Use ASME B16.47 for large-diameter steel flange RFQs from NPS 26 to NPS 60
ASME B16.47 Series A vs Series B Large-Diameter Flanges
Series A and Series B flanges of the same NPS and Class do not bolt together. At NPS 36 Class 150, Series A has 32 bolts of 1-1/2 in on a 42-3/4 in (1,085.9 mm) bolt circle; Series B has 44 bolts of 7/8 in on a 39-3/4 in (1,009.7 mm) circle. State the series on the RFQ; for a replacement, measure the bolt circle on the mating flange.
Key Points
State Series A or Series B; do not rely on ANSI flange, large flange or Class wording alone
Confirm whether the project follows MSS SP-44 continuity, API 605 replacement history or an owner drawing
Send dimensional report, MTC 3.1, NDT, PMI, bolting and packing requirements before price comparison
Series A and Series B at the same size
Pick a class and a size that both series tabulate to see the two flanges at one scale, with the dimensions that differ.
Pressure class
Flange type
View
Dimension
Turn both
- OOutside diameter
- 1168.4 mm46.00 in
- WBolt circle diameter
- 1085.9 mm42.75 in
- n × ⌀Bolt holes
- 32 × ⌀41.1 mm32 × ⌀1.62 in, 1-1/2 in bolts
- tfFlange thickness
- 88.9 mm3.50 in
- OOutside diameter
- 1057.1 mm41.62 in
- WBolt circle diameter
- 1009.7 mm39.75 in
- n × ⌀Bolt holes
- 44 × ⌀25.4 mm44 × ⌀1.00 in, 7/8 in bolts
- tfFlange thickness
- 50.8 mm2.00 in
Series B against Series A: smaller OD (−111.3 mm), smaller bolt circle (−76.2 mm), more, smaller bolts (44 × ⌀25.4 mm against 32 × ⌀41.1 mm), thinner flange (−38.1 mm).
O is the outside diameter, W the bolt circle diameter, n × ⌀ the number and diameter of the bolt holes and tf the flange thickness without the raised face. The models and drawings write a diameter with ⌀, the bolt circle with BC and equally spaced holes with EQ SP, with the table letter in brackets after the value; dimensions in mm. Both flanges are drawn at one scale. Drag a model to turn both, or use Front, Side and 3/4; on a phone, swipe sideways.
3D models drawn from the ASME B16.47 tables on our dimension finder. These are models, not photographs.
Engineering Selection Notes
Large-diameter flanges are expensive to remake, difficult to ship and highly sensitive to matching details at the bolted joint. In ASME B16.47 work, the buyer is not only selecting a pressure class; the buyer is selecting a dimensional family. Series A and Series B can both be valid B16.47 routes, but each has its own tables for outside diameter, thickness, bolt circle and hole count, so a flange ordered to one series is not assumed to mate with the other.
The standard keeps two dimensional families. Series A carries the former MSS SP-44 flanges and Series B the former API 605 flanges, as its foreword records, and each has its own dimension tables: Series A for Class 150 to 900, Series B for Class 75 to 900, with Class 75 tabulated only for Series B. Outside diameter, thickness, bolt circle and bolting are read from the table of the series named on the line, so the series is chosen by what the flange must mate with - the owner's piping specification for new work, the existing flange for a replacement - and not by price.
For procurement, the safest rule is to quote from the project specification or from measured existing dimensions, not from a short material list. A request such as 30 inch Class 300 flange A105 RF is incomplete for B16.47 because it omits the series, flange type, facing details, bore or schedule, material condition, inspection basis and whether the mating equipment is already Series A or Series B. Those missing fields create avoidable requotes and, worse, non-mating parts at site.
Source Basis
- ASME B16.47 2025 large-diameter flange scope - Used for B16.47 scope statements: NPS 26 through NPS 60, Class 75 through 900, pressure-temperature ratings, materials, dimensions, tolerances, marking and testing; flanges of cast or forged material and blind flanges of cast, forged or plate material; and the origin of the two series that the standard's foreword records - Series A from the MSS SP-44 flanges, Series B from the API 605 flanges.
