The pressure rating of API 5L ERW pipes is determined by standard specifications, wall thickness schedule, steel grade, and pipe diameter. The core factor is that wall thickness determines the lower limit of pressure capacity, while steel grade determines the upper limit. For most industrial applications (water, gas, fire fighting, and medium-to-low pressure oil and gas), ERW pipes are a completely reliable and economical choice; for high-pressure oil and gas trunk lines, API 5L high-grade ERW pipes can meet pressure requirements of 4-12 MPa.
Factors Determining Pipeline Pressure Rating:
The pressure-bearing capacity of ERW pipelines follows the formula:
δ = (P × D) / (2 × σs × Φ × F)
Where:
P: Design pressure (MPa)
D: Outer diameter (mm)
σs: Minimum yield strength of material (MPa)
Φ: Weld coefficient (up to 1.0 for ERW pipes)
F: Strength design coefficient (0.3-0.72 depending on the region)
Classification by Pressure Rating Standards:
1. American Standard System (ANSI/ASME)
| Pressure Rating | Corresponding Wall Thickness Series | Applications |
| Class 150 | Sch 10 - Sch 40 | Low-pressure water and gas systems |
| Class 300 | Sch 40 - Sch 80 | Medium-pressure process pipelines |
| Class 600 | Sch 80 - Sch 160 | High-pressure oil and gas transmission |
2. Nominal Pressure (PN) System
| PN Rating | Corresponding Pressure (MPa) | Application |
| PN10-PN16 | 1.0 - 1.6 MPa | Water supply and drainage, fire protection |
| PN25-PN40 | 2.5 - 4.0 MPa | Industrial water pipes, medium-pressure gas pipes |
| PN64-PN100 | 6.4 - 10.0 MPa | High-pressure process pipelines |
Actual Pressure Parameters for Common Applications of ERW Pipes:
1. Low-pressure fluid transport pipes
| Standard | Wall thickness | Working pressure | Hydrostatic test pressure |
| ASTM A53 Gr.B | Sch 40 | Up to 1.21 - 2.07 MPa | Depending on specifications |
| BS EN 10255 | Medium/heavyweight | Maximum 2.5 MPa | 5.0 MPa (730 psi) |
| Fire sprinkler pipes | Sch 10/40 | 0.1 - 8.0 |
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2. Specific Specification Measured Data
The following are actual pressure ratings (working pressures) provided by a manufacturer:
| Outer diameter (mm) | Wall thickness (mm) | Maximum working pressure (MPa) | Test pressure (MPa) |
| 114.3 | 2.1 | 3.6 | 3.6 |
| 165.1 | 2.5 | 3.0 | 4.5 |
| 219.1 | 3.5 | 3.1 | 4.7 |
| 323.9 | 4.8 | 2.9 | 4.35 |
| 457.0 | 4.8 | 2.0 | 3.1 |
| 610.0 | 6.0 | 1.9 | 2.9 |
It can be seen that: for the same wall thickness, the larger the pipe diameter, the lower the pressure-bearing capacity; for the same pipe diameter, the thicker the wall, the higher the pressure-bearing capacity.
3. API 5L Line Pipeline (Oil and Gas Transmission)
| Steel Grade | Yield Strength | Application Pressure |
| X42 | 290 MPa | Medium and Low Pressure Gathering and Transmission (4-8 MPa) |
| X52 | 360 MPa | High Pressure Transmission (6-10 MPa) |
| X65-X80 | 450-550 MPa | Long-Distance High-Pressure Trunk Line (10-12 MPa) |
According to industry practice, ERW pipelines can operate at pressures of 4-12 MPa in natural gas transmission. Modern high-grade steel products (such as X65 and above) have been successfully applied to pipeline projects with pressures up to 10 MPa.
Pressure Rating Reference by Wall Thickness (Schedule):
| Sch No. | Wall thickness range | Applicable pressure rating | Typical application |
| Sch 10 | Thin wall | ≤ 1.6 MPa | Low-pressure water supply and drainage |
| Sch 40 | Standard wall thickness | 1.6 - 4.0 MPa | Water, gas, fire protection |
| Sch 80 | Thick wall thickness | 4.0 - 8.0 MPa | Medium and high pressure process pipelines |
| Sch 160 | Extra thick | 8.0 - 15.0 MPa | High-pressure oil and gas, chemical |
Pressure Rating for Different Application Areas:
| Application Area | Typical pressure range | Recommended wall thickness/steel grade | Applicable standards |
| Municipal water supply and drainage | 0.5 - 1.6 MPa | Sch 10 - Sch 40 | ASTM A53, EN 10255 |
| Fire sprinkler system | 0.1 - 1.6 MPa | Sch 10 - Sch 40 | ASTM A795, UL Listed |
| Low-pressure gas | 0.4 - 0.8 MPa | Sch 40 | ASTM A53, API 5L |
| Medium-pressure gas transmission | 0.8 - 4.0 MPa | Sch 40 - Sch 80 | API 5L X42-X52 |
| High-pressure oil and gas transmission | 4.0 - 12.0 MPa | Sch 80 - Sch 160 | API 5L X52-X80 |
| Industrial process pipeline | 1.6 - 10.0 MPa | Sch 40 - Sch 160 | ASME B36.10 |
API 5L Standard An internationally recognized pipeline standard that clearly specifies the use of ERW pipes for oil and gas transportation. High-grade steel (X52 and above) products are suitable for high-pressure conditions.Temperature Limitations: ERW carbon steel pipes are generally suitable for temperatures ranging from -29℃ to 200℃. For high-temperature conditions, specialized materials such as ASTM A106 must be selected.
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