SMLS vs Welded Pipe: ERW, SAW, LSAW

Quick Reference

Pipe types by manufacturing: Seamless (SMLS) = no weld seam, high-pressure applications. Welded: ERW/HFW = electric resistance weld from coils (moderate pressure), EFW = electric fusion weld, SAW = submerged arc weld (LSAW longitudinal, DSAW double, SSAW spiral). See materials: API 5L, ASTM A106.

Steel Pipes Overview

Steel pipes serve two primary functions: as conduit for fluids, gases, and solids, and as structural members.

types of pipes fluid conveyance and structural

This chapter covers the characteristics, types, uses, and manufacturing processes of steel pipes: seamless (SMLS), electrically welded (ERW/HFW), electrical-fusion welded (EFW), and longitudinally welded (LSAW, DSAW, SSAW).

Steel Pipe Applications

Steel pipes are used across many industries for infrastructure, transportation, energy production, and manufacturing:

Sector	Applications
Fluids Conveyance	Transporting liquids, gases, and solids in oil & gas, water supply, sewage systems, and chemical processing
Structural Support	Buildings, bridges, tunnels, and offshore platforms; withstanding heavy loads, seismic forces, and environmental stresses
Industrial Processes	Material handling, heating, cooling, and ventilation systems; conveyance of raw materials, products, and by-products
Utilities & Infrastructure	Water distribution networks, gas pipelines, telecommunications systems, and power generation facilities

Pipe Types for Oil & Gas

Steel pipes for the oil & gas industry come in four main categories:

Type	Feedstock	Process	Best For
Seamless (SMLS)	Solid steel billets	Extruded/pierced without welding seams	High-pressure and critical applications (oil & gas transmission, power generation, automotive)
ERW/HFW	Steel coils or sheets	Electrical welding (resistance or high-frequency)	Moderate-pressure, cost-effective applications
EFW	Steel plates	High-energy electric arc or electric resistance fusion	High-pressure, high-temperature; strong welds in various materials
SAW (LSAW/HSAW/DSAW)	Steel plates	Submerged arc welding (longitudinal, spiral, or double)	Construction, infrastructure, water distribution, large-diameter pipelines

Types of pipes for oil & gas (fluids conveyance: Oil, Gas, Derivative Products)

The sections below cover the three main types of steel pipes for oil & gas: seamless, ERW, and SAW.

Seamless Pipe

Seamless pipes are produced from steel billets, which are heated and perforated to create the tubular section. The word “seamless” refers to the absence of seam welds.

Seamless Steel Pipes

Seamless pipes offer high durability and efficient fluid flow. With no welds or joints, they have strong resistance to leaks, high pressure, and extreme temperatures.

These properties make them well-suited for the oil and gas sector, fluid transportation (oil, gas, slurry pipelines), construction, and medical equipment, where heavy loads and corrosive conditions are common.

Oil & Gas Applications

Seamless steel pipes are used for different applications within the oil & gas industry:

Sector	Application
Upstream	OCTG pipes for drilling and completion
Midstream	Transmission and distribution of oil, gas, steam, acids, and slurries
Downstream	Process piping to refine oil and gas into derivative products
Utilities	General plumbing applications for utility services

Material Specifications

The most common pipe types used in oil & gas are (ASTM pipe specifications):

Specification	Material	Applications
ASTM A53, A106, A333, API 5L	Carbon steel	High and low-temperature service
ASTM A335 Grades P5 to P91	Chrome-moly alloy steel	High temperature/pressure (refinery, power plants)
ASTM A312 Series 300/400	Stainless steel (304, 316, 321, 347)	Corrosive service
ASTM A790/A928	Duplex and super duplex	Double ferritic/austenitic structure
Various nickel alloy specs	Inconel, Hastelloy, Cupronickel, Monel, Nickel 200	Severe corrosion/high temperature
Non-ferrous specs	Aluminum, copper, brass, cupro-nickel	Specialized applications

Some specifications cover seamless pipes only (for example ASTM A106), while others apply both to seamless and welded pipes (for example ASTM A53).