- ASME B16.5 2025 scope - Used for the B16.5 boundary at NPS 1/2 through NPS 24 and the Class 2500 through NPS 12 note.
- ANSI note on ANSI/MSS SP-44-2026 - Used for current MSS SP-44 pipeline flange scope, NPS 12 through NPS 60, Class 150 through 900 and forged-steel / plate blind-flange notes.
- ASME B16.47-2020 front matter and contents (ASME) - Used for how the standard is laid out: separate dimension tables for Series A (Class 150 to 900) and Series B (Class 75 to 900), Class 75 tabulated for Series B only, a ring-joint facing table of its own and welding-end figures for welding neck flanges.
- ASME PCC-1 2022 bolted flange joint assembly scope - Used for bolted flange joint assembly and leak-tightness context when large flanges include gasket, bolting and assembly procedures.
- ISO 9712:2021 NDT personnel scope - Used for NDT method and personnel-qualification context for UT, MT, PT, RT, VT and related industrial NDT requirements.
- EN 10204:2004 Metallic products - Types of inspection documents (BSI) - The standard that defines the inspection documents, including the 3.1 inspection certificate based on specific inspection; used for the EN 10204 3.1 wording in the document checklist.
- Our MTC 3.1 guide, on a real BLD 3.1 certificate - Used for what a 3.1 certificate carries: the test results of the delivered heat, validated by our authorised inspection representative, independent of production.
ASME B16.47 Scope and Adjacent Standard Check
| Route | Verified public scope used in this guide | RFQ implication | Procurement warning |
|---|---|---|---|
| ASME B16.5 | Pipe flanges and flanged fittings NPS 1/2 through NPS 24; Class 150, 300, 400, 600, 900 and 1500 through NPS 24; Class 2500 through NPS 12 | Use B16.5 for normal ASME flange RFQs up to NPS 24, then move to B16.47 or project drawing review above that range | Do not price NPS 26 and larger from a B16.5 table extension |
| ASME B16.47 | Large-diameter steel flanges NPS 26 through NPS 60 with Class 75, 150, 300, 400, 600 and 900; includes pressure-temperature ratings, materials, dimensions, tolerances, marking and testing | State ASME B16.47 plus Series A or Series B, flange type, Class, facing, material and document scope | Do not write only ANSI flange or large flange; the series controls mating dimensions |
| ANSI/MSS SP-44-2026 | Steel pipeline flanges NPS 12 through NPS 60 with Class 150, 300, 400, 600 and 900; welding neck flanges are forged steel, while blind flanges can be forged steel or steel plate | Use when the pipeline specification calls MSS SP-44 or the project needs MSS continuity; confirm whether B16.47 Series A wording is accepted | Do not assume every B16.47 RFQ can be converted to MSS SP-44 certificate wording without buyer approval |
| Owner drawing / non-standard large flange | ASME's published scope covers flanges of cast or forged material and blind flanges of cast, forged or plate material; the standard's welding-end figures are drawn for welding neck flanges | For slip-on, custom nozzle, vessel, modified bore or non-standard drilling above NPS 24, attach the drawing and revision | Do not force a custom large flange into B16.47 only because the size is above NPS 24 |
Series A vs Series B Buyer Comparison
| Decision point | Series A | Series B | RFQ action |
|---|---|---|---|
| Origin | The former MSS SP-44 flanges, as the B16.47 foreword records | The former API 605 flanges, as the B16.47 foreword records | State the series exactly; convert legacy MSS SP-44 or API 605 wording only when the project permits it |
| Classes tabulated | Class 150, 300, 400, 600 and 900 | Class 75, 150, 300, 400, 600 and 900; Class 75 exists only in Series B | A Class 75 line is a Series B line; for every other class, name the series |
| Dimensions and drilling | Outside diameter, thickness, bolt circle, bolt count and bolt size from the Series A table of the class | The same items from the Series B table of the class; never read across from Series A | Ask for the dimension report against the exact series, not just NPS and Class |
