ASME B16.5 Flange Weight & Dimensions: Rigging & Bolting Calculation Guide

Specifying flange face dimensions is only half the field job. Crane lifts, pipe-rack deadload, and stress models need the total mated-pair assembly weight—two flanges, gasket, studs, and heavy hex nuts—not a single catalog flange mass. A frequent lookup is 6 inch flange OD in mm: B16.5 Class 150 is 280 mm; Class 300 is 320 mm.

Look up OD, thickness, PCD, bolting, and $W_{\text{pair}}$ in the interactive Flange Dimension & Weight calculator (ASME B16.5 NPS ½–24) — or jump to NPS 6 Class 300.

Quick Summary (TL;DR)

• Takeaway: Rigging and rack loads use mated-pair mass $W_{\text{pair}} = 2 W_f + W_g + n(W_{\text{stud}} + 2 W_{\text{nut}})$, not bare flange weight alone.
• Governing relation: $\text{PCD} = 2 R_{\text{bc}}$; WN hub bore follows Sch 40 / STD ID (B36.10M) in the FEK table.
• Code / basis: ASME B16.5 dimensional tables; gasket mass screening from B16.20-style catalog values in FEK.

Flange weight and dimensions in the field

Class, NPS, facing, and flange type set the envelope for wrench clearance, stud length, and lift plan. Pair this lookup with Gasket Dimension Selection for SWG / RTJ face sizes and Bolt Torque & Tensioning for PCC-1-style screening torque.

1. Core Formulas & Assembly Mass Calculation

$$W_{\text{pair}} = 2 \cdot W_f + W_g + n \cdot \left( W_{\text{stud}} + 2 \cdot W_{\text{nut}} \right)$$ $$\text{PCD} = 2 \cdot R_{\text{bc}}$$

Parameter Definitions

2. ASME B16.5 Dimensional Tolerances & Facing Specifications

Raised Face (RF) Height Differences

• Class 150 & 300: Feature a $1.6\text{ mm}$ ($1/16"$) raised face, which is included inside the nominal flange thickness ($T_f$).
• Class 600 through 2500: Feature a $6.4\text{ mm}$ ($1/4"$) raised face, which is added on top of the minimum flange thickness ($T_f$).

Key Standard Tolerances

• Bolt Circle Diameter (PCD): Tolerance limit of $\pm 1.5\text{ mm}$ ($\pm 0.06"$).
• Adjacent Bolt Hole Spacing: Tolerance limit of $\pm 0.8\text{ mm}$ ($\pm 0.03"$).
• Weld Neck Hub Bore: $+0.8\text{ mm} / -0.0\text{ mm}$ for $\text{NPS} \le 10$ to limit internal step at the butt weld.

3. Step-by-Step Worked Example (NPS 6 Class 300 Joint)

Field Problem Statement

Calculate envelope dimensions, stud bolting, wrench size, and total mated-pair assembly weight for an NPS 6 (DN 150) Class 300 Weld Neck Raised Face (WN RF) joint on Schedule 40 pipe.

Open the same duty in FEK: Flange Dimension & Weight · NPS 6 Class 300 (WN · RF).

Step 1: Extract ASME B16.5 Dimensions

FEK flangeDimension.json (same source as the live calculator) for NPS 6 Class 300 WN RF:

• Flange Outside Diameter ($OD_f$): $320.0\text{ mm}$
• Flange Thickness ($T_f$): $35.0\text{ mm}$
• Hub Bore Diameter: $154.1\text{ mm}$ (NPS 6 Sch 40 / STD ID)

Step 2: Determine Bolting Layout & Tool Specs

• Pitch Circle Diameter (PCD): $269.9\text{ mm}$ ($10.62"$)
• Bolting Pattern: $12 \times 3/4"$ studs ($L_{\text{stud}} = 120\text{ mm}$ screening)
• Bolt Hole Size ($d_h$): $22.2\text{ mm}$ ($7/8"$)
• Wrench / Spanner Size: $1-1/4"$ ($32\text{ mm}$) heavy hex nut socket

Step 3: Calculate Bare Flange Weight (2 Flanges)

Single NPS 6 Class 300 WN RF catalog mass $W_f = 19.10\text{ kg}$.

$$W_{2f} = 2 \times 19.10\text{ kg} = 38.20\text{ kg}$$

Step 4: Calculate Fastener Mass (12 Studs + 24 Heavy Hex Nuts)

FEK screening masses from the same JSON row (engine rounds stud mass to $0.01\text{ kg}$):

• $W_{\text{stud}} \approx 0.27\text{ kg}$, $W_{\text{nut}} = 0.118\text{ kg}$ → per set $0.506\text{ kg}$.

$$W_{\text{hw}} = 12 \times 0.506\text{ kg} = 6.07\text{ kg}$$

Step 5: Total Mated-Pair Assembly Rigging Mass

Adding the spiral-wound gasket screening mass ($W_g = 0.29\text{ kg}$):

$$W_{\text{pair}} = 38.20\text{ kg} + 0.29\text{ kg} + 6.07\text{ kg} = 44.56\text{ kg}$$

Conclusion: Crane rigging and pipe rack load calculations must account for $44.56\text{ kg}$ per joint for NPS 6 Class 300 WN RF in FEK — matching the calculator hero.

Interactive tool CTA

Frequently Asked Questions (FAQ)

Q1. What is a 6 inch flange OD in mm?

ASME B16.5 NPS 6 flange outside diameter depends on pressure class (WN RF screening in FEK):

Open 6-inch-class-150 or 6-inch-class-300. Pipe OD for NPS 6 is 168.28 mm — do not confuse pipe OD with flange OD.

Q2. Does Class 150 mean the maximum pressure is 150 psi?

No. Pressure class is a dimensionless designator. Maximum Allowable Working Pressure (MAWP) depends on temperature and material group. Check the Flange Pressure-Temperature Rating calculator for Group 1.1 / 2.2 screening.

Q3. When must ASME B16.47 be used instead of ASME B16.5?

ASME B16.5 covers sizes up to NPS 24. For NPS 26 to NPS 60, use ASME B16.47. Series A and Series B have different bolt circles and are not interchangeable.

Q4. Can I bolt a Flat Face (FF) flange directly to a Raised Face (RF) flange?

Never mate carbon steel RF flanges to cast iron or bronze FF flanges without removing the raised face or using a full-face gasket. The bending moment from the raised-face gap can crack brittle FF flanges.

Q5. Why does the FEK pair weight differ from a single flange catalog sheet?

Catalog sheets often list one flange. Field lifts and rack loads need two flanges + gasket + full stud/nut set ($W_{\text{pair}}$). That is why internet “flange only” masses understate crane demand.