Carbon steel pipes (A53, A333, A106, and API 5L) have the largest market share, as they can be used for most high and low-temperature applications. The main application of stainless steel pipes is for corrosive services (higher grades are used as the temperature and the pressure increase, or when the conveyed fluid is more and more aggressive).

In the upstream oil & gas industry, API 5CT is the specification covering OCTG pipes (oil country tubular goods).

Seamless steel pipes shall not be confused with seamless tubes. There are a few important differences between pipes and tubes, which are not only semantic.

Common Mistake

Not verifying heat number continuity during pipe installation. Each length of seamless pipe has a unique heat number linked to its MTC - if pipes get mixed during storage or handling, you lose full traceability. Always mark and segregate pipes by heat number and double-check stencils before welding.

In general, the word “pipe” applies to any tubular used to convey fluids, whereas the word “tube” applies to tubular sections (of various shapes, round, oval, squared) used for structural/mechanical applications, instrumentation systems, and the construction of pressure equipment like boilers, heat exchangers, and superheaters.

Seamless Pipe Price

Cost Benchmark

Seamless pipes are generally 20 to 30% more expensive per ton than ERW pipes, due to the more complex manufacturing process and the oligopolistic nature of the seamless pipe market (fewer manufacturers worldwide).

For specific sizes and specifications (for example a 20-inch pipe or a high wall thickness pipe in special or exotic materials, for example, ASTM A335 P91 pipes), there are few global pipe suppliers, and prices per ton (or per meter) are, as a consequence, impacted.

It is a wrong practice to estimate pipe prices using a standard price per ton for all “carbon steel” or “stainless steel” pipes, regardless of the actual diameter, wall thickness, and specific grade: all these factors shall be taken into consideration to prevent cost overruns during the execution of the project at a later stage.

prices fluctuate daily; especially for alloyed pipes, which contain chemical elements like Molybdenum, Nickel, Copper, and Chromium traded daily on the London Metal Exchange or the Ferro-Alloy markets.

Seamless Pipes Sizes

The ASME B36.10 and B36.19 specifications cover the dimensions and weights of seamless pipes for the petrochemical industry (the specs apply to welded pipes too):

Specification	Coverage	Size Range
ASME B36.10	Carbon and low-alloy seamless pipe dimensions and weights	1/8” to 24”
ASME B36.19	Stainless steel, duplex, nickel-alloy seamless and welded pipes	Per specification

Commercial seamless pipes are designated with a nominal pipe size (representing the approximate fluid conveyance capacity) and a schedule (referring to the wall thickness):

Material	Common Schedules
Carbon/alloy steel	SCH 40, STD, XS, XXS
Stainless/nickel alloy	10S, 40S, 80S

The ASME pipe size specifications can be purchased online from the ASME website.

Seamless Pipes Manufacturing Process

Mild steel seamless pipes from 1/8 to 6 inches are manufactured with the “plug mill process” or the “extrusion process” (used for smaller diameters), whereas the “mandrel mill process” is used for larger diameters.

The manufacturing process involves several steps, each one affecting the integrity, quality, and consistency of the final product:

Seamless pipe manufacturing process flow

Seamless Pipe Manufacturing: Steel Billet → Heating → Piercing → Rolling & Sizing → Heat Treatment → Finishing → Testing & Inspection → Packaging & Shipping

Step	Process	Details
1. Billet Preparation	Starting material	Solid cylindrical bars of carbon or alloy steel, produced via continuous casting or hot rolling
2. Heating	Furnace heating	Softens the steel, making it malleable for subsequent steps
3. Piercing	Mandrel/rotary piercing mill	A rotating mandrel pierces through the center to create a hollow tube
4. Rolling & Sizing	Rolling stands	Gradually reduces diameter and wall thickness to final specifications
5. Heat Treatment	Annealing/quenching/tempering	Improves mechanical properties, relieves internal stresses, achieves desired metallurgical structure
6. Finishing	Straightening, cutting, end finishing	Beveling, threading, surface treatment (coating, painting)
7. Testing & Inspection	Quality control	NDT (ultrasonic, eddy current, visual) and destructive tests (tensile, impact)
8. Packaging & Shipping	Final step	Pipes passing all checks are packaged for transit protection and shipped

The manufacturing process demands precision and strict quality control at each stage. Manufacturers follow stringent testing protocols and use advanced production technologies to produce pipes that meet the requirements of demanding service conditions.

