Industrial Valves: A Buyer's Guide to API 600, API 6D and the 7 Valve Types That Keep Process Plants Running

A single industrial valve failure can shut down a hydrocracker, a desalination train, or a 200 MW boiler feed pump within minutes. For EPC procurement engineers, project QA managers and trading-house sourcing leads, the right valve choice is the line between a clean punch-list handover and a multi-week punch-list headache. This guide walks through the seven valve types that cover 95 % of process-plant RFQs, the four standards (API 600, API 6D, API 602, API 603) that govern them, and the bundled flange / gasket / stud-bolt scope that ships with every valve from a mill-direct supplier like EZ Steel Industrial.

1. Why "Industrial Valves" Deserve Their Own RFQ Line

In a B2B piping context, industrial valves are not generic plumbing fittings. They are code-stamped, traceability-tracked, pressure-rated, fire-safe-tested devices that are matched to a piping class on a line-by-line basis. The EZ Steel Industrial product tree defines industrial valves as a standalone category that joins pipes, pipe fittings, pipe flanges, gaskets and stud bolts into a single bundled piping package. The same project almost never orders "valves only" — the valve body is bolted between two flanges with a gasket and a set of stud bolts, and the procurement team needs one supplier that can ship the whole joint.

The seven valve families that show up in process-plant RFQs are:

• Gate valve — isolation service, full-bore, bi-directional
• Globe valve — throttling and flow control
• Ball valve — quick on/off, tight shut-off, trunnion or floating
• Butterfly valve — large-diameter, low-weight, low-pressure
• Check valve — backflow prevention (swing, lift, dual-plate, Tilting disc)
• Plug valve — slurry, gas, and frequent-cycle service
• Safety / relief valve — over-pressure protection, ASME Section VIII

2. The Four API Standards You Will See Most Often

2.1 API 600 — Bolted-Bonnet Gate Valves for Refinery and Petrochemical Service

API 600 (current edition API 600 14th, 2021, with 2023 errata) covers gate, globe and check valves with carbon, ferritic alloy and stainless steel bodies for petroleum, petrochemical and related industries. The standard is the default specification for any Class 150 through Class 2500 refinery or steam-plant isolation valve, and it is the document most EPC specs default to when they say "per the latest API". The bonnet can be bolted or pressure-seal, the body is cast or forged, and the trim (seat, disc, stem) is governed by a separate trim number from API 600 Table 1.

A clean RFQ for an API 600 gate reads: "API 600 gate valve, 12 in × 300#, RF flanged ends, WCB body + 13Cr trim, NACE MR0175 for sour service, fire-safe to API 607, EN 10204 3.1 MTC." The 13Cr trim is the default for hydrocarbon service above 200 °C; F316 (316 SS) trim is used for corrosion service; alloy 825 trim is for hot H₂S; Monel 400 trim is for hydrofluoric acid alkylation units.

2.2 API 6D — Pipeline Valves for the Linepipe Itself

API 6D (current edition API 6D 25th, 2021, with 2024 addendum 2) is the specification for pipeline valves — the gate, ball, check and plug valves that sit in the linepipe itself rather than inside the plant fence. The 25th edition, effective November 2022, mandates fire-test compliance to API 6FA or API 607, low-emission packing per API 624, and a documented PMI (positive material identification) program on pressure-containing parts.

In practice, API 6D is the spec you see on cross-country gas trunklines, on offshore flowlines, on tank-farm manifolds, and on any project where the linepipe is API 5L X65 / X70 linepipe and the line must be piggable. A pipeline-spec ball valve is almost always trunnion-mounted, double-block-and-bleed, with full-opening bore to match the linepipe ID so that pipeline pigs can pass.

2.3 API 602 — Forged Compact Valves for Small-Bore Service

API 602 covers gate, globe and check valves that are forged rather than cast, in sizes NPS ½ through NPS 4, in Class 800 and below. The compact body makes API 602 the default for small-bore instrumentation, sample lines, chemical injection and utility stations inside a process plant. Forged body means the mechanical strength is higher than a cast body of the same schedule, and the wall thickness is thinner, which is why API 602 valves are typically 30–40 % lighter than the equivalent cast API 600 valve in the same line class.

