Have you ever had a problem classifying a cylindrical section?
Would you call it a tube or a pipe?
Like many people, you may see these two as the same thing.
After all, all hollow cylinders look almost similar.
But wait! Regardless of how similar they look, steel pipes and tubes have different characteristics.
Most people, even professionals working in relevant industries, sometimes use the term tube and pipe interchangeably.
To put to rest this confusion, we have listed below the main difference between steel tubes and pipes.
1. Size and Dimension
Tubes are smaller than pipes. These two are measured differently. Steel tubing sizes are measured using the exact outside diameter (OD).
Unlike tubes, steel pipes sizes and dimensions use nominal diameter (OD). They are usually sold in Nominal Pipe Size (NPS). You shouldn’t, however, confuse NPS to mean ID on smaller pipes. Originally, NPS OD was specified so that pipes with standardized wall thickness and OD would have pipe ID that was almost equal to the nominal pipe size.
Here is an example that illustrates how tubes and pipe differ in measurement. The actual outside diameter of 1¼ inches pipe is 1.625” , while 1¼ inches tube has exact outside diameter of 1.25”. The inside dimension or the capacity of the pipe is the most important property.
Because of the difference in size, tubes are used in applications that can accommodate smaller diameters while pipes are used in applications that require larger diameters. Pipe sizes usually range from ½ inch to several inches. But, it is uncommon to find a 10-inch tube.
2. Wall Thickness
Another differentiating factor is the thickness of tubes and pipes. The thickness of a pipe is often specified in schedules (the wall thickness of a pipe). The three popular pipe schedules are:
Among the three, SCH80 is quite heavy while SH40 is the most popular.
As indicated earlier, the thickness of a tube is important because it determines its strength. The thickness is usually classified by a gauge, especially for thinner tubing. Thicker tubing is specified by millimeters or fractions of an inch.
3. Tolerance & Structure
Tubes are generally more rigid than pipes. The tolerance, in this case, refers to wall thickness, diameter thickness, and straightness thickness. Most pipes are used for distribution and transportation, so the properties of roundness, straightness, and pressure are strictly specified.
To effectively transport or distribute gases or liquid, most pipes are round. Tubes, on the other hand, are not always round in shape. So if you have referred a rectangular hollow cylinder as pipe, chances are that you use the term interchangeably.
Besides this, steel tubes are normally seam welded while pipes are seamless. In most cases, pipes are pressure rated to avoid leakages.
4. Manufacturing Process & Cost
As we mentioned earlier, tubes are more tolerant than pipes. They usually require sturdy materials and a higher level of requirements to process. Tubes require thorough manufacturing process, testing, inspections than pipes. So, the delivery time for tubes is usually longer.
For these reasons, the yield of tubes is much lower than pipes. Because of a faster manufacturing process, pipes are often produced en masse.
The production cost of tubes is usually higher because the manufacturing process requires more labor, and material, and energy. This translates to a higher cost of these products.
Comparatively, the process of manufacturing pipes is simpler, so the production cost is lower. Moreover, they are often manufactured in masses. As you would expect, the prices of pipes are significantly lower.
As alluded to earlier, pipes are mostly used for transportation of liquid and gases such as oil, water, propane and sometimes steam. Because of this, more emphasis is put on the inside diameter. This is important because it tells you how much substance the pipe can carry. The pressure rating is also important and should be within transport range.
Since most pipes have larger diameters, they can accommodate larger applications. Pipes, especially in smaller diameters, can be used for other applications such as production casing and intermediate casing , though these applications are less popular.
You may already be asking yourself if tubes are of any importance if their main focus is outside diameter. Yes, tubes are used in applications that put more emphasis on precise outside diameters. They are also perfect for applications that require smaller diameters.
They are mainly used for structural purposes. Notable examples are industrial parts, weapon parts, medical tubes, heat exchanger tubes, cooler tubes, and boiler tubes.
As you can tell from these examples, tubes are mainly used in constructions, medical sector, and fabrications among other industries.
Tubes are mainly made of aluminum, mild steel, copper, brass, stainless steel, and chrome among other metals. A majority of pipes are made of low alloy steel or carbon steel . We will refer to these metals below, on the section on mechanical and chemical properties.
Apart from the reasons given earlier, the difference in the materials used to make these products could also explain the difference in applications and the cost of steel pipes and tubes.
Some common piping classes or standards are:
• ASTM A312 – This is a welded seamless stainless steel pipe
• The API range. This is now ISO 3183 – One of its classes in this range is e.g. API 5L Grade B – Also ISO L245. The number shows the yield strength.
• ASME SA106 Grade B – A seamless carbon steel pipe suitable for high-temperature applications
• ASTM A36 – A carbon-based pipe that is usually used in low pressure or structural applications.
• ASTM A795 – This steel pipe often used for fire sprinkler systems
Seamless pipes are suitable for a wide range of materials and grades. They are preferred for severe conditions. ALL CRA tubular and Per API 5CRA are seamless. Because of manufacturing limitations, seamless pipes are usually available in smaller diameters.
7. Mechanical & Chemical Properties
The mechanical quality of pipes and tubes is often measured using different parameters. For example, yield strength, pressure rating, and durability properties are important which choosing pipes. On the contrary, the tensile strength, hardness, and high precisions are important qualities of tubes.
The main chemical elements of pipes are manganese, Carbon, Phosphorus, Sulphur, and Silicon and some few microelements requirements. For tubing, the microelements are the main important chemical properties considered for quality.
Connecting pipes are more labor-intensive than joining tubes. The former requires welding, flanges, or threading alongside specific equipment. Welding offers more stability than simple joining.
Connecting tubes is generally simple and straightforward as it requires only brazing and flaring. It is also possible to carry out tube assembly through tube fittings, especially when firmer construction is needed.
9. Surface finish and ends
All pipes used for underground or field transportations are usually painted or finished with a coat of an antioxidant. Tubes, on the other hand, are typically subjected to a special polish treatment or sour cleaning depending on the field use.
Pipe ends are often in beveled form or plain for easier welding. Whereas, tubes usually come with coupling ends or special end finishes such as special screw thread and irregular ends.
10. Packaging and Quantity
Pipes are usually delivered in bulk. They may not need as much protection as tubes. The packaging usually offers protection to the surface of pipes from serious damage.
Tubes, especially for medical applications, are usually wrapped with a thin film around each tube or wooden box.
Hopefully, this article has helped you understand the difference between pipes and tubes. However, if you need more information, please email to pipe expert at email@example.com. We are a professional manufacturer of steel pipe, pipe fittings, and flange with over 20 years of excellent service to several clients across the world.
We use the latest manufacturing and testing equipment to allow us to run first-class production and inspections. You can, therefore, expect the best quality products.