API 602, Compact Steel Gate Valves
API 602 covers the small, heavy-walled gate valves on instrument, drain, vent and bypass lines. Forged bodies, compact dimensions, high pressure classes.
API 602, Compact Steel Gate Valves
API 602 exists because the small valves on the edge of a plant do not behave like the large ones. A two-inch drain valve at class 1500 needs a body that can hold the pressure in a compact envelope, and a casting is not the right way to get there.
The specification therefore assumes a forged body with a heavy wall, an extended bonnet on hot service, and a pressure test carried out to API 598. It is a small-bore document, and it stops well below the sizes where API 600 takes over.
Why forged rather than cast
Forging closes the material around the wall rather than filling a mould, which gives a denser section with less risk of the porosity that plagues small castings. On a small body holding high pressure, that difference is the design, not a nicety.
The trade-off is shape. A forged body has simpler geometry, so API 602 valves look plainer than cast valves of the same size. That is not a sign of a cheaper build; it is the intended construction.
Where the break point sits
In practice, projects run API 602 up to roughly two inches and switch to API 600 or API 6D above that, depending on the valve type and the project's own rule. The break point is normally written into the project piping specification rather than being left to the supplier.
That is worth checking before ordering: a quotation that offers an API 600 casting at one and a half inches may be perfectly sound, but it is not what a specification written around API 602 asked for.
Testing and marking
API 602 valves are tested to API 598, which since its later editions has included an emission-related option for the packing area where the buyer asks for it. The standard packing test remains the default.
Marking follows the general industry practice of showing size, class, body material and the manufacturer's identification. On small valves the marking can be cramped, so if traceability matters, ask for the marking to be on the nameplate rather than the body only.
From the works and the projects
Questions this page answers
Below roughly two inches on high-pressure service, and wherever the piping specification names it. Forged construction handles the wall thickness in a small envelope better than a casting.
Yes, the gate valve range includes forged steel small-bore designs alongside the cast steel API 600 family. Ask for the size and class and we will confirm which construction applies.
Extended bonnets are available where the service temperature requires the packing to be kept away from the line temperature. State the design temperature with the enquiry.