Carbon Steel and Stainless Steel Welded and Seamless Pipe

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Stainless steel pipe and carbon steel pipe are among the most commonly used standard pipes today. These pipes belong to tubular goods, which are manufactured according to various specifications and standards. Available in sizes from 1/8" to 72", pipes are sold by "nominal pipe size." The two predominant types of pipes are welded pipe and seamless pipe, both available in carbon steel and stainless steel. Welded pipe, also known as ERW (Electric Resistance Welded) pipe, is typically manufactured to A53 specification for carbon steel. Seamless pipe, which requires no welding, is generally made as per A106B specification for carbon steel. Stainless steel pipes are manufactured according to A312 specification and are available in both seamless and welded variants. The most commonly used stainless steel materials are 316 and 304.

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Types of Pipes and Tubular Goods

There are six primary types of pipes and tubular goods.

1. Standard Pipe:

   Standard metal pipes come in three variants - welded (ERW Pipe), seamless, and galvanized. They comprise 10% of all tubular products.

2. Line Pipe:

   Primarily used in Oil and Gas applications, this type includes ERW, FW, SAW, and DSAW pipes. Manufactured to API 5L Specification, they come in grades like X42, X50, and X60, representing 21% of all tubular products.

3. Oil Country Tubular Goods (OCTG):

   This category includes drill pipes, tubing, and casing used in the drilling and completion of oil and gas wells. Manufactured through ERW and Seamless methods, OCTG represents 35% of all tubular goods.

4. Pressure Tubing:

   Produced using seamless methods, this tubing is used for industrial and pressure applications and represents 2% of all tubular goods.

5. Mechanical Tubing:

   Utilized for mechanical and structural purposes, manufactured by ERW and seamless methods conforming to ASTM specification, mechanical tubing accounts for 17% of all tubular goods.

6. Structural Tubing:

   Typically used for support purposes, this tubing can be round or square and is produced using ERW methods. Utilized in fences, construction, and other support needs, they represent 15% of all tubing goods.

How Pipe is Measured?

Pipes are generally identified by "Nominal Pipe Size" (NPS) with wall thickness defined by "Schedule" (SCH). NPS is a dimensionless designator indicating size, but not the actual size, which can confuse newcomers to the piping industry. For NPS sizes 1/8 through 12, the outside diameter is defined by ANSI pipe sizes, and a schedule 40 pipe dimension for up to 12 NPS roughly equals the ID of the pipe. Pipe sizes 14 and above are less confusing as, for example, a 14 NPS equals a 14" OD (outer diameter).

ASME B 36.10 has more detailed information about pipe sizes. The industry norm for pipe size can vary between different pipe types. For standard pipes, a 4.5" OD pipe is referred to as 4" NPS. However, for line pipes and OCTG, it is called 4.5". Wall thickness is also designated differently – for standard pipes, pipe schedules are used, whereas line pipes and OCTG are typically referred to by wall thickness or weight per foot.

Weight of Pipe

Weight is measured in pounds per foot or kilograms per meter. Remember, the weight in the ANSI chart is "theoretical" and might not be the actual weight. Actual weight can vary based on pipe size tolerance.

W = ((OD-WT) x WT) x 10.69

W = Weight per linear foot
OD = Outer Diameter
WT = Wall Thickness

Pipe Manufacturing

Steel pipes are classified into two main categories:

• Welded Pipe
• Seamless Pipe

There are four primary methods for producing metal pipes:

1. Furnace Weld (FW), also called Continuous Weld
2. Electric Resistance Weld (ERW)
3. Submerged Arc Weld (SAW), also known as DSAW
4. Seamless (SMLS) method

Electric Resistance Weld Pipe (ERW)

ERW pipes are produced in sizes ranging from 1/8 to 24 NPS, created from flat sheet metals then cold-formed into cylindrical shapes and welded longitudinally. Continuous welded and electric resistance welded pipes are formed from rolls of coiled steel shaped into cylindrical forms and welded along the seams. Various methods, including revolving copper discs, fixed alloy Cu contacts, and induction coils, are used for welding the rolled strip by raising the steel edge temperature to 2600°F for effective welding. The rolling process exerts pressure that creates a welded seam, later removed during finishing. The welded pipe undergoes heat treatment, inspection, and hydro testing.

