generally do not recognize SSAW for trunk lines; Canada and Italy use it partially; and Russia uses it sparingly with very strict additional conditions.

This doesn't mean SSAW is of poor quality, but rather that it's the standard specification. If this isn't clear during the design phase, making changes during the construction drawing review stage will result in significant time and cost losses. So, under what circumstances should SSAW be prioritized over LSAW? The answer lies in the selection criteria below.

When to choose SSAW?

For large-diameter water transmission, low-pressure natural gas, pile foundation engineering, and structural support—in these non-critical scenarios—SSAW is the most cost-effective choice.

Conclusion: 

There is no absolutely better option among the three types of welded pipes, only the most suitable one. The core logic of selection is: choosing the solution with the lowest overall cost while meeting design specifications and operational safety requirements.

Selection Criteria	Recommended Pipe Type	Key Reasons
Diameter ≤ 24 inches, medium to low pressure, conventional media, cost-sensitive	ERW	High dimensional accuracy, lowest overall cost
Diameter ≥ 16 inches, high pressure, Class 1/2 areas, main lines	LSAW	Welds can be 100% RT inspected, highest quality reliability
Diameter ≥ 24 inches, medium to low pressure, Class 3/4 areas, non-critical scenarios	SSAW	Strong material adaptability, significant cost advantage for large diameters

Further Reading:

● Seamless vs Welded Steel Pipe: Process, Performance, Cost & Selection Guide
● ERW Pipe vs Seamless Pipe: Cost & Selection Guide