Types of Pipes: Seamless vs Welded (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.

Seamless pipes are produced without a seam, making them a go-to for high-pressure scenarios due to their uniform strength throughout. They’re formed by stretching a solid steel billet into a pipe shape, perfect for when integrity under pressure is non-negotiable.

Welded pipes come into play when length and diameter flexibility outweigh the seamless advantage. They fall into categories based on their welding process: Electric Resistance Welded (ERW) pipes are produced by forming steel - usually, a steel coil, strip, or sheet - into a tubular shape by applying high-frequency electrical currents (ERW pipes are ideal for moderate-pressure applications). HFW (High-Frequency Welded) pipes utilize a similar process but with higher frequencies, resulting in a finer weld seam, enhancing the pipe’s strength and efficiency.

SAW (Submerged Arc Welded) pipes are named for their fabrication process, where the weld is the submerged type. This category splits further into LSAW (Longitudinal), where the arc welds along the length; DSAW (Double Submerged Arc Welded), which involves double welding for extra thickness; and SSAW (Spiral), where the weld spirals around the pipe, lending it strength and flexibility, suitable for water applications. Besides these types of pipes used to convey fluids, another category is the “structural type” – i.e. pipes and tubes used for construction purposes. All these types of pipes are examined in this article.

Introducing Steel Pipes

Steel pipes are essential components in various industries and applications, serving as either conduit for fluids, gases, and solids and/or for structural applications.

types of pipes fluid conveyance and structural Their versatility, durability, and strength make them indispensable in sectors ranging from construction and infrastructure to oil and gas exploration. This chapter delves into 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), shedding light on their importance in modern society.

Steel pipes find extensive applications across diverse industries and sectors, contributing to infrastructure development, transportation, energy production, and manufacturing processes. Some common uses include:

• Fluids Conveyance: Steel pipes serve as conduits for transporting liquids, gases, and solids in industries such as oil and gas, water supply, sewage systems, and chemical processing.

• Structural Support: Steel pipes provide structural support in buildings, bridges, tunnels, and offshore platforms, withstanding heavy loads, seismic forces, and environmental stresses.

• Industrial Processes: In manufacturing and industrial processes, steel pipes facilitate the conveyance of raw materials, products, and by-products, playing vital roles in material handling, heating, cooling, and ventilation systems.

• Utilities and Infrastructure: Steel pipes are integral components of utilities infrastructure, including water distribution networks, gas pipelines, telecommunications systems, and power generation facilities, ensuring reliable and efficient operations.

Steel pipes for the oil & gas industry specifically, the topic of this article, come in four main categories, each designed to serve specific purposes and applications:

• Seamless Steel Pipes (SMLS): Manufactured without welding seams, seamless steel pipes offer uniformity, strength, and reliability, making them ideal for high-pressure and critical applications such as oil and gas transmission, power generation, and automotive manufacturing.

• Electrically Welded Pipes (ERW/HWF): this category includes ERW and HFW pipes, both fabricated starting from steel coils or sheets and an electrical welding process

• Electrical Fusion Welded Pipes (EFW): pipes are fabricated through a process that involves heating and combining steel materials through electric fusion. This method utilizes either a high-energy electric arc or a high-pressure electric resistance method to melt and fuse materials together to form a coherent structure. EFW pipes are recognized for their strong welds and are typically used in high-pressure and high-temperature applications

• Submerged Arc-Welded Steel Pipes (SAW): Fabricated by welding plates, submerged arc-welding pipes come in various forms, including longitudinal (LSAW), spiral (HSAW), and double weld (DSAW). They find applications in construction, infrastructure, water distribution, and industrial processes.

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

Let’s now delve into the characteristics of the three main types of steel pipes for the oil & gas industry, namely seamless steel pipes, ERW steel pipes, and SAW steel pipes:

Seamless Pipe

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

Seamless Steel Pipes Seamless pipes are widely renowned for their exceptional durability and superior efficiency in fluid flow. Due to their seamless surface and absence of welds or joints, they exhibit outstanding resistance to leaks, high pressure, and extreme temperatures.

These qualities make them an ideal choice not only in the oil and gas sector but also in fields ranging from fluid transportation (oil, gas, slurry pipelines) to construction and medical equipment, where they have proven vital for withstanding heavy loads and resisting corrosion.

