Class 600 vs Class 900 Valve

Quick Answer

Class 600 valves are rated for a maximum working pressure of 1,480 psig (102 barg) at 100°F in WCB carbon steel. Class 900 valves handle up to 2,220 psig (153 barg) under the same conditions. Choose Class 900 when your design pressure-temperature exceeds the Class 600 envelope.

Detailed Comparison

Both Class 600 and Class 900 fall under ASME B16.34 for pressure-temperature ratings and are used in high-pressure services such as upstream production, high-pressure gas transmission, and refinery reactor circuits. The jump from Class 600 to Class 900 adds roughly 50 percent more pressure capacity, but also increases weight, cost, and bolt complexity.

Feature	Class 600	Class 900
Max pressure at 100°F (38°C), WCB	1,480 psig (102 barg)	2,220 psig (153 barg)
Max pressure at 500°F (260°C), WCB	890 psig (61.4 barg)	1,335 psig (92 barg)
Max pressure at 800°F (427°C), WCB	415 psig (28.6 barg)	625 psig (43.1 barg)
Body wall thickness (6” gate)	~25 mm	~33 mm
Flange bolt size (6”)	1” dia.	1-1/8” dia.
Approx. weight (6” gate valve)	~200 kg	~320 kg
Relative cost	1.0x (baseline)	1.6-2.2x
End connections	RF, RTJ, BW	RF, RTJ, BW
Common applications	HP gas pipelines, refinery units, FPSO topsides	Wellhead, Christmas tree, HP/HT process systems
Gasket type (RTJ)	Ring joint (R or RX)	Ring joint (R, RX, or BX)

When to Specify Class 900

Class 900 is typically required in upstream oil and gas (wellhead and manifold systems), high-pressure gas compression, and HP/HT (high-pressure/high-temperature) refinery services. The additional wall thickness provides margin for corrosion allowance in sour or erosive environments.

For most downstream refinery and petrochemical applications, Class 600 provides sufficient pressure capacity. Moving to Class 900 without justification adds significant procurement cost and extends delivery lead times, as fewer foundries stock Class 900 castings.

Material Considerations

At higher pressure classes, material selection becomes critical. WCB carbon steel covers most ambient to moderate-temperature services, but for temperatures below -29°C, low-temperature carbon steel (LCC per ASTM A352) or low-alloy steel (LF2 per ASTM A350) must be specified. For sour service (H2S), NACE MR0175 compliance applies regardless of pressure class.

The ASME flange rating tables used for flanges are the same tables applied to valve pressure-temperature limits.

Common Mistake

Do not assume that a higher pressure class automatically provides a better valve. Overspecifying the class increases weight, cost, and bolting torque requirements without adding functional benefit if the design conditions fit within the lower class.

Read the full guide to valve types