API 602: Compact Forged Steel Gate, Globe & Check Valves (NPS 4 and Smaller)

Reviewed by the Crestflo Engineering Team

> In one line: API 602 is the American Petroleum Institute (API) standard for compact, forged steel gate, globe, and check valves in sizes NPS 4 (DN 100) and smaller for the petroleum and natural-gas industries. It sets the scope, pressure classes, including the signature Class 800 rating, end connections, body and bonnet construction, and materials for small-bore process-isolation valves. Crestflo builds small-bore forged and bar-stock isolation and check valves to the API 602 construction and ASME B16.34 rating basis in stainless and high-nickel/CRA alloys, made-to-order, with 6–8 week delivery.

Scope note: API 602 governs compact NPS ≤ 4 forged steel gate, globe and check valves, it is not API 600 (larger flanged, bolted-bonnet gate valves NPS 2 and up) or API 603 (corrosion-resistant bolted-bonnet gate valves). On this site, "valve" means an instrumentation / small-bore process valve, not a residential plumbing or automotive valve. API 602 is a valve design standard; pressure–temperature rating comes from ASME B16.34 and pressure testing follows API 598.

Request your API 602-basis valve RFQ → · sales@crestflousa.com · +1 346 594 9005

Also known as: API 602 designations & related terms

Specifications, line lists and datasheets all render this standard differently. Every designation below, though, points to the same compact forged steel valve standard.

This standard often gets nicknamed the "compact valve standard" when it shows up on small-bore isolation and instrument-root packages. The reason: its Class 800 rating, paired with threaded or socket-weld ends, is why engineers call it out specifically.

API 602 standard at a glance: attributes

The standard's exact minimum wall-thickness and dimensional tables are copyrighted and fixed by the current edition; this page summarizes scope, classes, ends and materials rather than reproducing the document. Values per applicable standard; customizable to requirement.

What is API 602?

API 602 is an American Petroleum Institute standard covering compact, forged steel gate, globe, and check valves in sizes NPS 4 (DN 100) and smaller, meant for use in the petroleum and natural-gas industries. The American Petroleum Institute (API) publishes it. It's harmonized internationally with ISO 15761.

API 602 is best read through one word: compact. API 602 valves are the small-bore end of the process-valve family. They're the isolation and check valves you find at instrument roots, drains, vents, sample points and small process lines, spots where a full-size flanged gate valve would just be overkill. These valves run at high pressure in small bores, and that's precisely why API 602 specifies bodies that are predominantly forged (or machined from bar stock) rather than cast. Forging gives continuous grain flow, and it produces a sound, defect-free pressure boundary even in a thick, compact section.

API 602 covers three valve types, gate (isolation), globe (isolation and throttling), and check (backflow prevention), and it defines how each is built: the pressure classes it can carry, the end connections it can take, the bonnet joint that closes it, and the body materials it is forged from. Pressure–temperature rating itself is not set inside API 602; the standard references ASME B16.34 for that, and pressure testing follows API 598.

Who publishes API 602, and what is the latest edition?

The American Petroleum Institute (API) writes and maintains API 602, and it revises the standard on a periodic cycle. The document is harmonized with its ISO twin, ISO 15761, so people often cite the two together. Contract references vary by revision, though, so cite whatever edition your project specification names and check it against the current API catalog rather than assuming a fixed year.

Where can I get the API 602 PDF?

API 602's full text is a copyrighted, licensed document, sold by API and authorized resellers such as ANSI and Accuris. This page just summarizes the standard's scope, classes, ends and materials for engineering reference. It doesn't reproduce or distribute the document itself. If you're doing compliance work, buy the current official edition. Don't rely on unofficial "free download" copies or an "API 602 manual" reprint, since either one might be superseded.

API 602 scope & size range: NPS 4 (DN 100) and smaller

API 602 applies to valves NPS ¼ through NPS 4 (DN 8 to DN 100) in petroleum and natural-gas service. That small-bore window is the whole point of the standard. It's where high line pressures meet small bores, and a compact forged body simply does more than a cast or oversized alternative could.

Small-bore process isolation and instrument-root service is the constant across a service framing that spans upstream, midstream and downstream oil and gas, refining, petrochemical, power and LNG. When a plant needs a high-pressure block or check valve on a ½″ or ¾″ line, tap, gauge root or drain, API 602 is the governing construction standard.