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

• Upstream operations (OCTG pipes)

• Midstream (transmission and distribution of fluids, such as oil, gas, steam, acids, and slurries)

• Downstream (process piping to refine oil and gas in derivative products)

• General plumbing applications for utility services

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

• ASTM A53, A106, A333, and API 5L (types of carbon steel pipes for high and low-temperature carbon steel)

• ASTM A335 Grades P5 to P91 (chrome-moly alloy steel pipes for high temperature and pressure, for refinery and power plant applications)

• ASTM A312 Series 300 and 400 (stainless steel pipes in grades 304, 316, 321, 347)

• ASTM A790/A928 (duplex and super duplex pipes with double ferritic and austenitic structure)

• Various nickel alloys material specifications (Inconel, Hastelloy, Cupronickel, Monel, Nickel 200)

• Specifications for non-ferrous pipes (aluminum, copper, brass, cupro-nickel)

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 (and 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 key specification covering OCTG pipes (oil country tubular goods).

Seamless steel pipes shall not be confused with seamless tubes. Indeed, 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

Seamless pipes have a higher price per ton than ERW pipes, generally 20 to 30% higher, due to their fairly complex production process (more articulated than the manufacturing process of ERW and LSAW pipes) and because the number of seamless pipe manufacturers is rather limited (the market has an oligopolistic nature).

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.

Due to this fact, 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. Moreover, 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):

• The ASME B36.10 specification covers carbon and low-alloy seamless pipe sizes (dimensions and weights) between 1/8 and 24 inches

• The ASME B36.19 specification, instead, covers the dimensions and weights of stainless steel, duplex, nickel-alloy seamless, and welded pipes

Commercial seamless pipes are designated with a nominal pipe size (representing the approximate fluid conveyance capacity of the pipe) and with a “schedule”, which refers to the thickness of the pipe (the most common are schedule 40, STD, XS, XXS for carbon/alloy pipes, and 10S, the 40S and 80S for stainless and nickel alloy pipes).

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

Seamless Pipes Manufacturing Process

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

In general, the manufacturing process of seamless pipes involves several steps, each crucial for ensuring the integrity, quality, and consistency of the final product:

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

Steel Billet Preparation. The process begins with steel billets-solid cylindrical bars made from carbon steel or alloy steel through continuous casting or hot rolling.

Heating. Billets are heated in a furnace to soften the steel, making it malleable for subsequent steps.

Piercing. Heated billets are pierced using a mandrel mill or rotary piercing mill. A rotating mandrel pierces through the center to create a hollow tube.

Rolling and Sizing. The hollow tube passes through rolling stands, gradually reducing diameter and wall thickness to meet final specifications.

Heat Treatment. Pipes undergo annealing, quenching, or tempering to improve mechanical properties, relieve internal stresses, and achieve the desired metallurgical structure.

Finishing. Additional processes include straightening, cutting to length, end finishing (beveling, threading), and surface treatment (coating, painting).

Testing and Inspection. Quality control includes NDT methods (ultrasonic, eddy current, visual inspection) and destructive tests (tensile, impact testing).

Packaging and Shipping. Pipes passing all checks are packaged for transit protection and shipped to customers.

Overall, the manufacturing process of seamless pipes requires precision, expertise, and attention to detail to produce high-quality pipes that meet the demanding requirements of various industries and applications. By following stringent quality control measures and employing advanced manufacturing technologies, seamless pipe manufacturers can deliver reliable and durable products that contribute to the infrastructure, construction, and industrial development of society.

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 starting 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 key 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 the last few years, ERW pipes have become an efficient alternative to seamless pipes, both in terms of price and performance, due to the modern welding technologies adopted by ERW pipe manufacturers (for example HFI and HFW, high-frequency welding). These advancements in welding technologies have reduced, over time, the technical superiority of seamless pipes vs ERW pipes, making them interchangeable at least in some applications (low/medium pressure and temperature). Of course, seamless pipes will always benefit from the intrinsic superior mechanical strength of steel billets vs. coils and plates.

ERW Pipe Manufacturing Process

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

The most common welding technique used for oil and gas pipes is the so-called “high-frequency induction technology” (ERW-HFI), consisting of the application of an induction current on the outer surface of the pipe able to generate a robust seam weld and joining the two sides of the steel coil very tightly.

