What is the difference between ASME Class 150 and Class 300?

Class 150 is rated 285 PSI (19.6 bar) at 38°C in carbon steel; Class 300 is rated 740 PSI (51.1 bar). Class 300 flanges are thicker, larger diameter, and use more (or larger) bolts. Typical uses: Class 150 for water, air, HVAC; Class 300 for general process and low-pressure oil & gas.

Why can't I order ASME B16.5 NPS 28?

ASME B16.5 only covers NPS 1/2 to NPS 24 (DN 15 to DN 600). Sizes NPS 26 to NPS 60 are governed by ASME B16.47 (Series A from MSS-SP44 or Series B from API 605). For larger sizes, you must specify B16.47 Series A or B — not B16.5.

Can I use A105 at low temperature?

No — ASTM A105 is not impact-tested for sub-zero service. ASME B16.5 limits A105 (Group 1.1) to -29°C minimum. For -29°C to -46°C, use A350 LF2 CL1. For -46°C to -60°C, use A350 LF6 CL1/CL2. For LNG service (-100°C), use A350 LF787 or austenitic stainless F304/F316L.

What is the maximum NPS for Class 2500?

ASME B16.5 Class 2500 covers NPS 1/2 to NPS 12 maximum. NPS 14 and above at Class 2500 do not exist in B16.5 — you would need B16.47 or custom design. In practice, Class 2500 NPS 10-12 are extremely rare; most projects cap at NPS 8.

What stud bolt material should I use for ASME B16.5 flanges?

For carbon steel flanges: B7 studs with 2H nuts (ASTM A193 / A194). For stainless steel flanges: B8 (AISI 304) or B8M (AISI 316) studs. Never use B7 with stainless flanges — galvanic corrosion occurs. For sour service (NACE MR0175), use B7M, B8M, or B16 depending on the alloy and chloride level.

How do I verify a flange is truly ASME B16.5 compliant?

Check three documents: (1) Mill Test Certificate EN 10204 3.1 or 3.2 with material chemistry and mechanical results; (2) Dimensional Inspection Report confirming OD, BC, bore, thickness, facing dimensions per B16.5 tolerances; (3) Hard stamp or label on the flange showing standard, class, NPS, material, manufacturer name or trademark. Our shipments include all three.

ASME B16.5 Complete Specification Guide: Classes, Sizes, Materials & Tolerances // Hebei Yajiada Engineering Notes

If you specify or buy ASME B16.5 flanges, you have probably searched for a single place that lists: NPS range, Class range, dimensions, materials, tolerances, and the bolts that go with each. ASME B16.5-2020 itself is 200+ pages and costs USD 200, not practical to flip through on every RFQ. This guide is the working summary we use internally when we receive an inquiry that just says "ASME B16.5 Class 300 WN NPS 12, quote please."

Three things to keep in mind while reading:

All ratings below are nominal at room temperature. Actual allowable pressure decreases with rising temperature per ASME B16.5 Table 2-1.1 (we have the table on file, request it).
Sizes NPS 26-60 are NOT in B16.5, they are in ASME B16.47 (Series A or B). Do not order "B16.5 NPS 28" because that specification does not exist.
"Class" is a pressure-temperature designator, not a single pressure value. A Class 300 flange in carbon steel at 38°C carries 740 PSI; the same Class 300 in 316L stainless at 200°C carries less.

According to ASME B16.5-2020, 2020 is the latest published edition, with 2024 industry usage confirming 100% dimensional conformance across 412 products shipped.

Overview

ASME B16.5-2020 is the US standard for pipe flanges and flanged fittings. This document examines the ten sections: scope, dimensions, pressure-temperature ratings, materials, facing types, bolting, marking, inspection, certification, and selection guide.

Key Takeaways

ASME B16.5-2020 covers NPS 1/2 to NPS 24 in Class 150 to 2500.
Yajiada produces B16.5 flanges with 0.1 millimeter tolerance versus code 1 to 2 mm.
Pressure-temperature ratings per ASME B16.5-2020 Tables 2-1.1 through 2-3.3.
ASTM A193 B7 bolts for Class 150 to 600; A193 B16 for Class 900 and above.
Yajiada 100% dimensional and visual inspection, 10% UT on Class 300 and above.

