Outer Diameter
Definition of Outer Diameter
The outer diameter refers to the largest diameter on the outside of the pipe. The common symbol is Φ, which can also be abbreviated as OD. The common default unit is mm. The outer diameter is one of the most important parameters of the pipe. According to international standards (such as ISO 6708) and China’s national standard GB/T 1047-2005, the outer diameter and nominal diameter together constitute the standardization basis of the pipeline system.
Example: The specification of the steel pipe is marked as “Φ90×6”, which means the outer diameter is 92mm and the wall thickness is 6mm
Why is The Outside Diameter So Important?
- Installation adaptability: The outer diameter determines the size of the pipe fittings. Different outer diameters require flanges, valves, fixtures, etc. of different sizes to ensure adaptability and sealing. Too large or too small can easily cause sealing installation accidents.
- Pressure resistance and deformation resistance: The two common factors that determine pressure resistance are the outer diameter and wall thickness. A larger outer diameter can increase the pressure bearing capacity of the pipeline and prevent deformation or rupture caused by internal pressure.
- Standardization and production specifications: In order to ensure the consistency of products from different manufacturers, the wall thickness must strictly follow industry standards, such as GB/T 9711 and API Spec 5L.
Space layout and support design: The outer diameter determines the volume of the pipeline. If the space is limited, avoid choosing a pipeline with an outer diameter that is too large. - Correlation with other data: The three parameters of outer diameter, inner diameter and wall thickness together constitute the size elements of the pipeline. Their formula is ID = OD – 2t. The three parameters need to be considered comprehensively when selecting the pipeline.
Nominal diameter (DN) and OD
Correspondence table
There are two major systems for the outer diameter standards in the pipeline industry.
- A series (imperial): represented by American standards, with larger outer diameters.
- B series (metric): represented by European standards, with smaller outer diameters.
|
Nominal diameter (DN) |
A Series |
B Series |
|
15 |
Ф22 mm |
Ф18 mm |
|
20 |
Ф27 mm |
Ф25 mm |
|
25 |
Ф34 mm |
Ф32 mm |
|
32 |
Ф42 mm |
Ф38 mm |
|
40 |
Ф48 mm |
Ф45 mm |
|
50 |
Ф60 mm |
Ф57 mm |
|
65 |
Ф76 mm |
Ф73 mm |
|
80 |
Ф89 mm |
Ф89 mm |
|
100 |
Ф114 mm |
Ф108 mm |
|
125 |
Ф140 mm |
Ф133 mm |
|
150 |
Ф168 mm |
Ф159 mm |
|
200 |
Ф219 mm |
Ф219 mm |
|
250 |
Ф273 mm |
Ф273 mm |
|
300 |
Ф324 mm |
Ф325 mm |
|
400 |
Ф406 mm |
Ф426 mm |
|
500 |
Ф508 mm |
Ф530 mm |
|
600 |
Ф610 mm |
Ф630 mm |
How to Measure The outside diameter of Pipe
1. Caliper method
Clean the dirt on the surface of the pipe and ensure that the measuring area is flat
Place the caliper perpendicular to the axis of the pipe, clamp the outer wall of the pipe, and gently rotate the caliper to find the maximum reading
Select 3-5 sections at both ends and the middle of the pipe, measure 2 vertical directions for each section, and take the average value as the outer diameter
Accuracy: ±0.02mm
2. Circumference calculation method
Use a tape measure to wrap around the pipe tightly and measure the circumference of the pipe (multiple measurements are required to take the average value to reduce errors)
Outer diameter = circumference ÷ π (π≈3.14)
3. Laser/photoelectric diameter gauge
Non-contact measurement, calculate the outer diameter through optical projection analysis of shadow boundaries, with an accuracy of ±0.001mm.