The manufacturing process of Electric Resistance Welded (ERW) pipes involves several steps:

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

Steel Coil Preparation. Flat steel strips rolled into coils (carbon or low-alloy steel) undergo surface treatment such as pickling or coating.

Uncoiling and Straightening. Coils pass through rollers and straightening machines for uniform alignment.

Forming and Edge Preparation. The strip passes through forming rolls to create a cylindrical shape. Edges are cleaned of burrs and oxides.

ERW Welding. Electrical resistance generates heat to fuse the edges together, using high-frequency induction or rotary contact welding.

Heat Treatment. Annealing or stress relieving improves mechanical properties and weld integrity.

Sizing and Shaping. Tubes pass through sizing rolls to achieve final dimensions and tolerances.

Cutting and Finishing. Pipes are cut to length and finished (beveling, threading, coating).

Testing and Inspection. NDT methods (ultrasonic, eddy current) and destructive tests (tensile, hydrostatic) ensure quality.

Packaging and Shipping. Pipes are packaged for protection during transit.

HFW Pipes

HFW pipes, or High-Frequency Welded pipes, are a type of welded steel pipe manufactured using high-frequency electric resistance welding (ERW) technology. This process involves passing a high-frequency electric current through the edges of the rolled steel strips that are being formed into a pipe shape. The high-frequency current heats the edges to the point where they can be fused together to form a strong, longitudinal weld seam. HFW pipe manufacturing is distinguished by its use of high-frequency (typically in the range of hundreds of kHz to several MHz) electric currents, which make the welding process more efficient and result in a high-quality weld.

HFW Pipes

Key Characteristics of HFW Pipes

• Efficient Welding Process: The high-frequency electric resistance welding process is highly efficient, allowing for faster welding speeds compared to lower-frequency welding methods. This efficiency makes HFW pipes suitable for large-scale production.

• Strong Weld Seam: The HFW process produces a weld seam with a narrow heat-affected zone (HAZ), which enhances the strength and durability of the weld area. The narrow HAZ also minimizes the grain coarsening effect, preserving the steel’s mechanical properties.

• Versatility in Applications: HFW pipes can be used in a wide range of applications, from low-pressure fluid transport to structural and mechanical uses. They are particularly favored in the oil and gas industry for line pipes, as well as in construction for structural and scaffolding purposes.

• Material and Size Range: HFW pipes can be manufactured from a variety of materials, including carbon steel, alloy steel, and stainless steel, and are available in a wide range of diameters and wall thicknesses to suit different applications.

Manufacturing Process

• Uncoiling and Flattening: The process starts with uncoiling the steel coil and flattening it into a strip.

• Edge Milling: The edges of the strip are then milled to prepare them for welding, ensuring clean, parallel surfaces that will form the weld seam.

• Forming: The strip is gradually formed into a cylindrical shape by passing it through a series of rollers.

• Welding: As the edges of the formed cylinder come together, a high-frequency electric current is applied to heat and fuse the edges, creating the longitudinal weld seam.

• Cooling, Sizing, and Cutting: After welding, the pipe is cooled, and then passed through sizing rollers to ensure it meets the specified diameter and roundness requirements. Finally, the pipe is cut to the desired length.

Applications of HFW Pipes

HFW pipes find applications across various sectors, including:

• Oil and Gas Industry: For transporting crude oil, natural gas, and refined products.

• Water and Wastewater Management: For water mains, distribution pipelines, and sewage systems.

• Construction and Infrastructure: Used in structural applications, scaffolding, fencing, and as conduits for electrical and communication cables.

• Automotive and Mechanical: For manufacturing structural components and precision mechanical parts.

HFW pipes are valued for their high quality, efficiency of production, and versatility, making them a preferred choice for many industries requiring welded steel pipes.

ERW vs. Seamless Pipes

A common question: “Should I use ERW or seamless for my project?” Here’s 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 a “must-go” 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). Therefore, the difference between DSAW vs. 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 starting from steel coils.

In the oil and gas industry, large-diameter API 5L LSAW pipes are used to 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. 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

Key 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

The manufacturing process of Electric Fusion Welded (EFW) pipes involves several key steps that use high-temperature electric arcs to fuse metal together, creating a strong and durable welded joint. This process is particularly suitable for producing large-diameter pipes from plate material and can be used with a variety of steel types, including carbon steel, stainless steel, and alloy steel. Here’s an overview of the EFW pipe manufacturing process:

1. Material Selection and Preparation

The process begins with the selection of the appropriate steel plate material, based on the required chemical composition and mechanical properties for the intended application.