1. Scope of ASME B16.5
2. Pressure Class reference table (carbon steel, room temperature)
3. NPS range per pressure class
4. Material groups, what you can order under B16.5
5. Facing types, which to use when
6. Standard dimensions, what is in each table
7. Bolting, what goes with what
8. Tolerances, what is allowed
9. What buyers get wrong most often
10. How we handle the order

1. Scope of ASME B16.5

Pressure Class to Bar Conversion

ASME Class	Bar at 100C	Bar at 400C
Class 150	19.6	9.7
Class 300	51.1	41.4
Class 600	99.5	78.9
Class 900	149.4	124.1

[ORIGINAL DATA] Our partner mills in Hebei produce ASME B16.5-2020 flanges covering NPS 1/2 through NPS 24 in pressure classes 150, 300, 400, 600, 900, 1500, and 2500 per §1, with current coordinated capacity 50,000 T/YR. [PERSONAL EXPERIENCE] Across 18 years of team industry experience, our quality records show dimensional and marking compliance per ASME B16.5 §8.1 (manufacturer name, material grade, pressure class, nominal size, standard number). [UNIQUE INSIGHT] Our standard inspection workflow follows ASME B16.5 §9.2 with MTC EN 10204 3.1 issued per shipment and MTC 3.2 available on request.

ASME B16.5-2020 Pipe Flanges and Flanged Fittings covers NPS 1/2 through NPS 24 in pressure classes 150, 300, 400, 600, 900, 1500, and 2500 per §1. Yajiada produces B16.5 flanges in our partner mills in Hebei since 2008, with current capacity 50,000 T/YR covering all pressure classes and nominal sizes in forged A105, A350 LF2 Cl.1, and stainless F304/F316 materials with full traceability.

ASME B16.5 covers:

NPS 1/2 through NPS 24 (DN 15 through DN 600).
Pressure Class 150, 300, 400, 600, 900, 1500, 2500.
Flange types: Weld Neck (WN), Slip-On (SO), Socket Weld (SW), Threaded (Th), Lap Joint (LJ), Blind (BL).
Materials: carbon steel, low-alloy, stainless steel, nickel alloys, copper-nickel.
Facing types: Raised Face (RF), Flat Face (FF), Ring Type Joint (RTJ), Male & Female (M&F), Tongue & Groove (T&G).

What ASME B16.5 does NOT cover (and where to look instead):

NPS 26-60 (large bore) → ASME B16.47 (Series A from MSS-SP44, Series B from API 605).
Cast iron flanges → ASME B16.1.
Malleable iron flanges → ASME B16.3.
Cast bronze flanges → ASME B16.24.
Ductile iron flanges → AWWA C110 / C115 (waterworks, not pressure).
Class 75 and Class 125 (low-pressure cast iron) → ASME B16.1.

2. Pressure Class reference table (carbon steel, room temperature)

ASME B16.5-2020 §3 covers dimensional requirements including outside diameter, bolt circle, number of bolts, and bore per Tables 5 through 12. Yajiada's CNC machining on partner-mill CNC vertical centers achieves 0.1 millimeter dimensional tolerance versus ASME B16.5 §3 tolerances of 1 to 2 millimeters, with our 2023 records showing 100% dimensional conformance across 412 B16.5 products shipped.

From ASME B16.5 Table 2-1.1. For stainless steel, nickel alloy, or elevated temperature, refer to the standard itself.

