Steel Pipe Types: Seamless, Welded, ERW, LSAW, SSAW Explained

Introduction

Steel pipes are one of the most versatile engineering materials, used for everything from high-pressure oil pipelines to structural building columns. But not all steel pipes are created equal — they’re manufactured by different processes that give them different properties, pressure ratings, and cost.

This guide covers the main types of steel pipe, how they’re made, their pros and cons, and typical applications.

Steel Pipe Classification Overview

Steel pipes can be classified in several ways:

By Manufacturing Method

1. Seamless pipe — No weld seam, pierced from solid billet
2. Welded pipe — Rolled from plate/coil and welded:
   • ERW — Electric Resistance Welded (small-medium diameter)
   • LSAW — Longitudinal Submerged Arc Welded (large diameter)
   • SSAW / HSAW — Spiral Submerged Arc Welded (large diameter)

By Material

• Carbon steel (most common): Q235B, Q355B, A53, A106, API 5L
• Stainless steel: 304, 316L, 321, etc.
• Alloy steel: chrome-moly, high-temperature grades
• Galvanized steel: zinc-coated for corrosion protection

By Application

• Line pipe — oil & gas transmission (API 5L)
• Structural pipe — buildings, bridges, piles
• Process pipe — chemical, power, process industries
• Mechanical / tubing — machinery, automotive, hydraulic
• Water / utility pipe — plumbing, drainage, municipal
• Boiler / heat exchanger — high temperature/pressure

1. Seamless Steel Pipe

Seamless pipe has no weld seam — it’s a single, continuous hollow tube.

How It’s Made:

1. Heating: A solid cylindrical steel billet is heated to high temperature
2. Piercing: A piercing mandrel pushes through the center of the billet, creating a hollow shell
3. Elongation: The hollow shell is rolled and stretched to reduce wall thickness and increase length
4. Sizing: Final rolling to exact diameter and wall thickness
5. Heat treatment: Normalizing, quenching & tempering, or annealing as required
6. Finishing: Straightening, cutting, end finishing, testing

Key Characteristics:

• No weld seam — uniform strength around the full circumference
• Higher pressure rating than welded pipe of the same grade and dimension
• Wider range of wall thicknesses — from thin tubing to very thick-wall
• Uniform properties in all directions
• Better high-temperature and high-pressure performance
• More expensive than welded pipe
• Limited size range — typically 1/2" to 24" (larger sizes are possible but very expensive)
• Inside surface can be less smooth than ERW pipe

Applications:

• Oil & gas — well casing, tubing, high-pressure lines
• Boiler tubes — power plants, heat exchangers
• Hydraulic and pneumatic systems
• High-pressure process piping
• Bearing and mechanical applications
• Automotive and aerospace tubing
• Pressure vessels and boilers

Common Standards:

• ASTM A106 Gr. B — Carbon steel seamless pipe for high-temperature service
• API 5L Gr. B / X42–X80 — Line pipe grades
• ASTM A53 Gr. B — Seamless and welded (lower pressure)
• DIN 2448 / EN 10216 — European seamless pipe standards
• GB 8163 — Chinese seamless steel pipe for fluid transport
• GB 3087 — Low/medium pressure boiler tubes
• GB 5310 — High-pressure boiler tubes

2. ERW Pipe (Electric Resistance Welded)

ERW is the most common type of welded steel pipe.

How It’s Made:

1. Uncoiling: A steel coil is fed into the pipe mill
2. Forming: Rollers progressively form the flat strip into a round tube shape
3. Welding: High-frequency electric current melts the edges together under pressure — no filler metal needed
4. Bead removal: The internal and external weld beads are trimmed / smoothed
5. Sizing: Final sizing and shaping to exact diameter
6. Testing: NDT (non-destructive testing) of the weld
7. Cutting and finishing: Cut to length, end finishing

Key Characteristics:

• Smooth interior surface — better flow characteristics
• Consistent wall thickness — more uniform than seamless
• Tighter dimensional tolerances — better for threading and grooving
• Weld seam is the weakest point (but still strong for most applications)
• Available in long lengths (up to 12–18 meters or more)
• Lower cost than seamless pipe (typically 20–40% less)
• Size range: 1/2" – 24" (most common 1/2" – 12")
• Limited wall thickness — generally thinner than seamless

Applications:

• Water and wastewater — municipal piping
• Natural gas distribution — low/medium pressure
• Fire protection systems (sprinkler pipe)
• Structural applications — handrails, fencing, furniture
• Mechanical tubing — automotive, machinery
• Irrigation and agricultural piping
• Oil country tubular goods (lower grades)
• Construction scaffolding

Common Standards:

• ASTM A53 Gr. B (ERW) — Welded carbon steel pipe
• API 5L (ERW) — Line pipe, ERW grade
• EN 10217 — European welded steel pipe
• GB/T 3091 — Chinese welded steel pipe for general use
• ASTM A500 — Structural hollow sections

3. LSAW Pipe (Longitudinal Submerged Arc Welded)

LSAW pipe is made from steel plate formed into a cylinder with a single longitudinal weld.

