When must ASME B16.47 be used instead of ASME B16.5?

ASME B16.5 covers sizes from NPS 1/2 up to NPS 24. For large-diameter piping NPS 26 through NPS 60, you must specify ASME B16.47. Crucially, B16.47 contains two non-interchangeable standards: Series A (heavier, fewer large bolts, MSS SP-44 origin) and Series B (compact, many small bolts, API 605 origin). Series A and B will not bolt together.

Why does Class 600 have a 1/4 inch raised face while Class 150/300 has 1/16 inch?

Per ASME B16.5, Class 150 and 300 flanges have a 1.6 mm (1/16 in) raised face, which is *included* within the nominal flange thickness T. Class 600, 900, 1500, and 2500 flanges have a 6.4 mm (1/4 in) raised face, which is *added in addition* to the minimum flange thickness T to provide deeper gasket containment under extreme hydrostatic bolt loads.

What is total mated-pair assembly weight and why is it critical for field engineering?

Total mated-pair assembly weight equals 2 flanges + 1 gasket + full stud & nut set (two heavy-hex nuts per stud). In field construction and piping stress analysis, using only single-flange catalog mass severely underestimates pipe rack deadweight and rigging crane loads (e.g. 12 large studs and 24 nuts can add 15–25% extra weight to the joint).

8" Class 150 Flange Dimension & Weight | ASME & API Calculations

Engineering Reference & ASME Code Basis

1. Core Formula & Variable Definitions

ASME B16.5 (Pipe Flanges and Flanged Fittings NPS 1/2 - 24) · ASME B16.47 (Large Diameter Steel Flanges NPS 26 - 60) · ASME B16.20 (Metallic Gaskets for Pipe Flanges) · ASME B18.2.1 / B18.2.2 (Heavy Hex Bolts & Nuts)

W_pair = 2W_f + W_g + n(W_stud + 2W_nut) · PCD = 2R_bc

ASME B16.5 / B16.47 Flange Envelope, Bolt Pattern & Total Joint Assembly Mass

B16.5 Scope NPS ½ ~ 24B16.47 Scope NPS 26 ~ 60Classes 150 ~ 2500Facings RF (1/16" or 1/4") / FF / RTJ

Weld-neck raised-face (WN RF), slip-on (SO), and blind flanges for NPS 1/2 through NPS 24 in Pressure Classes 150 through 2500 are dimensioned in ASME B16.5. Large diameter flanges (NPS 26 through NPS 60) are governed by ASME B16.47 (Series A / MSS SP-44 vs Series B / API 605). Hub bore matches standard pipe schedule inside diameter per ASME B36.10M. Total mated-pair mass accounts for two flanges, one gasket, and all threaded stud bolts with two heavy-hex nuts each.

Class (Pressure Rating Class) — Dimensionless class designation (150, 300, 600, 900, 1500, 2500) representing pressure-temperature envelope.
OD_f (Flange Outside Diameter) — Total outside diameter of the circular flange forging (mm or in).
T_f (Minimum Flange Thickness) — Flange ring thickness excluding raised face height (mm or in).
PCD (Pitch Circle Diameter (Bolt Circle)) — Diameter of the circle passing through the centers of all bolt holes (mm or in).
n × d_h (Bolt Hole Configuration) — Total number of bolt holes (n) and drilled hole diameter (d_h = stud diameter + 1/8 in / 3.2 mm).
W_f (Single Flange Mass) — Nominal catalog weight of bare forged flange (kg or lb).
W_pair (Mated Joint Assembly Mass) — Combined weight of 2 flanges + 1 gasket + n complete stud/nut sets (kg or lb).

2. Allowances, Tolerances & Standards

ASME B16.5 establishes strict dimensional tolerances on flange forging, bolt hole spacing, and facing finishes to guarantee leak-tight sealability and bolt alignment across field spools.

Raised Face Height & Finish1/16" (Cl 150/300) vs 1/4" (Cl ≥ 600)

Class 150 & 300 have a 1.6 mm (1/16 in) raised face included in catalog thickness T. Class 600 through 2500 have a 6.4 mm (1/4 in) raised face added on top of thickness T. Standard RF finish is serrated concentric or spiral grooves (Ra 3.2 ~ 6.3 µm / 125 ~ 250 µin).

