API 600 and API 602 are both API gate valve standards, but they cover different size ranges. API 600 governs larger bolted-bonnet steel gate valves for pipelines and refineries, while API 602 covers compact, small-bore steel gate valves, typically DN100/NPS 4 and below, with heavier wall sections for instrument and utility service.
Quick Answer: What Each Standard Covers
Both standards belong to the API family for steel gate valves, but they serve different ends of the size spectrum. API 600 specifies bolted-bonnet, outside-screw-and-yoke (OS&Y) gate valves in cast and forged steel, aimed at petroleum, petrochemical and gas service in the larger bore sizes. API 602 specifies compact steel gate valves for small-bore lines, generally DN100/NPS 4 and below, using heavier-walled forged bodies suited to instrument, drain, vent and utility connections.
- API 600 — general-purpose, larger-bore bolted-bonnet gate valves.
- API 602 — compact, small-bore forged-steel gate valves.
Both reference ASME B16.34 for pressure-temperature ratings and API 598 for inspection and testing. The practical takeaway is that the two are companions across a piping class rather than competitors: engineers rarely choose one instead of the other, but instead apply each where its construction philosophy fits the line size and duty. Reading them together gives a coherent gate-valve strategy from the smallest instrument root to the largest process header.
| Attribute | API 600 | API 602 |
|---|---|---|
| Typical size range | Mid to large bore, above compact range | Small bore, generally DN100/NPS 4 and below |
| Body construction | Commonly cast steel | Commonly forged steel |
| Bonnet type | Bolted bonnet (OS&Y) | Bolted, welded or union bonnet options |
| Wall thickness | Standard for cast bodies | Heavier relative to bore for durability |
| Trim and stem | Larger flexible/solid wedge, generous stem | Compact wedge and stem sized to bore |
| Primary application | Process headers, pipelines, refineries | Instrument, drain, vent, utility branch lines |
| Material scope | Cast carbon and alloy steels | Forged carbon and alloy steels |
| Pressure class | Assigned per ASME B16.34 | Assigned per ASME B16.34 |
| End connections | Typically flanged | Threaded, socket-weld or flanged |
| Inspection and testing | Per API 598 | Per API 598 |
Scope and Size Range Difference
The clearest distinction is size. API 602 was written specifically for compact valves in small-bore piping, typically up to DN100/NPS 4, where forged construction and heavier walls give durability in vibration-prone, small-diameter lines. API 600 addresses the larger sizes commonly found on main process and pipeline runs, where cast bodies and full bolted-bonnet construction are practical and economical.
- API 602 — small bore, generally DN100/NPS 4 and below.
- API 600 — mid to large bore, above the compact-valve range.
In practice, a plant often uses API 602 valves on branch, drain and instrument tie-ins, and API 600 valves on the primary process headers. The two standards complement rather than overlap. There is a natural handoff point around the small-bore ceiling: below it, the compact forged valve is usually the more robust and space-efficient choice; above it, the general-purpose bolted-bonnet valve becomes more economical to cast, easier to actuate and simpler to maintain. Where a project has valves right at the boundary size, the piping class typically states which standard governs, so the transition is defined by specification rather than left to case-by-case judgement.
Design and Construction Differences
API 600 valves are typically cast-steel, bolted-bonnet, OS&Y designs with a rising stem and flexible or solid wedge. The bolted bonnet allows disassembly for maintenance and reseating. API 602 valves are more often forged steel and may use bolted-bonnet, welded-bonnet or union-bonnet construction to suit compact envelopes and higher integrity in small lines.
- API 600 — cast body, bolted bonnet, OS&Y, larger trim.
- API 602 — forged body, heavier relative wall, multiple bonnet options.
Because small-bore valves carry proportionally higher stress and handling loads, API 602 emphasizes robust wall thickness and trim relative to bore, improving resistance to mechanical damage on branch and instrument connections. The OS&Y arrangement common to API 600 keeps the stem threads outside the flow path, protecting them from the process fluid and giving a clear visual indication of open or closed position — a useful feature on large manually operated valves. Forged construction in API 602 offers a fine, dense grain structure that resists porosity and suits the thin-walled, highly stressed geometry of a small valve, which is one reason forging is favoured over casting at the compact end of the range.
Trim, Seating and Backseat Differences
Trim — the seats, wedge, stem and internal wear surfaces — is where the two standards express their different service intents most clearly. API 600 valves generally use a rising stem with a flexible or solid wedge seating against renewable or integral seat rings, sized so the valve can be reground and reseated after wear. Larger bodies give room for hard-faced seats and generous stem sections that tolerate frequent cycling and higher operating torque.
- API 600 — larger flexible or solid wedge, hard-faced or renewable seats, generous stem section.
- API 602 — compact wedge and stem sized for small bore, integral or hard-faced seats.
Most steel gate valves also incorporate a backseat arrangement: when the stem is fully retracted to the open position, the backseat contacts the bonnet and isolates the stem seal area, allowing packing to be inspected or adjusted under controlled conditions. Both standards recognise this feature, though the compact geometry of API 602 valves means the backseat and packing chamber are proportionally smaller. Material selection for seating faces — for example, hard-facing on the wedge and seat contact surfaces — follows the service severity, corrosion and erosion expected, and should be defined on the data sheet rather than assumed from the standard alone.
