What is SCH 20 Steel Pipe?
SCH 20 steel pipe is a thin-wall pipe classification defined under ASME B36.10 / B36.19 standards, mainly used in low-pressure and non-critical piping systems. It prioritizes flow capacity and cost efficiency over pressure resistance.
Key Characteristics of SCH 20 Steel Pipe
Wall Thickness: Relatively thin compared to SCH 40 or SCH 80
Pressure Rating: Suitable for low-pressure conditions
Weight: Lightweight, easy to handle and install
Cost: More economical due to reduced material usage
Engineering Rule:
The higher the schedule number, the thicker the pipe wall.
SCH 20 = light-duty / low-pressure application
SCH 20 Steel Pipe Dimensions (Large Sizes Reference)
|
Pipe Size
|
OD (inch)
|
OD (mm)
|
WT (inch)
|
WT (mm)
|
Weight (lb/ft)
|
Weight (kg/m)
|
|
8″ (NPS200)
|
8.625
|
219.1
|
0.25
|
6.35
|
22.36
|
33.31
|
|
10″ (NPS250)
|
10.75
|
273
|
0.25
|
6.35
|
28.04
|
41.77
|
|
12″ (NPS300)
|
12.75
|
323.8
|
0.25
|
6.35
|
33.38
|
49.73
|
|
14″ (NPS350)
|
14
|
355.6
|
0.312
|
7.92
|
45.61
|
67.90
|
|
16″ (NPS400)
|
16
|
406.4
|
0.312
|
7.92
|
52.27
|
77.83
|
|
18″ (NPS450)
|
18
|
457
|
0.312
|
7.92
|
58.94
|
87.71
|
|
20″ (NPS500)
|
20
|
508
|
0.375
|
9.53
|
78.60
|
117.15
|
|
22″ (NPS550)
|
22
|
559
|
0.375
|
9.53
|
86.61
|
129.13
|
|
24″ (NPS600)
|
24
|
610
|
0.375
|
9.53
|
94.62
|
141.12
|
|
26″ (NPS650)
|
26
|
660
|
0.5
|
12.7
|
136.17
|
202.72
|
|
28″ (NPS700)
|
28
|
711
|
0.5
|
12.7
|
146.85
|
218.69
|
|
30″ (NPS750)
|
30
|
762
|
0.5
|
12.7
|
157.53
|
234.67
|
|
32″ (NPS800)
|
32
|
813
|
0.5
|
12.7
|
168.21
|
250.64
|
|
34″ (NPS850)
|
34
|
864
|
0.5
|
12.7
|
178.89
|
266.61
|
|
36″ (NPS900)
|
36
|
914
|
0.5
|
12.7
|
189.57
|
282.27
|
SCH 20 Wall Thickness (Small Sizes)
|
NPS
|
OD (inch)
|
WT (inch)
|
WT (mm)
|
|
1/2″
|
0.84
|
0.065
|
1.65
|
|
1″
|
1.315
|
0.065
|
1.65
|
|
2″
|
2.375
|
0.065
|
1.65
|
|
4″
|
4.5
|
0.083
|
2.11
|
|
6″
|
6.625
|
0.083
|
2.11
|
|
8″
|
8.625
|
0.083
|
2.11
|
Standard Basis: ASME B36.10M
NPS vs Actual Diameter (Common Misconception)
NPS (Nominal Pipe Size) ≠ actual inner diameter (ID)
For NPS ≤ 12″:
NPS is only a designation, not equal to OD or ID
For NPS ≥ 14″:
NPS ≈ actual outer diameter (OD in inches)
Example:
NPS 12″ pipe → OD = 12.75″ (323.8 mm), not 12″
Where is SCH 20 Steel Pipe Used?
Typical Applications
HVAC chilled water systems
Fire protection auxiliary piping (low-pressure sections)
Agricultural irrigation systems
Light industrial fluid transfer
Structural use in non-load-bearing applications
Selection Logic:
Use SCH 20 where flow rate matters more than pressure strength.
Advantages and Limitations of SCH 20 Steel Pipe
- Advantages
Lower material cost
Easier fabrication and installation
Higher flow efficiency (larger internal diameter)
- Limitations
Not suitable for high-pressure systems
Limited mechanical strength
Not recommended for critical or hazardous service
FAQ
Q1: Is SCH 20 pipe suitable for high-pressure systems?
No, it is designed for low-pressure applications only.
Q2: What is the difference between SCH 20 and SCH 40?
SCH 40 has a thicker wall and higher pressure resistance than SCH 20.
Q3: Does SCH 20 have a fixed inner diameter?
No, the inner diameter varies depending on wall thickness and tolerances.
Q4: Why choose SCH 20 pipe?
For cost savings and improved flow in low-pressure systems.
Conclusion
SCH 20 steel pipe is a lightweight, cost-effective solution for low-pressure piping systems. While it cannot handle high-pressure conditions, it performs well in applications where flow efficiency, ease of installation, and cost control are the primary concerns.
Understanding SCH 20 dimensions and wall thickness helps engineers avoid overdesign and optimize system performance, ensuring both technical reliability and economic efficiency.
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