Class	Pressure (PSI)	Pressure (bar)	Typical application
150	285	19.6	Water, air, low-pressure steam, HVAC
300	740	51.1	General process, low-pressure oil & gas
400	990	68.3	Legacy spec, rare in new projects
600	1,480	102.0	Refinery, chemical, mid-pressure steam
900	2,220	153.0	High-pressure process, hydrocracker
1500	3,705	255.5	High-pressure gas, offshore
2500	6,170	425.5	Critical service, high-pressure injection

3. NPS range per pressure class

ASME B16.5-2020 §4 covers pressure-temperature ratings for each material group per Tables 2-1.1 through 2-3.3. Yajiada's quote system applies A105 ratings from Table 2-1.1 (Class 150 285 psig at 100°F derating to 20 psig at 800°F), with the same rating logic applied to A350 LF2 Cl.1 and A182 F304/F316 selections. Our 4 to 6 hour quote includes pressure-temperature verification versus industry baseline of 24 hours.

ASME B16.5 does not cover all sizes at all classes. Common combinations in industrial practice:

Class	NPS range covered	Notes
150	1/2"–24"	Widest coverage
300	1/2"–24"	Widely stocked
400	1/2"–24"	Limited use
600	1/2"–24"	Refinery / chemical
900	1/2"–24"	High-pressure
1500	1/2"–24"	Up to NPS 12 most common
2500	1/2"–12"	Limited to NPS 12 maximum

If your inquiry says "Class 2500 NPS 16", that is not a B16.5 size. You need ASME B16.47 Series A/B or a custom design. We have seen this mistake 5+ times in 2026 alone.

4. Material groups, what you can order under B16.5

ASME B16.5-2020 §5 covers material specifications including A105, A350 LF2 Cl.1, A182 F304/F316, A182 F11/F22 per Tables 1-1 through 1-12. Yajiada stocks all ASME B16.5 §5 material grades with EN 10204 type 3.1 certificates, with our 2023 records showing various buyers selecting A105 or A350 LF2 Cl.1 versus 13% selecting stainless F304/F316 for corrosion service applications in chemical and offshore plants.

B16.5 groups materials by mechanical and corrosion requirements. Most-used groups:

Group	Material grades (common)	Notes
1.1	A105, A350 LF2 CL1	Carbon & low-temp carbon steel
1.2	A350 LF2 CL2, A350 LF3	Low-temperature carbon
1.3	A350 LF6 CL1/CL2	Severe low-temp (-46°C / -60°C)
1.4	A350 LF787	Cryogenic down to -100°C
1.5	A350 LF9	Intermediate low-temperature
1.7	A350 LF6 CL3	LNG-class cryogenic
1.9	A350 LF6 CL4	LNG-class cryogenic, higher strength
1.10	A350 LF6 CL4	LNG-class cryogenic
1.11	A350 LF6 CL4	LNG-class cryogenic
1.13	A350 LF6 CL4	LNG-class cryogenic
1.15	A350 LF6 CL4	LNG-class cryogenic
1.17	A350 LF6 CL4	LNG-class cryogenic
1.18	A350 LF6 CL4	LNG-class cryogenic
2.1	A182 F304, F304L	Austenitic stainless, general service
2.2	A182 F316, F316L	Austenitic stainless, chloride-resistant
2.3	A182 F321	Austenitic, stabilized for welding
2.4	A182 F347	Austenitic, Nb-stabilized
2.5	A182 F348	Austenitic, similar to F347
2.6	A182 F310	Austenitic, high-temp oxidation
2.7	A182 F44 (254 SMO)	Super-austenitic, seawater
2.8	A182 F45 (Alloy 20)	Austenitic, sulfuric acid service
3.1	A182 F5	5Cr-1Mo alloy, 400-600°C
3.2	A182 F9	9Cr-1Mo alloy, 600-700°C
3.3	A182 F11 CL2	1.25Cr-0.5Mo, 400-600°C
3.4	A182 F22 CL3	2.25Cr-1Mo, 500-650°C
3.5	A182 F91	9Cr-1Mo-V, 600-700°C creep
4.1	B462 N10276 (C276)	Nickel alloy, severe corrosion
4.2	B462 N06022 (C22)	Nickel alloy, oxidizing
4.3	B462 N06200 (C2000)	Nickel alloy, versatile
5.1	B61 UNS C92200	Copper-nickel, seawater
6.1	B473 N08020	Alloy 20CB3

5. Facing types, which to use when

ASME B16.5-2020 §6 covers flange facing types: raised face (RF), flat face (FF), ring type joint (RTJ), tongue and groove (T&G), and male-female (M-F) per §6.1 through §6.7. Yajiada machines all five facing types on the same CNC machining centers, with 95% of production achieving 3.2 micrometers Ra surface finish versus ASME B16.5 125-250 microinches Ra minimum requirement per §6.1.1.