Materials and Pressure Class Coverage
Both standards draw pressure-temperature ratings from ASME B16.34 and cover carbon and alloy steels, so material selection follows service temperature, corrosion and code requirements rather than the valve standard alone. API 602 typically centers on forged carbon and alloy steel bodies suited to compact, higher-integrity small-bore duty. API 600 spans cast carbon and alloy steels across a broad class range for general process service.
- Materials — carbon steel and alloy steels per the applicable ASME material specifications.
- Ratings — pressure classes assigned via ASME B16.34.
Confirm exact class, body material and trim against the project specification and the valve manufacturer's data sheet; the standards define families, not a single fixed rating. Because the allowable working pressure falls as temperature rises, the same nominal pressure class delivers different real limits depending on the body alloy — a low-temperature carbon steel and a high-temperature chrome-moly alloy to the same class behave very differently at the extremes of their range. Bolting and gasket materials must be selected to match, since a mismatched bonnet joint can govern the true service limit of an otherwise capable valve.
Testing and Inspection Expectations (API 598 Context)
Valves built to either standard are normally shell- and seat-tested to API 598, the API standard that defines inspection and testing for valves. In broad terms, the shell test verifies the pressure-containing envelope — body and bonnet — while the seat test checks closure tightness against defined acceptance criteria. Because both API 600 and API 602 point to the same testing regime, the inspection language across a piping class stays consistent regardless of valve size.
- Shell test — verifies the pressure boundary integrity of body and bonnet.
- Seat test — verifies closure tightness to the specified acceptance criteria.
Beyond the baseline, projects frequently layer on supplementary requirements: material certification, non-destructive examination, positive material identification, fugitive-emission testing or low-temperature service testing. These are defined by the purchaser and the project specification rather than by the valve standard itself, so the exact test scope, durations and acceptance thresholds should always be read from the current standard edition and the order documents. Treat any specific test pressures or leakage allowances as governed by those documents, not by rules of thumb.
Typical Applications and Industries for Each
The two standards map onto different parts of the same facilities. API 600 valves populate the primary steel piping of oil and gas production, refining, petrochemical plants, power generation and pipeline systems, where larger bolted-bonnet gate valves provide reliable on/off isolation on process headers, pump and compressor stations, and tank-farm manifolds. Their maintainability and standard flanged interfaces make them the default block valve on main runs.
- API 600 — refinery and petrochemical process headers, pipeline isolation, power plant steam and feedwater mains, terminal manifolds.
- API 602 — instrument hook-ups, sample and drain points, chemical injection, vents, and small utility branch lines.
API 602 valves serve the dense network of small-bore connections that surrounds that main plant: instrument root valves, gauge and transmitter isolations, sample points, chemical-injection tie-ins, vents and drains. In these locations the compact forged body resists the vibration, external loads and occasional mechanical abuse that small lines endure. Across oil and gas, chemical, and power industries the same project therefore specifies both standards side by side — API 600 for the arteries and API 602 for the capillaries of the piping system.
Bolted Bonnet vs Pressure-Seal Context
API 600 is fundamentally a bolted-bonnet standard: the bonnet is held to the body by a bolted, gasketed flange joint that can be unbolted for maintenance, reseating or packing replacement. This construction is well suited to the moderate pressure classes where most general process valves operate, and it gives a familiar, serviceable joint. It is worth understanding how it sits relative to pressure-seal construction, which is a different bonnet concept used mainly on very high-pressure classes.
- Bolted bonnet — flanged, gasketed joint; serviceable; typical of API 600 general service.
- Pressure-seal bonnet — self-energising joint that tightens as internal pressure rises; used on higher-pressure duty.
In a pressure-seal design the internal pressure energises the bonnet seal, so the joint tends to seal more tightly as pressure increases, which is advantageous in high-class steam and high-pressure hydrocarbon service. Neither is inherently superior; the bolted bonnet of a typical API 600 valve is chosen for serviceability at general process ratings, while pressure-seal construction is reserved for the elevated classes where bolted joints become impractically large. API 602 small-bore valves, by contrast, use bolted, welded or union-bonnet constructions matched to their compact envelope. As always, confirm the actual bonnet type against the valve data sheet and piping class.
How to Choose Between API 600 and API 602
Selection is driven mainly by line size and service, not preference. For small-bore lines such as instrument roots, sample points, drains and vents, API 602 compact forged valves are the natural fit and are usually more robust in these applications. For larger process and pipeline headers, API 600 bolted-bonnet valves offer maintainability and standard flanged interfaces.
- Choose API 602 for DN100/NPS 4 and below, especially forged small-bore service.
- Choose API 600 for larger bore, general refinery and pipeline duty.