| Facing | RF, FF or RTJ as ordered; ring-joint dimensions come from the standard's ring-joint facing table | RF, FF or RTJ as ordered; ring-joint dimensions come from the standard's ring-joint facing table | State the face and ring number before quotation, and confirm that the ring-joint table covers your series, size and class |
| Choosing the series | Owner specifications or existing flanges that call for Series A, including lines specified to MSS SP-44 | Owner specifications or existing flanges that call for Series B, including replacements on lines built to API 605 | For brownfield replacement, measure existing OD, bolt circle, hole count and hole diameter before ordering |
B16.47 RFQ Field Checklist
| RFQ field | Minimum data to send | Why it matters | Evidence to request |
|---|---|---|---|
| Size and rating | NPS 26 to NPS 60 plus Class 75, 150, 300, 400, 600 or 900 | Sets the B16.47 table family and pressure-temperature check basis | Quotation line item and dimensional report |
| Series | Series A or Series B, or exact legacy MSS SP-44 / API 605 requirement | Controls OD, bolt circle, bolting and mating compatibility | Series-stated drawing or supplier dimension sheet |
| Flange type | Weld neck, blind or drawing-controlled special flange | B16.47 core supply is not a blanket route for every large flange shape | Drawing revision, flange type and machining scope |
| Facing and gasket | RF, FF, RTJ, ring number, surface finish and gasket note where specified | Changes machining, inspection and bolted-joint compatibility | Face / groove dimensional report and gasket or ring reference |
| Material and product form | ASTM / ASME grade, forged / cast / plate allowance for blinds, heat treatment and impact note | Controls MTC, forging route, plate acceptance and service-temperature review | MTC 3.1, heat treatment record and impact / hardness results where required |
| Inspection and handover | Dimensional report, PMI, UT, MT, PT, third-party inspection, packing and marking language | Late inspection additions change lead time and make offers non-comparable | ITP, NDT reports, marking photos and export packing list |
Inspection and Document Controls for Large-Diameter Flanges
| Control | Large-diameter reason | What to check | RFQ note |
|---|---|---|---|
| Dimensional report | A small error in bolt circle, hole count, thickness or face detail can prevent field fit-up | OD, bolt circle, hole count, hole diameter, thickness, bore / schedule, face and RTJ groove where applicable | Require dimensions against ASME B16.47 Series A or Series B, not only against B16.47 |
| MTC 3.1 | Large forged or blind flanges need traceable material evidence before shipment release | Heat number, material grade, chemistry, mechanical test results, heat treatment and authorized inspection signature | State EN 10204 3.1 or project certificate wording in the first RFQ |
| NDT | Heavy forgings, high-pressure flanges, RTJ grooves and project-critical joints often require documented checks | UT, MT, PT, RT, VT or project methods with qualified personnel and acceptance criteria | Specify method, procedure, level, report language and witness hold point early |
| Bolting and gasket review | Large joints are sensitive to gasket seating, bolt loading and assembly practice | Bolt grade, washer / nut scope, gasket type, RTJ ring number and any ASME PCC-1 assembly expectation | Separate flange supply from bolt / gasket / assembly scope so price and responsibility are clear |
| Marking and export packing | Large flanges are often shipped in mixed batches and may be handled at several ports or laydown yards | Size, Class, Series, material, heat number, item number, face, packing mark and document language | Match marking, MTC, dimensional report and packing list line by line |
Practical Checklist
- Governing route: ASME B16.47-2025, MSS SP-44-2026, legacy API 605 wording or owner drawing
- Size and class: NPS 26 to NPS 60 plus Class 75, 150, 300, 400, 600 or 900
- Series: Series A or Series B, confirmed against mating equipment or existing flange measurements
