At this size the PN16 and PN25 connection dimensions happen to be the same; they still do not match Class 150 (bolt circle 125 mm versus 120.7 mm, metric versus inch bolting, different outside diameters). At other sizes, PN16 and PN25 also diverge from each other. Do not assume a “near miss” can be pulled up with a spanner.
Raised-face serration
ASME B16.5 specifies a serrated finish on the standard raised face, produced as concentric or phonographic (spiral) grooves, with a typical roughness of Ra 3.2 to 6.3 µm (125 to 250 µin). That finish is what the gasket is designed to bite into. A scratch that cuts across the serration, a dent, or a face that has been heavily polished smooth is a functional defect, not a cosmetic one. In the sample report a scratch across the inlet raised-face serration was classified as Major.
EN 1092-1 uses its own facing types (for example Type B raised face) and its own surface-finish requirements. Specify the facing standard that matches the gasket and the companion flange — do not assume the ASME finish and an EN facing are equivalent without checking.
Face-to-face: ASME B16.10 versus EN 558
ASME B16.10 gives face-to-face and end-to-end dimensions for valves in the ASME class system. EN 558 gives face-to-face and centre-to-face dimensions for metal valves in numbered series (the series reflect historical DIN, ISO, BS and ANSI lengths).
Some EN 558 series were chosen so that, for a given valve type and rating, the length matches a historical ASME B16.10 dimension. That does not make the documents interchangeable. Name one system on the approved drawing. In the sample report, a Class 150 NPS 2 flanged gate valve is shown with a 178 mm face-to-face, which is the published ASME B16.10 length for that type and class (7 in).
Design specifications: API 600, ASME B16.34 and EN 1984
Flange dimensions and face-to-face lengths are not the design standard for the valve itself:
- API 600 is the widely specified product standard for bolted-bonnet steel gate valves with flanged or butt-welding ends (the valve in the sample report).
- ASME B16.34 sets pressure–temperature ratings, wall thickness and other design rules for flanged, threaded and welding-end valves, and is often specified alongside the product standard.
- EN 1984 is the European product standard for steel gate valves, typically combined with EN 1092-1 flanges, EN 558 face-to-face and EN 12266-1 testing.
A PO that says “API 600, EN 1092-1 PN16 flanges” is asking for a mix and needs an explicit, approved arrangement. The cleaner approach is to keep the design, flange, face-to-face and test standards in the same family, unless a documented exception has been agreed.
What to write into the purchase order
- Flange standard and rating (ASME B16.5 Class …, or EN 1092-1 PN … and facing type) — not “Class 150 / PN16” as if they were the same.
- Face-to-face standard (ASME B16.10 or a stated EN 558 series).
- Design / product standard (API 600, ASME B16.34, EN 1984, or another named standard) and the test standard (see API 598 vs EN 12266-1 vs ISO 5208).
- That flange faces are protected until installation, and that a damaged serration is a rejectable defect.
Sources
- ASME B16.5, Pipe Flanges and Flanged Fittings — asme.org
- ASME B16.10, Face-to-Face and End-to-End Dimensions of Valves — asme.org
- ASME B16.34, Valves — Flanged, Threaded, and Welding End — asme.org
- EN 1092-1, Flanges and their joints — Circular flanges for pipes, valves, fittings and accessories, PN designated — Part 1: Steel flanges
- EN 558, Industrial valves — Face-to-face and centre-to-face dimensions of metal valves with flanged, socket-welded or threaded ends
- API 600, Steel Gate Valves — Flanged and Butt-welding Ends, Bolted Bonnets — API publications store
- EN 1984, Industrial valves — Steel gate valves
- Our sample valve PSI report (fictitious data), Sections 2, 6 and 7.
We report facts from the samples inspected. Standards named in these guides are public standards we work to, not certifications or accreditations we hold. We do not issue product certificates or accreditation marks. Test pressures, durations, leakage rates and acceptance numbers must be read from the licensed edition named in your purchase order; we do not reproduce copyrighted tables from the standards.
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