The steel plates are then cut to size and cleaned to remove any surface impurities or oxides that could affect the quality of the weld.

2. Forming

The cut plates are formed into a cylindrical shape using a press or a rolling machine. This step is crucial for ensuring that the edges align properly for welding.

For large-diameter pipes, the plates might be pre-bent at the edges to facilitate better alignment and welding.

3. Edge Preparation

The edges of the formed cylinder are then carefully prepared to ensure that they are clean and properly aligned. This may involve machining or grinding the edges to create a bevel, which helps to achieve a full penetration weld.

4. Welding

The primary feature of the EFW process is the use of an electric arc to heat the edges of the steel to a molten state. An electric arc is generated between an electrode and the steel material.

The molten steel edges are then fused together using pressure. In some cases, filler material may be added to ensure a strong and uniform weld seam.

The welding process may be performed using one or more passes, depending on the thickness of the steel plate and the required properties of the weld.

5. Post-Weld Heat Treatment (PWHT)

After welding, the pipe may undergo post-weld heat treatment to relieve stresses and ensure that the welded area has properties consistent with the rest of the material. This involves heating the entire pipe or the weld area to a specified temperature and then cooling it under controlled conditions.

6. Inspection and Testing

The welded pipe is subjected to various inspections and tests to ensure that it meets the required specifications and quality standards. This includes visual inspection, dimensional checks, non-destructive testing (such as ultrasonic or radiographic testing), and mechanical testing (such as tensile and impact tests).

7. Finishing

Any final processing, such as cutting the pipe to length, beveling the ends, or applying surface treatments, is completed. The pipe is then marked with relevant information, including material grade, size, and heat number, for identification and traceability.

8. Quality Assurance

Throughout the manufacturing process, quality assurance measures are in place to ensure that each step is performed correctly and that the final product complies with all relevant standards and customer requirements.

The EFW pipe manufacturing process is complex and requires precise control at each stage to produce high-quality pipes suitable for critical applications in industries such as oil and gas, chemical processing, and utilities.

EFW pipes manufacturing process

Structural Pipes

Structural pipes are steel pipes designed and used primarily for structural purposes rather than for conveying fluids. These pipes are utilized in a wide array of construction and engineering applications due to their strength, durability, and versatility.

Structural steel pipes

Key Features of Structural Pipes

• Strength and Durability: Structural pipes are known for their high strength-to-weight ratio, making them an efficient choice for supporting structures under loads without adding excessive weight.

• Versatility: They can be used in a variety of shapes, sizes, and thicknesses, allowing for flexibility in design and application. They can also be manufactured from different materials, including carbon steel, alloy steel, and stainless steel, to meet specific environmental and mechanical requirements.

• Cost-Effectiveness: Compared to other structural materials like concrete or solid steel bars, structural pipes offer cost savings due to their strength, ease of installation, and lower maintenance requirements.

• Ease of Fabrication and Assembly: Structural pipes can be easily cut, welded, and assembled into various configurations, facilitating quick and efficient construction.

Applications of Structural Pipes

• Building and Construction: Used as columns, trusses, and frameworks in buildings, stadiums, bridges, and other structures.

• Infrastructure: Piling for foundations, signposts, and guardrails along roads and highways.

• Industrial and Mechanical: Supports machinery and industrial equipment, conveyance systems, and as part of the structural framework in factories and plants.

• Agricultural: Frames for greenhouses, barns, and fencing.

• Architectural: Aesthetic purposes, such as handrails, balustrades, and architectural features.

Piling Pipes

Piling pipes are structural pipes driven into the ground or seabed to provide foundational support for various structures such as buildings, bridges, piers, and other constructions. These pipes are used as pile foundations, where they transfer the load of the structure to the stronger soil or rock layers deep below the surface, providing stability and support. Piling pipes can be made of steel, concrete, or wood, with steel being the most common due to its strength, durability, and resistance to environmental factors.

piling pipes (source: Arntzen Pipe)

Key Characteristics of Piling Pipes

• High Strength: Piling pipes are designed to withstand high stress and loads, making them suitable for supporting heavy structures.

