API 600 Cast Steel Gate Valve — Metal Seat, Z40H, Class 150 to 2500, for Oil & Gas

This API 600 cast steel gate valve is the metal-seated, rising-stem (OS&Y) design for oil and gas, petrochemical and utility service. It is supplied across the full ASME pressure class range from Class 150 to Class 2500, with the bonnet construction and gasket style changing with pressure class — bolted bonnet through Class 900, pressure seal bonnet for Class 1500 to 2500. The standard body is ASTM A216 WCB; ASTM A351 CF8 (304) and CF8M (316) bodies are available for corrosive service. The valve is designated Z40H in the Chinese national model system, which corresponds to an API 600 rising-stem gate valve with a flange connection and a metal (hard-faced) seat.

Standards

Design and Manufacture: Cast steel gate valve to API 600 or API 6D.
Inspection and Test: API 598, API 600 or API 6D.
End flange dimension: ASME B16.5 (for NPS ≤ 24); API 605 or ASME B16.47 series A / MSS SP-44 (for NPS > 24).
BW end dimension: ASME B16.25.
Socket-weld dimension: ASME B16.11.
Face to face and end to end: ASME B16.10.
Pressure-temperature ratings: ASME B16.34.

Selection Notes: How the Design Changes Across Class 150–2500

The distinguishing feature of this page is the coverage of the full ASME class range. The table below summarises how the gasket style and bonnet construction change with pressure class — this is the part of an API 600 gate valve that differs most across the class range, and the part most often asked about on a line schedule.

The bolted bonnet covers Class 150 through Class 900; the pressure seal bonnet covers Class 1500 and Class 2500. Where a specific line schedule calls for a gasket style other than the standard for that class, the requirement should be stated on the inquiry.

Trim choice on the WCB version: Trim 1 (13Cr seat and 13Cr wedge) is the standard selection for general non-corrosive service. Trim 5 (Stellite on seat and wedge sealing surfaces) is preferred where erosion and wear resistance is required, such as throttling duty or high-velocity lines. Trim 8 (13Cr wedge with STL seat) is a middle-ground specification frequently requested in refinery and petrochemical line schedules. For corrosive media, the body, bonnet and trim can be supplied in ASTM A351 CF8 (304) or CF8M (316).

Operating torque on larger sizes: on large-size valves, the torque required to open and close the valve increases sharply with size and pressure class. A rolling bearing is fitted between the stem nut and the stem above the following size thresholds to reduce the operating torque — NPS ≥ 10 at Class 150, NPS ≥ 8 at Class 300, NPS ≥ 6 at Class 600 and NPS ≥ 5 at Class 900. Below these thresholds, a plain stem nut is sufficient.

Features

1. Bonnet Gasket Style

Stainless steel + flexible graphite combined gasket is used for Class 150 gate valve;
Stainless steel + flexible graphite spiral wound gasket is used for Class 300 gate valve;
Stainless steel + flexible graphite spiral wound gasket is used for Class 600 gate valve, and ring joint gasket is also optional for Class 600 gate valve;
Ring joint gasket is used for Class 900 gate valve;
Pressurized seal design is used for Class 1500 to Class 2500 gate valve.

2. Packing Seal

As usual, flexible graphite is used for packing material. PTFE or combined packing material can also be used if requested by the customer. The surface roughness between the packing and packing seal is Ra 3.2 μm, so that the stem contacts the packing surface tightly but rotates freely. The roughness of the stem sealing face is Ra 0.8 μm after being precisely machined, to ensure reliable tightness.

3. Body and Bonnet Connection

Class 150 to Class 900 gate valves are usually connected with bolted bonnet design.
Class 1500 to Class 2500 gate valves usually adopt pressure seal bonnet design.

4. Operation

Hand wheel or bevel gear box is usually used for gate valve operation. Chain wheel and electric actuator can also be used for gate valve operation if requested by the customer.

5. Disc Design

NPS ≥ 2 gate valves are flexible wedge gate; NPS < 2 gate valves are solid wedge gate.

6. Backseat Design

All gate valves have backseat design. In most cases, the carbon steel gate valve is fitted with a renewable back seat. For stainless steel gate valve, the back seat is machined directly in the bonnet or machined after welding. When the gate valve is at fully open position, the sealing of the backseat is very reliable.

7. Stem Design

The stem is integral forged design. The minimum diameter of the stem shall be as per the standard requirement. The connection of the stem and disc is T type. The strength of the connecting area is bigger than that of the T threaded part of the stem. The strength test of that area conforms to API 591.

The original source references API 591 for the stem-to-disc connection strength test. API 600 Section 5.7 also covers the stem-to-disc connection; please confirm with engineering which specification is cited on the material test report before publishing.

8. Stem Nut

Usually, the stem nut is made of ASTM A439 D2. It can also be made of copper alloy or other materials if requested by the customer. For large sized gate valves (NPS ≥ 10 Class 150, NPS ≥ 8 Class 300, NPS ≥ 6 Class 600, NPS ≥ 5 Class 900), a rolling bearing is fitted between stem nut and stem in order to minimise the torque for easy operation.

9. Seat

For carbon steel gate valve, the seat is usually forged steel. The seat sealing surface is overlay welded with hard alloy specified by the customer. Renewable threaded seat is used for NPS ≤ 10 gate valves, and welded-on seat is also optional if requested by the customer. Welded-on seat is used for NPS ≥ 12 carbon steel gate valves. For stainless steel gate valve, the seat is integral with body, or it can be machined directly after hard alloy welding. Threaded or welded type seat is also optional for stainless steel gate valve.

Parts and Material List

Swipe horizontally to see all materials

Parts No. 17 Stem Nut: original source listed "A439 02" in the CF8 column — corrected to A439 D2 to match the other columns. Parts No. 9 and 21: original source had "ASTMA193" without a space — corrected to "ASTM A193" throughout. Confirm against the material certificate before publication.

Frequently Asked Questions