Table of content
Introduction
Whether producing or using carbon steel pipes, it is necessary to understand their performance, thickness, diameter, etc., where diameter includes outer diameter and inner diameter. According to production standards, there will be specified outer diameters during production. How to determine the outer diameter when using it? You can check the markings on the outside of the steel pipe or measure the outer diameter yourself.
How to measure and mark the outer diameter of the steel pipe. Knowing the importance of outer diameter.
Outer diameter: The straight-line distance from one outer edge of a steel pipe to another.
If the production standard for steel pipes is ASME/ANSI B36.10M standard, there are corresponding dimensions and outer diameters in this standard. That is, the actual outer diameter of a 4-inch 40 carbon steel pipe is usually 4.500 inches (114.3 mm).
What Does OD (Outside Diameter) Mean?
Outer diameter (OD) is an important data of a pipeline, which represents the outer wall diameter of the steel pipe. Knowing the OD and thickness can determine the inner diameter. Knowing these three items allows for the correct selection of connected fittings, flanges, or valves.
Namely:
- Outer diameter, also known as OD: the external diameter of a pipeline.
- Inner diameter or ID: the internal diameter of the pipeline.
- Wall thickness: The thickness of the material in the outer and inner diameters.
Why OD Is Important in Carbon Steel Pipes
Because understanding the outer diameter of the steel pipe is crucial for selecting the corresponding fittings.
- Compatibility of pipe fittings: Knowing the outer diameter of the pipe fittings that need to be connected, as well as the outer diameter of the flange and valve, will determine the compatibility.
- Pressure rating: The outer diameter and wall thickness simultaneously determine the pressure rating that the steel pipe can withstand.
- Flow rate: The flow rate mainly depends on the inner diameter, of course, knowing the outer diameter can also calculate the inner diameter well.
- Maintenance and replacement: Knowing the outer diameter can better select suitable accessories when parts need to be replaced.
If different outer diameters are chosen, it may cause misalignment and leakage.
Carbon Steel Pipe OD vs Nominal Pipe Size (NPS)
In addition to the outer diameter, the nominal pipe size NPS is also a common identification in steel pipes. What is the relationship between these two?
NPS is a standardized label for pipeline size, which may differ from the actual outer diameter as it is allowed to have up and down differences during production.
- Pipelines below 14 inches typically have an outer diameter larger than NPS.
- Pipelines over 14 inches typically have an outer diameter size equal to NPS.
For example:
| Nominal Pipe Size (NPS) | Actual OD (inches) | Actual OD (mm) |
|---|---|---|
| 1/2″ | 0.840 | 21.34 |
| 3/4″ | 1.050 | 26.67 |
| 1″ | 1.315 | 33.40 |
| 2″ | 2.375 | 60.33 |
| 4″ | 4.500 | 114.30 |
| 8″ | 8.625 | 219.08 |
| 12″ | 12.750 | 323.85 |
| 14″ | 14.000 | 355.60 |
So, the actual outer diameter of a 4-inch carbon steel pipe may be 4.5 inches.
Standard Carbon Steel Pipe OD Chart (ASME B36.10M)
The ASME standard specifies the outer diameter, inner diameter, wall thickness, etc. of steel pipes. Here is a relatively simple data table:
| Pipe Size (NPS) | Schedule | Outside Diameter (OD) | Wall Thickness (in) | Wall Thickness (mm) |
|---|---|---|---|---|
| 1″ | 40 | 1.315″ | 0.133 | 3.38 |
| 2″ | 40 | 2.375″ | 0.154 | 3.91 |
| 4″ | 40 | 4.500″ | 0.237 | 6.02 |
| 6″ | 40 | 6.625″ | 0.280 | 7.11 |
| 8″ | 40 | 8.625″ | 0.322 | 8.18 |
| 10″ | 40 | 10.750″ | 0.365 | 9.27 |
How to Measure Carbon Steel Pipe OD
There are usually two methods for manually measuring the outer diameter of carbon steel pipes:
- Measure the circumference of the steel pipe using a tape measure, divide the measured circumference by 3.1416, and calculate the outer diameter.
- Measure the outer edge length of the steel pipe directly using a caliper.
When selecting suitable connecting fittings or flanges, it is necessary to measure the outer diameter.
Common Pipe Schedules and OD Examples
The pipeline schedule usually includes outer diameter, inner diameter, and wall thickness.
Normally, the outer diameter is fixed, but the inner diameter of the steel pipe may change over time during use.
For example:
- 2″ Schedule 40→ OD = 2.375″, Wall Thickness = 0.154″
- 2″ Schedule 80 → OD = 2.375″, Wall Thickness = 0.218″
Although the outer diameters of these two are the same, their wall thicknesses are different. The thicker the wall thickness, the greater the pressure it can withstand.
Applications Where OD Matters
Outer diameter is particularly important in practical use, whether it is industrial pipelines or structural supports.
- Structural support: It can determine the load-bearing capacity of its structure.
- Oil and gas pipelines: You can choose pipelines that are more suitable for withstanding high pressure.
- HVAC system: Ensure its aesthetics and practicality.
- Manufacturing and welding: The outer diameter plays a crucial role in ensuring the continuity of the welding surface.
Summary
In short, OD plays a very important role in steel pipes. It is necessary to know the outer diameter of steel pipe connections or edge fittings and flanges.
When choosing, it is important to note:
- NPS is not equal to OD.
- The choice of OD is related to the safety of the pipeline system.
- For pipes produced by manufacturers with markings, actual measurements are also required.
Having understood the importance of the outer diameter of steel pipes, I believe you also have a reference value when choosing connectors.