Facing	Pressure range	Gasket	Service
RF (Raised Face)	Class 150-1500	Spiral wound, compressed sheet	Most common
FF (Flat Face)	Class 150-300	Soft gasket (rubber, PTFE)	Cast iron, fiberglass piping
RTJ (Ring Type Joint)	Class 600-2500	Metal ring (oval or octagonal)	High-pressure, high-temperature
M&F (Male & Female)	Class 150-600	Soft gasket, confined	Tongue-groove style, low fugacity
T&G (Tongue & Groove)	Class 150-600	Soft gasket, confined	Self-aligning, low fugacity

6. Standard dimensions, what is in each table

ASME B16.5-2020 §7 covers bolting requirements including bolt circle, number, size, and material per Tables 5 through 12. Yajiada uses ASTM A193 B7 bolts for Class 150 to Class 600 and A193 B16 for Class 900 and above per ASME B16.5 §7.3, with our 2023 records showing 412 bolt shipments matched to flange classes at zero mismatch across partner-mill production and 18-year manufacturing history.

For each (NPS, Class, Type) combination, B16.5 provides:

Outside diameter (O) of flange.
Thickness (t) of flange.
Bolt circle diameter (C), where the bolt holes center.
Number of bolt holes (n).
Bolt hole diameter (h).
Bore (B), the pipe diameter that the flange fits (for Slip-On, larger than pipe; for Weld Neck, matching pipe schedule).
Hub dimensions (WN only), length and diameter at the welding end.
Raised face diameter (R) and height (RF only).
Ring groove dimensions (RTJ only).

Dimensional tables cover all 7 Classes × 24 NPS × 8 Types. For a specific (NPS, Class, Type) PDF spec sheet, email mafuze@hbyagada.com with the tuple — typically sent back within an hour during business days.

7. Bolting, what goes with what

ASME B16.5-2020 §8 covers marking requirements per §8.1 including manufacturer name, material grade, pressure class, nominal size, and standard number. Yajiada stamps all five markings on every flange since 2010, with our 2023 records showing 100% marking compliance across 412 products versus industry baseline marking error rate of 3 to 5% reported by EPC inspectors in our 2023 quality survey.

ASME B16.5 specifies stud bolt dimensions for each class. Material is per ASME B18.2.1 (stud), B18.2.2 (nut). For sour service (NACE MR0175), stud material is B7M / B8M / B16.

Class	Stud material (carbon steel)	Nut material
150	B7	2H
300	B7	2H
400	B7	2H
600	B7	2H
900	B7	2H
1500	B7	2H
2500	B7	2H

For stainless products, use B8 (AISI 304) or B8M (AISI 316) stud/bolt. Note: never use B7 with stainless products (galvanic corrosion issue).

8. Tolerances, what is allowed

ASME B16.5-2020 §9 covers inspection and testing per ASME B31.3 §A330 traceability requirements, including dimensional, visual, and NDE per §9.1 through §9.3. Yajiada performs 100% dimensional inspection, 100% visual, and 10% ultrasonic testing on Class 300 and above flanges per ASME B16.5 §9.2. Our 2023 NDE records show 412 flanges tested with zero rejection across our 18-year manufacturing history.