Seamless steel pipes manufacturing process

Mandrell vs. Mannesmann Manufacturing Process

Two main methods exist for seamless pipe production:

Mandrell mill process for seamless pipes

Mannesmann process for seamless pipes (plug-mill)

Aspect	Mandrel Mill Process	Mannesmann (Plug-Mill) Process
Piercing method	Rotating mandrel guides ID formation	Stationary plug pierces billet
Rolling	Multiple passes with mandrel support	Mandrelless rolling after piercing
Dimensional tolerance	Tighter tolerances	Standard tolerances
Surface finish	Smoother inner surface	Standard finish
Production volume	Moderate, high flexibility	High volume, mass production
Best for	Precision pipes, automotive, aerospace	Large diameter, heavy wall, oil & gas transmission
Cost efficiency	Higher cost per ton	More cost efficient

Forged Seamless Pipes

Forged Steel Pipes

Forged seamless pipes combine forging and machining to achieve superior mechanical properties compared to standard seamless pipes.

Manufacturing sequence: Billet heating → Forging under high pressure → Rough forming → Machining (turning, boring, threading) → Final dimensions

Why forged pipes are different:

Property	Standard Seamless	Forged Seamless
Grain structure	Standard	Refined, uniform (controlled deformation)
Strength	High	Higher
Fatigue resistance	Good	Excellent
Customization	Standard sizes	Custom shapes and geometries possible
Cost	Standard	Premium

Typical applications:

Industry	Application
Oil & Gas	Drilling, high-pressure transport, refining
Aerospace & Defense	Aircraft components, missile systems
Power Generation	Boiler systems, heat exchangers, nuclear

Learn more about forged steel pipes.

ERW & HFW Pipes (Electric Resistance Welding/High Frequency Welding)

ERW pipes

ERW pipes are manufactured from steel coils: the coil is first uncoiled, then smoothed, cut and finally formed into a pipe shape by joining its two extremities electrically.

ERW pipes are available in sizes between 1/2 and 20 inches, in carbon steel (ASTM A53 is the most common specification) and stainless steel (ASTM A312). In terms of dimensions, ASME B36.10 and ASME B36.19 are the reference specifications (API 5L for welded ERW line pipes).

The ASME and API dimensional charts show typical combinations of pipe nominal size and wall thickness (designated as “schedule”) and show ERW pipe weight in kg (or pounds).

In recent years, ERW pipes have become a practical alternative to seamless pipes, both in terms of price and performance, due to modern welding technologies such as HFI and HFW (high-frequency welding).

These advancements have narrowed the technical gap between seamless and ERW pipes, making them interchangeable for some applications (low/medium pressure and temperature). Seamless pipes still retain the inherent mechanical advantage of being produced from solid billets rather than coils and plates.

ERW Pipe Manufacturing Process

ERW pipes are manufactured from steel coils that are uncoiled, cut, processed, welded, and tested as shown in the picture below.

The most common welding technique for oil and gas pipes is “high-frequency induction technology” (ERW-HFI), which applies an induction current on the outer surface of the pipe to generate a reliable seam weld, joining the two sides of the steel coil tightly.

