ASME B16.47 · Standard reference
ASME B16.47-2025 marking requirements (Section 4)
Section 4 of ASME B16.47-2025 defines the identification markings that must appear on every large-diameter flange covered by the standard. The baseline is MSS SP-25, with paragraph 4.2 adding the B16.47-specific content: manufacturer identity, material specification and grade, pressure class, size, conformance to B16.47, and — for ring-joint flanges — the R groove number.
Marking is the buyer's traceability link between the flange, the material certificate and the pressure rating. The class number marked on the flange selects the pressure–temperature table, the material marking selects the material group, and the size marking is the NPS designation, not the bore. The standard does not prescribe a layout or a marking method; it lists what must appear.
- Clause
- Section 4, pp. 3-4
- Baseline
- MSS SP-25 (para. 4.1)
- Class mark
- 75, 150, 300, 400, 600 or 900
- Conformance mark
- B16 or B16.47
- Size mark
- NPS number
- Ring-joint
- R + ring-groove number
Required identification markings
Paragraph 4.2 is written as a list of elements rather than a sample stamp, so several arrangements are acceptable. The table records each element with the requirement that applies to it.
B16.47 · ASME B16.47-2025
| Marking element | Requirement | Clause |
|---|---|---|
| Manufacturer | Manufacturer's name or trademark applied to the flange. | 4.2.1 |
| Material — castings | ASTM specification, grade identification symbol, and the melt number or melt identification. | 4.2.2(a) |
| Material — forgings and plate | ASTM specification number and grade identification symbol. | 4.2.2(b) |
| Trade designation (optional) | The manufacturer may add a trade name for the grade, provided the symbols cannot be confused. | 4.2.2(c) |
| Pressure class | The class number: 75, 150, 300, 400, 600 or 900. | 4.2.3 |
| Standard conformance | The designation B16 or B16.47, preferably adjacent to the class designation. The prefix 'ASME' is optional. | 4.2.4 |
| Size | The NPS identification number. | 4.2.6 |
| Ring-joint flange | The letter R and the corresponding ring-groove number on the edge (periphery) of the flange. | 4.2.7 |
| Temperature (optional) | Not required; if marked, the temperature must be shown with its corresponding tabulated pressure rating. | 4.2.5 |
| Multiple material grades (optional) | If the material meets more than one specification or grade, more than one may be marked, following ASME BPVC Section II, Part D, Appendix 7. | 4.2.8 |
| Case number | When the flange meets an ASME Case, the marking includes 'Case ##'. | 4.2.9 |
The standard does not fix the order or the layout of these marks; the column on the right gives the paragraph for each requirement.
What is not required — and the exception to watch
- Temperature marking is not required. If a temperature is stamped, it must be paired with the tabulated pressure rating for that material at that temperature, so the mark cannot be misread as a separate rating.
- The 'ASME' prefix before B16 or B16.47 is optional; the conformance designation itself is what matters.
- Multiple-grade marking is at the manufacturer's option, not an obligation. The pressure rating of any of the marked grades may then be used, provided the marking follows the BPVC guidance.
- A heat number or melt number is mandatory on cast flanges but not on forged or plate flanges, where the minimum is the ASTM specification number plus the grade symbol. In practice heat identity is carried on the inspection certificate and is frequently added to the flange by agreement.
- The general marking practice comes from MSS SP-25, to which Section 4 is the B16.47-specific addition. An ASME Boiler and Pressure Vessel Code, Section II specification number may replace an ASTM number where its requirements are identical or more stringent.
An illustrative marking string
Because B16.47 does not publish a sample stamp, the order of the characters is a manufacturer choice. A forged Series A flange could read 'ACME 26 B16.47 300 A105' — manufacturer, NPS 26, standard conformance, Class 300, A105 forging. A cast flange must add the melt number, for example 'ACME 30 B16.47 150 A216 Gr. WCB M4471'. A ring-joint flange adds the letter R and its groove number. These strings are illustrative only; check that every element required by para. 4.2 appears on the actual flange and matches its certificate.
ASME B16.47 marking — questions
Is a heat number required on a forged B16.47 flange?
Not by Section 4.2. Forged and plate flanges must show the ASTM specification number and grade identification symbol, while cast flanges must also show the melt number or melt identification. A heat number on a forging is a traceability improvement, usually tied to the inspection certificate, rather than a minimum marking requirement of the standard.
Does the flange have to say 'ASME B16.47'?
It must carry the conformance designation B16 or B16.47, preferably next to the class mark. The 'ASME' prefix is optional, so 'B16.47' or 'B16' alone is sufficient. The class number must also be present because that is what selects the pressure–temperature table.
Is a temperature stamp required?
No. Temperature marking is not required on B16.47 flanges. If a temperature is marked, the corresponding tabulated pressure rating for the material must be shown with it, so the pair cannot be separated or misread.
What is the R marking on a ring-joint flange?
The edge or periphery of every ring-joint flange must be marked with the letter R followed by the ring-groove number that identifies the groove size. The groove dimensions themselves are in Table 30 (Table 30C); the R marking lets the groove be identified without measuring it.