Pipe vs. Tube: They Look Similar, But They’re Not. Here’s When to Use Each.

At first glance, pipes and tubes seem identical—both hollow metal cylinders. But they’re distinct products, each with unique uses and traits. 

Pipes are hollow cylinders mainly used for transporting fluids and gases. Tubes (which can also be square or rectangular)  on the other hand, serve as the structural support in mechanical parts or for precision use. 

When choosing between pipes and tubes, remember to focus on their key differences: application, shape, sizing, and cost.

What Is A Pipe?

A pipe is defined by the American Society of Mechanical Engineers (ASME) as “a tubular product having a circular cross-section, and specified by a nominal size and a schedule. Pipes are intended primarily for conveying fluids and gases.”

The International Organization for Standardization (ISO) refers to pipes as “A tubular product for the conveyance of fluids, typically specified by a nominal size and wall thickness, with a circular cross-section.” The conveyed fluid includes liquids like water, oil, chemicals, and gases such as natural gas, propane, and compressed air.

According to ASME, pipes are grouped into different types. This grouping is based on three rules: what the pipe is made of, how it’s manufactured, and what it’s used for.

1. When grouping pipes by the material they’re made from, there are four main kinds: Carbon Steel Pipes, Stainless Steel Pipes,  Alloy Steel Pipes, and Non-Metallic Pipes.
2. Based on how the pipes are formed, pipes are classified into Seamless Pipes, Welded Pipes, and Cast Pipes.
3. The ASME also groups pipes by what they’re used for in industry; there are five main types

Process Piping: for chemical, petrochemical, and pharmaceutical processes.

Power Piping: for power generation, including boilers, steam turbines, and nuclear power plants.

Oil and Gas Piping: for liquid petroleum (such as crude oil, gasoline) transportation, as well as gas transmission and distribution.

Plumbing and Fire Protection Piping: for building services (such as potable water supply and HVAC) and slurry transportation (such as mining waste).

Nuclear Piping: Specialized piping engineered for use in nuclear power plants.

What Is A Tube?

According to ASME, a tube is a hollow product with a continuous circular or any other cross-sectional shape. The ISO doesn’t give a direct definition for “tube.” But it does mention tubes in some specific uses—like the tubes used in wells for the oil and natural gas industries.

Tubes come in various shapes, materials, and manufacturing methods. They can be used to support structures or for special jobs, such as moving fluids precisely or making mechanical parts.

The ASME puts tubes into different types based on what they are made of, how they are made, and what they are used for.

By material, tubes are often either carbon steel or stainless steel.
By manufacturing method, tubes can be seamless or welded.
By application, ASME defines three main categories:

• Tubes for Boilers, Superheaters, and Heat Exchangers– seamless ferritic and austenitic stainless steel tubes used in these systems.
• Tubes for General Service–seamless and welded austenitic stainless steel tubes with a standard wall thickness, used in normal, low-, or high-temperature situations.
• Tubes for Mechanical Engineering Applications– seamless stainless steel tubes for machines that need resistance to corrosion or strength at high temperatures.

What Are The Differences Between Pipe and Tube?

The differences between Pipe and Tube are in industrial applications, shape, sizing and measurement, and cost. Understanding these distinctions can help you find the right product.

1. Shape Differences Between Pipe and Tube

Shape is the most obvious difference between pipes and tubes, and this comes from the different needs they have in different industries.

● Pipe Shape

Almost all pipes are cylindrical (round in cross-section). This shape works best for carrying fluids and gases.

– It reduces the friction of the liquid flow, which reduces pressure loss and waste.

–  The pressure is spread evenly over the pipe walls, so there are fewer weak points and less chance of bursting or leaking under high pressure. This is very important for holding liquids or gases under high pressure, like oil or gas.

– It is also easy to connect with fittings like elbows and tees. These fittings do not block the flow, and they make manufacturing and installation simpler.

● Tube Shape

Tubes can be made in many shapes, such as round, square, rectangular, oval, elliptical, and even special shapes like triangular or hexagonal. The shape depends on what the tube will be used for.