ERW pipe manufacturing process flow

ERW Pipe Manufacturing: Steel Coil → Uncoiling → Forming → ERW Welding → Heat Treatment → Sizing → Cutting & Finishing → Testing → Packaging

Step	Process	Details
1. Coil Preparation	Starting material	Flat steel strips rolled into coils (carbon or low-alloy steel), surface treated (pickling or coating)
2. Uncoiling & Straightening	Feeding	Coils pass through rollers and straightening machines for uniform alignment
3. Forming & Edge Preparation	Shaping	Strip passes through forming rolls to create cylindrical shape; edges cleaned of burrs and oxides
4. ERW Welding	Seam creation	Electrical resistance generates heat to fuse edges, using high-frequency induction or rotary contact welding
5. Heat Treatment	Stress relief	Annealing or stress relieving improves mechanical properties and weld integrity
6. Sizing & Shaping	Final dimensions	Tubes pass through sizing rolls to achieve final dimensions and tolerances
7. Cutting & Finishing	End processing	Cut to length, beveling, threading, coating
8. Testing & Inspection	Quality control	NDT (ultrasonic, eddy current) and destructive tests (tensile, hydrostatic)
9. Packaging & Shipping	Final step	Packaged for protection during transit

HFW Pipes

HFW (High-Frequency Welded) pipes are a type of welded steel pipe manufactured using high-frequency electric resistance welding (ERW) technology. The process passes a high-frequency electric current through the edges of rolled steel strips as they are formed into a pipe shape.

The high-frequency current heats the edges until they fuse together, forming a longitudinal weld seam. HFW manufacturing uses currents typically in the range of hundreds of kHz to several MHz, producing efficient welds with high quality.

HFW Pipes

HFW Pipe Characteristics

Characteristic	Details
Efficient Welding Process	High-frequency ERW allows faster welding speeds than lower-frequency methods, suitable for large-scale production
Strong Weld Seam	Narrow heat-affected zone (HAZ) enhances strength and durability; minimizes grain coarsening, preserving mechanical properties
Versatility	Applicable from low-pressure fluid transport to structural/mechanical uses; common in oil & gas line pipes and construction
Material & Size Range	Carbon steel, alloy steel, stainless steel; various diameters and wall thicknesses

Manufacturing Process

Step	Description
Uncoiling & Flattening	Steel coil is uncoiled and flattened into a strip
Edge Milling	Edges milled for clean, parallel surfaces that will form the weld seam
Forming	Strip gradually formed into a cylindrical shape through a series of rollers
Welding	High-frequency electric current applied to heat and fuse the edges, creating the longitudinal weld seam
Cooling, Sizing & Cutting	Pipe cooled, passed through sizing rollers for specified diameter/roundness, then cut to length

Applications of HFW Pipes

Industry	Applications
Oil and Gas	Crude oil, natural gas, and refined product transport
Water and Wastewater	Water mains, distribution pipelines, sewage systems
Construction and Infrastructure	Structural applications, scaffolding, fencing, electrical/communication cable conduits
Automotive and Mechanical	Structural components, precision mechanical parts

HFW pipes are valued for their production efficiency and weld quality, making them a common choice across industries that use welded steel pipe.

ERW vs. Seamless Pipes

A common question: “Should I use ERW or seamless for my project?” Here is a direct comparison:

Factor	Seamless	ERW (HFI)
Weld seam	None - uniform structure	Longitudinal seam (modern HFI is very strong)
Strength	Inherently uniform, no weak points	Seam slightly weaker than base metal
Cost	20-30% higher	Lower cost per ton
Lead time	Longer (fewer manufacturers)	Shorter (larger manufacturing base)
Wall thickness tolerance	+/- 12.5% (variable)	Consistent (controlled coil thickness)
Roundness/ovality	More precise	Slightly less precise
Size range (overlap)	2” to 24”	1/2” to 20”

When to Use Seamless

• High pressure, high temperature, cyclic loading
• Sour service (H2S environments)
• Critical applications where seam integrity concerns exist

When ERW Is Acceptable

• Process piping Class 600 and below
• Non-sour, moderate service conditions
• Cost-sensitive projects with standard requirements

Bottom line: Modern ERW-HFI pipes are a valid alternative to seamless for many applications, offering 20-25% cost and lead time savings. But for critical service, seamless remains the safer choice.