Bolt Circle & Hole Spacing Tolerance±1.5 mm (±0.06 in)

ASME B16.5 limits center-to-center adjacent bolt hole spacing tolerance to ±0.8 mm (±0.03 in), and pitch circle diameter tolerance to ±1.5 mm (±0.06 in) to prevent bolt binding during stud makeup.

Bore & Hub Thickness Tolerance+0.8 mm / -0.0 mm

Weld-neck hub bore diameter tolerance is +0.8 mm / -0.0 mm for NPS ≤ 10, and +1.6 mm / -0.0 mm for NPS 12 to 18 to minimize internal step discontinuity and flow turbulence at the butt-weld seam.

B16.47 Series A vs Series BNon-Interchangeable

Series A (MSS SP-44 origin) has heavier flanges, larger bolt circles, and fewer, thicker bolts designed for piping. Series B (API 605 origin) has compact flanges with smaller, more numerous bolts for equipment nozzles. Bolt patterns do not mate.

Quick Reference Lookup Table

ASME B16.5 weld-neck RF — Class 150 selected sizes
NPS	Flange OD (mm)	Thickness T (mm)	Bolt circle (mm)	Bolts
2"	152.4	17.5	120.7	4 × 5/8"
4"	228.6	23.8	190.5	8 × 5/8"
6"	279.4	25.4	241.3	8 × 3/4"
8"	342.9	28.6	298.5	8 × 3/4"
10"	406.4	30.2	362.0	12 × 7/8"
12"	482.6	31.8	431.8	12 × 7/8"

NPS 4 values match this app’s Class 150 row. Other sizes are B16.5 handbook screening dimensions — confirm facing and hub on the vendor drawing.

3. Material & Code Limitations

Pressure Class (e.g. 150, 300) does not represent working pressure in psi or bar. Maximum allowable working pressure (MAWP) decreases drastically with increasing operating temperature per ASME B16.5 Table 2 rating charts.

Material Group	Temperature Range	Allowable Stress / Limit	Engineering Notes
Group 1.1: Carbon Steel (ASTM A105 / A350 LF2)	-29 °C to 425 °C (-20 °F to 800 °F)	Cl 150: 19.6 bar @ 38 °C → 6.5 bar @ 300 °C; Cl 300: 51.1 bar @ 38 °C → 39.8 bar @ 300 °C	Most common flange material. Class 150 undergoes severe thermal derating above 100 °C due to bolt relaxing and gasket deformation risks.
Group 2.1: Stainless Steel (ASTM A182 F304 / F304L)	-196 °C to 538 °C (-320 °F to 1000 °F)	Cl 150 (F304L): 15.9 bar @ 38 °C → 8.4 bar @ 200 °C	Lower allowable pressure at ambient than carbon steel because austenitic low-carbon stainless has lower yield strength.
Group 2.2: Stainless Steel (ASTM A182 F316 / F316L)	-196 °C to 538 °C (-320 °F to 1000 °F)	Cl 150 (F316L): 15.9 bar @ 38 °C → 8.9 bar @ 200 °C; Cl 300: 41.4 bar @ 38 °C	Resistant to pitting corrosion in chloride/acid service. Mo content provides slightly higher allowable rating than 304L at elevated temperatures.
Group 2.8: Duplex Stainless (ASTM A182 F51 / F53)	-50 °C to 300 °C (-58 °F to 572 °F)	Cl 150: 20.0 bar @ 38 °C → 14.8 bar @ 200 °C	High strength duplex alloy provides superior pressure ratings up to 300 °C max limit (avoid 475 °C embrittlement range).

Code Applicability & Safety Boundaries

Class 150 Flange Limitations: ASME B16.5 Class 150 flanges are prohibited from severe cyclic conditions and should not be tested above 1.5× ambient rating (max 29.4 bar for A105) or used above 425 °C.
Flat Face (FF) vs Raised Face (RF) Mating: Never mate a cast iron or bronze FF flange to a carbon steel RF flange without removing the raised face or using a full-face gasket; bending moments from bolting will crack the cast iron flange.
Rigging & Lifting Mass Calculation: When planning pipe spool crane lifts, always use total mated-pair assembly weight (2 flanges + gasket + studs + nuts) rather than individual flange catalog weights.