• Durability: They are often treated or manufactured from materials that are resistant to corrosion, wear, and environmental degradation, ensuring long-term structural integrity.

• Versatility: Piling pipes can be used in a variety of soil and environmental conditions. They can be driven into the ground using different methods, including impact hammering, vibration, or pressing, depending on the ground conditions and the project requirements.

• Customizability: These pipes come in various sizes, lengths, and materials to match the specific needs of a project. They can also be filled with concrete to enhance their load-bearing capacity and stability.

Applications of Piling Pipes

• Building Foundations: Piling pipes provide foundational support for high-rise buildings, especially in areas with soft soil that cannot support heavy structures.

• Bridges and Piers: They are used to anchor bridges and piers firmly into the ground or seabed, ensuring stability against environmental and operational loads.

• Retaining Structures: In constructions such as retaining walls and quay walls, piling pipes are used to withstand lateral forces from earth and water.

• Offshore Structures: Piling pipes form the foundational support for offshore platforms and wind turbines, securing them against the dynamic forces of waves, wind, and other marine challenges.

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, ensuring they meet defined standards for chemical composition, mechanical properties, dimensions, and other important factors. These specifications help ensure that structural pipes are suitable for their intended structural applications in construction, infrastructure, and various engineering projects. Here are some key ASTM specifications for structural pipes:

ASTM A500

Title: Standard Specification for Cold-Formed Welded and Seamless Carbon Steel Structural Tubing in Rounds and Shapes

Description: ASTM A500 is a widely used specification that covers cold-formed welded and seamless carbon steel structural tubing in round, square, and rectangular shapes. It is commonly used in structural applications such as building frames, bridges, and general structural supports. ASTM A500 grades categorize pipes based on their mechanical properties, including Grades A, B, C, or D.

ASTM A53

Title: Standard Specification for Pipe, Steel, Black and Hot-Dipped, Zinc-Coated, Welded, and Seamless

Description: Although ASTM A53 is often associated with standard pipes used for fluid conveyance, it is also applicable to structural applications. ASTM A53 covers seamless and welded black and hot-dipped galvanized steel pipe. It includes requirements for the grade, chemical composition, and mechanical properties, making it suitable for structural supports and framing in buildings and infrastructure.

ASTM A252

Title: Standard Specification for Welded and Seamless Steel Pipe Piles

Description: ASTM A252 covers nominal (average) wall steel pipe piles of cylindrical shape and applies to pipe piles in which the steel cylinder acts as a permanent load-carrying member or as a shell to form cast-in-place concrete piles. It is commonly used in foundation applications, including bridge construction, building foundations, and other structural supports.

ASTM A572

Title: Standard Specification for High-Strength Low-Alloy Columbium-Vanadium Structural Steel

Description: While ASTM A572 primarily covers structural steel plates, it is relevant to structural pipes as well, particularly when they are made from steel plates rolled into cylindrical shapes and welded. ASTM A572 steel is known for its high strength and is used in high-stress structural applications.

ASTM A618

Title: Standard Specification for Hot-Formed Welded and Seamless High-Strength Low-Alloy Structural Tubing

Description: ASTM A618 covers hot-formed welded and seamless high-strength low-alloy square, rectangular, round, or special-shape structural tubing for welded, riveted, or bolted construction of bridges and buildings and for general structural purposes. It emphasizes grade, chemical composition, and tensile properties.

EN Materials for Structural Pipes

European Norms (EN) standards are crucial in defining the specifications for materials used in structural pipes within Europe and many other parts of the world. These standards ensure uniformity, quality, and safety across materials used in construction and engineering projects. Here are some key EN material standards for structural pipes:

EN 10210

Title: Hot finished structural hollow sections of non-alloy and fine grain steels

Description: EN 10210 specifies the technical delivery conditions for hot-finished hollow sections of circular, square, rectangular, or other shapes. It covers structural pipes made from non-alloy and fine-grain steels, focusing on dimensional tolerances, chemical composition, and mechanical properties. It’s used for construction projects requiring high strength and toughness.

