Summary of Changes: what the 2025 edition changed
The headline is that the 2025 edition makes technical changes, not just editorial ones. The pressure–temperature ratings were recalculated after the rating ceilings in Nonmandatory Appendix A changed; the material and bolting specification lists grew; the bore ('B') dimension and the minimum-hub-height rule in the dimension tables were revised; and the threaded-flange figures changed. Around those sit new definitions, new guidance, a new appendix and updated references.
The committee's margin note ([25]) flags every changed location, and each entry carries an ASME record number. The table below regroups the page-by-page entries into the subjects a buyer actually works with, keeping the record numbers so each line can be traced to the List of Changes in Record Number Order (printed p. xix). 'C' tables are the U.S. Customary companions of the SI tables.
| Area | Section / table | What changed | Practical impact |
|---|---|---|---|
| Pressure–temperature ratings | Tables 2‑1.1 to 2‑3.19 (SI) and their C (U.S. Customary) companions | All rating tables revised (records 21‑1888, 22‑564, 23‑2509) | Allowable pressures were re-issued, not just re-typeset. Read 2025 values before reusing a 2020 or 2017 rating on a drawing or datasheet. |
| Pressure–temperature ratings | Nonmandatory Appendix A — Tables A‑1 and A‑2 (rating ceiling pressures) | Ceiling pressures revised (record 22‑2110); tables also revised under 21‑1888 | The ceilings the p/T tables are built on changed. This is the mechanism behind the Foreword's statement that ratings were revised after adopting new ceiling values. |
| Pressure–temperature ratings | Table 2‑2.13 and Table 2‑2.13C (new) | Added for Material Group 2.13, duplex materials (records 21‑1888, 23‑2509) | Duplex stainless flanges now have a dedicated rating table. Check the grade against Group 2.13 rather than an adjacent group. |
| Pressure–temperature ratings | Tables 2‑2.10C and 2‑2.12C | At 1 000 °F, working pressure for Classes 400–2500 revised; Note (2) added (records 21‑1888, 23‑2509) | The 1 000 °F entries in those U.S. Customary tables moved. Hot-service designs that sit close to a limit need re-checking. |
| Pressure–temperature ratings | C rating tables generally — temperature columns and notes | First temperature entry under 'Temp., °F' revised in many C tables; metric temperatures in notes rounded to the nearest degree; notes revised and reordered (records 21‑1888, 22‑564, 23‑2509) | Do not assume the first row or the notes of a C table are identical to the 2020 printing. |
| Materials | Table 1.1‑1 — List of Material Specifications | Revised (records 16‑1229, 21‑1888, 23‑2509) | The master material list changed. Confirm the ASTM specification named on the purchase order is still listed for the intended material group. |
| Materials | Table 1.1‑1 — nickel-alloy Groups 3.1, 3.6 and 3.12 | Specifications for Groups 3.1 (35Ni‑35Fe‑20Cr‑Cb) and 3.12 (46Fe‑24Ni‑21Cr‑6Mo‑Cu‑N) corrected, and a second forging/plate specification added for Group 3.6 (33Ni‑42Fe‑21Cr), all by errata (record 21‑1145) | Some nickel-alloy entries were wrong or incomplete in the previous printing — re-check certificates and material test reports against the 2025 list. |
| Materials | Tables 1.1‑1, 2‑3.7, 2‑3.8 and 2‑3.12 to 2‑3.14, with their C companions | ASTM B462 and ASTM B564 forging specification materials added (record 16‑1229) | Two more nickel-alloy forging specifications are recognised in the material and rating tables, widening the supply options for nickel-alloy flanges. |
| Materials — bolting | Table 1.1‑2 — List of Bolting Specifications | ASTM A320 L7M added under intermediate-strength bolting; ASTM B511 (N08830), B572 (N06230) and B637 (N07740, N07718) added under nickel and special alloy (record 22‑651); notes revised, reordered and clarified (records 21‑1888, 21‑2211, 22‑651) | New bolt grades are now inside the standard, including low-temperature L7M and nickel-alloy grades. Re-read the notes before pairing bolts with a flange material. |