ERW pipe is available in common specifications such as ASTM A53, A135, A252, A500, A795, API 5L, and API 5CT. The most common specs are A53 and API 5L.

Seamless Pipe

Seamless pipes are produced in sizes from 1/8 to 36" nominal. Without a longitudinal seam or weld, seamless pipes are created by piercing a solid round billet to leave behind a hollow, seamless pipe. There are two main production methods:

1. Hot Rotary Piercing
2. Extrusion Process Method

In the Extrusion Process, hot billets are formed into seamless pipes by forcing them through extrusion dies and over a forming mandrel. The Hot Rotary Piercing method, commonly used for seamless pipe production, involves forcing hot billets through rotating heavy rollers over a mandrel or piercing plug, creating an opening through the cylindrical billets.

Seamless pipes undergo various finishing operations such as straightening, inspection, hydro testing, and imaging. They are widely used in pressure piping, construction, petrochemical, and oil refinery applications. Seamless pipes are available in specifications like ASTM A53, A106, A252, A333, A335, A501, A523, A589, API 5L, and API 5CT, with A106B being the most common.

End finishes for seamless pipes include plain ends, either beveled or square cut. Seamless carbon steel pipes are available in black, bare, galvanized, or epoxy-coated versions.

Steel Pipe Lengths

Steel pipes are generally supplied in 21 ft lengths. They also come in Single Random Length (SRL), which ranges from 17 ft to 24 ft, and Double Random Length (DRL), ranging from 37 ft to 44 ft.

Steel Pipe End Finish

Common types of metal pipe end finishes include:

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1. Threaded and Coupled
2. Threaded without Coupling
3. Plain End - Cut Square
4. Beveled for Welding - 30 deg bevel
5. Grooved End - Cut or rolled for mechanical coupling

Different steel pipe end finishes are shown below:

 

Coupling: For extra-strong and double extra-strong pipes, couplings are taper-threaded and recessed for all sizes. The picture above illustrates straight-tapped couplings and recessed straight-tapped couplings.

Steel Pipe Identification and Marking

Steel pipes come in various classifications, grades, weights, and schedule numbers, making identification essential. Pipe markings include paint stencils, stamped markings, or attached tags.

Pipe identification as per ASTM

The picture below shows marking requirements as per ASTM specifications

Pipe identification as per API

Marking requirements according to API specification are shown in the following picture.

 Metal Pipe Finishing Processes

The most common finish on metal pipes is lacquer coating to prevent corrosion and protect against weathering, also known as Black Iron Pipe. Other finishes include:

1. Bare Metal
2. Pickled only
3. Pickled and Oiled
4. Galvanized Pipe

Galvanizing involves zinc coating as a sacrificial element to prevent corrosion. Pipes are hot-dipped in molten zinc, providing robust protection inside and out with a standard zinc weight of 1.8 oz per sq ft.

Steel Pipe Coating and Lined Steel Pipe

Pipes' corrosion resistance can be enhanced through long-lasting corrosion-resistant coatings, often surpassing lacquer or galvanized finishes. There are three main types of Corrosion Protective Coating for Steel Pipes:

Metallic Coating

Non-Metallic Coating

Pipe Wrapping

Steel Pipe Material

Metal Pipes come in different material grades:

• A106B/A53B/API 5L-X42/API 5L B

• Stainless Steel 304

• Stainless Steel 316

• Super Stainless A20

• Duplex Stainless D2205

• Nickel Alloy A200

• Nickel Alloy A400

• Nickel Alloy A600

Stainless Steel Pipe

Stainless steel is an iron-based alloy containing at least 16% chromium. Nickel is another crucial alloying element in stainless steel pipes, making them highly resistant to corrosion and oxidation at almost any temperature.

Stainless steel welded and seamless pipes are used to resist corrosion, perform at high temperatures, offer a clean look, and minimize maintenance costs. A key feature of stainless steel pipes is their ability to maintain structural integrity even with thinner walls, such as SCH 5 and SCH 10, and the use of fusion welding eliminates the need for threading.

Type 304 stainless steel pipes are generally used for corrosive-resistant applications in chemical plants, refineries, paper mills, and food industries. Type 304L has a maximum carbon content of 0.035%, and like 304, it is not recommended for use between 800°F and 1650°F due to carbide precipitation at grain boundaries.

