Industrial valve RFQs are full of codes: API 600, API 602, API 623, ASME B16.34, Class 150… If you are new to process valves — or you buy UL/FM fire protection products and are expanding into industrial lines — here is what the main API design standards actually mean when you place an order.
API Standards Are Design & Construction Rules
The American Petroleum Institute (API) publishes valve standards that fix wall thickness, stem diameter, materials, testing and dimensions, so that a “Class 300 API 600 gate valve” from any compliant manufacturer is mechanically equivalent. The project engineer specifies the standard; the buyer’s job is to make sure the quoted valve genuinely complies.
The Big Three for Steel Valves
API 600 — Bolted-Bonnet Cast Steel Gate Valves
The workhorse standard for cast steel gate valves NPS 1–24 and larger, Class 150–2500. Key buyer points: full-bore wedge design, renewable seat rings, OS&Y rising stem, and minimum wall thickness heavier than ASME B16.34 alone requires.
API 602 — Compact Forged Steel Valves (NPS ≤ 4)
Small-bore forged gate, globe and check valves in A105, LF2 or F316L — the thousands of small valves around pumps, instrument roots and drains. Bonnet options matter here: bolted, welded, or pressure-seal.
API 623 — Steel Globe Valves
The globe-valve companion to API 600: heavier walls than generic B16.34 globes, defined trim numbers, and standardized face-to-face so they drop into the same line.
Codes You See Next to Them
- ASME B16.34 — the base pressure-temperature rating code nearly all steel valves reference.
- ASME B16.10 — face-to-face dimensions (interchangeability in the pipe rack).
- API 598 — shop pressure testing: shell test and seat leakage acceptance.
- NACE MR0175 / ISO 15156 — sour (H2S) service material rules.
- ISO 15848-1 — fugitive-emission (stem leakage) type testing.
What This Means for Your RFQ
A clean industrial valve inquiry states: size, ASME class, standard (e.g. API 600), body/trim materials, end connections, operator, and any overlays — NACE, fire-safe (API 607), cryogenic (BS 6364), or low-emission (ISO 15848-1). With those eight items, any competent supplier can quote in one pass, with datasheets you can submit to the end client.
The Three Standards Side by Side
| API 600 | API 602 | API 623 | |
|---|---|---|---|
| Valve type | Gate | Gate, globe and check — compact | Globe |
| Construction | Bolted bonnet, cast steel | Forged steel, bolted or welded bonnet | Bolted bonnet, cast steel |
| Typical size range | Larger line sizes | Small bore, commonly NPS 4 and below | Larger line sizes |
| Where it shows up | Refinery and process isolation | Instrument, drain, vent and small-bore process | Throttling and regulating duty |
All three sit on top of ASME B16.34, which supplies the pressure–temperature ratings, and none of them replaces it. API adds construction requirements — wall thickness, stem and backseat design, trim material combinations, testing — on top of the B16.34 rating framework.
The Class 800 Question
Class 800 causes more confusion than any other designation on a forged-valve datasheet, because it is not one of the standard ASME B16.34 classes. It is an intermediate designation used for forged small-bore valves, with ratings derived between the adjacent standard classes. Practically, it means a heavier-walled small-bore valve than Class 600 without stepping to Class 900 — which is exactly why it is so common on socket-weld and threaded valves. Ask for the pressure–temperature table rather than assuming an equivalence.
Trim Numbers: What They Encode
An API trim number is shorthand for a combination of seating surface, disc and stem materials defined in a table within the standard. Trim 1, for example, designates 13 Cr (410-type) seating surfaces — a general-service default. Hardfaced trims appear where erosion, throttling or cycling would damage a softer seat. The important habit: quote the trim number and the edition of the standard, because the table is edition-specific and “Trim 8” without a reference has caused more than one substitution dispute.
What to Put in the RFQ
- Standard and edition (API 600 / 602 / 623, plus ASME B16.34).
- Size, class, and the design pressure at the design temperature — not just the class.
- Body material grade and trim number.
- End connections and required face-to-face standard.
- Test standard and leakage acceptance criterion.
- Any overlay requirements: fire-safe, NACE, low-emission, PED.
- Documentation type under EN 10204.
Frequently Asked Questions
Is API 600 “better” than ASME B16.34?
They are complementary. B16.34 gives pressure-temperature ratings; API 600 adds gate-valve-specific construction minimums on top of it.
Can I use API 602 valves above NPS 4?
API 602 formally covers NPS 4 and smaller. Above that, specify API 600 (gate) or API 623 (globe) cast valves.
Do these standards fix the price?
No — material grade, bonnet type, trim and origin drive cost. Same standard, very different price points; that is why we quote project-by-project.
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