API 602 valve types: gate, globe & check valves

API 602 governs three compact valve types. Each one handles a different job on a small-bore line.

The transactional demand behind "API 602 gate valve," "API 602 globe valve" and "API 602 check valve" is a search for the small-bore hardware itself. Crestflo builds the instrumentation counterparts, forged and bar-stock isolation, throttling and non-return valves, to the API 602 construction basis; see the monoflange, double block & bleed and bleed valve ranges for related small-bore isolation.

API 602 pressure classes & the Class 800 rating

API 602 valves are rated in the standard ASME pressure classes, Class 150, 300, 600, 800 and 1500, with the pressure–temperature rating itself set by ASME B16.34. The class most associated with the standard is Class 800.

Class 800 is a compact-valve special class. It sits between Class 600 and Class 1500, and it exists for one reason: small-bore forged valves. There's no ASME B16.5 flange equivalent for Class 800, so the rating applies to threaded, socket-weld and butt-weld (welded-end) valves rather than flanged ones. That's exactly the compact, small-bore construction API 602 governs. So when a datasheet calls for a "Class 800 gate valve," it's almost always an API 602 valve.

Pressure, temperature values derate with temperature per ASME B16.34, based on the specific body material. Values follow the applicable standard and can be adjusted to requirement.

API 602 end connections & their dimensional standards

API 602 allows the full range of small-bore end connections, and each one gets sized to its own ASME standard. That's why a single API 602 valve can be ordered threaded, socket-weld, butt-weld, flanged or with an extended body.

The extended-body design shows up on compact API 602 valves: the body's forged with an integral nipple, so the valve threads or welds straight into a header or vessel boss and skips a joint entirely. Threaded and socket-weld ends dominate at Class 800. A Class 800 socket-weld gate valve is, in fact, the classic API 602 configuration, since that class carries no flange rating.

API 602 body, bonnet, stem & trim construction

API 602 defines how the compact valve is built as a pressure vessel.

• Body. Mostly forged steel, though sometimes machined from bar stock, giving a sound, continuous grain-flow pressure boundary in a thick, compact section.
• Bonnet joint. Bolted-bonnet designs show up most often. API 602 also recognizes welded-bonnet (seal-welded or all-welded), union-bonnet and pressure-seal constructions. All-welded bonnets fit high-integrity, fugitive-emission-sensitive service, since a gasketed joint is a leak path.
• Stem. Usually rising-stem / OS&Y (outside screw and yoke) or inside-screw. Non-rising options exist where headroom is tight.
• Trim & seat. Seat and trim material and hardness get matched to the service. Back-seating protects the stem packing while the valve operates.
• Wall thickness. API 602 sets minimum wall thickness in its own tables, and the result is lighter and more compact than the heavier-wall API 600 gate valve. Those per-size values are copyrighted and fixed by the current edition, so they aren't reproduced here.

Values per applicable standard; customizable to requirement.

API 602 materials: from A105 carbon steel to high-nickel & CRA alloys

API 602 bodies are forged from carbon steel (ASTM A105) or austenitic stainless / alloy forgings (ASTM A182 F304, F316, F321, F11, F22, F51, etc.), see ASTM A182 for the forging grades. For clean hydrocarbon service under ordinary conditions, A105 or F316 will do the job.

For sour, chloride-bearing, high-temperature or acid service, standard grades hit their limit fast, and that's exactly where alloy choice starts to matter. Crestflo forges and machines the same compact API 602 construction in corrosion-resistant and high-nickel alloys, covering the cases where A105 or F316 simply won't hold up against the media.

Explore the full materials range for compositions and properties. Crestflo supplies these as instrumentation valves, fittings and tubing, not bar, sheet or mill product.

API 602 vs API 600 vs API 603: how they differ

API 602 is easily confused with its sibling API gate-valve standards. The distinction comes down to size, weight and metallurgy.

API 602 handles the compact, small-bore end of the family, built from forgings. API 600 takes the larger, heavier flanged bolted-bonnet gate valves. API 603 covers bolted-bonnet gate valves made for corrosion resistance. ISO 15761 is API 602's international counterpart, while BS 5352, now withdrawn, was once the British equivalent.

