Standards · ASME and ASTM · ASME B16.5

ASME B16.5: Pipe flanges and flanged fittings NPS 1/2 through NPS 24

Pressure-temperature ratings, materials, dimensions, tolerances, marking and testing of steel pipe flanges and flanged fittings in the Class system – the US counterpart of the PN flange world.

Issued by: ASME
Edition (publisher, as of 2 October 2026): 2025
Dimension standard: Pipe flanges and flanged fittings NPS 1/2 through NPS 24
European counterpart: EN 1092-1 (PN) / EN 1759-1 (Class)
Belongs with: ASTM A105/A105M · ASTM A182/A182M · ASTM A350/A350M · ASME B16.47 · ASME B16.25
At Zickwolff: we carry – from stock or to order, lead time on request

Scope: sizes, classes, grades

NPS 1/2 to 24 in Classes 150, 300, 400, 600, 900 and 1500, Class 2500 up to NPS 12. Flange types weld neck, slip-on, threaded, lap joint, socket weld and blind, facings RF (standard), FF, RTJ, tongue-and-groove, male-and-female. Above NPS 24 see B16.47.

Product form

Forgings and castings, blind flanges also from plate. Material by ASTM specification (A105, A350, A182 ...) – the flange standard names the material groups, the material standard the steel.

The European counterpart – and the limits of the comparison

EN 1092-1 (PN designated steel flanges) is the European counterpart in function, EN 1759-1 the European standard for flanges with Class designation.

Class and PN are not convertible: a Class is a dimensionless rating that depends on material group and temperature, PN a nominal pressure at 20 °C. Outside diameters, bolt circles, bolt counts and bolt sizes (inch) differ – a Class 150 flange does not bolt to a PN 16 flange of the same DN. Materials of ASME flanges carry no presumption of conformity under the PED.

“To ASME” means three different things Dimensions to an ASME standard with a European material, dimensions plus an ASTM material, or a whole line designed to ASME B31. Under the Pressure Equipment Directive and the operating law these are not the same case – and the stamp on the part says nothing about the later inspection regime.

ASME B16.47: Large diameter steel flanges NPS 26 through NPS 60

Continues B16.5 above NPS 24: ratings, materials, dimensions, tolerances, marking and testing of large steel flanges in two series.

NPS 26 to 60, Classes 75 (Series B only), 150, 300, 400, 600 and 900. Series A (formerly MSS SP-44): heavier, fewer and larger bolts, RTJ available. Series B (formerly API 605): compact, more and smaller bolts. The two series are not interchangeable – the series must be stated in every order.

As for B16.5, plus the series: same NPS and Class in Series A and B give different outside diameters, bolt circles, bolt counts and weights.

Large flanges to B16.47 we procure to order – please state series, Class, NPS, type, facing and material.

Marking on the part

Usual marking: manufacturer, NPS, Class, material specification and grade (e.g. A105 or SA-105), heat code, the mark B16 or B16.5, RTJ flanges with R and groove number.

The standard family: dimensions, material, pipe

ASTM A105/A105M · ASTM A182/A182M · ASTM A350/A350M · ASME B16.47 · ASME B16.25

At Zickwolff

Flanges to B16.5 in A105, A182 and A350 are part of our range – weld neck, slip-on, blind and threaded in the common Classes, from stock or to order, with inspection certificate 3.1 to EN 10204. Tell us NPS, Class, type, facing and material.

Dimensions Dimension tables for this standard are on our page flange dimensions ASME B16.5. For the weld neck flange there is also a dimensional drawing with tolerances for each class and NPS: weld neck flange ASME B16.5.

Frequently asked questions about ASME B16.5

What does "to ASME" mean on a part?

Three different things: dimensions to an ASME standard (B16.5, B16.9) with a European material (P265GH), dimensions plus an ASTM material (A105, A234 WPB), or a complete line designed to ASME B31.1/B31.3. Under the PED and the Betriebssicherheitsverordnung these are not the same – the stamp B16.9 says nothing about the later inspection regime.

Does a Class 150 flange fit a PN 16 flange?

Usually not: outside diameter, bolt circle and bolt holes differ, and the Class is no nominal pressure. Only a few sizes happen to share a bolt pattern – check the dimension tables, never the name.

Is Class 150 the same as 150 psi?

No. The Class is a dimensionless rating – the permissible pressure depends on material group and temperature – an A105 flange of Class 150 is rated about 20 bar at room temperature and much less when hot. See our rule of thumb "Class 150 is not 150 psi".

Series A or Series B above NPS 24?

Whatever the mating flange has. Series A (ex MSS SP-44) is the heavier, more common one, Series B (ex API 605) the compact one – they are not interchangeable, so the series belongs in every order.

Parts to ASME and ASTM – from one source

Tell us standard, size (NPS and schedule or Class), material grade, certificate and quantity – we check what is in stock, what we procure and which European part would do the same job.

Send an inquiry

Your inquiry to Zickwolff

Send us what you have – designation, standard, quantity, date. We will clarify the rest with you.

One item or a question

Send inquiry

Not in stock? We procure it – single items too.

Designation, standard and quantity are enough.

Several items

Send bill of materials

200 items? One parts list is enough – we deliver complete.

Attach it as a file.

Helpful if already known: project and country, date needed, certificates, packaging and language of the packing lists. If anything is missing, we will ask.

It is urgent

Request express

When do you need it? Express delivery, to the site if required.

Tell us by when you need the material – we will tell you what is possible.

← Back to ASME and ASTM standards

Basis: the publicly accessible scopes and abstracts of ASME and ASTM (editions as of 2 October 2026), manufacturer catalogues, a trade reference catalogue DIN/EN/ASME and specialist sources for marking and impact test values – the legal statements follow Directive 2014/68/EU and the German Betriebssicherheitsverordnung. No standard text was reproduced – the current original edition is binding. Comparisons with EN grades are orientation, not equivalence. Information without guarantee, no legal advice, no prices.