ASME B16.5 is the standard published by ASME (American Society of Mechanical Engineers) covering pipe flanges and flanged fittings for pressure piping systems. It defines dimensions, materials, pressure-temperature ratings, bolt patterns, and facing types for flanges from NPS 1/2 to NPS 24 across seven pressure classes (150, 300, 400, 600, 900, 1500, 2500).
The current edition is ASME B16.5-2025, approved by ANSI on April 10, 2025 and mandatory from January 1, 2026. A 6-month transition period (until June 30, 2026) applies to projects already in progress per Appendix L. The 2025 edition adds new materials (Titanium Gr.2 & 5), tightens sealing tolerances, mandates 100% UT/MT for Class 900-2500 flanges, requires full material traceability, and introduces dedicated provisions for hydrogen, CCS, and marine applications.
Zhengzhou Huitong (HT Pipe) manufactures and supplies ASME B16.5-2025 compliant flanges in carbon steel (A105/WCB), stainless steel (F304/F316L), alloy steel (F5/F9/F22), and Titanium Grade 2 & 5 across all standard flange types and pressure classes, with full Mill Test Certificates (MTC) per EN 10204 3.1 and complete process traceability documentation.
1. Standard Scope & Designation
ASME B16.5 applies to pipe flanges and flanged fittings used in pressure piping systems:
| Parameter |
Specification Range |
Notes |
| Size Range (NPS) |
NPS 1/2 through NPS 24 |
Larger sizes: ASME B16.47 Series A & B |
| Pressure Classes |
Class 150, 300, 400, 600, 900, 1500, 2500 |
Higher ratings: ASME B16.47 or B16.36 |
| Temperature Range |
-29°C to +595°C (-20°F to +1100°F) |
Per material group and pressure class; Ni/Duplex now covers -29°C to 815°C (2025) |
| Bolt Pattern |
4-bolt to 20-bolt circles |
Bolts: UNC thread series (B16.5 Table) |
| Applicable Piping Codes |
ASME B31.1, B31.3 (2024 editions), B31.5, B31.9 |
Aligned with B31.1/B31.3 (2024) and B16.34 (2025) per §1.3 |
Scope Statement (ASME B16.5-2025): "This Standard covers pressure-temperature ratings, materials, dimensions, tolerances, marking, testing, and the methods of designated flanges for pipe flanges and flanged fittings. It covers flanged fittings made from cast or forged materials and blind flanges and made from cast, forged, or plate materials."
| Standard |
Issuing Body |
Scope |
Current Edition |
| ASME B16.5 |
ASME International |
Flanges NPS 1/2 – NPS 24, Class 150-2500 |
B16.5-2025 ★ |
| ASME B16.47 |
ASME International |
Large flanges NPS 26 – NPS 60, Class 75-2500 |
Series A (Weld Neck) & B (Weld Neck & Blind) |
| ASME B16.36 |
ASME International |
Orifice flanges NPS 1/2 – NPS 24 |
Class 150–2500 |
2. Flange Types Covered by ASME B16.5
ASME B16.5 covers six flange types, each suitable for different service conditions:
| Abbrev. |
Type |
Available Classes |
Typical Application |
| WN |
Weld Neck |
All classes (150–2500) |
High-pressure, high-temp, critical service; best fatigue resistance |
| SO |
Slip-On |
Class 150–300 |
Low-pressure, low-cost; requires fillet welds inside and outside |
| SW |
Socket Weld |
Class 150–2500 (limited to NPS 1/2–3) |
Small bore, high-pressure; limited to NPS 3 max in B16.5 |
| TH |
Threaded |
Class 150–2500 |
No welding required; NPT threaded connections; use caution with thick-walled pipe |
| LJ |
Lap Joint |
Class 150–2500 |
Corrosive service; requires stub-end backing; back flange can be reusable |
| BL |
Blind |
All classes (150–2500) |
End cover, blank, or spacer; no pipe connection |
2.1 Flange Facing Types
| Code |
Facing Type |
Raised Height |
Gasket Type |
| RF |
Raised Face |
1.5 mm (1/16 in.) for Cl 150–600; 6.4 mm (1/4 in.) for Cl 900+ |
Ring gasket (spiral wound, RTJ, Jacketed) |
| FF |
Flat Face |
None (flush face) |
Full face gasket (rubber, compressed fiber) |
| RTJ |
Ring Type Joint |
Groove in flange face |
Ring gasket (oval or octagonal, metallic) |
| LF |
Large Male & Female |
6.4 mm (1/4 in.) tongue & groove |
T&G gasket |
| SM |
Small Male & Female |
1.5 mm (1/16 in.) tongue & groove |
T&G gasket |
2025 Update — Low-Stress Sealing (§7.3, NEW): The 2025 edition introduces a new clause for Low-Seating Stress (LSI) gaskets. Sealing face surface roughness is now strictly defined as Ra ≤ 12.5 μm, and flatness tolerance is tightened to ±0.05 mm (§7.2). These changes significantly reduce assembly-caused leaks and improve compatibility with modern low-preload gasket systems.
