In the oil and gas, petrochemical, and process industries, pressure resistance is a fundamental concept for the design and selection of equipment. Flanges, valves, and pressure vessels are frequently described using designations such as “Class 150,” “Class 300,” and “Class 600.” Many aspiring engineers and industry users wonder
what Class 150 means and what percentage of the specified pressure the equipment can withstand.
In this article, we will analyze the concept of compressive strength, the equivalent load (bar) for each compressive strength, and the associated design features.
The concept of pressure level
The compressive strength, or pressure index, is a measure of a component’s mechanical ability to withstand the internal pressure of fluids . This value is typically determined according to ASME B16.5 for flanges and ASME B16.34 for valves.
Simply put: the higher the pressure resistance, the greater the pressure and temperature that a flange or valve can withstand.
What is Category 150?
Class 150 is the lowest standard pressure class in the ASME classification and is typically used for low-pressure and deep-freeze systems.
At room temperature (approx. 38 °C or 100 °F ) a Class 150 flange can withstand a pressure of approximately 285 psi, which is about 19.6 bar .
However, it should be noted that the permissible pressure decreases with increasing temperature. For example, the permissible pressure for class 150 at a temperature of approximately 200 °C is about 140 psi (approximately 9.6 bar ).
How often does level 150 occur?
For a more precise answer, please consult the following table (based on the carbon steel grades ASTM A105 and the ASME B16.5 standards):
| Temperature (°C) | Permissible pressure (psi) | Equivalent pressure (bar) |
|---|---|---|
| 38 degrees Celsius (100 degrees Fahrenheit) | 285 pounds per square inch | ≈ 19.6 bar |
| 93 degrees Celsius (200 degrees Fahrenheit) | 260 pounds per square inch | ≈ 17.9 bar |
| 150 degrees Celsius | 235 pounds per square inch | ≈ 16.2 bar |
| 200 degrees Celsius | 200 pounds per square inch | ≈ 13.8 bar |
| 300 degrees Celsius | 170 pounds per square inch | ≈ 11.7 bar |
| 400 degrees Celsius | 140 pounds per square inch | ≈ 9.6 bar |
Therefore, a nominal pressure of 150 typically corresponds to 19–20 bar at room temperature.
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Comparison of category 150 with other categories
| pressure level | Pressure (psi) at 38°C | Equivalent pressure (bar) | general purpose |
|---|---|---|---|
| Class 150 | 285 pounds per square inch | ≈ 19.6 bar | Low-pressure system , water, air, light steam |
| Model 300 | 740 pounds per square inch | ≈ 51 bar | Medium-pressure pipelines, industrial steam |
| Model 600 | 1480 pounds per square inch | ≈ 102 bar | Gas pipelines and high-pressure systems |
| Model 900 | 2220 pounds per square inch | ≈ 153 bar | Oil refineries and special operations |
| Model 1500 | 3705 pounds per square inch | ≈ 255 bar | pressure vessel |
| Model 2500 | 6170 pounds per square inch | ≈ 425 bar | Special applications for high voltage |
Relationship between nominal pressure, temperature and material
The crucial point is that the compressive strength depends not only on the pressure, but also on the operating temperature and the material of the rim or the container .
For example:
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If the rim is made of stainless steel , it can withstand higher pressures and higher temperatures than carbon steel.
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Cast iron, on the other hand, has low compressive strength and is not suitable for withstanding high pressures.
Therefore, when planning pipelines, engineers consider not only the nominal pressure, but also the fluid material and the operating temperature.
Applying a 150-degree chamfer
Edge profiles of the 150 series are most commonly used in industrial applications due to their low cost and ease of installation . Application areas:
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Water supply and sewage systems
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Low-pressure steam
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Food and pharmaceutical industries
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Cooling pipes of the power plant
In contrast, high-pressure oil and gas pipelines typically use pipes of class 300 and higher.
Relevant standards
The most important criteria for determining the nominal pressure values are:
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ASME B16.5 : Applies to lips
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ASME B16.34 : Applicable Valves
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ASME Volume 8 : Pressure Vessel Design
These standards contain detailed tables of permissible pressures for each temperature and material.
Design and safety tips
The following points should be taken into account when selecting flanges or tanks:
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The design pressure must always be higher than the operating pressure of the system.
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The design temperature must take into account the maximum ambient or liquid temperature.
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The use of inferior flanges in high-pressure systems can lead to leaks or breaks .
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In steam or oil circuits, the pressure drop caused by high temperatures must be taken into account in the calculations.
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Be sure to use the manufacturer’s material certificate and conformity certificates.
Finally
Pressure class 150 is one of the most common and economical pressure classes in industry.
At room temperature, it withstands pressures of approximately 19–20 bar , but its pressure resistance decreases with increasing temperature.
Choosing the right flange or vessel directly impacts safety, system lifespan, and maintenance costs. For low-pressure and cryogenic systems, Class 150 is an ideal and cost-effective choice; however, for more demanding applications, flanges with a higher rating should be used.