2.4 API 603 — Corrosion-Resistant Bolted-Bonnet Gate Valves

API 603 (current edition API 603 9th, 2021) is the twin of API 600 written specifically for austenitic stainless steel and nickel-alloy gate, globe and check valves. The body is normally CF8M, CF3M, CN7M (alloy 20) or a duplex grade, and the trim is full stainless or alloy to match. API 603 is the standard you see in chlorine service, phosphoric acid service, seawater cooling, and any Class 150 / 300 process line where carbon steel would corrode.

3. The Seven Valve Types and Where Each One Fits

3.1 Gate Valve — The Workhorse Isolation Valve

A gate valve is built around a wedge or slab gate that lifts vertically to open and seats back down to close. The flow path when fully open is straight and unrestricted, so the pressure ｄｒｏｐ is the lowest of any valve type. Gate valves are designed for full-open or full-close service — they should not be used to throttle flow, because partial-open throttling erodes the seating surfaces and causes seat leakage a few cycles later.

Best fit: main block valves on gas trunklines, isolation valves on steam lines above 100 psig, refinery block valves around reactors and columns, hydrocracker feed and discharge. Standard: API 600 for cast body, API 602 for forged small-bore, API 6D for pipeline isolation. End connections: RF or RTJ flanged, butt-weld for high-pressure.

3.2 Globe Valve — The Throttling Specialist

A globe valve uses a plug-and-seat arrangement inside a Z-shaped body to force the fluid to change direction. The Z-pattern gives globe valves excellent throttling behaviour and predictable flow-vs-position curves, but it also means a much higher pressure ｄｒｏｐ than a gate or ball valve. Globe valves are the right pick wherever the line is meant to be modulated — feedwater regulation, chemical injection control, level-control dump valves, desuperheater spray water.

Standard: API 600 cast body, API 602 forged small-bore, BS 1873 cast steel, DIN 3356. End connections: RF or RTJ flanged, butt-weld for high-pressure feedwater.

3.3 Ball Valve — The Quick Shut-Off Standard

A ball valve uses a spherical ball with a cylindrical bore; rotating the ball 90° turns the flow fully on or fully off. The two structural choices are floating ball (held in place by the two seat rings, used in low-pressure Class 150 / 300 service) and trunnion-mounted ball (the ball is anchored on top and bottom stems, used in Class 600 and above and in pipeline service). A trunnion ball with a full-opening bore can pass a pipeline pig; a reduced-port ball is cheaper but restricts flow and is not piggable.

Best fit: tank-farm isolation, gas-distribution block valves, ESD (emergency-shut-down) valves, hydrocarbon block-and-bleed manifolds. Standard: API 6D for pipeline, API 608 for industrial ball, ASME B16.34 for general industrial. End connections: RF or RTJ flanged, butt-weld, NPT or SW for small-bore.

3.4 Butterfly Valve — The Large-Diameter Lightweight

A butterfly valve rotates a disc 90° inside the flow stream. Wafer-style and lug-style bodies are compact, light, and cheap in sizes above 24 in. Triple-offset butterfly valves (TOBV) are the workhorse for high-temperature and high-pressure service where the seat is metal-to-metal rather than resilient. Butterfly valves are the right choice for large-diameter, low-pressure water, air, HVAC, and low-pressure hydrocarbon service where the weight saving matters more than the absolute shut-off tightness.

Standard: API 609 for triple-offset and high-performance butterfly, MSS-SP for wafer and lug. End connections: wafer, lug, double-flanged (for larger sizes and ease of maintenance).

3.5 Check Valve — Backflow Prevention

A check valve allows flow in one direction only and closes automatically when flow reverses. The three common constructions are swing check (the disc swings on a hinge), lift check (the disc lifts vertically on a seat), and dual-plate (wafer) check (two half-discs open on a central hinge). Tilting-disc check valves are a fourth option, used on high-velocity gas service where slamming and water hammer must be minimised.

Best fit: pump-discharge protection, compressor-discharge protection, linebreak prevention, prevention of backflow into a lower-pressure header. Standard: API 6D for pipeline, API 594 for wafer check, BS 1868 for swing check, ASME B16.34 for general.

3.6 Plug Valve — Slurry, Gas and Frequent Cycle

A plug valve rotates a tapered or cylindrical plug inside the body. Lubricated plug valves can be adjusted in-line to take up wear; non-lubricated plug valves use a sleeve liner (PTFE or RPTFE) for tight shut-off. Plug valves are the right pick for slurry, mud, sand-laden fluids, and for service that is cycled many times per day — they are mechanically simple, easy to repair in-line, and tolerate dirty fluids better than a ball valve.