3. Flange Materials — ASME B16.5-2025 Material Groups
ASME B16.5 assigns flange materials to groups based on composition and service capabilities. The 2025 edition refines material grouping (§5.2), corrects the N08800 classification error, and adds new Titanium grades. Ni/Duplex temperature data is expanded to -29°C to 815°C (Tables 2C–2F).
3.1 Group 1 — Carbon Steel & Low-Alloy Forgings
| ASTM Spec |
Grade / Class |
Min. Tensile / Yield |
Max. Temp |
| ASTM A105 / SA-105 |
Forgings |
485 / 250 MPa (70 / 36 ksi) |
427°C |
| ASTM A181 / SA-181 |
Gr. I / II Forgings |
480 / 260 MPa (70 / 38 ksi) |
425°C |
| ASTM A350 LF2 |
Normalized + Tempered |
485 / 250 MPa (70 / 36 ksi) |
-50°C cryogenic |
| ASTM A216 WCB / WCC |
Castings (for reference) |
485 / 250 MPa (70 / 36 ksi) |
425°C |
3.2 Group 2 — Alloy Steel Forgings
| ASTM Spec |
Grade / Class |
Min. Tensile / Yield |
Max. Temp |
| ASTM A182 F1 |
0.5Mo |
480 / 260 MPa (70 / 38 ksi) |
455°C |
| ASTM A182 F5 / F5a |
5Cr-0.5Mo |
485 / 275 MPa (70 / 40 ksi) |
510°C |
| ASTM A182 F9 |
9Cr-1Mo-V (P91-type) |
585 / 380 MPa (85 / 55 ksi) |
595°C |
| ASTM A182 F11 / F12 |
1.25Cr-0.5Mo-Si |
485 / 275 MPa (70 / 40 ksi) |
510°C |
| ASTM A182 F22 |
2.25Cr-1Mo |
485 / 275 MPa (70 / 40 ksi) |
540°C |
3.3 Group 3 — Stainless Steel Forgings
| ASTM Spec (A182) |
Grade / UNS |
Min. Tensile / Yield |
Max. Temp |
| F304 / F304L / F304H |
S30400 / S30403 / S30409 |
515 / 205 MPa (75 / 30 ksi) |
540°C (316L: 425°C) |
| F316 / F316L / F316H |
S31600 / S31603 / S31609 |
515 / 205 MPa (75 / 30 ksi) |
540°C (316L: 425°C) |
| F321 / F321H |
S32100 / S32109 |
515 / 205 MPa (75 / 30 ksi) |
540°C |
| F347 / F347H |
S34700 / S34709 |
515 / 205 MPa (75 / 30 ksi) |
595°C |
| F310 / F310H |
S31000 / S31009 |
515 / 205 MPa (75 / 30 ksi) |
595°C |
| F51 (Duplex 2205) |
S31803 / S32205 |
620 / 450 MPa (90 / 65 ksi) |
315°C |
3.4 Group 4 — Duplex / Super-Duplex & Special Alloys
| ASTM Spec (A182) |
Grade / UNS |
Min. Tensile / Yield |
Typical Use |
| F53 (2507 Super-Duplex) |
S32750 |
800 / 550 MPa (116 / 80 ksi) |
Offshore, seawater, sour service |
| F55 (Zeron 100) |
S32760 |
750 / 550 MPa (109 / 80 ksi) |
High-chloride, sour gas (NACE) |
| F44 (254 SMO) |
S31254 |
650 / 300 MPa (94 / 43 ksi) |
Seawater, bleach plant, desalination |
| B462 (Alloy 20) |
N08020 |
550 / 240 MPa (80 / 35 ksi) |
Phosphoric acid, chemical process |
3.5 Group 5 — Titanium Alloys NEW in 2025 Edition (Table 2D)
| ASTM Spec |
Grade / UNS |
Min. Tensile / Yield |
Max. Temp |
| ASTM B381 / B348 Gr.2 |
Grade 2 / R50400 |
344 / 275 MPa (50 / 40 ksi) |
316°C (aerospace & offshore) |
| ASTM B381 / B348 Gr.5 |
Grade 5 / Ti-6Al-4V / R56400 |
896 / 828 MPa (130 / 120 ksi) |
316°C (high-strength aerospace) |
2025 Note: Titanium flanges require Phased Array Ultrasonic Testing (PAUT) per §9.3.3. The 2025 edition also corrects the N08800 classification error found in the 2020 edition and expands Ni/Duplex material temperature data to -29°C to 815°C via revised Tables 2C–2F.
