ASME B16.34: Valves: Flanged, Threaded, and Welding End (Standard Explained)

ASME B16.34 is the American Society of Mechanical Engineers standard titled "Valves, Flanged, Threaded, and Welding End." It sets the pressure-temperature ratings, dimensions, materials, non-destructive examination, marking and testing requirements for cast, forged and fabricated industrial valves in NPS ¼ and larger. Every conforming manufacturer rates a given body material and class the same way. That's what makes B16.34 useful: a specifier can compare valves on a like-for-like pressure boundary instead of taking a vendor's word for it.

People often confuse this standard with its neighbors, so it's worth stating the scope plainly. ASME B16.34 sets the rules for valve ratings, wall thickness and marking. That's a different document from ASME B16.5, which covers pipe flanges, from ASME B16.10, which handles valve face-to-face dimensions, and from API 6D, which addresses pipeline valves. Each one owns a different part of the problem.

Small-bore instrumentation shut-off valves usually fall below the standard's formal NPS scope. Crestflo still applies B16.34's pressure-temperature and wall-thickness principles to its double block and bleed valves and to larger-bore instrument valves.

Also known as: ANSI/ASME B16.34, B16.34 and the valve ratings standard

Buyers and project specifications reference this standard in several forms. It's written as ANSI/ASME B16.34 (an American National Standard), shortened to B16.34, B16-34 or "ASME B16 34," and described in prose as the valve standard for flanged, threaded and welding-end valves, or simply the valve pressure-temperature rating standard. The current edition is designated ASME B16.34-2025, superseding the -2020, -2017 and -2013 editions.

What ASME B16.34 covers (scope and end connections)

ASME B16.34 doesn't care what a valve does. Gate, globe, check, ball, plug, butterfly, whatever the industrial valve body happens to be, it's in scope so long as it uses one of the covered end types. Those ends are flanged, threaded (NPT), butt-welding (BW) and socket-welding (SW), and they apply to bodies of NPS ¼ and larger. Inside that boundary, the standard spells out pressure-temperature ratings, minimum body wall thickness, which body and bonnet materials are acceptable, marking requirements, and the shell/seat pressure-test and examination regime.

What it leaves out matters just as much. Face-to-face and end-to-end laying dimensions aren't its job; ASME B16.10 handles those. Flange dimensions aren't either. That's ASME B16.5 territory.

Current edition and revision history

ASME B16.34-2025 is the current edition, with B16.34-2020, -2017, and -2013 as the recent prior ones. These editions aren't interchangeable in a contractual sense. Always design and procure to the specific edition your project specification or piping class invokes, because ratings tables and examination requirements can change between revisions. Crestflo builds to whichever edition is named on the purchase order.

ASME B16.34 pressure-temperature ratings

A valve's rating under B16.34 isn't a single number. It's a curve. For each material group, the standard publishes a pressure-temperature (P-T) rating table: the maximum allowable working pressure drops as metal temperature climbs, since the material's allowable stress derates with heat. Cold working pressure (CWP) is the rating at ambient temperature. For temperatures that fall between tabulated points, ratings come from linear interpolation. So a valve carries both a class and a material group, and together those two fix its allowable pressure at any service temperature. Exact P-T cell values are published in the current licensed edition and reproduced per that edition. They're "customizable to requirement" only in the sense that you pick the class, group and alloy suited to your duty. For the underlying concept, see Crestflo's guide to pressure-temperature derating.

ASME B16.34 pressure classes (150 to 4500)

B16.34 organizes ratings into standard pressure classes. The tabulated classes are:

"Class 800" isn't a B16.34 flanged class. It's a compact-valve rating defined by API 602 for gate, globe and check valves. If a specification calls for Class 800, it's pointing at the API 602 family (or a bolted-bonnet compact-valve family), not a B16.34 flanged class. Crestflo sets values per the applicable standard, and these can be customized to requirement.

Standard Class, Special Class and Limited Class

For a given material and pressure class, B16.34 lays out three rating tiers.

The technical difference specifiers care about most is Standard vs Special Class: Special Class earns higher allowable ratings, but only because the body castings and forgings pass mandatory supplementary NDE that Standard Class skips. Want the higher rating? Then you accept the extra examination.