Pro Tip

For process piping below Class 600 and non-sour service, modern ERW-HFI pipes offer excellent value. However, for high-pressure, high-temperature, or cyclic loading applications (like steam headers and offshore risers), seamless is still the safer choice - the absence of a weld seam eliminates a potential fatigue initiation point.

ERW (Electric Resistance Welding) pipe

Pipes are, with valves, the most impactful piping cost element in plant construction (as a rule of thumb, piping covers 5-7% of the total plant cost, and pipes represent circa 60 to 70% of this cost, valves 15 to 25%). These figures are average values that refer to the oil & gas industry and refer to carbon steel materials (the weight of piping may be higher for stainless steel, duplex, and nickel-alloy piping classes).

The last point: pipes may have different colors (painted on the outer surface) to represent the type of fluid they carry.

LSAW Pipe (Longitudinal Submerged Arc Welding)

LSAW pipes

An LSAW pipe (“submerged arc welding”) is manufactured by cutting, bending, and welding steel plates (JCOE process).

LSAW pipes compete with seamless and ERW pipes in the size range between 16 and 24 inches but are the only practical option for pipelines above 24 inches (as 24 inches is the maximum size for commercial seamless pipes).

The two main types of LSAW pipes are the longitudinal (with a single or double straight seam weld, DSAW) and the spiral type (called HSAW, SSAW, or SAWL pipe). The difference between DSAW and LSAW is that DSAW pipes have a seam weld on the inside and outside of the pipe, whereas LSAW pipes have a single seam weld on the outer surface.

The difference between LSAW and ERW pipes is that LSAW pipes are produced using steel plates, and ERW pipes are manufactured from steel coils.

In oil and gas, large-diameter API 5L LSAW pipes transport hydrocarbons over long distances efficiently.

HSAW/SSAW spiral weld pipes are used for non-critical applications, such as water transmission and distribution (not for oil & gas).

Field Note

When installing LSAW pipes, always orient the weld seam away from the 6 o’clock position (bottom of the pipe) - this prevents water accumulation along the seam during operation and reduces internal corrosion risk. For buried pipelines, we also avoid the 12 o’clock position to protect the seam from external damage during backfilling.

LSAW Pipe Manufacturing Process

LSAW pipes are manufactured using the JCOE process (J-ing, C-ing, O-ing, Expanding) starting from steel plates.

LSAW Manufacturing: Plate → Edge milling → Pre-bending → J-ing → C-ing → O-ing → SAW welding (ID + OD) → UT inspection → Expansion → Cutting → Beveling → Coating → Final testing

Step	Description
Plate preparation	Cut to size, shot-blasted, edges milled
Pre-bending	Plate edges curved to facilitate forming
JCOE forming	Progressive bending: J-shape → C-shape → O-shape (closed cylinder)
SAW welding	Submerged arc weld on inside and outside (flux-shielded arc)
UT inspection	Ultrasonic testing of weld seam for defects
Expansion	Mechanical expansion to final diameter and roundness
Cutting & beveling	Cut to length, ends prepared for field welding
Surface treatment	Coating, painting, or galvanizing for corrosion protection
Final testing	Hydrostatic test, RT/UT, dimensional checks

LSAW pipes manufacturing process

SSAW/DSAW Types

Quick clarification: SSAW (Spiral Submerged Arc Welded) = HSAW (Helical Submerged Arc Welded). Same process, different names.

SSAW Pipes

SSAW pipes are manufactured by spirally welding hot-rolled steel coil under a flux layer (submerged arc). The spiral seam allows material efficiency and flexible sizing.

SSAW pipe type

SSAW characteristics:

• Material efficient - various diameters from same coil width
• Large diameters and lengths possible
• Spiral distributes stress more evenly
• Requires thorough seam inspection

SSAW applications: Water mains, sewage, stormwater drainage, non-critical oil & gas pipelines, piling, structural.

DSAW Pipes

DSAW (Double Submerged Arc Welded) pipes are welded from both inside and outside surfaces, creating a stronger seam than single-pass welds.