4. Pressure-Temperature Ratings — Group 1 Carbon Steel (A105 / WCB)
Allowable pressure in bar (MPa) at design temperature. Per ASME B16.5-2025 Tables 2-3.1. Verify against project-specific P-T data. For hydrogen, CCS, and marine applications, refer to Appendix G (2025 edition).
| Temp (°C) |
Class 150
bar |
Class 300
bar |
Class 400
bar |
Class 600
bar |
Class 900
bar |
Class 1500
bar |
Class 2500
bar |
| -29 to 38 |
19.6 |
51.1 |
68.1 |
102.1 |
153.2 |
255.3 |
425.5 |
| 50 |
19.2 |
50.1 |
66.8 |
100.2 |
150.3 |
250.5 |
417.5 |
| 100 |
17.7 |
46.3 |
61.8 |
92.7 |
139.0 |
231.7 |
386.2 |
| 150 |
15.8 |
42.2 |
56.3 |
84.4 |
126.6 |
211.0 |
351.7 |
| 200 |
13.8 |
38.5 |
51.3 |
77.0 |
115.5 |
192.5 |
320.8 |
| 250 |
11.7 |
35.4 |
47.2 |
70.8 |
106.2 |
177.0 |
295.0 |
| 300 |
9.3 |
33.3 |
44.4 |
66.6 |
99.9 |
166.5 |
277.5 |
| 350 |
6.8 |
31.6 |
42.1 |
63.1 |
94.7 |
157.8 |
263.0 |
| 375 |
5.5 |
30.5 |
40.7 |
61.0 |
91.5 |
152.5 |
254.2 |
| 400 |
3.5 |
29.5 |
39.3 |
59.0 |
88.5 |
147.5 |
245.8 |
| 425 |
— |
28.6 |
38.1 |
57.2 |
85.8 |
143.0 |
238.3 |
| 427 |
— |
28.5 |
38.0 |
57.0 |
85.5 |
142.5 |
237.5 |
Note: Class 150 rated to 425°C but with severely reduced pressure. Group 1 (A105/WCB) is limited to 427°C. For higher temps, use Group 2 alloy steel (F9/F22) or Group 3 stainless (F347). For hydrogen/CCS/marine, refer to Appendix G of B16.5-2025.
4.1 Pressure-Temperature — Group 3 Stainless Steel (A182 F304/F316)
| Temp (°C) |
Class 150
bar |
Class 300
bar |
Class 400
bar |
Class 600
bar |
Class 900
bar |
Class 1500
bar |
Class 2500
bar |
| -29 to 38 |
19.0 |
49.6 |
66.2 |
99.3 |
148.9 |
248.2 |
413.7 |
| 100 |
17.7 |
46.3 |
61.7 |
92.6 |
138.9 |
231.5 |
385.8 |
| 200 |
15.7 |
41.8 |
55.7 |
83.6 |
125.4 |
209.0 |
348.3 |
| 300 |
14.3 |
38.7 |
51.5 |
77.3 |
116.0 |
193.3 |
322.2 |
| 400 |
13.4 |
36.5 |
48.7 |
73.0 |
109.5 |
182.5 |
304.2 |
| 500 |
12.0 |
34.5 |
46.1 |
69.1 |
103.7 |
172.8 |
288.0 |
| 538 |
11.6 |
33.4 |
44.5 |
66.8 |
100.2 |
167.0 |
278.3 |
| 540 |
11.5 |
33.3 |
44.4 |
66.5 |
99.8 |
166.3 |
277.2 |
Note: F304/F316/F321 rated to 540°C. F347/F310 rated to 595°C. For F316L, limit is 425°C. Full tables per ASME B16.5-2025 Tables 2-3.1.