| Materials — bolting | Table 1.1‑2, Notes (6) and (11) | Wording of 'corresponding material' clarified (record 21‑2211) | Removes an ambiguity about which bolt material may be used with which flange material when the bolting is bought separately. |
| Dimensions — hub geometry | Figures 7 and 8; Tables 8, 11, 14, 16, 18, 20 and 22 (and their C companions) | Hub height H and a new Note (1) added to Figures 7 and 8; method for the minimum hub height revised (record 22‑2183) | Hub geometry was re-ruled, not just redrawn. Read hub and length-through-hub values from the 2025 edition rather than a 2020 drawing. |
| Dimensions — bore | Tables 8, 11, 14, 16, 18, 20 and 22 (and their C companions) | The 'B' dimension (the bore shown in the flange figures) revised for slip-on, socket-welding, welding-neck and lapped flanges (record 21‑579) | The inside diameter is a dimensioned value, not a note. Compare the 2025 table with any 2020 or 2017 bore dimension before accepting a part. |
| Dimensions — threaded flanges | Table 8 / 8C (Class 150) and Table 11 / 11C (Class 300) figures | Class 150 threaded figure now shows threads continuing to the flange face; Class 300 threaded figures now include a counterbore (record 23‑628) | Threaded-flange geometry changed — relevant when machining, gauging or inspecting threaded flanges. |
| Dimensions — errata corrections | Table 7 (Class 150 drilling templates) and Table 8 / 8C (Class 150 flanges) | NPS 20 outside diameter O corrected from 693 to 698; NPS 14 outside diameter O corrected from 553 to 533 (records 21‑1134, 21‑1133) | Two outside diameters printed in the 2020 edition were wrong. The 2025 figures (698 mm and 533 mm) are the ones to use. |
| Dimensions — errata corrections | Table 5 and Table 5C (ring-joint groove details) | Class 2500 NPS 2½ groove depth E corrected from 9.522 to 9.53; a dimensionless row under NPS 24 in Table 5C deleted and alignment corrected (records 21‑1372, 22‑1148) | Groove depth affects ring-joint gasket seating — verify the groove against the 2025 table. |
| Figures and editorial | Figures 1, 2 and 12 | General Note (b) revised in Figures 1 and 2 (record 22‑567); U.S. Customary values added to Figure 12 (record 21‑1122) | Clarifications rather than new requirements, but worth a fresh look if drawings or specifications quote those figures. |
| Definitions and wording | Clause 1.11 (new); Clauses 2.2, 5.3.5(a) and 6.1.1 | Definitions of may, shall and should added; 'must' changed to 'shall' and related sentences revised to match (record 22‑2279) | The clauses were reworded to match the new definitions rather than to change a value. Contract or specification wording that quotes the clause may differ. |
| Definitions and guidance | Clauses 2.4, 2.5.3, 5.1.2 and 5.3.4 | Guidance added; the last sentence of Clause 5.3.4 deleted (record 21‑1888) | Part of the same change record that added the General Notes in the rating and material tables and Nonmandatory Appendix G — read them together. |
| Testing | Clauses 2.6 and 8.1 | Requirements for system hydrostatic testing revised (record 21‑1849) | Check hydrostatic test pressures and procedures in inspection and test plans against the new wording. |
| Appendices | Nonmandatory Appendix G — Low Temperature Applications (new) | Added for determining minimum temperature limits for materials (record 21‑1888) | A new nonmandatory method for determining minimum design temperature, with a table of example minimum use temperatures. The appendix is not reproduced here; read it in the current edition. |
| Appendices | Mandatory Appendix II — References | References updated (record 23‑2265) | The reference standards cited by B16.5 moved on; update any reference list in a specification or QA system that tracks them. |
| Editorial | Titles of complementary SI / U.S. Customary table pairs; Clause 7.3 | Titles revised to state the applicable system of units (Summary of Changes introduction, printed p. xiv); Clause 7.3 editorially revised | Easier to tell SI from U.S. Customary tables. No technical effect. |
Grouped summary of the committee's change list, not a verbatim copy. Record numbers are ASME change-record numbers. Values of the revised tables are not reproduced here because the revised rating, material and dimension tables are not reproduced here.