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What Are Steel Pipes?

Steel pipes are hollow, elongated steel products primarily used for conveying fluids (such as petroleum, natural gas, water, gas, steam, etc.) and also for manufacturing mechanical components and engineering structures. Due to their lightweight yet high-strength properties, they have replaced traditional solid steel in many applications, becoming the material of choice. Additionally, steel pipes are commonly used in the production of various conventional weapons, such as gun barrels and artillery shells.

Manufacturing Process

Seamless Steel Pipe:

Produced by piercing a solid tube blank or steel ingot, followed by hot rolling, cold rolling, or cold drawing. Throughout this process, no weld seam forms inside the pipe, hence the name “seamless.”

Hot Rolling: A solid round billet is heated and pierced, then rolled and elongated through a series of rolling mills until the desired dimensions and wall thickness are achieved.

Cold Drawing / Cold Rolling: Based on the hot-rolled pipe, cold drawing or cold rolling is used to further reduce the diameter and wall thickness while improving dimensional accuracy and surface finish.

Welded Pipe: 

Welded pipes are typically made from stainless steel plates or strips that are cold-formed into a cylindrical shape and then welded. The main welding methods include:

TIG Welding: Uses a tungsten electrode and an inert gas shield to weld the edges of the plate. It produces high-quality welds and is often used for pipes with strict quality requirements.

Laser Welding: Uses a high-energy-density laser beam for welding. It offers fast welding speed and a small heat-affected zone.

Plasma Welding: Falls between TIG and laser welding in terms of energy density. It is suitable for thicker materials.

Resistance Welding (ERW – Electric Resistance Welding): Heats the edges using electrical current until they fuse together. It is highly efficient but may produce welds of lower quality compared to TIG welding.

Characteristics of Seamless Steel Pipes

1. High Pressure Resistance: With no welded seams, seamless steel pipes feature a more uniform overall structure, granting them superior pressure resistance. They are suitable for use in harsh environments involving high pressure and high temperatures.

2. High Precision: Seamless steel pipes feature smooth inner and outer walls with high dimensional accuracy, making them suitable for applications demanding low fluid resistance and precise flow control.

3. Excellent Corrosion Resistance: Seamless steel pipes can utilize specialized materials and surface treatment technologies to enhance corrosion resistance and extend service life.

Characteristics of Welded Pipes

1. High Production Efficiency: The relatively simple production process of welded pipes enables continuous and automated manufacturing, significantly boosting production efficiency.

2. Lower Cost: Due to their straightforward production method and high material utilization, welded pipes offer relatively low costs, making them suitable for high-volume, low-cost applications.

3. Diverse Specifications: Welded pipes can be produced in various diameters, wall thicknesses, and lengths to meet diverse engineering requirements.

Structural Strength

Due to differences in manufacturing processes, the structural strength and risk resistance of the two materials are fundamentally distinct, serving as the core basis for selection in industrial applications.

Seamless Steel Pipe:

Lacking welded seams, seamless steel pipes feature a continuous and complete metallic structure. When subjected to pressure, impact, or high temperatures, stress is evenly distributed across the entire pipe wall. This prevents localized fractures caused by material variations at welds or welding defects such as incomplete fusion or porosity.

Welded pipes

The strength of welded pipes is directly influenced by weld quality: if welding processes meet standards, weld strength can approach that of the base material. However, if processes are substandard, defects like slag inclusions or cracks may form at the weld, creating “structural weaknesses.” Under high pressure, low temperatures, or frequent vibration, these welds are more prone to failure.

Application Areas

Seamless Steel Pipes:

High-Pressure and Critical Applications: The preferred choice for high-pressure, high-temperature, and high-strength environments such as oil and gas transmission, high-pressure boilers, chemical equipment, hydraulic systems, and nuclear power plants. In these applications, safety is paramount, and seamless tubes offer unmatched reliability.

Applications Demanding Consistency: Precision machinery structures, aerospace, and other scenarios with stringent requirements for pipe strength and reliability.

Welded Pipes:

Low-Pressure and General-Purpose Applications: Widely used for conveying low-pressure fluids like water, gas, and air. Their cost advantage and flexible sizing make them ideal for construction, structural engineering, furniture manufacturing, sports equipment, and similar fields.

Large-Diameter Projects: Long-distance oil and gas pipelines (especially spiral welded pipes), urban water supply and drainage networks, and other projects requiring large diameters and extended lengths.

Performance Characteristics

Seamless steel pipes, lacking welded seams, generally exhibit superior pressure-bearing capacity and are suitable for demanding environments such as high-pressure and high-temperature applications. Additionally, seamless steel pipes offer relatively higher precision and surface smoothness, making them ideal for scenarios with stringent performance requirements.

Welded pipes: Although their pressure-bearing capacity is slightly lower than seamless steel pipes, they are more cost-effective and offer greater convenience in processing and installation.