5. Flange Dimensions — Class 150 & Class 300 (Selected NPS)
Key dimensions for Weld Neck (WN) flanges. Full tables per ASME B16.5-2025 Tables. For Class 400/600/900/1500/2500, refer to B16.5 Tables 6 through 12. Bolt hole tolerances and flange thickness tolerances have been optimized in the 2025 edition (§6.5).
5.1 Class 150 — Weld Neck Flange Dimensions (mm)
| NPS |
OD
A |
Bore
B |
Bolt
Circle C |
Bolt
Dia D |
No.
Bolts |
Flange
Thk C |
Min.
Length E |
| 1/2 |
89 |
22.9 |
60.3 |
M12 |
4 |
11.2 |
47.8 |
| 1 |
108 |
34.0 |
79.2 |
M16 |
4 |
13.8 |
52.3 |
| 2 |
152 |
60.5 |
120.7 |
M16 |
4 |
17.5 |
63.5 |
| 4 |
229 |
114.3 |
190.5 |
M16 |
8 |
22.3 |
76.2 |
| 6 |
279 |
168.3 |
241.3 |
M20 |
8 |
25.4 |
88.9 |
| 8 |
343 |
219.1 |
298.5 |
M20 |
8 |
29.0 |
101.6 |
| 10 |
406 |
273.1 |
362.0 |
M20 |
12 |
30.2 |
101.6 |
| 12 |
483 |
323.9 |
431.8 |
M20 |
12 |
32.5 |
114.3 |
| 16 |
540 |
355.6 |
489.0 |
M24 |
16 |
35.1 |
117.2 |
| 24 |
762 |
609.6 |
692.2 |
M27 |
20 |
41.1 |
152.4 |
5.2 Class 300 — Weld Neck Flange Dimensions (mm)
| NPS |
OD
A |
Bore
B |
Bolt
Circle C |
Bolt
Dia D |
No.
Bolts |
Flange
Thk C |
Min.
Length E |
| 1/2 |
95 |
22.9 |
66.7 |
M14 |
4 |
14.2 |
52.3 |
| 1 |
125 |
34.0 |
88.9 |
M16 |
4 |
17.5 |
60.5 |
| 2 |
165 |
60.5 |
127.0 |
M16 |
8 |
20.7 |
73.1 |
| 4 |
254 |
114.3 |
200.0 |
M20 |
8 |
28.4 |
95.2 |
| 8 |
381 |
219.1 |
330.2 |
M20 |
12 |
36.5 |
117.2 |
| 12 |
520 |
323.9 |
457.2 |
M24 |
16 |
43.7 |
130.0 |
| 24 |
830 |
609.6 |
749.3 |
M30 |
24 |
57.2 |
178.0 |
Note: All dimensions per ASME B16.5-2025. For dimensions of SO, SW, TH, LJ, and BL flanges, refer to B16.5 Tables 7–12. Bolt hole tolerances are optimized in the 2025 edition (§6.5).
6. Bolt & Gasket Specifications
6.1 Bolt / Stud Specifications by Pressure Class
| Pressure Class |
Bolt Type |
Common Bolt Sizes (NPS) |
Material (ASTM) |
| Class 150 |
Hex bolts or studs |
NPS 1/2–3/4: M12; NPS 1–2: M16; NPS 3–12: M20; NPS 14–24: M24 |
ASTM A193 B7 / A194 2H |
| Class 300 |
Stud bolts (double-end) |
NPS 1/2: M14; NPS 3/4–1: M16; NPS 1.5–3: M20; NPS 4–8: M24; NPS 10+: M27 |
ASTM A193 B7 / A194 2H |
| Class 600–900 |
Full-length stud bolts |
M14–M27 depending on NPS; larger for high-pressure |
ASTM A193 B7 / A194 2H |
| Class 1500–2500 |
Full stud bolts |
M14–M48; large bolts at highest pressure classes |
ASTM A193 B7 / A194 2H or B16 |
6.2 Gasket Selection Guide
| Gasket Type |
Facing Type |
Service Conditions |
Temperature Limit |
| Compressed Fiber |
FF (full face) |
Low pressure, water, air |
~200°C |
| Spiral Wound (SS/Graphite) |
RF |
General hydrocarbon, steam, chemical |
~650°C |
| Ring Joint (Soft Iron / SS) |
RTJ |
High pressure, critical service |
~600°C |
| Jacketed (SS/Graphite) |
RF |
Moderate temp, corrosive media |
~450°C |
| PTFE / Graphite filled |
RF |
Corrosive chemicals, pure media |
PTFE: 260°C; Graphite: 450°C |
| LSI Gasket (Low-Seating Stress) |
RF |
Low bolt load applications; fragile gaskets |
Per gasket manufacturer |
2025 Note: The 2025 edition introduces a new Low-Seating Stress (LSI) gasket clause (§7.3) and specifies Ra ≤ 12.5 μm surface roughness and ±0.05 mm flatness for sealing faces. Always verify flange facing finish matches gasket manufacturer requirements.