Testing, emissions & sour service under API 602

API 602 valve is qualified against the standards its design references, not against a compression-fitting standard. Here's what the proof stack looks like:

• Pressure, shell, and seat testing follows API 598, the acceptance-test language shared across the API valve family.
• Pressure-temperature rating follows ASME B16.34, derated for the body material and temperature.
• Fugitive-emission qualification follows ISO 15848 (and API 624 for rising-stem valves) wherever a low-emission stem seal is called for.
• Sour-service metallurgy follows NACE MR0175 / ISO 15156 for H₂S-bearing service. This is what keeps a small-bore valve from cracking under sour gas.

Crestflo instrumentation valves get a 100% seat- and shell-leak test in house, and can be tested to API 598 acceptance criteria on request. Metallurgy is NACE MR0175-compliant. Every part ships with EN 10204 3.1 material traceability (3.2 available on request) and carries a heat/lot number. Certificates and traceability records are kept in quality / traceability.

Crestflo small-bore valves built to the API 602 basis

Crestflo builds small-bore forged and bar-stock isolation and check valves to the API 602 construction and ASME B16.34 rating basis, in stainless, super-duplex, 6Mo and high-nickel/CRA alloys, on a made-to-order, made-to-print basis. When your specification calls API 602, the Engineering Team confirms the applicable construction, rating and test basis and issues the documentation for your line.

Datasheets and CAD models go out to customers on request. Price and cost get quoted per requirement, since there's no shelf price on an engineered small-bore valve. Send your spec for a firm quote, and the Engineering Team will confirm the valve, construction and documentation.

Request your API 602-basis valve RFQ →

Request API 602-basis small-bore valves

Send your requirement to the Crestflo Engineering Team, valve type (gate, globe, or check), material or grade, size and end connections, pressure class (including Class 800), quantity, and any test standard (API 598) or NACE sour-service target you need. They'll confirm the valve and documentation for your line.

RFQ, tell us what you need:

• Name
• Company name
• Email
• Phone
• Requirement description (valve type, material, size, class, end connections, quantity, service conditions)

Request the RFQ & valve documentation →

Secondary paths: browse instrumentation valves · request a sample · become a distributor · contact Crestflo.

US contact: sales@crestflousa.com · +1 346 594 9005 · Houston, TX.

Stock & lead time: standard items ship from ready stock; specials are made to order, with a 6–8 week delivery. Origin is Indian, though US or European melt is available on request, and full material traceability comes with it.

Why Crestflo for API 602-basis small-bore valves

• The standard is published, not buried. API 602's scope, Class 800 rating, end connections and material path all live here as HTML-native data. The valves themselves are built to that same construction basis.
• A manufacturer and supplier, not a reseller. Crestflo is a direct API 602 gate valve manufacturer and supplier. It forges and machines its own compact small-bore valves, running CNC, VMC and EDM in house. Testing covers hydraulic proof, burst, impulse and pneumatic checks, PMI and in-house NDT; destructive testing happens at ISO/IEC 17025-accredited labs, and third-party inspection is available on request.
• The alloy advantage. The same API 602 construction in super-duplex, 6Mo, Alloy 20, Inconel, Monel and Hastelloy covers sour, chloride and acid service, where A105 or F316 simply won't hold up.
• Traceability on every part. EN 10204 3.1 MTC (3.2 on request) and a heat/lot number on every part.
• Lead time that moves projects. Ready stock for standard items, made-to-order for specials, 6–8 week delivery.
• Honest origin. Indian origin; US / European melt available on request, with full material traceability.
• Small MOQ and private label, both imperial and metric, customizable to requirement.
• Certified quality system: ISO 9001 / 14001 / 45001 & PED certified.

Crestflo is the instrumentation arm of a four-decade-old export house recognized by the Government of India, with a long delivery record across the Middle East. Manufacturing runs deep here, even though the brand itself stays focused on serving US customers. We Engineer Confidence.

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Explore related standards, valves & materials

Standards hub: Standards hub · ASME B16.34 · API 598 · API 607 · API 6D · API 6FA · ISO 15848 · NACE MR0175 · ASME B1.20.1 · ASME B16.11 · ASTM A182 · EN 10204 MTC

Valves: Instrumentation valves · Needle valve · Check valve / NRV · Gauge root valve · Monoflange valve · Double block & bleed · Bleed valve

Materials & quality: 316/316L · Super Duplex 2507 · Inconel 625 · Traceability · Testing & inspection

Industries: Oil & gas · Downstream refining · Petrochemical & chemical