Standard: API 6D for pipeline, ASME B16.34 for general, MSS-SP for lubricated plug.

3.7 Safety / Relief Valve — Over-Pressure Protection

A safety valve (or relief valve) is a spring-loaded or pilot-operated valve that opens automatically at a set pressure to protect a pressure vessel or piping system from over-pressure. They are governed by ASME Section VIII (vessels) and ASME Section I (boilers) on the sizing side, and by API 520 / 521 on the sizing methodology. In a piping RFQ the safety / relief valve is almost always a separate line item, but the discharge piping, the inlet piping and the bolted flanges are all bundled into the same piping scope as the rest of the industrial valves.

4. Quick-Reference: Standard by Valve Type

5. Material Selection — The Other Half of an RFQ

Half the work in an industrial-valve RFQ is the material. The right trim and the right body material protect against corrosion, against temperature creep, and against NACE MR0175 sour-service cracking. The five body materials that cover 90 % of orders are:

• WCB (ASTM A216 WCB) — cast carbon steel for non-corrosive service from -29 °C to 425 °C. Default for gate, globe, ball and check up to Class 600.
• LCC (ASTM A352 LCC) — low-temperature carbon steel for service down to -46 °C. Used in LNG, ethylene and cold-section refinery units.
• CF8M (ASTM A351 CF8M) — 316 stainless steel cast equivalent. Default for corrosion service, seawater, chemical and pharmaceutical.
• CN7M (ASTM A351 CN7M) — alloy 20 cast equivalent. Sulphuric acid, phosphoric acid and nitric acid service.
• CD3MN (ASTM A890 CD3MN, duplex 4A) — duplex stainless steel for chloride-bearing and sour service where 316 would pit.

A common RFQ mistake is to call out "stainless steel valve" without naming the cast or wrought grade. Always specify the ASTM/ASME material number on the data sheet — it determines the casting supplier, the welding procedure, the PMI scope and the test pack. A 316 stainless steel valve with 304 stainless trim will fail in coastal seawater service within months; a CF8M body with CF8M trim and a 17-4PH stem will give 20 years of service.

6. The Bolted Joint — Why a Valve Never Ships Alone

An industrial valve never reaches a project site by itself. The valve body is bolted between two pipe flanges, sealed with a gasket, and held together by a set of stud bolts and two heavy hex nuts. A complete joint on a 6-inch 300# line is therefore four line items — one valve, two flanges, one gasket, one set of bolts — and any one of them being wrong means the joint does not make pressure.

EZ Steel Industrial ships valves together with:

• Steel flanges per ASME B16.5, B16.47, EN 1092-1, GOST or JIS — RF, FF, RTJ facing matched to the valve's raised-face or ring-joint groove
• Gaskets per ASME B16.21 (spiral-wound, ring-joint, compressed non-asbestos, graphite) matched to the service fluid, pressure and temperature
• Stud bolts and heavy hex nuts per ASME B16.5, ASTM A193 B7 / B16, ASTM A194 2H / 7 — matched to the flange class and the corrosion service

Bundling the joint under one PO, one MTC pack and one shipment line removes the most common RFQ error — flanges arriving with 150# drilling and valves drilled for 300# — and removes the second most common error — stud bolts rated for the wrong temperature class. The savings on documentation time and on field rework typically pay for the bundling premium on the first heat-exchanger alone.

7. Buyer's RFQ Checklist for an Industrial Valve Order

8. How EZ Steel Industrial Bundles a Valve Order

EZ Steel Industrial, founded 1994 and based in Changsha, China, ships industrial valves as part of a full bundled piping scope. The same project team that issues the MTC for the carbon steel pipe also issues the MTC for the matching flanges, the matching gaskets, the matching stud bolts and the matching valve — so the inspector signs one document pack, the warehouse receives one container, and the field erector opens one crate per line.

The manufacturing base covers carbon steel (ASTM A216 WCB), low-temperature carbon steel (ASTM A352 LCC), stainless steel (ASTM A351 CF8 / CF8M / CF3M), alloy steel (ASTM A217 WC6 / WC9 / C5 / C12) and duplex / super-duplex (ASTM A890 CD3MN / CE8MN), with full ISO 9001 lab testing and optional third-party witness from SGS, BV, DNV, TUV or LR. The annual capacity is 480,000+ tonnes across pipes, fittings, flanges, gaskets, stud bolts and valves, and the export team works to one weekly production-and-shipment plan per project, so the on-site delivery sequence matches the erection sequence.