7. Industries & Applications
ASME B16.5-2025 Appendix G introduces dedicated P-T ratings for hydrogen, CCS (Carbon Capture & Storage), and marine environments. The standard also encourages use of recyclable materials to support sustainability.
| Industry |
Common Classes |
Typical Materials |
| Oil & Gas / Onshore |
Class 150, 300, 600 |
A105, WCB, F316L, F51 |
| Offshore Platforms |
Class 300, 600, 900 |
F316L, F53, F55, A350 LF2 |
| Power Generation |
Class 150, 300, 600 |
A105, WCB, F5, F9, F22, F347 |
| Chemical & Petrochemical |
Class 150, 300, 600 |
A105, F304L, F316L, F904L, B462 |
| Desalination / Seawater |
Class 150, 300 |
F316L, F53, F55, DUPLEX |
| Hydrogen & CCS NEW App G |
Class 150, 300, 600, 900 |
F316L, F51, F53, A350 LF2, Ti Gr.2 |
| Refinery & Hydroprocessing |
Class 300, 600, 900 |
A105, F5, F9, F22, WCB |
8. Marking, Traceability & NDT Requirements
ASME B16.5-2025 introduces significantly expanded marking requirements, full process traceability (§10), and mandatory NDT for Class 900-2500 and Titanium flanges (§9). All welding procedures must comply with ASME BPVC Section IX-2025.
8.1 Required Marking (per §10 & B16.5-2025)
| Marking Element |
Required For |
Description |
| Manufacturer's Name or Logo |
All flanges |
Pressure-containing components must bear fabricator identification |
| Material Designation |
All flanges |
ASTM specification and grade (e.g., A182 F316, A105, Gr.2 Ti) |
| Pressure Class |
All flanges |
Class 150, 300, 400, 600, 900, 1500, or 2500 |
| Size (NPS) |
All flanges |
Nominal Pipe Size designation (e.g., NPS 4, NPS 12) |
| Heat / Melt Number |
All flanges |
2025 ADDITION — Full traceability per §10.2.2 |
| Batch / Lot Traceability Code |
All flanges |
2025 ADDITION — Links heat to raw material certificate |
| NR (Not Rated) Suffix |
If specific rating not applicable |
Where a material does not carry a specific class rating |
| "B16.5-2025" |
All flanges |
Standard designation and year of issue |
8.2 NDT Requirements — Class 900-2500 & Titanium NEW in 2025
| NDT Method |
Scope (§9.3) |
Acceptance Criteria |
| Ultrasonic Testing (UT) NEW §9.3.2 |
Class 900-2500, stress concentration zones |
100% UT required; no relevant indications exceeding acceptance standard |
| Magnetic Particle Testing (MT) NEW §9.3.2 |
Class 900-2500, stress concentration zones |
100% MT required; no linear indications > 1.5 mm |
| Phased Array UT (PAUT) NEW §9.3.3 |
Titanium Grade 2 & 5 flanges (all classes) |
Mandatory for titanium per §9.3.3; superior for anisotropic materials |
| Visual Inspection |
All flanges |
Per §9.1; surface condition, dimensional compliance, flange face finish |
8.3 Traceability — Full Process Chain NEW §10.2.2
| Traceability Stage |
Documentation Required |
Standard Reference |
| Raw Material |
Mill Test Certificate (MTC) per EN 10204 3.1; heat number, chemistry, mechanical properties |
§10.2.2 |
| Forging / Casting |
Process route card, heat treatment records, mechanical test results |
§10.2.2 |
| NDT Results |
UT/MT/PAUT reports for Class 900-2500 and Titanium flanges |
§9.3 |
| Dimensional Inspection |
Inspection record verifying B16.5 dimensions and tolerances |
§6 |
| Welding (if applicable) |
WPS, PQR, WPQ per ASME BPVC Section IX-2025; welder qualification records |
§8.4, BPVC IX-2025 |
| Final Inspection |