– Round tubes:Used in cars to move fluids (more precise than small pipes) or as support rods. Their circular shape gives them strong resistance to twisting because stress is spread evenly.

– Square and rectangular tubes: Popular in construction (e.g., railings, furniture frames, building columns). Square tubes spread weight evenly over all four sides, making them strong under pressure. Rectangular tubes have high resistance to bending and torsion, and are often used as the frame for structures.

-Other shapes: Used in industries where special shapes improve weight, strength, or other qualities, such as in aerospace.

Pipes are almost always round because this shape works best for moving fluids under pressure. Tubes can be made in many shapes, which makes them more versatile in use.

2.Differences in Sizes and Measurements of Pipe and Tube

The sizing of pipes and tubes follows entirely different logics, which is rooted in their core functions.

● Pipe Sizing

Pipe size is measured using a standard system. In the United States, it’s called Nominal Pipe Size (NPS). In other countries, it’s called Nominal Diameter (DN). This measurement is based on the pipe’s approximate inner diameter (ID).

For example, a 2-inch NPS pipe does not actually have an outside diameter (OD) of 2 inches. A 2-inch NPS steel pipe has an OD of 2.375 inches, as set by industry standards. This system is designed to show how much fluid or gas a pipe can carry. The nominal size gives a rough idea of the inner diameter, which affects flow capacity.

Pipes also have a  standardized “schedule” number that shows wall thickness, such as Sch. 40 or Sch. 80. A higher number means a thicker wall. For example, a Schedule 80 pipe is stronger than a Schedule 40 pipe of the same size. Thicker walls allow pipes to handle higher pressure, which is important for moving fluids like oil or gas safely.

● Tube Sizing

Tube size is defined by its actual outer diameter (OD) and wall thickness, with precise measurements in inches or millimeters. For example, a tube marked “10 mm OD × 1 mm wall” means the outside is exactly 10 mm wide and the wall is 1 mm thick, giving it an inside diameter (ID) of 8 mm.

This sizing system prioritizes on the outside size and strength of the tube. This is because tubes are often used where a perfect fit and strong structure are important. In mechanical assemblies, a tube must match the exact dimensions of other components to function properly. They come in many sizes — from very small 1 mm OD tubes used in medical tools to large 300 mm OD tubes for structural support.

Pipes are sized by nominal bore and wall thickness schedule, tailored to flow capacity and the pressures they can handle. Tubes, on the other hand, use exact outer diameter and wall thickness measurements for more precision.

3. Which Costs More, Pipe or Tube?

Precision stainless steel tubes cost 1.5 to 2 times more than stainless steel pipes of the same nominal size and material. This is because tubes are made by cold drawing, which is more expensive and requires very exact measurements.

Industrial aluminum alloy tubes cost about one-third the price of a 1-meter precision PVC pipe (used for low-pressure water). PVC pipes are made by extrusion and cutting with tight size limits, while aluminum tubes are finished to high quality.

The difference in cost between pipes and tubes can be attributed to three factors: complexity of manufacturing processes, strictness of tolerances and quality control, and, of course, material selection.

● Manufacturing Processes

Pipes are produced using processes optimized for scalability and cost efficiency, with minimal emphasis on ultra-precise dimensions. Pipes are typically hot-rolled, a process that prioritizes speed and large-scale output over tight dimensional control.

Tubes require specialized, multi-step processes to meet strict tolerances and structural demands, driving up production costs. Tubes often undergo cold-rolling, which enhances surface quality and tightens tolerances but is more resource-intensive than hot-rolling.

● Tolerances and Quality Control

Tolerances for pipes are loose, as their primary role (fluid transport) depends more on flow capacity than exact dimensions. Testing focuses on basic pressure resistance, keeping quality control costs low.

By contrast, tubes require tight tolerances for applications like structural frameworks, medical devices, or automotive components—where fit and strength are essential. Rigorous testing (e.g., dimensional inspections, stress tests) and compliance with strict standards increase testing and quality assurance costs.

● Material Requirements

Pipes often use standard, cost-efficient materials (e.g., carbon steel, PVC) suited for fluid transport. Tubes, however, often require high-grade, precision alloys(e.g., stainless steel for corrosion resistance, aerospace-grade metals for strength-to-weight ratios) to meet structural or environmental demands. These materials are inherently more expensive than the standard metals.

