ERW Pipe Pressure Rating

The pressure rating of 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:

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	-

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

Precautions:

1. Weld Coefficient: Modern ERW pipes can achieve a weld coefficient of up to 1.0, meaning the weld strength is equal to or equal to the base material strength. This is the technical basis for ERW pipes to be used in pressure-bearing conditions.
2. Hydrostatic Test Pressure: Standards require each pipe to undergo a hydrostatic test. The test pressure is usually 1.5 times the working pressure or a fixed value specified in the standard.

3. 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.
4. 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.

5. Pressure Rating Selection Principles: Low to Medium Pressure (≤4.0 MPa): 

Ordinary ERW pipe (Sch 40) is sufficient; 

High Pressure (4.0-10.0 MPa): High-grade steel (X52 and above) + thick-walled (Sch 80 and above) is required; 

Ultra-High Pressure (>10.0 MPa): Careful evaluation is required; 

Seamless pipes or straight-seam submerged arc welded pipes may be used in some projects.

Frequently Asked Questions:

1. What is the pressure rating of ERW pipe?
The pressure rating of ERW pipe refers to the maximum internal working pressure that the pipe can safely withstand under specific conditions. It is not a fixed value, but rather depends on a combination of factors, including pipe size (outer diameter), wall thickness, steel grade, manufacturing standards, and operating temperature.

The pressure rating of ERW pipe follows a basic principle: wall thickness determines the lower limit of the pressure rating (the thicker the wall, the higher the pressure resistance), and the steel grade determines the upper limit of the pressure rating (the higher the strength, the higher the pressure resistance).

2. What is the pressure rating of MS ERW pipe?
ASTM A53 Gr. B is the most mainstream international standard. The allowable stress for ERW pipe under working pressure is 138 MPa (20 ksi, 100°F).

● US Standard Fire Protection System Reference: According to ASTM A53/A795 standards, the commonly used working pressure for carbon steel ERW black pipes used in fire sprinkler systems is 175 psi (1.21 MPa) or 300 psi (2.07 MPa).
● In the Indian market, MS ERW pipes mainly follow IS 1239 (small and medium diameter) and IS 3589 (large diameter) standards. For fire protection systems: IS 3589 Fe 410 grade MS ERW pipe is commonly used in fire protection main piping networks and requires a 5 MPa hydrostatic test.
● Under the European system, the hydrostatic test pressure for MS ERW pipe (material grade S195T) is uniformly ≥5.0 MPa, with the working pressure varying depending on the wall thickness series.

3. What is the difference in pressure rating between ERW pipe and seamless pipe?
For applications with pressures exceeding 4,000 psi, seamless pipe is recommended, such as for conveying high-pressure, high-temperature, or hazardous media.

4. What are the temperature limitations for ERW pipe?
The applicable temperature range for ERW carbon steel pipe is -29°C to 200°C, with short-term up to 400°C. ASME B31.3 specifies a maximum operating temperature of 425°C for carbon steel materials; above this temperature, alloy materials must be used.

5. What is the pressure rating of API 5L ERW pipe?
API 5L is an internationally recognized standard for line pipes. According to industry practice, ERW pipes can operate at pressures of 4-12 MPa in natural gas transportation.

6. How does threaded connection affect the pressure rating of ERW pipes?
Threaded connections have significantly lower permissible working pressures than plain-end pipes.

This is because:
Threading reduces the effective wall thickness of the pipe;
Stress concentration occurs at the thread root;
There is a potential risk of leakage.

7. What is the weld coefficient? Why is it important for ERW pipes?
The weld coefficient is a parameter in the ASME standard used to reflect the weld quality of welded pipes, represented by the letter E.

Seamless pipe: E = 1.0 (no weld, no reduction)
ERW pipe (not 100% non-destructive testing): E = 0.85
ERW pipe (100% ultrasonic or radiographic testing): Can reach E = 1.0

Read more: Carbon Steel ERW Pipe Specification or ERW Pipe Thickness Chart