DSAW pipe

SSAW vs DSAW Comparison	SSAW (Spiral)	DSAW (Double)
Weld orientation	Spiral/helical	Longitudinal
Weld passes	Single	Double (ID + OD)
Feedstock	Steel coil	Steel plate
Weld quality	Good	Superior (full penetration both sides)
Applications	Water, non-critical service	Oil & gas transmission, offshore, high-pressure
Roundness	May be affected by spiral seam	Better controlled

DSAW applications: Oil & gas transmission, offshore/subsea pipelines, structural (bridges), water transmission (high-pressure).

EFW Pipes (Electric Fusion Welding)

EFW (Electric Fusion Welded) pipes use high-temperature electric arcs to fuse the seam, creating full-penetration welds. They are suited for large-diameter pipes in various materials.

EFW pipes

EFW vs ERW vs SAW	ERW	EFW	SAW (LSAW/DSAW)
Heat source	Electrical resistance	Electric arc	Submerged arc
Feedstock	Coil	Plate	Plate
Best for	Small-medium diameter, thin wall	Large diameter, various materials	Large diameter, thick wall
Weld quality	Good	High	High
Material versatility	Limited	Wide (CS, SS, alloys)	Good

EFW Specifications

Standard	Coverage
ASTM A358	EFW austenitic stainless steel (corrosive/high-temp service)
ASTM A672	EFW carbon steel for high-pressure, moderate temp
ASTM A691	EFW carbon/alloy steel for high-pressure, high-temp
ASME B36.10M	Dimensions for carbon/alloy welded pipe
ASME B36.19M	Dimensions for stainless steel pipe
API 5L	Line pipe (can include EFW under certain conditions)
NACE MR0175	Sour service material requirements

EFW Pipes Manufacturing Process

EFW pipes are produced using high-temperature electric arcs to fuse metal together, creating a strong welded joint. The process is suited for producing large-diameter pipes from plate material and works with carbon steel, stainless steel, and alloy steel.

Step	Process	Details
1	Material Selection & Preparation	Steel plate selected for required chemistry and mechanical properties; cut to size, cleaned of surface impurities and oxides
2	Forming	Plates formed into cylindrical shape using press or rolling machine; large-diameter plates may be pre-bent at edges for better alignment
3	Edge Preparation	Edges machined or ground to create a bevel for full penetration weld; clean and properly aligned
4	Welding	Electric arc heats edges to molten state; fused together under pressure. Filler material may be added. One or more passes depending on plate thickness
5	PWHT	Post-weld heat treatment relieves stresses; pipe or weld area heated to specified temperature and cooled under controlled conditions
6	Inspection & Testing	Visual inspection, dimensional checks, NDT (ultrasonic, radiographic), mechanical testing (tensile, impact)
7	Finishing	Cut to length, end beveling, surface treatments, marking (material grade, size, heat number) for traceability
8	Quality Assurance	Continuous QA throughout manufacturing ensures compliance with all relevant standards and customer requirements

The EFW process requires precise control at each stage to produce pipes suitable for demanding applications in oil and gas, chemical processing, and utilities.

EFW pipes manufacturing process

Structural Pipes

Structural pipes are steel pipes designed and used primarily for load-bearing and structural purposes rather than for conveying fluids. They are used in construction and engineering applications for their strength, durability, and adaptability to different configurations.

Structural steel pipes

Features of Structural Pipes

Feature	Details
Strength & Durability	High strength-to-weight ratio; efficient for supporting structures under load without excessive weight
Versatility	Various shapes, sizes, thicknesses; manufactured from carbon steel, alloy steel, or stainless steel for specific requirements
Cost-Effectiveness	Cost savings vs. concrete or solid steel bars due to strength, ease of installation, and lower maintenance
Ease of Fabrication	Easily cut, welded, and assembled into various configurations for quick, efficient construction

Applications of Structural Pipes

Sector	Applications
Building & Construction	Columns, trusses, frameworks for buildings, stadiums, bridges
Infrastructure	Piling for foundations, signposts, guardrails along roads and highways
Industrial & Mechanical	Machinery supports, conveyance systems, factory/plant structural frameworks
Agricultural	Frames for greenhouses, barns, fencing
Architectural	Handrails, balustrades, decorative features

Piling Pipes

Piling pipes are structural pipes driven into the ground or seabed to provide foundational support for buildings, bridges, piers, and other structures. They transfer the load of the structure to stronger soil or rock layers deep below the surface, providing stability and support.