- Flange type: weld neck, blind or drawing-controlled special flange; attach drawing for non-standard large flanges
- Facing: RF, FF, RTJ or drawing-controlled face, including ring groove / ring number / surface finish notes
- Material: exact ASTM / ASME or project grade, heat treatment condition, impact temperature and substitution policy
- Inspection: MTC 3.1, dimensional report, PMI, UT, MT, PT, hardness, third-party witness or ITP requirement
- Logistics: quantity, weight handling constraints, packing, marking language, destination and required delivery window
Common RFQ Mistakes
- Ordering a large ASME flange by NPS and Class without saying Series A or Series B
- Assuming Series A and Series B bolt together because both are ASME B16.47
- Using MSS SP-44 or API 605 legacy wording without confirming the accepted B16.47 series in the current project specification
- Adding RTJ facing after quotation even though the selected series and class must support the ring groove requirement
- Requesting a large slip-on or special nozzle flange as B16.47 without attaching a drawing and owner approval basis
- For brownfield replacement, trusting worn flange markings instead of measuring OD, bolt circle, hole count and hole diameter
- Comparing a forged blind quote with a plate blind quote when the project has not approved plate material
- Leaving NDT, PMI, dimensional report, MTC 3.1 or third-party hold points until the pre-shipment stage
FAQ
Is ASME B16.47 the same as ASME B16.5?
No. ASME B16.5 covers pipe flanges and flanged fittings through NPS 24, while ASME B16.47 covers large-diameter steel flanges from NPS 26 through NPS 60. The RFQ should use the correct standard boundary.
Are B16.47 Series A and Series B interchangeable?
No. The two series share 54 size and class combinations, and the bolt circle is different in every one of them. Bolt count alone does not identify the series: in 18 of the 54 the count is the same, and at NPS 30 Class 900 both series use 20 bolts of 3 in, on a 42-3/4 in (1,085.9 mm) circle in Series A and a 40-3/4 in (1,035.1 mm) circle in Series B. Take the series from the project specification, or measure the existing flange.
Is Class 75 available in both B16.47 series?
No. ASME B16.47 tabulates Class 75 only for Series B; Series A starts at Class 150, and both series go up to Class 900.
What should a B16.47 RFQ include?
Include NPS, Class, Series A or B, flange type, facing, material grade, bore or schedule, quantity, MTC 3.1, dimensional report, NDT or PMI requirements, packing and destination.
Which ASME B16.47 flanges do you make?
We supply ASME B16.47 Series A and Series B flanges across NPS 26 to NPS 60, in the classes and sizes the standard tabulates for each series. Our D51 mill rolls rings up to 1,500 mm OD and 240 mm thick; larger rings are forged by partner forges near our plant in Dingxiang. Send the series, class, flange type and facing with the RFQ.
Author & Verification
Written by: Tom Fan, Sales Director, BLD Forge Direct (Shanxi Baolongda Forging Co., Ltd.)
Reviewed by: Fu Guangming, Senior Engineer (Heat Treatment)
Last verified: 2026-10-28
Revision log
- 2026-10-28 - Opened with the answer and an NPS 36 Class 150 example from the B16.47 tables; the interchangeability answer counts the 54 size and class combinations both series share; the supply answer states the rings we roll and those forged by partner forges.
- 2026-10-14 - Added the Series A and Series B figure: both flanges side by side, in 3D and as drawings, for any size and class the two series share.
PDF Datasheets for RFQ Review
ASME B16.5 Flanges RFQ Datasheet
Use this PDF for ASME flange RFQs where NPS, Class, facing, material and inspection scope need to be aligned before quotation.
High Pressure Flanges RFQ Datasheet
Use this PDF when Class 600, 900, 1500, 2500 or RTJ / NDT requirements must be reviewed with the B16.47 article.
Send your RFQ or drawing directly to BLD Forge Direct.
Email quote@bldforgedirect.com with standard, drawing, material, quantity and inspection requirements.