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| Pressure Class | Max Pressure at 38°C (bar) | Max Pressure at 38°C (PSI) | Typical Application | Common Standard |
|---|---|---|---|---|
| Class 150 | 19.6 | 285 | General service, water, steam, utility | ASME B16.5 |
| Class 300 | 51.1 | 740 | Process piping, refinery, HVAC | ASME B16.5 |
| Class 600 | 102.1 | 1480 | High-pressure process, gas pipelines | ASME B16.5 |
| Class 900 | 153.2 | 2220 | High-pressure refinery, offshore | ASME B16.5 |
| Class 1500 | 255.3 | 3705 | Very high-pressure O&G, wellhead | ASME B16.5 |
| Class 2500 | 425.5 | 6170 | Ultra high-pressure, subsea, wellhead | ASME B16.5 |
Values at ambient temperature (−29 to 38°C) for Material Group 1.1 (ASTM A105). Pressure ratings decrease with temperature. Verify against ASME B16.5 Table 2-1.1 for design purposes.
Technical ArticlesASME B16.5 pressure classes (150 to 2500) define a flange's allowable pressure at a given temperature — not a fixed PSI rating. Start with your system's maximum operating pressure and temperature, then check the material-specific pressure-temperature rating table, since the same class rating drops as temperature rises. Always size to the worst-case combination in the line, and confirm the mating flange, gasket and bolting are rated to the same class.
B7 (Cr-Mo alloy steel) is the default stud bolt grade for general high-temperature and high-pressure piping. B7M is the same base material held to a lower hardness limit for NACE MR0175 sour service, where H₂S exposure makes standard B7 prone to cracking. B8M (SS 316) is used where corrosion resistance matters more than raw strength, such as stainless piping systems or mildly corrosive process fluids. When in doubt, sour service and material compatibility with the flange/piping — not just pressure — should drive the choice.
Type 2.1 is a simple statement of compliance from the manufacturer, without actual test results. Type 2.2 adds test results, but from non-specific, non-traceable testing. Type 3.1 is the most common for industrial piping — a certificate validated by the manufacturer's own authorized QC, with results specific and traceable to the supplied batch. Type 3.2 goes further, requiring validation by an independent third-party inspector (TPI) in addition to the manufacturer, typically specified for critical or safety-related components.
Raised Face (RF) is the most common configuration, with a small raised area around the bore that concentrates gasket seating stress for a reliable seal — standard for Class 150 to 2500 in most piping. Flat Face (FF) flanges have no raised area and are typically used to mate with cast iron valves/fittings, which can crack under the concentrated load an RF flange would apply. Ring Type Joint (RTJ) uses a metal ring gasket seated in a machined groove, giving a metal-to-metal seal capable of handling higher pressures and temperatures — common in high-pressure oil & gas service.
L-type bolts have a simple hooked bend and suit lighter loads such as light machinery bases and general structural anchoring. J-type bolts have a deeper J-shaped hook for improved pull-out resistance under moderate to heavy loads, commonly used for structural steel columns. U-type (or loop) bolts anchor from both ends for the highest pull-out resistance, typically specified for heavy equipment foundations, turbine bases and compressor pads where uplift and vibration loads are significant.
Schedule (SCH) designates a fitting's wall thickness for a given nominal pipe size — it does not describe the outer diameter, which stays constant across schedules. SCH 40 is the general-purpose standard-weight thickness used across most industrial piping. SCH 80 (extra strong) is used for higher-pressure service or where added wall thickness improves corrosion allowance. XXS (double extra strong) is thicker still, reserved for the most demanding high-pressure or erosive service conditions.