What are the pressure ratings for industrial valves according to ASME B16.34?

Steel valve rating is the single most important line on a certification document, yet it remains one of the most misunderstood figures in the piping industry. When a procurement engineer matches valve class to pipe flange class without checking the temperature charts, or when a project treats "Class 300" as if it meant 300 pounds of working pressure, the result is over-pressure risk, premature failure, or needless cost from over-specification. This article answers the question directly: what are the pressure ratings for industrial valves according to ASME B16.34, how are they defined, and how should you actually apply them.

As a manufacturer and integrated supplier of industrial metal piping systems since 1994, EZ Steel Industrial has supplied valves and complete project packages to oil and gas, petrochemical, power, marine, and infrastructure projects. Understanding valve pressure class is the foundation of every specification we help customers write.

ASME B16.34 Puts Class Numbers Into Table Columns

ASME B16.34 is the governing American standard for steel valves with flanged, threaded, and welding ends. It is the standard that defines pressure-temperature ratings for gate, globe, check, and ball valves in nominal pipe sizes from about NPS 1/2 up to NPS 24, with larger sizes covered through related product standards. Within B16.34 you will find pressure classes, material groups with allowable stress values, minimum shell wall thickness formulas, and end connection requirements that line up with ASME B16.5 and B16.47 flanges.

The important thing to understand is that a class number is a group designation, not a pressure value in any unit. Class 150, 300, 600, 900, 1500, and 2500 are labels that point to a column inside a pressure-temperature table. The real allowable pressure depends on three things: the class column, the body material group, and the operating temperature. Whenever someone quotes a pressure class without a material and a temperature, the number is incomplete.

Cold Working Pressure: The Numbers That Matter at Ambient

At ambient temperature, the range around -29 °C to 38 °C, ASME B16.34 gives what engineers call the cold working pressure. For Group 1.1 materials, basically ASTM A216 WCB and similar carbon steels, the cold working pressures are the familiar reference numbers:

ASME Class	CWP at ambient (bar)	CWP at ambient (PSI)
150	19.6	285
300	51.7	740
600	103.4	1,480
900	155.1	2,235
1500	258.6	3,705
2500	431.0	6,180

Each step roughly doubles the allowable pressure for carbon steel. Note that these values apply only to carbon steel Group 1.1. Stainless steel, chrome-moly alloys, and nickel alloys have different absolute values at the same class, so the correct table always depends on the actual body material.

Temperature Derating Is Where Most Specification Errors Happen

Steel loses strength as temperature rises, and the pressure-temperature tables in B16.34 reflect that loss directly. ｓｅｌｅｃｔ a class based on the cold working pressure alone and you can find yourself over the limit the moment the line heats up. Consider a carbon steel Class 150 valve. At ambient it allows 19.6 bar, but at 300 °C the allowable pressure falls to roughly 10.4 bar. A process working at 15 bar and 300 °C would be beyond the rated pressure of a Class 150 carbon steel valve, so a Class 300 valve would be required.

The same pattern applies to all classes and all materials, but each material de-rates at its own pace. Austenitic stainless steels such as the CF8 and CF8M groups hold their strength reasonably well through moderate temperatures but decline more steeply above roughly 400 °C. Chrome-moly alloys such as WC6 and WC9 keep useful strength to much higher temperatures, which is exactly why they are specified for boiler steam and other hot services.

Material Groups Determine How Far a Valve Can Be Rated

ASME B16.34 groups body materials so that each group has its own pressure-temperature table. A few groups cover the majority of industrial work:

Material Group	Typical Grades	Max Tabulated Temperature
1.1	A216 WCB, WCC, A105	about 425 °C
1.9	A217 WC6	about 593 °C
1.10	A217 WC9	about 593 °C
2.1	A351 CF8, CF8M	depends on grade
3.4	A182 F316 forged	depends on grade

Material selection and class selection are coupled decisions. A Class 1500 valve in WCB carbon steel and a Class 1500 valve in WC9 share the same class label but carry different rating tables. Above the material limit, the valve simply cannot be rated for that class regardless of how the numbers look at ambient temperature.