Final inspection report, pressure test record (if required), conformity assessment |
§9.1 |
| Delivery Package |
CMTR (Certified Material Test Report) with full traceability chain from raw material to delivery |
§10.2.2 (2025 NEW) |
9. Related Standards & Cross-References
ASME B16.5-2025 is cross-referenced with ASME B31.1/B31.3 (2024 editions) and ASME B16.34 (2025 edition) per §1.3. Key companion standards for flange selection, installation, and code compliance:
| Standard |
Title |
2025 Edition |
Relationship to B16.5 |
| ASME B31.1 |
Power Piping Code |
2024 |
Mandatory reference for power plant piping |
| ASME B31.3 |
Process Piping Code |
2024 |
Mandatory reference for refinery/chemical |
| ASME B31.5 |
Refrigeration Piping Code |
Current |
Referenced for cryogenic/chilled media |
| ASME B16.34 |
Valves — Flanged & Welded |
2025 |
Aligned with B16.5 for valve flange compatibility |
| ASME B16.47 |
Large Diameter Steel Flanges |
Current |
Large flanges NPS 26-60; complements B16.5 |
| ASME B16.36 |
Orifice Flanges |
Current |
Specialty flanges for flow measurement |
| ASME BPVC Sec.IX |
Welding Qualification |
2025 |
WPS/PQR/WPQ for flange welding (§8.4) |
| ASME BPVC Sec.V |
NDT Methods |
Current |
UT/MT/PAUT acceptance criteria (§9.3) |
| MSS SP-25 |
Standard Marking System |
Current |
Marking requirements per §10 |
| EN 10204 |
Metallic Products — Inspection Documents |
Current |
3.1 MTC / CMTR documentation format |
| API 6A / 6D |
Wellhead & Pipeline Valves |
Current |
Valve flanges compatible with B16.5 classes |
10. How to Order ASME B16.5-2025 Flanges
When requesting a quote or placing an order for ASME B16.5-2025 flanges from HT Pipe, please specify the following parameters. Clear specification ensures correct manufacturing, inspection, and documentation per the standard.
| No. |
Parameter |
Example |
Notes |
| 1 |
Standard |
ASME B16.5-2025 |
Mandatory from Jan 1, 2026; 6-month transition to Jun 30, 2026 |
| 2 |
Flange Type |
Weld Neck (WN) |
WN, SO, SW, TH, LJ, or BL |
| 3 |
Pressure Class |
Class 300 |
150, 300, 400, 600, 900, 1500, 2500 |
| 4 |
Size (NPS) |
NPS 4 (DN100) |
NPS 1/2 to NPS 24 |
| 5 |
Facing Type |
RF (Raised Face) |
RF, FF, RTJ, LF, SM. Ra ≤ 12.5 μm per §7.2 (2025) |
| 6 |
Material / Grade |
A182 F316L |
Specify ASTM spec + grade; Ti Gr.2/5 now in Table 2D (2025) |
| 7 |
Schedule / Wall Thickness |
Schedule 40 / STD |
Matches pipe bore; affects WN bore dimension |
| 8 |
Bore / End Preparation |
Beveled for welding (BW) |
Beveled (BW), threaded (NPT), plain end for LJ |
| 9 |
Service / Application |
Hydrogen service, 35 bar, 180°C |
Required for H2/CCS/marine per App G (2025) |
| 10 |
NDT & Documentation |
UT/MT report + EN 10204 3.1 CMTR |
Class 900-2500 requires 100% UT/MT; Ti requires PAUT (2025) |
| 11 |
Quantity & Delivery |
10 pcs, CIF Shanghai, 30 days |
Quantities, incoterms, lead time, port of destination |
11. ASME B16.5-2025 vs 2020 — Key Changes Summary
ASME B16.5-2025 (ANSI approved April 10, 2025; mandatory from January 1, 2026) introduces significant technical updates compared to the 2020 edition. A 6-month transition period (until June 30, 2026) applies to projects already in progress per Appendix L. Below is a comprehensive comparison of the most impactful changes for engineers, procurement teams, and manufacturers.
