Standard steel pipe sizes (DN/NPS)
Generally, the diameter of the steel pipe can be divided into outer diameter, inner diameter, and nominal diameter. The outside diameter of the seamless steel tube is denoted by the letter D, then the outside diameter dimension and wall thickness. Take the seamless steel tube with an outer diameter of 100 and a wall thickness of 3mm as an example, which is represented by D100*3.
Regarding the identification of the nominal size of pipes, there are mainly the metric system in millimeters (DN, the unit can be omitted) and the imperial system in inches (NPS) in the world. The imperial system with inches as the unit is mainly adopted by American standards, but most American standards also support the metric nominal size identification method.
DN is the nominal diameter, also known as the average outer diameter. This is because the pipe wall of the metal pipe is very thin, and the outer diameter of the pipe is almost the same as the inner diameter of the pipe, so the average value is taken as the pipe diameter. DN is the nominal diameter. The nominal diameter (or called the nominal diameter) is the common diameter of various pipes and pipeline accessories.
DN is the most critical parameter dedicated to pipeline components.
When the nominal diameter is measured in inches, NPS is the identification code. Whether DN or NPS is used, the piping assembly standard shall give a relationship between DN(or NPS) and outer diameter (such as piping, fittings), or DN(or NPS) and inner diameter (such as valves).
What is the pipe schedule?
SCH40 is the table number of American standard seamless steel pipe, which means that the thickness of the American standard seamless steel pipe withstands internal pressure is 40mm.
There are three ways to express the thickness of the steel pipe wall: pipe table number, steel pipe wall thickness, and pipe weight. “Sch” is a method of expressing the wall thickness by the pipe number.
1) Expressed by pipe table number (Sch):
For carbon steel pipe wall thickness: 10 grades such as Sch10, 20, 30, 40, 60, 80, 100, 120, 140, 160 (if S is added after the number, it means stainless steel pipe);
For stainless steel wall thickness series, there are four grades: 5S, 10S, 40S, and 80S
2) Expressed by tube weight, such as STD (standard), XS (thick ), XXS (extra-thick )
3) Expressed in terms of steel pipe wall thickness, that is, “pipe outer diameter × wall thickness”, such as φ89×4
Schedule 40 steel pipe dimensions
| NPS | DN | Outside Diameter | Inside Diameter | Wall Thickness | Nominal Weight (Mass) per unit Length | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Designator | Designator | (Inches) | (mm) | (Inches) | (mm) | (Inches) | (mm) | Plain End (lb/ft) | Plain End (kg/m) | Threads & Couplings(lb/ft) | Threads & Couplings(kg/m) |
| 1/8 | 6 | 0.405 | 10.3 | 0.269 | 6.8 | 0.068 | 1.73 | 0.24 | 0.37 | 0.25 | 0.37 |