ASME B16.34 material groups and referenced ASTM specs

B16.34 sorts acceptable body, bonnet and closure materials into numbered material groups, each tied to specific ASTM product specifications. In broad families, Group 1.x covers carbon and low-alloy steels, Group 2.x covers austenitic stainless steels, and Group 3.x covers nickel alloys, and each group carries its own P-T rating table. The table below maps the alloys Crestflo works in to the ASTM specs B16.34 references and to their on-site material pages. Confirm the exact group number for your specified alloy and edition on the RFQ.

ASME B16.34 body wall thickness

B16.34 sets a minimum body wall thickness for the pressure boundary, and this depends on NPS and pressure class. The standard tabulates the values, backed by an underlying formula. The point of the requirement is simple: it guarantees the shell can hold the rated pressure with margin. A valve can't claim a class its wall thickness won't support. You read the exact minimum-wall values from the applicable edition's table for the specified size and class. Those values can only be adjusted through class and material selection. Reducing wall thickness below the tabulated minimum isn't an option.

Marking, testing and examination

Conforming valves carry marking per B16.34 and MSS SP-25, manufacturer, class, material designation, NPS and, where applicable, ring-joint number. Every valve is subject to a hydrostatic shell (body) pressure test and a closure (seat) test; Special Class additionally requires supplementary NDE (radiographic, ultrasonic, magnetic-particle or liquid-penetrant examination) on the pressure-boundary castings or forgings. Inspection and test procedures are frequently executed to API 598, the companion valve inspection-and-test standard. Crestflo runs 100% seat and shell leak testing on its manifolds and valves, with in-house NDT and PMI, and third-party inspection on request.

How ASME B16.34 relates to other valve standards

B16.34 sits at the center of a whole web of ratings that other codes and standards lean on. Below, we stack it up against the standards specifiers most often encounter alongside it.

Construction standards built on top of these ratings work the same way. API 600 covers bolted-bonnet steel gate valves and API 623 covers steel globe valves; each spells out its own body-design and trim rules but defers to ASME B16.34 for pressure-temperature ratings. So a valve built to API 600 or API 623 still carries a B16.34 class and material group.

Which Crestflo valves conform to ASME B16.34

Crestflo makes instrumentation valves and flow-control components, and its valve line qualifies to the applicable valve standards, ASME B16.34 and the relevant API valve standards, rather than to fitting standards. The double block and bleed valves are built per ASME B16.34, with flanged and screwed ends and a working pressure up to 3,000 psi. Small-bore instrumentation shut-offs (1/16″–1″) often fall below the standard's formal NPS scope. Because of that, Crestflo applies ASME B16.34's pressure-temperature and wall-thickness design principles to them anyway, and documents the material basis the standard requires.

Crestflo supplies sour-service materials, including 316/316L, 6Mo, duplex, super-duplex and high-nickel alloys, compliant with NACE MR0175 / ISO 15156 and PED, where specified. Every part gets a heat/lot number stamped on it and ships with an EN 10204 MTC 3.1 (3.2 available on request); for details, see material traceability. Origin is Indian, though that's not the only option: US and European melt can be arranged on request, with full material traceability maintained throughout; see origin & compliance.

Why Crestflo for ASME B16.34 valves

Crestflo runs the instrumentation side of an export house that's been around for four decades, carries Government-of-India recognition, and has a delivery record across the Middle East. That heritage in critical-service supply now backs a valve program serving US customers. Here's the offer: ready stock on standard items, made-to-order on specials, and 6–8 week delivery. The company holds ISO 9001, 14001, 45001 and PED certification. Every seat and shell gets 100% leak testing, backed by in-house NDT and PMI. Heat-number traceability runs on every single part, and private-label plus made-to-print work is available too. Class, rating-tier and material-group structure are published in full, so engineers can check conformance before a print ever gets sent. We Engineer Confidence.

Request a quote for B16.34-class valves, request a sample, or grab the distributor line card from Crestflo.

Frequently asked questions about ASME B16.34

Related standards and resources

• Standards library, every governing spec mapped to conforming alloys and products
• API 6D, API 602, API 598, related valve standards
• ASME B31.3 · ASME B16.11 · NACE MR0175
• Double block & bleed valve · monoflange valve
• DBB vs monoflange · pressure-temperature derating

Reviewed by the Crestflo Engineering Team