| Change Area |
ASME B16.5-2020 (Previous) |
ASME B16.5-2025 (Current) |
| New Materials Added |
No Titanium in material tables. Group 5 covered Ni alloys only. |
NEW — Titanium Grade 2 (ASTM B381/B348) and Titanium Grade 5 (Ti-6Al-4V, ASTM B381/B348) added to Table 2D. PAUT required per §9.3.3. |
| N08800 Classification |
N08800 was incorrectly classified in material tables. |
CORRECTED — N08800 classification error corrected in §5.2 and related tables. |
| Sealing Face Roughness |
No explicit Ra requirement. Surface finish left to manufacturer/gasket maker discretion. |
NEW — Sealing face roughness explicitly limited to Ra ≤ 12.5 μm (§7.2). Tightens consistency and gasket performance. |
| Sealing Face Flatness |
Flatness tolerance not explicitly specified for flange sealing faces. |
NEW — Flatness tolerance tightened to ±0.05 mm (§7.2). Critical for LSI gaskets and high-pressure sealing. |
| NDT — Class 900-2500 |
UT/MT requirements for high-class flanges existed but less stringent. No explicit 100% coverage mandate for stress zones. |
NEW §9.3.2 — 100% Ultrasonic Testing (UT) and/or Magnetic Particle Testing (MT) mandated for stress concentration zones of Class 900-2500 flanges. Acceptance criteria aligned with BPVC V. |
| NDT — Titanium |
No specific NDT requirement for titanium flanges (material was not in standard). |
NEW §9.3.3 — Phased Array Ultrasonic Testing (PAUT) required for all Titanium Grade 2 and Grade 5 flanges. PAUT is superior for anisotropic titanium microstructures. |
| Traceability Requirements |
Basic traceability via MTC (EN 10204 3.1) was customary but not mandated by B16.5 as a process chain. |
NEW §10.2.2 — Full process traceability from raw material to delivery is now explicitly mandated. CMTR must document heat number, batch, NDT results, and inspection chain. Traceability code required on flange marking. |
| LSI Gasket Compatibility |
No specific clause for Low-Seating Stress (LSI) gaskets. Compatibility with modern low-preload gaskets was addressed by gasket manufacturers' instructions only. |
NEW §7.3 — Explicit clause for Low-Seating Stress (LSI) gaskets added. Combined with §7.2 Ra ≤ 12.5 μm and ±0.05 mm flatness, this significantly reduces assembly-caused leaks in modern gasket systems. |
| Hydrogen, CCS & Marine (App G) |
No dedicated appendix for hydrogen, CCS, or marine applications. Engineers referenced external guidance (ASME B31.3 Chapter IX, API 617, etc.). |
NEW Appendix G — Dedicated P-T ratings and guidance for hydrogen, carbon capture and storage (CCS), and marine environments. Addresses embrittlement, hydrogen-induced cracking, and seawater corrosion. Includes NACE MR0175/ISO 15156 compatibility references. |
| Ni/Duplex Temperature Range |
Ni alloy and Duplex stainless P-T data tables had limited high-temperature coverage. |
EXPANDED — Ni/Duplex material temperature data expanded to -29°C to 815°C via revised Tables 2C–2F. Provides clearer guidance for high-temp Ni alloy and super-duplex applications. |
| Bolt Hole Tolerances |
Bolt hole tolerance specified in earlier dimensional tables. |
OPTIMIZED — Bolt hole tolerance requirements refined in §6.5 for better interchangeability and assembly fit. |
| Cross-References Updated |
Referenced ASME B31.1 and B31.3 (2018 editions); ASME B16.34 (2017). |
UPDATED §1.3 — Aligned with ASME B31.1 and B31.3 (2024 editions) and ASME B16.34 (2025 edition). Welding references updated to ASME BPVC Section IX (2025 edition). |
| Sustainability / Recyclability |
No sustainability provisions in the standard. |
NEW — The 2025 edition encourages use of recyclable flange materials and sustainable manufacturing practices. Reflects growing industry demand for ESG compliance in flange procurement. |
| Appendix L — Transition |
N/A (new appendix in 2025). |
NEW Appendix L — Defines 6-month transition period (Jan 1, 2026 to June 30, 2026) for projects already in procurement/construction using B16.5-2020. Allows continued use of 2020 edition for legacy projects during transition. |
Frequently Asked Questions (FAQ)
1. When does ASME B16.5-2025 become mandatory?
ASME B16.5-2025 is mandatory from January 1, 2026 (ANSI approved April 10, 2025). A 6-month transition period per Appendix L allows projects already in procurement or construction phases to continue using the 2020 edition until June 30, 2026. Always verify with your project's engineering team and applicable jurisdictional requirements.