| 1/4 | 8 | 0.54 | 13.7 | 0.364 | 9.2 | 0.088 | 2.24 | 0.43 | 0.63 | 0.43 | 0.63 |
| 3/8 | 10 | 0.675 | 17.1 | 0.493 | 12.5 | 0.091 | 2.31 | 0.57 | 0.84 | 0.57 | 0.84 |
| 1/2 | 15 | 0.84 | 21.3 | 0.622 | 15.8 | 0.109 | 2.77 | 0.85 | 1.27 | 0.86 | 1.27 |
| 3/4 | 20 | 1.05 | 26.7 | 0.824 | 20.9 | 0.113 | 2.87 | 1.13 | 1.69 | 1.14 | 1.69 |
| 1 | 25 | 1.315 | 33.4 | 1.049 | 26.6 | 0.133 | 3.38 | 1.68 | 2.5 | 1.69 | 2.5 |
| 5/4 | 32 | 1.66 | 42.2 | 1.38 | 35.1 | 0.14 | 3.56 | 2.27 | 3.39 | 2.28 | 3.4 |
| 3/2 | 40 | 1.9 | 48.3 | 1.61 | 40.9 | 0.145 | 3.68 | 2.72 | 4.05 | 2.74 | 4.04 |
| 2 | 50 | 2.375 | 60.3 | 2.067 | 52.5 | 0.154 | 3.91 | 3.66 | 5.44 | 3.68 | 5.46 |
| 5/2 | 65 | 2.875 | 73 | 2.469 | 62.7 | 0.203 | 5.16 | 5.8 | 8.63 | 5.85 | 8.67 |
| 3 | 80 | 3.5 | 88.9 | 3.068 | 77.9 | 0.216 | 5.49 | 7.58 | 11.29 | 7.68 | 11.35 |
| 7/2 | 90 | 4 | 101.6 | 3.548 | 90.1 | 0.226 | 5.74 | 9.12 | 13.57 | 9.27 | 13.71 |
| 4 | 100 | 4.5 | 114.3 | 4.026 | 102.3 | 0.237 | 6.02 | 10.8 | 16.07 | 10.92 | 16.23 |
| 5 | 125 | 5.563 | 141.3 | 5.047 | 158.2 | 0.258 | 6.55 | 14.63 | 21.77 | 14.9 | 22.07 |
| 6 | 150 | 6.625 | 168.3 | 6.065 | 154.1 | 0.28 | 7.11 | 18.99 | 28.26 | 19.34 | 28.58 |
| 8 | 200 | 8.625 | 219.1 | 7.981 | 202.7 | 0.322 | 8.18 | 28.58 | 42.55 | 29.35 | 43.73 |
| 10 | 250 | 10.75 | 273 | 10.02 | 254.5 | 0.365 | 9.27 | 40.52 | 60.29 | 41.49 | 63.36 |
| Standard Pipe | |||||||||||
| 121 | 300 | 12.75 | 323.8 | 12 | 304.8 | 0.375 | 9.52 | 49.61 | 73.78 | 51.28 | 76.21 |
| NPS 12 dimensions are for standard wall pipe, not schedule 40. | |||||||||||
Schedule 80 steel pipe dimensions
| NPS | DN | Outside Diameter | Inside Diameter | Wall Thickness | Nominal Weight (Mass) per unit Length | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Designator | Designator | (Inches) | (mm ) | (Inches) | (mm) | (Inches) | (mm) | Plain End (lb/ft) | Plain End (kg/m) | Threads & Couplings(lb/ft) | Threads & Couplings(kg/m) |
| 1/8 | 6 | 0.405 | 10.3 | 0.215 | 5.5 | 0.095 | 2.41 | 0.31 | 0.47 | 0.32 | 0.46 |
| 1/4 | 8 | 0.54 | 13.7 | 0.302 | 7.7 | 0.119 | 3.02 | 0.54 | 0.8 | 0.54 | 0.8 |
| 3/8 | 10 | 0.675 | 17.1 | 0.423 | 10.7 | 0.126 | 3.2 | 0.74 | 1.1 | 0.74 | 1.1 |
| 1/2 | 15 | 0.84 | 21.3 | 0.549 | 13.9 | 0.147 | 3.73 | 1.09 | 1.62 | 1.09 | 1.62 |
| 3/4 | 20 | 1.05 | 26.7 | 0.742 | 18.8 | 0.154 | 3.91 | 1.48 | 2.2 | 1.48 | 2.21 |
| 1 | 25 | 1.315 | 33.4 | 0.957 | 24.3 | 0.179 | 4.55 | 2.17 | 3.24 | 2.19 | 3.25 |
| 5/4 | 32 | 1.66 | 42.2 | 1.278 | 32.5 | 0.191 | 4.85 | 3 | 4.47 | 3.03 | 4.49 |
| 3/2 | 40 | 1.9 | 48.3 | 1.5 | 38.1 | 0.2 | 5.08 | 3.63 | 5.41 | 3.65 | 5.39 |
| 2 | 50 | 2.375 | 60.3 | 1.939 | 49.3 | 0.218 | 5.54 | 5.03 | 7.48 | 5.08 | 7.55 |
| 5/2 | 65 | 2.875 | 73 | 2.323 | 59 | 0.276 | 7.01 | 7.67 | 11.41 | 7.75 | 11.52 |
| 3 | 80 | 3.5 | 88.9 | 2.9 | 73.7 | 0.3 | 7.62 | 10.26 | 15.27 | 10.35 | 15.39 |