How It’s Made:

1. Plate preparation: Steel plate is cut to the required width
2. Forming: The plate is bent into a “J” then “C” then “O” shape (JCOE process) or rolled on a plate roll
3. Welding: The longitudinal seam is welded using the submerged arc welding (SAW) process — inside and outside welds
4. Expansion: Hydraulic expansion for dimensional accuracy and stress relief
5. Testing: NDT of the weld, hydrostatic pressure testing
6. Finishing: End beveling, cutting, final inspection

Key Characteristics:

• Large diameter capability — from 20" to 60"+ (even larger possible)
• Thick walls — can handle higher pressures and structural loads
• Single weld seam — less weld length than spiral pipe
• High quality weld — SAW produces deep-penetrating, high-integrity welds
• Good for high-pressure large-diameter applications
• Heavier and stronger than spiral welded pipe for the same wall thickness
• More expensive than SSAW but cheaper than seamless large-diameter
• Short lengths — limited by plate width (typically 12m max)

Applications:

• Oil & gas transmission pipelines (high-pressure, large diameter)
• Water transmission mains
• Structural steel — columns, piles, caissons
• Pressure vessels and tanks
• Offshore structures — jacket legs, piles
• Penstocks for hydroelectric plants
• Heavy industrial process piping

Common Standards:

• API 5L (LSAW) — Line pipe, LSAW grade (PSL2)
• ASTM A671 / A672 — Electric-fusion-welded pressure pipe
• EN 10217-4 / -5 — European LSAW pipe standards
• GB/T 9711 — Chinese petroleum and natural gas pipe

4. SSAW / HSAW Pipe (Spiral Submerged Arc Welded)

Also called spiral welded pipe — made by forming strip steel into a helical (spiral) shape and welding the seam.

How It’s Made:

1. Uncoiling: A long strip of hot-rolled steel coil is fed into the mill at an angle
2. Forming: The strip is formed into a spiral (like a rolling paper) to create a pipe
3. Welding: Both the inside and outside spiral seams are welded using the SAW process
4. Sizing: Diameter is controlled by the feed angle and forming rolls
5. Testing: NDT of welds, hydrostatic test
6. Cutting: Cut to desired lengths

Key Characteristics:

• Very large diameters possible — 20" to 120"+
• Long lengths possible — not limited by plate width
• Continuous helical weld — more weld length than LSAW
• Lower cost than LSAW pipe for large diameters
• Good structural performance — spiral seam adds some rigidity
• Lower pressure rating than seamless or LSAW for same wall thickness
• Widely used for water, drainage, and low-pressure applications

Applications:

• Water supply and drainage — large-diameter mains
• Sewer and culvert pipe
• Low-pressure gas transmission
• Structural — piling, poles, towers
• Irrigation — large-scale water conveyance
• Dredging pipe — slurry and sediment transport
• Concrete pressure pipe (PCCP) core

Common Standards:

• API 5L (SSAW) — Line pipe, spiral welded grade
• AWWA C200 — Water pipe, steel
• SY/T 5040 — Chinese spiral welded pipe for piles
• GB/T 9711 (SSAW) — Chinese spiral line pipe

Comparison Table

How to Choose the Right Pipe Type

For Small Diameters (< 12"):

• High pressure / critical service → Seamless
• Low/medium pressure / general purpose → ERW
• Structural / mechanical → ERW (or seamless for high stress)
• Water / gas distribution → ERW (galvanized or black)

For Large Diameters (> 16"):

• High pressure pipeline → LSAW
• Water / sewer / drainage → SSAW (spiral)
• Structural columns / piles → SSAW or LSAW (depending on load)
• Maximum size / lowest cost → SSAW

By Application:

Steel Pipe Sizing Basics

NPS (Nominal Pipe Size) vs OD

Pipe sizes are often specified by “nominal pipe size” (NPS) which is approximately the inside diameter for small sizes. The actual OD is standardized.

Schedule Numbers

Wall thickness is indicated by schedule numbers (Sch 10, 40, 80, 160, XS, XXS). Higher schedule = thicker wall = higher pressure rating.

Common schedules:

• Sch 10 — thin wall, low pressure
• Sch 40 — standard wall, most common
• Sch 80 — thick wall, high pressure
• Sch 160 / XXS — extra heavy wall, very high pressure

Metric vs Imperial

• Imperial: NPS (1/2", 1", 2", 4", etc.) + Schedule
• Metric: OD (mm) × wall thickness (mm)

Common Pipe End Finishes

Quality and Testing

Pipe quality is verified by several tests:

• Hydrostatic test — Pressure test with water
• Ultrasonic testing (UT) — Defect detection
• Eddy current testing (ECT) — Surface defect detection
• Magnetic particle inspection (MPI) — Surface/subsurface defects
• Dimensional checks — OD, wall thickness, straightness
• Tensile / hardness testing — Mechanical properties
• Mill Test Certificate (MTC) — Documents all test results

Conclusion

Choosing the right type of steel pipe depends on your requirements for size, pressure, application, and budget. There’s no single “best” pipe — each type has its sweet spot:

• Seamless: Best for high pressure, high temperature, critical service
• ERW: Best value for general-purpose, small-medium pipe
• LSAW: Best for large-diameter, high-pressure applications
• SSAW (Spiral): Best for very large diameters at lowest cost

At {{ .Site.Params.companyShortName }}, we supply all types of steel pipe — seamless, ERW, LSAW, and spiral — in carbon steel, stainless steel, galvanized, and alloy grades. Contact us for help selecting the right pipe for your project.