Surface Quality

Seamless steel pipes undergo high-temperature hot rolling, forming a layer of iron oxide scale on the surface that affects smoothness. For high-precision surfaces, additional post-processing such as cold drawing and polishing is required.

The raw material steel strip for welded pipes has a smooth surface. After forming, the weld seam undergoes treatment, resulting in inner and outer surfaces that are typically flatter and smoother than seamless pipes.

Corrosion Resistance

Seamless steel pipes possess superior corrosion resistance due to their monolithic structure, which eliminates potential hazards like intergranular corrosion in weld zones caused by heat-affected zones.

The weld zones of welded pipes undergo microstructural changes during high-temperature welding, making them more susceptible to corrosion initiation. In certain specialized media or environments, welds may corrode earlier than the base material.

How to Choose Between Seamless and Welded Pipes

1. Consider the operating environment: First, select the appropriate pipe material based on the project’s environmental conditions and usage requirements. For instance, in high-temperature, high-pressure, or corrosive environments, seamless steel pipes should be prioritized; whereas in general construction or low-pressure transportation applications, welded pipes offer an economical and practical choice.

2. Pay Attention to Pipe Specifications: Select appropriate pipe specifications based on project requirements. Both welded and seamless pipes offer multiple specifications, including diameter, wall thickness, and length.

3. Focus on Material Quality: When selecting pipes, pay attention to material indicators such as chemical composition, mechanical properties, and corrosion resistance to ensure compliance with relevant standards and specifications.

4. Consider Cost Factors: While meeting project requirements, cost considerations are also important. Generally, welded pipes have lower production costs and are relatively inexpensive, whereas seamless steel pipes involve more complex manufacturing processes and thus carry higher costs.

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TP 304 (UNS S30400) is one of the most commonly used stainless steel grades, containing about 18% chromium and 8% nickel, with excellent corrosion resistance, good formability and welding performance. ZIZI can provide different grades (Class 1~Class 5), different sizes and customized specifications according to customers’ needs to ensure reliability and durability under severe working conditions.

ASTM A358 EFW Pipe Specification

ASTM A358 Standard Scope

ASTM A358 TP316 Stainless Steel EFW Pipe specification covers electric-fusion-welded austenitic chromium-nickel stainless steel pipe suitable for corrosive or high-temperature service, or both, or for general applications.

The dimensionless designator NPS (nominal pipe size) has been substituted in this standard for such traditional terms as “nominal diameter,” “size,” and “nominal size.”

This specification covers the grades of alloy and stainless steel listed in Table 1. The selection of the proper grade and requirements for heat treatment shall be at the discretion of the purchaser, dependent on the service conditions to be encountered.

Five classes of pipe are covered as follows:

ASTM A358 Class 1 – Pipe shall be double welded by processes employing filler metal in all passes and shall be completely radiographed.
ASTM A358 Class 2 – Pipe shall be double welded by processes employing filler metal in all passes. No radiography is required.
ASTM A358 Class 3 – Pipe shall be single welded by processes employing filler metal in all passes and shall be completely radiographed.
ASTM A358 Class 4 – Same as Class 3 except that the weld pass exposed to the inside pipe surface may be made without the addition of filler metal (see 6.2.2.1 and 6.2.2.2).
ASTM A358 Class 5 – Pipe shall be double welded by processes employing filler metal in all passes and shall be spot radiographed.

Chemical Composition of ASTM A358 TP304 EFW Pipe

Mechanical Properties of ASTM A358 TP304 EFW Pipes

ASTM A358 Grade 304 EFW Pipes Physical Properties

Grade 304 Stainless Steel EFW Pipe Equivalent Grades

Material Characteristics

Strong corrosion resistance: TP 304 stainless steel pipe contains more than 18% chromium and more than 8% nickel, this composition gives it excellent corrosion resistance, excellent resistance to oxidation, acid and alkali and other media, can maintain good performance in a variety of corrosive environments.

Good heat resistance: can maintain stable mechanical properties at high temperatures, can withstand a certain degree of high-temperature environments, suitable for a number of occasions with temperature requirements.

Excellent processing performance: easy to cut, bend and weld, easy to carry out a variety of processing operations, is conducive to on-site installation and processing, can reduce the construction difficulty and cost.

Convenient cleaning and maintenance: smooth surface, not easy to accumulate dirt, and not easy to rust, daily cleaning and maintenance work is relatively simple, to ensure the long-term stable operation of the piping system.