| 7/2 | 90 | 4 | 101.6 | 3.364 | 85.4 | 0.318 | 8.08 | 12.52 | 18.63 | 12.67 | 18.82 |
| 4 | 100 | 4.5 | 114.3 | 3.826 | 97.2 | 0.337 | 8.56 | 15 | 22.32 | 15.2 | 22.6 |
Standard steel pipe sizes
| Specification | Outer diameter (mm) | Wall thickness (m)m | minimal wall thickness (mm) | Extra think(mm) | Welded steel pipe（6 meters） | hot-dipped galvanized steel pipe（6 meters） | |||
|---|---|---|---|---|---|---|---|---|---|
| Nominal Diameter | Inches | 1 meter(kg) | 1 pipe (kg) | 1 meter(kg) | 1 pipe (kg) | ||||
| DN15 | 1/2 | 21.3 | 2.8 | 2.45 | 3.25 | 1.28 | 7.68 | 1.357 | 8.14 |
| DN20 | 3/4 | 26.9 | 2.8 | 2.45 | 3.5 | 1.66 | 9.96 | 1.76 | 10.56 |
| DN25 | 1 | 33.7 | 3.2 | 2.8 | 4 | 2.41 | 14.46 | 2.554 | 15.32 |
| DN32 | 5/4 | 42.4 | 3.5 | 3.06 | 4 | 3.36 | 20.16 | 3.56 | 21.36 |
| DN40 | 3/2 | 48.3 | 3.5 | 3.06 | 4.5 | 3.87 | 23.22 | 4.1 | 24.6 |
| DN50 | 2 | 60.3 | 3.8 | 3.325 | 4.5 | 5.29 | 31.74 | 5.607 | 33.64 |
| DN65 | 5/2 | 76.1 | 4 | 3.5 | 4.5 | 7.11 | 42.66 | 7.536 | 45.21 |
| DN80 | 3 | 88.9 | 4 | 4.75 | 8.38 | 50.28 | 8.88 | 53.28 | |
| DN100 | 4 | 114.3 | 4 | 5 | 10.88 | 65.28 | 11.53 | 69.18 | |
| DN125 | 5 | 140 | 4.5 | 5.5 | 15.04 | 90.24 | 15.942 | 98.65 | |
| DN150 | 6 | 168.3 | 4.5 | 5.5 | 18.18 | 109.08 | 19.27 | 115.62 | |
| DN200 | 8 | 219.1 | 6 | welded steel pipe | 31.53 | 189.18 | |||
| DN200 | 8 | 219.1 | 6.5 | hot-dipped galvanized steel pipe | 36.12 | 216.72 | |||
FAQ
A. What are the connection methods of pipe fittings?
G1/4, G1/8 means pipe thread, 1/4, and 1/8 inches.
Pipe joints include pipe thread, taper thread, R thread, etc.; connection methods include welding, flaring, quick-plug, taper sleeve, and so on.
B. What does 1/2 , 3/4, 1, 1216 , 2025 represent?
1/2 , 3/4, and 1 are the nominal diameters in the pipe standard. They are commonly known as the names of half-inch or 4-point, 6-point, 1-inch pipe or fittings, such as 4-point pipe, 4-point elbow, etc., which are mostly used for water pipes. 1216 and 2025 refer to the inner diameter and outer longitude of the tube, in millimeters. Example 12/16 is a pipe with an inner diameter of 12 mm and an outer diameter of 16 mm, which is mostly used for plastic pipes. 1/2 , 3/4 , 1 are inch sizes, each inch = 25.4 mm, commonly used on steel pipes.
C. What is the nominal diameter?
The nominal diameter is the size indicated by numbers for all piping accessories in the piping system. The nominal diameter is a convenient round integer for reference and has only a non-strict relationship with the processing size. The nominal diameter is marked with the letter “DN” followed by a number.
D. What is a flange?
The flange is a disc-shaped part, which is the most common in pipeline engineering. Flanges are used in pairs. A flange is an interconnecting part between pipes for the connection between pipe ends. Flanges are also used at the inlet and outlet of the equipment for the connection between two pieces of equipment.