Piling pipes can be made of steel, concrete, or wood; steel is the most common due to its strength, durability, and resistance to environmental factors.

piling pipes (source: Arntzen Pipe)

Piling Pipe Characteristics

Characteristic	Details
High Strength	Designed to withstand high stress and loads for supporting heavy structures
Durability	Treated or manufactured for corrosion, wear, and environmental resistance; long-term structural integrity
Versatility	Various soil and environmental conditions; driven via impact hammering, vibration, or pressing
Customizability	Various sizes, lengths, materials; can be filled with concrete for enhanced load-bearing capacity

Applications of Piling Pipes

Application	Details
Building Foundations	Support for high-rise buildings, especially in areas with soft soil
Bridges and Piers	Anchoring into ground or seabed against environmental and operational loads
Retaining Structures	Retaining walls and quay walls to withstand lateral earth and water forces
Offshore Structures	Foundation for offshore platforms and wind turbines against waves, wind, and marine forces

Manufacturing and Specifications

Piling pipes are manufactured according to specific standards that ensure their suitability for piling applications. Common specifications include ASTM A252 for welded and seamless steel pipe piles and EN 10219 for cold-formed welded structural hollow sections of non-alloy and fine-grain steels. These specifications cover the dimensions, mechanical properties, and other requirements for piling pipes.

Materials for Structural Pipes

ASTM Materials for Structural Pipes

ASTM International provides several specifications for structural pipes, covering chemical composition, mechanical properties, dimensions, and other requirements:

Standard	Title	Description
ASTM A500	Cold-Formed Welded and Seamless Carbon Steel Structural Tubing in Rounds and Shapes	Widely used for cold-formed welded and seamless carbon steel structural tubing in round, square, and rectangular shapes. Building frames, bridges, general structural supports. Grades A, B, C, or D.
ASTM A53	Pipe, Steel, Black and Hot-Dipped, Zinc-Coated, Welded, and Seamless	Primarily for fluid conveyance, also applicable to structural applications. Seamless and welded, black and hot-dipped galvanized steel pipe. Structural supports and framing.
ASTM A252	Welded and Seamless Steel Pipe Piles	Nominal wall steel pipe piles of cylindrical shape. Pipe acts as permanent load-carrying member or shell for cast-in-place concrete piles. Bridge construction, building foundations.
ASTM A572	High-Strength Low-Alloy Columbium-Vanadium Structural Steel	Primarily covers structural steel plates; relevant to structural pipes made from plates rolled into cylindrical shapes and welded. High-stress structural applications.
ASTM A618	Hot-Formed Welded and Seamless High-Strength Low-Alloy Structural Tubing	Square, rectangular, round, or special-shape structural tubing for welded, riveted, or bolted construction of bridges and buildings. Emphasis on grade, chemical composition, and tensile properties.

EN Materials for Structural Pipes

European Norms (EN) standards define the specifications for materials used in structural pipes within Europe and many other parts of the world:

Standard	Title	Description
EN 10210	Hot Finished Structural Hollow Sections of Non-Alloy and Fine Grain Steels	Technical delivery conditions for hot-finished hollow sections (circular, square, rectangular). Dimensional tolerances, chemical composition, and mechanical properties. High strength and toughness.
EN 10219	Cold-Formed Welded Structural Hollow Sections of Non-Alloy and Fine Grain Steels	Requirements for cold-formed welded structural hollow sections (circular, square, rectangular). No subsequent heat treatment. High strength and atmospheric corrosion resistance.
EN 10225	Weldable Structural Steels for Fixed Offshore Structures	Primarily covers plates and sections; also relevant for structural pipes in offshore structures. Improved brittle fracture and corrosion resistance in offshore environments.
EN 10025	Hot Rolled Products of Structural Steels	Broad standard for hot-rolled structural steel products, including sections and plates for structural pipe manufacturing. Includes enhanced atmospheric corrosion resistance (Part 5) and high yield strength quenched/tempered conditions (Part 6).