ASTM A358 Stainless Steel EFW Pipe Dimension

ASTM A358 Stainless Steel EFW Pipe Tolerance

Application Areas

Chemical industry

Food and beverage industry

Pharmaceutical industry

Paper and textile industry

Desalination and shipbuilding industry

Construction industry

You can get an offer for products in below material forms:

-Pipe and Tube (EN 10216-5, ASTM A213, ASTM A249, A312, A790,)

-Forged Fitting and Flange (ASTM A182 , ASTM A105,ASTM B564 )

-Butt Weld Fittings (ASTM A234, ASTM A403,ASTM A815)

-Round bar , Billet (ASTM A276, ASTM A479)

– Plate, Sheet, Strip(ASTM A240, EN 10028-7, A480)

-Bolting, Nuts（ASTM A193, A194, A320）

ASTM A358 TP 304 EFW Pipe Exported Countries

We Export ASTM A358 TP 304 EFW Pipe to Saudi Arabia, United Arab Emirates, Qatar, Bahrain, Oman, Kuwait, Turkey, Egypt, Yemen , Syria, Jordan, Cyprus, Singapore, Malaysia, Indonesia, Thailand, Vietnam, South Korea, Japan, Sri Lanka, Maldives, Bangladesh, Cambodia, Argentina, Bolivia, Brazil, Venezuela, Colombia, Ecuador, Guyana, Paraguay, Uruguay, United States Of America, Canada, Mexico, Panama, Jamaica, Bahamas, Denmark, Norway, Germany, France,Italy, United Kingdom, Spain, Belgium, Greece, Czech Republic, Portugal, Hungary, Albania, Austria, Finland, Ireland, Croatia, Malta, Nigeria, Algeria, Angola, South Africa, Libya, Egypt, Sudan,  Europe, Africa, Asia, North America, South America, Middle East.etc

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Zizi is manufacturer, supplier and stockist of steel pipes, we offers different types stainless steel pipe in various dimensions have a large inventory.

Stainless steel pipes is indispensable and widely used type in process industries. It contains chromium which offers it great resistance to various corrosion like seawater and acidic substance.

Types of Stainless Steel Pipe

Based on microstructure, stainless steel pipe can be:

1. Austenitic Stainless Steel Pipe

There are two subgroups of Austenitic stainless steel: 300 Series and 200 Series.

Most common grades are 304, 316,309,310

2. Ferritic Stainless Steel Pipe

It is high chromium, magnetic stainless steel pipe with low carbon content. The common used type are 406, 410L, 430, 439, 441, 434, 436, 444, 445, 446, 447

3. Martensitic Stainless Steel Pipe

They are usually used in mechanical properties or wear resistance applications. The commonly used grades are Type 431, EN1.4313, Type 630.

4. Duplex / Super Duplex Stainless Steel Pipe

It is also a family of stainless steel. It consists of two phases—austenite and ferrite. They are usually divided into three groups based on their pitting corrosion resistance. The commonly types are UNS S32304, 32205, 32750, 32520, 32760.

Seamless Pipe and Welded Pipe

Differ from the manufacture methods, the most prominent type in industry are seamless pipe and welded pipe.

Seamless(SMLS) pipe begins as a billet (which is a solid cylindrical hunk of stainless steel).  The billet will be formed into hollow billet while still hot. Then rolling and stretching into certain sizes. Generally speaking stainless steel seamless pipe do not need heat treatment.

Welded pipe begins as a metal strip called skelp, the skelp will be cut and rolled into shape. Welded pipe usually need heat treatment after manufacture. The advantages of ERW welded pipe is the seam is nearly can’t seen.

We usually seen welded pipe are weaker due to thee seam it has. However, the enhanced manufacture technique allows it performs as desire. And seamless pipe also has its own weakness that the wall thickness could be inconsistent after rolling and stretching.

Line Pipe Dimensions

Stainless steel pipe supplier Zizi supplies steel pipes in following ranges:

Standard: ASTM A312, ASTM A790, ASTM A928, ASTM A213, ASTM A269, ASTM A358, ASTM A778 , DIN 1850, DIN 17457, DIN 17458, EN 10217-7, EN 10357, EN-10296-2

Diameter: 1/8″ to 4″

Wall Thickness: Sch 5S, Sch10S, Sch20, STD, Sch40, XS, Sch80, Sch120, Sch160, XXS.

Length: Cut Length, Single Random, Double Random.

Pipe Type: Seamless, ERW, SSAW, LSAW

End Type: Plain End, Beveled End, Screw End.

Coating: FBE, 2LPE, 3LPE, as requirement.

Those dimensions are necessary for pipe ordering and manufacturing .

Pipe Prices and Weight

According to the kilogram price of stainless steel and the total weight of pipes we calculate the total price.

The total weight of steel pipe is based on their diameter, thickness, length and quantity.

Weight Formula of Steel Pipes:

Weight (Kg/m) = (OD-THK)*THK*0.02466 (CS) or 0.02491 (SS)

• OD is the outside diameter
• THK means the wall thickness.

High Quality Steel Pipe Supplier

High quality stainless steel supplier Zizi puts large attention to the quality control. Quality is the key to obtain customers’ satisfaction.

We are ISO certificate steel pipe supplier and we gain the certifications of ABS, LR, API, CE and so on. Our employees adhere to and contribute to  our quality system in every aspect of our business. From row materials purchasing to the package, we have executive standard and strict execute it.

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