The parameters of steel pipes are usually expressed using the pipe specification (Schedule, SCH for short). This specification does not directly reflect the actual wall thickness of the pipe, but is a series of wall thickness indicators. Steel pipes of the same nominal diameter can have different wall thicknesses according to different SCH values. The design of pipe specifications originated from the American Petroleum Institute (API) and the American Society of Mechanical Engineers (ASME), which are used to provide standardized pipe selection for pressure and temperature changes in pipe systems.
Common series of pipe specifications (SCH) include SCH 5, 5S, 10, 10S, 20, 20S, 30, 40, 40S, 60, 80, 80S, 100, 120, 140, 160. Generally speaking, the larger the SCH value, the thicker the pipe wall and the higher the pressure resistance of the pipe.
SCH 40 and SCH 80 are the most commonly used specifications in industry, especially in the oil, gas, chemical and construction industries. They are popular mainly because these industries often involve high-pressure environments, so thicker-walled pipes are required to withstand greater working pressures.
The following is a table of wall thicknesses corresponding to standard pipe specifications (SCH). The specific data varies depending on the diameter of the steel pipe. The following will show the wall thickness ranges of each specification under several common outer diameters (OD):
|
Nominal size [inches]
|
Outside diameter [inches]
|
Outside diameter [mm]
|
Wall thickness [inches]
|
Wall thickness [mm]
|
Weight [lb/ft]
|
Weight [kg/m]
|
|
1/8 inches
|
0.405 inches
|
10.3 MM
|
0.068 inches
|
1.73 MM
|
0.24 lb/ft
|
0.37 kg/m
|
|
1/4 inches
|
0.540 inches
|
13.7 MM
|
0.088 inches
|
2.24 MM
|
0.42 lb/ft
|
0.84 kg/m
|
|
1/2 inches
|
0.840 inches
|
21.3 MM
|
0.109 inches
|
2.77 MM
|
0.85 lb/ft
|
1.27 kg/m
|
|
3/4 inches
|
1.050 inches
|
26.7 MM
|
0.113 inches
|
2.87 MM
|
1.13 lb/ft
|
1.69 kg/m
|
|
1 inches
|
1.315 inches
|
33.4 MM
|
0.133 inches
|
3.38 MM
|
1.68 lb/ft
|
2.50 kg/m
|
|
1 1/4 inches
|
1.660 inches
|
42.2 MM
|
0.140 inches
|
3.56 MM
|
2.27 lb/ft
|
3.39 kg/m
|
|
1 1/2 inches
|
1.900 inches
|
48.3 MM
|
0.145 inches
|
3.68 MM
|
2.72 lb/ft
|
4.05 kg/m
|
|
2 inches
|
2.375 inches
|
60.3 MM
|
0.154 inches
|
3.91 MM
|
3.65 lb/ft
|
5.44 kg/m
|
|
2 1/2 inches
|
2.875 inches
|
73.0 MM
|
0.203 inches
|
5.16 MM
|
5.79 lb/ft
|
8.63 kg/m
|
|
3 inches
|
3.500 inches
|
88.9 MM
|
0.216 inches
|
5.49 MM
|
7.58 lb/ft
|
11.29 kg/m
|
|
3 1/2 inches
|
4.000 inches
|
101.6 MM
|
0.226 inches
|
5.74 MM
|
9.11 lb/ft
|
13.57 kg/m
|
|
4 inches
|
4.500 inches
|
114.3 MM
|
0.237 inches
|
6.02 MM
|
10.79 lb/ft
|
16.07 kg/m
|
|
5 inches
|
5.563 inches
|
141.3 MM
|
0.258 inches
|
6.55 MM
|
14.62 lb/ft
|
21.77 kg/m
|
|
6 inches
|
6.625 inches
|
168.3 MM
|
0.280 inches
|
7.11 MM
|
18.97 lb/ft
|
28.26 kg/m
|
|
8 inches
|
8.625 inches
|
219.1 MM
|
0.322 inches
|
8.18 MM
|
28.55 lb/ft
|
42.55 kg/m
|
|
10 inches
|
10.750 inches
|
273.0 MM
|
0.365 inches
|
9.27 MM
|
40.48 lb/ft
|
60.31 kg/m
|
|
12 inches
|
12.750 inches
|
323.8 MM
|
0.406 inches
|
10.31 MM
|
53.52 lb/ft
|
79.73 kg/m
|
|
14 inches
|
14 inches
|
355.6 MM
|
0.375 inches
|
11.13 MM
|
54.57 lb/ft
|
94.55 kg/m
|
|
16 inches
|
16 inches
|
406.4 MM
|
0.500 inches
|
12.70 MM
|
82.77 lb/ft
|
123.30 kg/m
|
|
18 inches
|
18 inches
|
457.0 MM
|
0.562 inches
|
14.27 MM
|
104.67 lb/ft
|
155.80 kg/m
|
|
20 inches
|
20 inches
|
508.0 MM
|
0.594 inches
|
15.09 MM
|
123.11 lb/ft
|
183.42 kg/m
|
|
24 inches
|
24 inches
|
610.0 MM
|
0.688 inches
|
17.48 MM
|
171.29 lb/ft
|
255.41 kg/m
|
|
32 inches
|
32 inches
|
813.0 MM
|
0.688 inches
|
17.48 MM
|
230.08 lb/ft
|
342.91 kg/m
|
Applications of Common Specifications
SCH 40:
Applications: Most commonly used in low- and medium-pressure liquid or gas delivery systems, such as municipal water supply systems and low-pressure natural gas pipelines.
Advantages: Economical price, can meet most standard pressure and temperature requirements.
SCH 80:
Applications: Suitable for systems that require higher pressure bearing capacity, such as oil and gas pipelines, high-pressure transmission pipelines in chemical plants.
Advantages: Compared with SCH 40, it has a thicker pipe wall and can be used at higher working pressures.
SCH 160:
Applications: Mostly used in extremely high-pressure scenarios, such as industrial boilers, high-pressure steam delivery systems, and some deep well drilling projects.
Advantages: The pipe wall is very thick and can withstand extremely high pressures.
Factors affecting wall thickness selection
Working pressure: High-pressure systems require thicker wall pipes (such as
SCH 80 or SCH 160).
Temperature: The strength of the pipe may decrease under high temperature conditions, so a thicker wall thickness needs to be selected to compensate for this effect.
Materials: Steel pipes made of different materials have different strengths. Commonly used materials include carbon steel, stainless steel, and alloy steel. Different materials have an important impact on the choice of wall thickness.
In summary, the pipe specification SCH is a standardized system for identifying the wall thickness of steel pipes. Although SCH itself does not directly reflect the actual wall thickness, it is closely related to the nominal diameter and pressure bearing capacity of the pipe. When choosing a suitable pipe, engineers usually decide what specifications of steel pipe to use based on specific working conditions, such as pressure, temperature, material, and other factors.
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