Type 316SS pipe is highly resistant to pitting due to 2-3% molybdenum addition, making it suitable for environments with acids, brines, sulfur water, and sea water. Like 304L, 316L stainless steel pipes have a maximum carbon content of 0.035%.

Manufactured to ASTM A312 and A358 specifications, welded stainless pipes range from 1/8" to 24" NPS. Seamless Stainless Steel Pipe is made to ASTM A312 and A376 specifications, available from 1/8" to 14" nominal size.

Steel Pipe Country of Origin

Steel pipes are manufactured globally, traded across different countries. Notable names in the pipe industry include US Steel, ArcelorMittal, Nippon Steel, Nucor Corp, Hyundai Steel, ThyssenKrupp, Vallourec, Hebei Iron and Steel Group, Posco, Jiangsu Shagang, Ulma Piping, Shultz USA, and Webco.

Q&A Steel Pipe

Based on extensive experience, here are key points customers inquire about:

• Steel pipe is sold by nominal pipe size and schedule. It's essential to mention both.
• A106 B is the most common seamless pipe specification. Customers often request A106B pipe, implying a carbon steel seamless pipe per A106B. Note that A106 is not a specification for stainless steel pipe.
• For pipe sizes 10 inches and above, schedule numbers like SCH 40 and SCH 80 do not always mean Standard and Extra Heavy respectively. Refer to pipe charts for accurate wall thickness specifications.
• A53 grade B is the most common welded pipe specification, meaning a pipe produced by the ERW process.
• Welded pipes have no weld seam inside or outside, as the seam is removed during manufacture.
• Pipe sizes smaller than 2" are available in continuous weld pipe, also known as A53 grade A.
• Stainless steel pipes are available in welded and seamless configurations and in 316 and 304 grades. Other grades are available but less common.
• Stainless steel pipe is standard in thin-wall Schedule 10 designations.
• Stainless steel pipe schedules are specified by an "s" after the schedule number, such as Sch 10s, Sch 40s, Sch 80s.
• Stainless steel pipe schedules do not always correlate with carbon steel schedules. Check ANSI pipe charts for accurate schedule and wall thickness determination.
• Pipes are mainly sold in SRL (Single Random Length) or DRL (Double Random Length). SRL means the pipe is 17-24 ft long, and DRL means it is 37-44 ft long.
• Most pipes sold have a lacquer finish. Specify if you want bare pipes when ordering.
• Epoxy coating is available upon request.
• Common pipe end types include plain or beveled ends. Threaded ends are available upon request.

Types of Seamless Carbon Steel Pipes

Carbon steel pipe is widely used in construction and manufacturing for conveying fluids and solids. Despite the variety in carbon steel pipes, they share attributes like strength, hardness, and durability. Each type of seamless carbon steel pipe is designed for specific applications. This article examines different types of seamless carbon steel pipes, their benefits, drawbacks, and best usage practices.

The main types of seamless carbon steel pipes include hot rolled seamless steel pipe (HRS), cold rolled seamless steel pipe (CRS), and cold drawn seamless steel pipe (CDS). Each category has variants for specific applications, like oil or gas transportation.

Hot Rolled Seamless Tube

Manufactured from heated round billets and formed into cylindrical shapes, hot-rolled seamless pipes are used in engineering applications requiring higher strength than cold-rolled or CDS pipes. The heat treatment process enhances their hardness and strength, making them suitable for high-temperature and high-pressure environments. The advantages include cost-effectiveness, robust construction, and customizability. Drawbacks are their weight, making transportation and installation challenging. These pipes are ideal for large projects involving high pressures and temperatures.

Cold Rolled Seamless Tube

Cold-rolled seamless pipes are shaped from hot-rolled steel through a series of rolls. They are harder and more brittle than hot-rolled steel, allowing for precise machining and shaping required for equipment needing precision. Advantages include greater resistance to corrosion and wear, better machinability, and lower costs. Drawbacks include insufficient strength compared to hot-rolled steel, a higher likelihood of cracking, and limited customizability. These pipes are suitable for smaller applications that don’t require high strength or precision.

Cold Drawn Seamless Tube

Cold-drawn tubes are made by forcing hot-rolled tubes through one or more dies, densifying the material and increasing its strength. They are perfect for applications requiring critical strength and pressure resistance, such as automotive hydraulic lines. Benefits include high strength, low cost, and precise shape manufacturing. Drawbacks include potential