2. Can I still use ASME B16.5-2020 flanges after January 1, 2026?
Per Appendix L of the 2025 edition, flanges manufactured to ASME B16.5-2020 may still be used for projects already in progress (procurement, fabrication, or construction) during the transition period ending June 30, 2026. For new projects starting after January 1, 2026, ASME B16.5-2025 compliance is required. Check with your engineering contractor and applicable code jurisdiction.
3. What are the most important changes in ASME B16.5-2025 for buyers and specifiers?
The most impactful changes for procurement are: (1) Titanium Grade 2 & 5 now available in the standard — ideal for offshore, desalination, and aerospace; (2) 100% UT/MT required for Class 900-2500 — this increases inspection costs and lead time; (3) Full traceability per §10.2.2 — your MTC must now include a complete process chain from raw material to delivery; (4) Appendix G for Hydrogen/CCS — explicit ratings for H2 and carbon capture projects; (5) LSI gasket clause (§7.3) and Ra ≤ 12.5 μm surface finish requirement — ensure gasket compatibility with updated facing specifications.
4. What is the difference between PAUT and conventional UT for titanium flanges?
Phased Array Ultrasonic Testing (PAUT) uses multiple ultrasonic elements and electronic beam steering to inspect complex geometries with superior sensitivity compared to conventional single-probe UT. For titanium flanges, PAUT (§9.3.3, 2025 edition) is preferred because: (1) Titanium has anisotropic microstructures that scatter conventional UT beams; (2) PAUT provides 2D/3D imaging for more reliable defect detection; (3) PAUT can inspect curved hub sections and weld zones more effectively. The 2025 edition mandates PAUT for Titanium Grade 2 and Grade 5 flanges.
5. How does ASME B16.5-2025 Appendix G affect hydrogen flange specification?
Appendix G of ASME B16.5-2025 provides the first comprehensive, dedicated guidance for flange selection in hydrogen, CCS (Carbon Capture & Storage), and marine environments within B16.5 itself. Key implications: (1) Reduced P-T ratings may apply for high-pressure hydrogen due to hydrogen-induced cracking (HIC) and embrittlement risks; (2) Material compatibility references align with NACE MR0175/ISO 15156; (3) Recommended materials include F316L, F51 (2205 duplex), F53 (2507), A350 LF2, and Titanium Grade 2; (4) For CCS, compatibility with CO2 streams (including wet CO2 and acid gases) is addressed. Engineers should verify project-specific H2 purity, pressure, and temperature against the App G P-T charts.
6. What traceability documentation should I request for ASME B16.5-2025 flanges?
Per §10.2.2 of ASME B16.5-2025, you should request a Certified Material Test Report (CMTR) including: (1) Raw material MTC per EN 10204 3.1 with heat number, chemical analysis (C, Mn, P, S, Si, Cr, Ni, Mo, etc.), tensile strength, yield strength, elongation, and Charpy impact values; (2) Heat number traceability code stamped on the flange (per §10 marking); (3) Forging/casting process records and heat treatment records; (4) NDT reports (UT/MT reports for Class 900-2500; PAUT reports for Titanium); (5) Dimensional inspection records per B16.5 Tables; (6) Final pressure test results (if required); (7) WPS/PQR/WPQ for any welded fabrication. HT Pipe provides complete CMTR packages with every flange shipment.
Download ASME B16.5 Standards
Download the official ASME B16.5 standard documents from the official ASME Digital Collection. For ASME B16.5-2025 (mandatory Jan 1, 2026), purchase from the ASME Store. The 2020 edition remains available during the transition period ending June 30, 2026.
Ready to Source ASME B16.5-2025 Flanges?
Zhengzhou Huitong Pipe Fittings Co., Ltd. (HT Pipe) is a professional manufacturer and exporter of ASME B16.5 pipe flanges, now fully compliant with the 2025 edition requirements. We supply Weld Neck, Slip-On, Socket Weld, Threaded, Lap Joint, and Blind flanges in carbon steel (A105), stainless steel (F304/F316L), alloy steel (F5/F9/F22), and Titanium Grade 2 & 5 — across all pressure classes (150–2500). Every flange ships with full EN 10204 3.1 CMTR, complete traceability documentation, and NDT reports (UT/MT/PAUT as applicable).