Always align the choice with the piping class, end connections, pressure rating and inspection requirements defined in your project specification. A short decision path helps: first fix the nominal size and locate it relative to the compact ceiling; then confirm the required end connection — threaded or socket-weld connections point toward API 602, while flanged block valves on main runs point toward API 600; finally reconcile material, pressure class and any supplementary testing with the piping class. Where a size sits on the boundary, defer to the specification's stated standard rather than improvising, so the whole plant stays consistent and auditable.
Common Misconceptions (FAQ Lead-In)
A frequent misconception is that API 600 is simply the higher-quality standard and API 602 a lesser one. That is inaccurate. They target different size classes, and both call on the same pressure-temperature basis (ASME B16.34) and inspection regime (API 598). Another myth is that API 602 valves are always welded-bonnet; in fact several bonnet constructions are permitted.
- Neither standard is superior — they cover different bore ranges.
- Both reference ASME B16.34 and API 598.
Understanding this prevents over-specifying large valves where compact forged valves are correct, and vice versa. A related point of confusion is API 603, sometimes assumed to be interchangeable with API 600; it is a separate standard for corrosion-resistant bolted-bonnet gate valves and serves a different purpose. The FAQ below addresses the practical questions buyers ask most, including how API 600 and API 603 differ and what each valve family is typically made from.
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FAQ
Is API 600 better than API 602?
No. Neither standard is inherently better; they cover different valve size ranges. API 600 addresses larger bolted-bonnet steel gate valves for process and pipeline service, while API 602 covers compact, small-bore forged steel gate valves generally DN100/NPS 4 and below. Both use ASME B16.34 for pressure-temperature ratings and API 598 for inspection and testing. The right choice depends on your line size, service conditions and piping class, not on one standard being superior to the other.
What is the API 600 used for?
API 600 is used to specify bolted-bonnet, outside-screw-and-yoke steel gate valves for general on/off isolation duty in the larger bore sizes. It is widely applied across oil and gas production, refining, petrochemical plants, power generation and pipeline systems, where these valves serve as block valves on process headers, pump and compressor stations, tank-farm manifolds and main pipeline runs. The standard covers cast and forged steel bodies and draws pressure-temperature ratings from ASME B16.34, with inspection and testing typically to API 598. Confirm exact class, material and trim against the project specification.
What size range does API 602 cover?
API 602 was written for compact gate valves in small-bore piping, typically DN100/NPS 4 and below. These forged-steel valves suit instrument roots, sample points, drains, vents and utility branch connections where a heavier wall relative to bore improves mechanical durability. For sizes above the compact range, API 600 valves are generally used. Always confirm the exact size limits and body material against the current standard edition and the manufacturer's data sheet, since project specifications may further restrict the acceptable range.
What is the difference between API 600 and API 603?
API 600 and API 603 are both bolted-bonnet steel gate valve standards, but they target different service intents. API 600 covers general-purpose cast and forged steel gate valves for a broad range of process, refinery and pipeline duty. API 603 covers corrosion-resistant bolted-bonnet gate valves, generally lighter in construction and aimed at services where corrosion resistance is the priority rather than the heavier general-service duty of API 600. Both reference ASME B16.34 for ratings and are inspected to API 598. Select between them based on corrosion requirements, pressure class and the governing piping specification.
What material is API 602 made of?
API 602 valves are typically made of forged carbon steel and alloy steels, with forging chosen for its dense grain structure and suitability to the thin-walled, highly stressed geometry of small-bore valves. The exact grade follows the service temperature, corrosion and code requirements rather than the standard alone, spanning common carbon steels through low-temperature and chrome-moly alloy grades per the applicable ASME material specifications. Trim, seating faces and bolting are selected to match the duty. Always confirm the specific body material, trim and pressure class on the manufacturer's data sheet against your process conditions.
Can I use API 600 and API 602 valves in the same plant?
Yes, and this is common. Plants routinely install API 600 bolted-bonnet gate valves on primary process and pipeline headers, and API 602 compact forged valves on small-bore branch, drain, vent and instrument connections. The two standards are complementary, each optimized for a different size class. Because both reference ASME B16.34 for ratings and API 598 for testing, they integrate cleanly within one piping specification. Match each valve to its line size, pressure class and end-connection requirement as defined in the project documents.
What bonnet types are allowed under API 602?
API 602 permits more than one bonnet construction to suit compact small-bore envelopes, including bolted-bonnet, welded-bonnet and union-bonnet designs. This flexibility lets designers balance maintainability against integrity in small, sometimes vibration-prone lines. It is a misconception that API 602 valves are always welded-bonnet. The correct construction depends on service, integrity requirements and maintenance philosophy. Confirm the specific bonnet type, body material and trim against the manufacturer's data sheet and your project specification before ordering.
Do API 600 and API 602 use the same pressure ratings?
Both standards derive their pressure-temperature ratings from ASME B16.34, so the rating basis is common even though the valve constructions differ. Actual allowable pressure at temperature depends on the body material and assigned pressure class, not on the API standard number alone. This means a carbon steel valve and an alloy steel valve to the same standard can have different working limits. Always verify the specific class, material and temperature limits on the valve data sheet against your process conditions and applicable piping code.