API 600 and API 602 both cover steel gate valves for oil, gas and process service — but they are not interchangeable. One is built for cast, large-bore refinery isolation; the other for forged, compact instrument and process lines. Confusing the two in an RFQ wastes inspection time and often means a re-order. This guide separates the two standards so you specify the right one the first time.
What Each Standard Covers
API 600 (Steel Gate Valves — Flanged and Butt-welding Ends, Bolted Bonnets) is the workhorse standard for cast steel gate valves on process and refinery piping. Typical construction is bolted bonnet, OS&Y (outside screw and yoke), rising stem, with flanged or butt-weld ends. Size range commonly runs from about DN50 (2") upward through DN300 and larger Class ratings (Class 150 through 2500 depending on design). Body material is usually carbon steel or low-alloy castings (e.g. WCB, WC6, WC9), with trim selected for the media.
API 602 (Gate, Globe, and Check Valves for Sizes DN 100 [NPS 4] and Smaller for the Petroleum and Natural Gas Industries) targets compact steel valves — in practice, forged gate valves for small-bore lines, most often ≤ DN50 (2") on instrument, utility and high-pressure process take-offs. Construction is typically forged body, bolted or welded bonnet, OS&Y or inside-screw options depending on class. Ends are socket-weld, threaded or flanged. Forged construction suits higher classes in small sizes without the wall-thickness penalties of casting.
In short: API 600 gate valve = cast steel, large isolation; API 602 forged = compact, small-bore isolation. Same family of duty (full open / full close), different manufacturing envelope and size class.
API 600 vs API 602 at a Glance
| Factor | API 600 | API 602 |
|---|---|---|
| Primary construction | Cast steel body | Forged steel body (typical) |
| Typical size range | ~DN50–DN300+ (2" and up) | Compact; commonly ≤DN50 (2"), standard covers to DN100 (4") |
| Ends | Flanged, butt-weld | Socket-weld, threaded, flanged |
| Bonnet | Bolted (standard) | Bolted or welded |
| Stem | OS&Y rising stem common | OS&Y or inside screw by design |
| Pressure class | Class 150–2500 (by design) | Class 150–2500; strong in higher classes at small DN |
| Typical duty | Refinery / process main-line isolation | Instrument, utility, small process branches |
| Weight / footprint | Larger, heavier | Compact, lighter |
When to Specify an API 600 Gate Valve
Choose API 600 when the line is mid-to-large diameter, isolation is infrequent, and the piping class already assumes cast steel gate valves with flanged or BW ends. Typical homes: crude and product lines, steam headers, tank farm isolation, and EPC process units where a straight-through, low-ΔP passage matters more than compact mass.
For reference, the PrimeFlow PF-GV-CS-DN100 carbon steel OS&Y gate valve covers DN50–300 at Class 150 — a routine API 600 gate valve envelope for oil, gas and petrochemical projects. Request Material 3.1 (or 3.2 where the EPC requires independent verification), confirm trim against the media, and state whether NACE MR0175 / ISO 15156 applies for sour service before accepting a quote.
If you are still deciding between a gate and a ball for isolation, see ball valve vs gate valve first; the standard choice only comes after the valve type is fixed.
When to Specify an API 602 Forged Gate Valve
Choose API 602 forged when the line is small-bore, space or weight is constrained, or the class is high enough that a forged body is more practical than a casting. Typical homes: instrument root valves, sample points, high-pressure utility take-offs, and skid packages where DN15–DN50 dominates the bill of materials.
API 602 does not replace API 600 on large lines. Quoting a forged compact valve against a DN100 Class 150 process isolation tag is a mismatch — and the reverse (casting a small instrument valve to API 600) is uneconomic. Match the standard to the size and construction the datasheet already implies.
Specifying: Class, Trim, NACE, Material Certs
The comparison table is a starting point. Four checks before you RFQ either standard:
- Size, class and ends. State DN/NPS, ASME Class (or PN if converted carefully), and end connection (RF flange, RTJ, BW, SW, NPT). Full-open gate valves are isolation only — not for throttling.
- Trim. API trim numbers (or equivalent material call-outs) set stem, disc and seat hardfacing. Match trim to temperature, media corrosivity and whether the duty is clean hydrocarbon, steam or sour gas. Do not leave trim as "standard" on a corrosive or sour tag.
- NACE / sour service. If H2S is present, specify NACE MR0175 / ISO 15156 compliance on body, bonnet and trim — and require hardness control documentation, not just a checkbox on the quote.
- Material certification. EN 10204 3.1 is the default for most commercial EPC packages; 3.2 (independent third-party) is common on critical or owner-witnessed items. State which you need. Pair with the design standard (API 600 or API 602) and any fire-safe / fugitive-emission extras the project requires.
If any of these are undecided, flag them in the RFQ rather than guessing. A valve that fails PMI, hardness or document review at inspection costs more than any unit-price saving. For broader isolating-valve selection context, see how to select a ball valve and ball valve vs gate valve.
Frequently Asked Questions
What is the main difference between API 600 and API 602?
API 600 covers cast steel gate valves for larger process and refinery isolation (typically from about 2" up). API 602 covers compact steel gate (and related) valves for small-bore service, most often forged and ≤2". Construction method and size envelope drive almost every other difference.
Is API 602 only for forged valves?
In practice, yes for most commercial supply — forged bodies dominate the compact range. The standard itself addresses compact steel gate, globe and check valves; confirm construction (forged vs cast) on the datasheet when the project requires it.
Can I use an API 600 valve on a DN25 instrument line?
Technically possible in some cast designs, but uneconomic and oversized. Specify API 602 forged for small-bore instrument and utility tags; reserve API 600 for the process isolation sizes the standard is written for.
Do I need NACE on every API 600 / API 602 valve?
No. NACE MR0175 / ISO 15156 applies when sour service (H2S) is present. State it only when the process conditions require it — and then require hardness and material documentation, not a marketing claim alone.
What material certificates should I request?
EN 10204 3.1 for most commercial packages; 3.2 when the EPC or owner requires independent verification. Align the cert level with the criticality of the tag, not with the catalog price band.
Send your requirement
Specify the right gate-valve standard the first time — send DN, Class, ends, trim, NACE need and cert level to PrimeFlow and source valves, pumps, fittings and seals as one consolidated shipment.
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