EN 10219

Title: Cold-formed welded structural hollow sections of non-alloy and fine-grain steels

Description: Similar to EN 10210, EN 10219 specifies requirements for cold-formed welded structural hollow sections of circular, square, or rectangular forms. It applies to pipes formed cold without subsequent heat treatment. EN 10219 is ideal for structural applications that require high strength and resistance to atmospheric corrosion.

EN 10225

Title: Weldable structural steels for fixed offshore structures – Technical delivery conditions

Description: Although EN 10225 primarily covers plates and sections, it is also relevant for structural pipes used in offshore structures. This standard includes specifications for weldable structural steels with improved resistance to brittle fracture and corrosion in offshore environments.

EN 10025

Title: Hot rolled products of structural steels

Description: EN 10025 is a broad standard that outlines the specifications for hot-rolled structural steel products, including sections and plates used to manufacture structural pipes. It encompasses several parts that define requirements for various grades and qualities of structural steel, including those with enhanced resistance to atmospheric corrosion (EN 10025-5) and those for high yield strength in quenched and tempered conditions (EN 10025-6).

Conclusion

The key differences between seamless, ERW (Electric Resistance Welded), and LSAW (Longitudinal Submerged Arc Welded) pipes lie in their manufacturing processes, characteristics, and applications. Here’s a comparison of these three types of pipes:

Manufacturing Process:

• Seamless Pipes: Seamless pipes are manufactured by extruding or piercing solid steel billets to form a hollow tube without any welding seams. This process involves heating the billet and then rolling it to produce the desired dimensions and thickness. Seamless pipes undergo minimal processing and are typically produced using hot or cold drawing techniques.
• ERW Pipes: ERW pipes are manufactured by forming a flat strip of steel into a cylindrical shape and then welding the edges together using electric resistance welding. In this process, the steel strip is passed through a series of rollers and formed into a tube, after which an electric current is passed through the edges to generate heat and form the weld seam.
• LSAW Pipes: LSAW pipes are manufactured by forming and welding steel plates into a cylindrical shape using longitudinal submerged arc welding. In this process, steel plates are bent into a cylindrical shape and then welded along the longitudinal seam using submerged arc welding, where an electric arc is generated between a welding electrode and the workpiece submerged in a granular flux.

Characteristics:

• Seamless Pipes: Seamless pipes have uniformity in composition and structure, with no weld seams, making them stronger and more reliable for high-pressure applications. They exhibit excellent corrosion resistance and are suitable for critical applications where leakage is not acceptable.
• ERW Pipes: ERW pipes have weld seams along the longitudinal axis, which may result in slightly weaker areas compared to seamless pipes. However, ERW pipes offer good dimensional accuracy, surface finish, and cost-effectiveness, making them suitable for a wide range of applications in construction, infrastructure, and manufacturing.
• LSAW Pipes: LSAW pipes have a longitudinal seam weld and offer higher strength and reliability compared to ERW pipes. They are suitable for applications requiring larger diameters and thicker walls, such as oil and gas transmission, piling, and structural support.

Applications:

• Seamless Pipes: Seamless pipes are commonly used in industries such as oil and gas exploration, refining, petrochemicals, power generation, automotive, and aerospace, where high-pressure and critical applications require leak-proof and durable piping systems.
• ERW Pipes: ERW pipes find applications in various industries, including construction, infrastructure, water distribution, plumbing, HVAC (heating, ventilation, and air conditioning), fencing, and agriculture, where cost-effective and readily available piping solutions are required.
• LSAW Pipes: LSAW pipes are used in applications requiring large diameters and heavy wall thicknesses, such as oil and gas transmission pipelines, offshore platforms, structural support in construction, piling for foundations, and transportation of bulk materials.

In summary, the choice between seamless, ERW, and LSAW pipes depends on factors such as the application requirements, budget, availability, and performance characteristics. Each type of pipe offers distinct advantages and limitations, and selecting the appropriate type is essential for ensuring optimal performance and reliability in various industrial and infrastructure projects.

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• Plastic Pipes - PVC, HDPE and other polymer pipes for various applications

Pipe Sizes and Dimensions

• ASME B36.10/B36.19 Pipe Size Charts - US standard dimensions for carbon and stainless steel pipes
• EN 10220/EN 10127 EU Pipe Sizes - European standard pipe dimensions

Pipe Sourcing

• Pipes Suppliers Worldwide - Directory of pipe manufacturers and stockists by region