How to Read a Pressure-Temperature Table

Using the tables correctly is straightforward once you know the steps. First, identify the body material group from the nameplate or the datasheet. Second, find the class column for the valve you are considering. Third, locate the row for the operating temperature, interpolating between tabulated rows if necessary. Fourth, confirm that the operating pressure is equal to or below the tabulated allowable pressure, including any project design margin.

Be careful not to extrapolate beyond the highest tabulated temperature for a material group. For WCB carbon steel, the table stops around 425 °C, and beyond that point the material group limit has been exceeded. If a valve is needed for a 450 °C steam line, the answer is an upgrade to WC6 or WC9 rather than a larger class in the wrong material.

Matching Valve Class to the Application

Class selection is application-specific, but some broad patterns hold across the oil and gas, power, chemical, and utility industries. Class 150 valves are common in water treatment, HVAC, low-pressure steam, firewater, and general utility service. Class 300 shows up on refinery and chemical process piping, medium-pressure steam, and LPG storage. Class 600 is typical for refinery hydrotreaters, gas processing, boiler feedwater, and high-pressure steam. Class 900 and above appear on power boiler steam stops, catalytic reformers, high-pressure separators, supercritical boiler circuits, and pressure-seal bonnet designs.

One related point that confuses buyers is Class 800, which is not a B16.34 class at all. Class 800 comes from API 602, which covers small forged steel valves, typically no larger than NPS 4, with socket-weld or threaded ends. If you see Class 800 on a datasheet, refer to API 602 tables rather than assuming it equals any B16.34 class.

PN vs ASME Class: Only an Approximation at Ambient

European projects often specify valves by PN, or Pressure Nominal, a designation that states a nominal pressure in bar at a reference temperature around 20 °C. The common rule of thumb that PN16 equals Class 150 and PN40 equals Class 300 is acceptable at ambient temperature only. At elevated temperatures, the EN pressure-temperature curves in standards such as EN 1092-1 and the ASME B16.34 curves diverge, so the apparent equivalence breaks down. For any hot service, verify the actual rated pressure in the appropriate standard at the operating temperature rather than trusting a nominal comparison.

Testing Validates the Rating

The pressure class is proven in the factory. Under API 598, the common shell test pressure is 1.5 times the cold working pressure, and the seat test is 1.1 times the cold working pressure at ambient temperature. So a Class 600 valve, with a cold working pressure near 103 bar, would be shell tested at roughly 155 bar. Because the test pressure scales with class, higher-class valves need thicker body walls, heavier flanges, and often pressure-seal bonnets, which is why a Class 600 valve is a much more substantial piece of hardware than a Class 150 valve of the same size.

A Practical Selection Workflow

Put the theory to work with a simple sequence. Establish the design pressure and design temperature for the service, including appropriate margins from the process design basis. Identify the valve body material and its B16.34 material group. Look up the pressure-temperature table for that group, find the temperature row at or above the design temperature, and ｓｅｌｅｃｔ the lowest class whose rated pressure at that temperature equals or exceeds the design pressure. Finally, check that the selected class also handles the maximum cold condition, including hydrostatic test scenarios and blocked-in conditions.

Get the Rating Right From the Start

An industrial valve is only as good as the rating on its nameplate. The class number tells you the column of a table, the material group sets the limits, and the temperature decides what pressure the valve can honestly carry. When all three are aligned, you get a specification that survives engineering review, withstands factory testing, and delivers safe service for years.

For industrial valves, gate and globe valves for pressure service, and complete piping packages for your next project, the EZ Steel Industrial team offers the manufacturing capabilities and technical support you need. Talk to us about sizing your valve class against your actual operating conditions before you place an order.