Tubes cost more than pipes because their manufacturing processes (cold drawing, precision welding, extrusion) are more complex. They also require stricter quality control and more precise measurements, and they often use special materials

Pipes, on the other hand, are cheaper because they are made in large quantities using simpler methods. They have looser size limits and use standard materials, which matches their main purpose of moving fluids at a lower cost.

● Table: Quick-Reference Comparison of Pipes and Tubes

The table below shows the main differences between pipes and tubes based on their basic features:

Comparison Item	Pipe	Tube
Main Use	Transporting fluids (gas, liquid)	Structural support, mechanical parts, and precision use
Typical Uses	Water lines, gas pipes, oil pipelines, drainage	Automotive parts, furniture frames, railings, instruments, and medical devices
Shape	Round	Round, square, rectangular, oval, elliptical, and even custom designs
Sizing	Measured by ID and Schedule (wall thickness)	Measured by OD and Gauge (wall thickness)
Tolerance	Looser	Tighter
Common Materials	Carbon steel, PVC, stainless steel	Carbon steel, stainless steel, Alloy steel
Manufacturing	Welded, seamless	Welded, seamless, cold-drawn
Precio	Usually lower	Usually higher (due to higher precision)

When to Use Pipes or Tubes

The choice between pipes and tubes depends entirely on the specific requirements of the application. Selecting the wrong component can lead to inefficiencies, safety risks, or increased costs. That’s why it’s important to match the part’s special features with what it needs to do.

When to Use Pipes

Pipelines are mainly used to transport fluids/gases over long distances, with their sizing, shape, and standards optimized for flow capacity and pressure containment. They are the ideal choice in the following scenarios:·

Residential and Commercial Plumbing: PVC or copper pipe is used to transport hot and cold water and wastewater. Standard fittings are used to connect the pipes.

Oil and Gas Industry: Seamless steel pipe transports crude oil, natural gas, and petroleum over long distances. Its thick wall allows it to withstand high pressure.

Water and Wastewater Systems:Large concrete or HDPE pipes carry city water or wastewater to treatment plants. Their round shape helps prevent clogs and keeps liquids flowing smoothly.

Chemical Processing: Stainless steel pipes move corrosive chemicals because they resist damage from chemicals and have no seams, which reduces the risk of dangerous leaks.

High-Pressure Steam Piping: In power plants and industrial facilities, pipe transports high-pressure steam efficiently.

HVAC Refrigerant Piping: Pipe performs best in this application because it can carry pressure in the form of refrigerant.

When to Use Tubes

Tubes are applied where structural strength, precise dimensions, or varied shapes are needed. Pipe is the better choice in the following situations:
Construction: Square or rectangular steel pipes are used for railings, staircases, building frameworks, and furniture like outdoor benches. The straight sides lead to better connections and provide exceptional load-bearing stability.

Automotive and Aerospace: Aluminum or titanium tubes are used for structural parts, fuel lines, and hydraulic systems. They are lightweight and fit precisely, which helps reduce vehicle weight while improving performance.

Medical Devices: Small-diameter stainless steel or plastic tubes are used in syringes, catheters, and surgical instruments. Its precise outer/inner diameter allows for proper drug delivery or safe implantation. Most tubes are made from biocompatible materials to minimize body reactions.

Mechanical Engineering:  Cylindrical steel tubes are used as shafts, support rods, or mechanical components like conveyor belts. Their strength and precise shape help equipment run smoothly.

Heat Exchangers and Boilers: The precise dimensions of the steel tubing enable efficient heat transfer.

Architectural and Aesthetic Applications: Smooth, precisely finished tubes are used when appearance matters, such as in handrails, display shelves, and furniture.

Resumen

Pipes and tubes may look similar, but they are designed differently and serve specific purposes in engineering, manufacturing, and construction. It’s not a matter of one being better — the choice depends on matching the unique design, size, and performance needs of each project.

If you’re still unsure, get project-specific advice from SUMEC METAL. Your professional steel supplier can save you time, money, and problems.