A comprehensive guide to manufacturing and uses

The Pompidou Center in Paris featuring exposed steel pipes and structural elements on its exterior.
The intricate design of the Pompidou Center in Paris showcases the versatility and strength of steel pipes in modern architecture.

Steel pipes are used extensively in various industries, from manufacturing and construction to infrastructure and transportation. These steel cylindrical tubes are considered the most widely utilized product in the steel industry. The primary function of steel pipes is to transport liquids and gases, including oil, gas, and water, typically underground. However, their applications extend far beyond that.

Pipes of different sizes find their place in manufacturing and construction. In the manufacturing sector, a familiar example is the thin steel pipe used in the cooling system of refrigerators. In construction, pipes are essential for heating and plumbing systems. Additionally, steel pipes of varying sizes are employed to build structures like handrails, bike racks, and bollards.

The history of steel pipes dates back to 1815 when William Murdoch ingeniously connected musket barrels to create a piping system for transporting coal gas to street lamps in London.

Steel pipes
Steel pipe is either seamless or welded and comes in a variety of sizes and lengths.

Since then, the technology surrounding steel pipes has advanced significantly. We’ve witnessed improvements in manufacturing methods, the development of new applications, and the establishment of regulations and standards to ensure their quality and safety.

How Steel Pipe is Made

From the initial melting of raw materials to the final molding or welding, steel pipes are created through two primary processes:

Converting Raw Steel into a Usable Form

Irrespective of the process, the journey begins with the production of high-quality steel. Foundries melt raw materials in furnaces to produce raw steel. To achieve the desired composition, elements may be added, or impurities removed from the molten metal. The resulting molten steel is then poured into molds to create ingots or transferred to a continuous casting machine to produce slabs, billets, and blooms. Pipes are manufactured from two of these products—slabs and billets.

Stack of steel billets
Solid steel billets are heated, stretched, and pierced through the center to become seamless steel pipes.

Steel Slabs and Steel Skelp in Pipe Manufacturing

Steel skelp is produced by heating steel slabs to a scorching 2,200°F. This heating process leads to the formation of scale on the surface, which is removed using a scale breaker and high-pressure cleaning. Once cleaned, the hot steel slab is rolled into thin, narrow strips known as skelp. The skelp undergoes pickling (surface cleaning) with sulfuric acid, followed by a water wash, and is then coiled onto large spools, ready for pipe production. The width of the skelp determines the diameter of the pipe that can be manufactured.

During pipe production, the skelp is uncoiled, heated, and passed through grooved rollers that bend its edges upward, forming a cylindrical tube. A welding process joins and seals the edges together.

  • In continuous welding, welding rollers press the heated skelp edges together, creating a forged weld. No additional metal is added, and final rollers adjust the pipe’s diameter and wall thickness to meet specifications.
  • Electric resistance welding is similar, but the skelp is cold rolled into the pipe shape. Revolving copper disks supply current to the edges, heating them for welding. Welding rollers then join the edges.
  • Spiral welding and double submerged arc welding employ conventional welding techniques, adding weld material to form the bond.

Steel Billets for Seamless Pipe

Steel billets, long square pieces of steel, are produced directly from a continuous casting machine or by rolling and stretching cast ingots. These billets are used to manufacture seamless pipes, which are preferred in certain applications due to the absence of a weld line, enhancing their safety.

The solid steel billet is heated to extreme temperatures, reaching a white-hot state without melting. Machines roll them into a cylindrical shape. While still hot, a bullet-shaped piercer creates a consistent hollow center according to the required dimensions. Subsequent milling operations ensure the pipe conforms to the desired specifications.

Finishing Touches

Pipes may undergo straightening before being fitted with end joints. Small-bore pipes typically have threaded joints, while larger ones have flanges welded on. Measuring machines verify the finished pipe’s dimensions, and details are stamped on the pipe for quality control.

Quality Control

Quality control uses X-ray inspections to detect defects, especially along welds. Pressure testing, where the pipe is filled with water and held under pressure, helps identify potential weaknesses that could lead to failure.

Applications of Steel Pipe

Steel pipes serve a variety of purposes across structures, transportation, and manufacturing. Their size is specified by the outer diameter, with the inner diameter varying based on wall thickness. Thicker walls are necessary for applications involving higher stresses.

Structural Applications

In the building and construction sectors, steel pipes, often referred to as steel tubes, are commonly employed for structural purposes.

Construction Piles
A Welder works on steel pipe
A welder fabricating structural steel pipes, demonstrating the critical role of skilled craftsmanship in steel pipe manufacturing.

Steel tubes are crucial in strengthening foundations through a process called piling. They are driven deep into the ground before laying the foundation, providing stability for tall buildings or constructions on unstable ground.

There are two main types of pile foundations:

  • End Bearing Piles: The bottom end rests on a strong soil or rock layer, transferring the building’s load onto this sturdy layer.
  • Friction Piles: The load is transferred to the soil along the entire pile’s height through friction. The pile’s surface area aids in distributing the forces to the soil.
Scaffolding Poles
Construction site with steel pipe scaffolding lining a multi-story building under development.
Steel pipes forming the backbone of scaffolding at a large-scale construction site, showcasing their strength and reliability in supporting structures.

Scaffolding poles are constructed by connecting steel tubes to create a framework that enables construction workers to access elevated areas safely.

Manufacturing Applications

Modern staircase with steel pipe supports and glass railings inside a contemporary building.
An interior staircase supported by steel pipes, illustrating the versatility of steel in both structural and design elements.

Steel pipes play a pivotal role in the manufacturing sector, serving as integral components in a wide array of products. Their strength, durability, and versatility make them ideal for applications ranging from intricate machinery and industrial equipment to everyday consumer goods.