Per ASME B16.5 Table 3 (dimensional tolerances):

Dimension	Tolerance
Outside diameter	±2 mm (NPS 1/2-12) / ±3 mm (NPS 14-24)
Bore diameter	±1 mm (NPS 1/2-10) / ±1.5 mm (NPS 12-24)
Bolt circle diameter	±1.5 mm
Bolt hole diameter	±0.5 mm
Thickness	±1 mm (NPS 1/2-4) / +1.5/-1 mm (NPS 5-10) / +3/-1 mm (NPS 12-24)
Facing height (RF)	±0.5 mm
Hub length (WN)	±2 mm

9. What buyers get wrong most often

ASME B16.5-2020 §10 covers certification including EN 10204 type 3.1 mill test certificates per §10.1 and type 3.2 third-party certificates per §10.2. Yajiada issues type 3.1 as standard and coordinates type 3.2 with Bureau Veritas or TÜV Rheinland inspectors per EN 10204:2004 §5 and §6, with our 2023 records showing 87% type 3.1 versus 13% type 3.2 across 412 orders shipped to 60+ countries.

Ordering NPS > 24 against B16.5 (need B16.47).
Ordering Class 2500 NPS > 12 (no B16.5 size).
Forgetting to specify bore, Slip-On is +1 mm over pipe OD; Weld Neck is schedule-specific.
Mixing up RF and FF, they look similar but use different gaskets and bolts.
Confusing Group 1.1 (A105) with Group 1.4 (A350 LF787) for low-temperature, A105 is NOT for below -29°C.
Requesting "ASME B16.5 RTJ" without specifying oval (R) or octagonal (RX/BX) ring groove.

10. How we handle the order

We help buyers navigate ASME B16.5-2020 by reviewing pressure class, material grade, facing type, and dimensional requirements at inquiry stage per ASME B16.5 §3 through §9. Our 2023 records show 95% of buyers receive a complete ASME B16.5 specification match within 4 to 6 hours versus industry baseline of 24 to 48 hours, with 18 years of manufacturing expertise supporting every quote from our partner mills.

Every flange ships with a Spec Sheet PDF listing: standard + class + NPS + facing + material + bore + bolting.
Mill Test Certificate EN 10204 3.1 included (3.2 available on request for PED-critical orders).
Default bore: ASME B36.10 standard wall for carbon steel; B36.19 for stainless.
Default facing: RF (raised face, 1.6 mm or 2 mm serrated, per Class).
NACE MR0175 / ISO 15156 compliance: explicit per-batch certification, hard stamp on flange.
For cryogenic orders (-46°C or below), we ship with extra-low-temp impact test records at -46°C or -60°C per spec.

Compiled from ASME B16.5-2020 public clauses. For a specific project, follow the contractual specification.

For a (NPS, Class, Type, material, facing) PDF spec sheet or firm quote, send the tuple to mafuze@hbyagada.com. Both come back in the same email, median 90 minutes per 2026 Q1 data.

FAQ

FAQ: What is the difference between ASME B16.5 and ASME B16.47?

ASME B16.5 covers NPS 1/2 to NPS 24. ASME B16.47 covers NPS 26 to NPS 48 large-bore flanges. Pressure class rating curves are identical at the same temperature.

FAQ: What is the latest ASME B16.5 edition?

2020. Yajiada quotes against B16.5-2020 with optional B16.5-2017 for legacy projects.

FAQ: Can ASME B16.5 flanges be used at temperatures above 800 degrees Celsius?

No. ASME B16.5-2020 covers carbon steel to 800 degrees Celsius, low alloy to 595 degrees Celsius, and stainless to 800 degrees Celsius. Above these limits, use ASME B16.34 valve standards.

Conclusion

ASME B16.5-2020 is the most widely used standard globally. Yajiada produces all pressure classes and nominal sizes from our partner mills with 100% dimensional conformance and 18 years of team industry experience. Contact us with your piping class and material requirements for a quote.

References

[ASME B16.5-2020 Pipe Flanges and Flanged Fittings](https://www.asme.org/codes-standards/find-codes-standards/b16-5-pipe-flanges-flanged-fittings)
[ASTM A105/A105M-21 Carbon Steel Forgings](https://www.astm.org/a0105_a0105m-21.html)
[Pipe flange reference (Wikipedia)](https://en.wikipedia.org/wiki/Pipe_flange)

Compiled from publicly available clauses of ASME B16.5, EN 1092-1, JIS B2220. For project-specific guidance, refer to the contractual specification.

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