4. Step-by-Step Worked Example

Field Verification

Determine the flange envelope dimensions, bolt pattern, stud specification, and total mated-pair assembly rigging weight for an NPS 6 (DN 150) Class 300 Weld-Neck Raised-Face (WN RF) joint connected to Schedule 40 pipe using ASTM A105 flanges and ASTM A193 B7 stud bolts.

Nominal Size:NPS 6 (DN 150)Pressure Class:Class 300Facing & Type:Weld-Neck Raised-Face (WN RF, 1.6 mm RF)Pipe Schedule:Schedule 40 (OD = 168.28 mm, t = 7.11 mm, ID = 154.06 mm)Flange Material:ASTM A105 Forged Carbon SteelFasteners:ASTM A193 B7 Studs + A194 2H Heavy Hex Nuts

Extract ASME B16.5 Envelope Dimensions

Per ASME B16.5 Table 11 for NPS 6 Class 300: Flange Outside Diameter OD_f = 317.5 mm (12.50 in), Minimum Thickness T_f = 36.5 mm (1.44 in), Overall Length through Hub L_h = 98.4 mm (3.88 in), Hub Bore ID = 154.06 mm (matches Sch 40).

Result:OD_f = 317.5 mm, T_f = 36.5 mm, Bore = 154.06 mm

Hub bore precisely matches Schedule 40 pipe ID to ensure smooth fluid transition without lip.

Determine Bolting Layout (PCD, Hole Count & Stud Size)

Per ASME B16.5 Table 12: Pitch Circle Diameter PCD = 269.9 mm (10.62 in), Number of Bolt Holes n = 12, Hole Diameter d_h = 22.2 mm (7/8 in), Stud Bolt Diameter = 3/4 in (M20), Recommended Stud Length L_stud = 120 mm (4.75 in) for RF facing.

Result:PCD = 269.9 mm, 12 × 3/4" Studs (L = 120 mm)

12 holes require a star-pattern tightening sequence across 3 torque passes.

Calculate Bare Flange Weight (2 Flanges)

Formula: W_2f = 2 · W_single_flange

Per ASME B16.5 catalog data, single NPS 6 Class 300 WN RF flange weight W_f ≈ 26.50 kg (58.4 lb). For 2 flanges: W_2f = 2 × 26.50 kg = 53.00 kg.

Result:W_2f = 53.00 kg (116.8 lb)

Represents bare forged steel mass for both mating flanges.

Calculate Complete Stud Bolt and Heavy-Hex Nut Mass

Formula: W_fasteners = n · (W_stud + 2 · W_nut)

3/4" × 120 mm B7 stud mass ≈ 0.38 kg; two 3/4" 2H heavy-hex nuts mass ≈ 2 × 0.15 kg = 0.30 kg. Per stud assembly = 0.68 kg. Total for 12 sets: W_fasteners = 12 × 0.68 kg = 8.16 kg.

Result:W_fasteners = 8.16 kg (18.0 lb)

Never omit heavy-hex nuts and stud extension when evaluating pipe rack deadload.

Calculate Total Mated-Pair Assembly Rigging Weight

Formula: W_pair = W_2f + W_gasket + W_fasteners

W_pair = 53.00 kg (flanges) + 0.35 kg (ASME B16.20 6" Cl 300 spiral-wound gasket) + 8.16 kg (bolting) = 61.51 kg.

Result:W_pair = 61.51 kg (135.6 lb)

Spool weight sheet and crane rigging plan must account for ~61.5 kg per NPS 6 Class 300 joint.

Conclusion: The complete NPS 6 Class 300 WN RF flanged joint has OD = 317.5 mm, PCD = 269.9 mm with 12 × 3/4" studs (120 mm length), and a total mated assembly weight of 61.51 kg. Hydrotest rating at ambient is 76.7 bar (1.5× ambient MAWP 51.1 bar).

5. Code Limitations & FAQ

No. Pressure class (150, 300, 600, etc.) is a dimensionless rating designator, not a constant pressure limit. Maximum Allowable Working Pressure (MAWP) is governed by material group and operating temperature per ASME B16.5 Table 2. For example, an ASTM A105 Class 150 flange is rated for 19.6 bar (285 psi) at 38 °C, but derates to 6.5 bar (95 psi) at 300 °C.