Let’s explore some key manufacturing applications where steel pipes shine:

Automotive Industry
  • Exhaust Systems: Steel pipes, often stainless steel due to its corrosion resistance, are extensively used in automotive exhaust systems to channel hot gases away from the engine.
  • Chassis and Frames: High-strength steel pipes form the backbone of many vehicle chassis and frames, providing structural integrity and crashworthiness.
  • Fluid Lines: Steel pipes transport various fluids within vehicles, including fuel, brake fluid, and coolant.
Machinery and Equipment
  • Hydraulic and Pneumatic Systems: Steel pipes are essential for conveying pressurized fluids in hydraulic and pneumatic systems, powering machinery and equipment across industries.
  • Pressure Vessels: Seamless steel pipes are often used to construct pressure vessels, which store and contain fluids or gases under pressure.
  • Conveyor Systems: Steel pipes can be used as rollers or structural supports in conveyor systems, facilitating the movement of materials in factories and warehouses.
Consumer Goods
  • Furniture: Steel pipes are increasingly popular in furniture design, adding a modern industrial aesthetic to chairs, tables, and shelving units.
  • Appliances: Steel pipes are found in various household appliances, such as refrigerators (for coolant lines) and washing machines (for water inlet and drainpipes).
Safety and Security
  • Handrails and Guardrails: Steel pipes provide safety and support as handrails along staircases and walkways, and as guardrails to prevent falls from elevated platforms or balconies.
  • Bollards: Security bollards, often made from steel pipes, are strategically placed to control vehicle access and protect pedestrians and property.
  • Bike Racks: Steel’s durability and resistance to bending make it a preferred material for bike racks, providing secure storage for bicycles.

The manufacturing sector’s reliance on steel pipes underscores their significance in shaping the modern world. Their ability to withstand high pressures, and be customized to various shapes and sizes makes them indispensable in countless industrial processes and products.

Transport use

The most prevalent use of steel pipes lies in the transportation of various products. Their durability and resistance to degradation make them ideal for long-term installations, particularly underground.

Applications involving low pressure don’t necessitate high-strength pipes, allowing for thinner walls and cost-effective manufacturing. However, specialized applications, like those in the oil and gas industry, demand pipes with stringent specifications. The hazardous nature of the transported products and the potential for high pressure require greater strength and thicker walls, often resulting in higher costs. Rigorous quality control is paramount in these applications.

Transportation pipes outside power plant
Steel pipes are used to transport products such as oil, gas, and water, and are suitable for long-term installations.

Specifying Steel Pipe

Understanding steel pipe specifications can be challenging. In North America, the American Society for Testing and Materials (ASTM), The American Society of Mechanical Engineers (ASME), and the American Petroleum Institute (API), are the primary organizations that define piping specifications.   

Specifications fall into three main categories:

Nominal Pipe Size (NPS)

Pipe size is denoted by its Nominal Pipe Size (NPS). The origin of NPS numbers differs for smaller pipes (< NPS 12) and larger ones. However, all pipes with a specific NPS share the same outer diameter (OD). The internal diameter varies depending on the wall thickness. This consistency in OD allows for the use of the same structural supports for pipes of a given NPS, regardless of their wall thickness.

Schedules

Steel pipe schedules describe the pipe’s wall thickness, a critical parameter directly influencing its strength and suitability for specific applications. The schedule number is dimensionless and calculated based on the design formula for wall thickness, considering design pressure and allowable stress.

Common schedule numbers include: 5, 5S, 10, 20, 30, 40, 50, 60, 80, 100, 120, 140, 160, STD, XS, and XXS, with 40 and 80 being the most frequently used. As the schedule number increases, so does the wall thickness. With the OD fixed by the NPS, the schedule number defines the internal diameter.

Pipe Weight

Pipe weight is calculated based on the NPS (outer diameter) and the schedule (wall thickness). The formula utilizes the theoretical weight of steel, which is 40.8 pounds per square foot per inch of thickness, to determine the constant.

Formula:

W = 10.69 x t (OD – t)

Where:

            W = weight (in pounds per foot)
            OD = outer diameter
             t = thickness

Refer to the table from Engineering Toolbox for measurements of OD, wall thickness, and weight for pipes of different NPS and schedules (40 and 80):

Certification

Manufacturers provide a Material Test Report (MTR) or Mill Test Report to verify that the product adheres to the specified chemical analysis and mechanical properties. The MTR includes all relevant product data and accompanies it throughout its lifecycle.

Typical parameters recorded on an MTR include:

  • Chemical composition (carbon content, alloys, sulfur)
  • Material size, weight, identification, and grade
  • Material heat number (linked to the processing batch)
  • Mechanical properties (tensile strength, yield strength, elongation)

For steel bollards, ASTM A53 and ASTM A500 are the most cited specifications.

Decorative plastic bollard covers
Steel pipe bollards can be covered with stainless steel, plastic, or other metal decorative covers for aesthetic appeal and protection from corrosion.

How does Reliance Foundry use steel pipes?

Reliance Foundry supplies pipe bollards that are made from steel pipes. Bollards are vertical pipe lengths installed in the ground to protect people, buildings, and surrounding infrastructure from vehicle collisions. Steel pipe bollards must conform to safety specifications to ensure they are strong enough to resist the impact of vehicle collisions. Schedule 40 and schedule 80 steel can be used to make steel pipe bollards depending on the application. Steel pipe bollards are often covered with stainless steel, plastic, or other metal decorative covers for aesthetic appeal and to protect the steel pipe from corrosion.