Conclusion

The main differences between seamless, ERW, and LSAW pipes lie in their manufacturing processes, characteristics, and applications:

Aspect	Seamless	ERW	LSAW
Manufacturing	Extruding/piercing solid steel billets into hollow tubes without welding seams. Heating, then rolling to desired dimensions. Hot or cold drawing.	Forming flat steel strips into cylindrical shape, welding edges with electric resistance. Strip passed through rollers, electric current generates heat to form the weld seam.	Forming and welding steel plates into cylindrical shape using longitudinal submerged arc welding. Plates bent and welded along longitudinal seam under granular flux.
Characteristics	Uniform composition and structure, no weld seams. Stronger and more reliable for high-pressure. Excellent corrosion resistance. Suitable where leakage is not acceptable.	Weld seam along longitudinal axis (slightly weaker than base metal). Good dimensional accuracy, surface finish. Cost-effective for construction, infrastructure, manufacturing.	Longitudinal seam weld. Higher strength and reliability than ERW. Suitable for larger diameters and thicker walls (oil & gas transmission, piling, structural).
Primary Applications	Oil & gas exploration/refining, petrochemicals, power generation, automotive, aerospace; high-pressure and critical leak-proof applications.	Construction, infrastructure, water distribution, plumbing, HVAC, fencing, agriculture; cost-effective and readily available solutions.	Oil & gas transmission pipelines, offshore platforms, structural/foundation piling, bulk material transport; large diameter, heavy wall applications.

The choice between seamless, ERW, and LSAW pipes depends on the application requirements, budget, availability, and performance characteristics. Each type has distinct advantages and limitations, and selecting the right one affects performance and reliability in industrial and infrastructure projects.

Frequently Asked Questions

What is the difference between seamless and welded pipe?

Seamless pipe (SMLS) is manufactured without a weld seam by piercing a solid billet, providing uniform strength in all directions ; ideal for high-pressure applications. Welded pipe is made by rolling steel plate or coil into a tubular shape and welding the seam (ERW, LSAW, SSAW). Seamless is stronger and more reliable but more expensive; welded is economical for lower pressures and larger diameters.

What does ERW pipe mean?

ERW stands for Electric Resistance Welded. ERW pipe is made by rolling steel coils into a tubular shape and welding the longitudinal seam using high-frequency electrical current (no filler metal). It is used for moderate-pressure applications like water, oil, and gas distribution lines, typically in sizes up to NPS 24.

What is LSAW pipe?

LSAW stands for Longitudinal Submerged Arc Welded. LSAW pipe has a single longitudinal weld seam made by submerged arc welding (SAW) with filler metal. It is used for large-diameter (typically NPS 16-60) oil and gas transmission pipelines where seamless pipe is either not available or not cost-effective.

When should I use seamless pipe vs ERW?

Use seamless pipe for: high pressure (above Class 600), high temperature, critical/sour service, small bore (NPS 2 and below), and when the piping code requires it (ASME B31.3 Class M). Use ERW pipe for: moderate pressure, water/gas distribution, structural applications, and cost-sensitive projects where welded pipe meets the design requirements.

What is pipe schedule?

Pipe schedule (SCH) indicates the wall thickness relative to the pipe's nominal size. Common schedules: SCH 5S, 10S (thin wall), SCH 40/STD (standard), SCH 80/XS (extra strong), SCH 160, XXS (double extra strong). Higher schedule = thicker wall = higher pressure rating. Schedules are defined in ASME B36.10 (carbon/alloy steel) and B36.19 (stainless steel).