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Flange Size Chart Reading Guide

Understanding flange dimension tables is essential for proper flange selection, procurement, and installation. This guide explains how to read and interpret ASME flange size charts.

Key Dimensions in Flange Charts

1. Nominal Pipe Size (NPS)

The designated pipe size the flange connects to. Note that NPS does not equal actual pipe diameter for sizes above NPS 12.

2. Outside Diameter (OD)

The overall diameter of the flange. Critical for ensuring proper clearance in piping racks and equipment layouts.

3. Bolt Circle Diameter (BC)

The diameter of the circle passing through bolt hole centers. Essential for flange alignment and bolt hole matching.

4. Number of Bolts

Varies by size and pressure class. Higher pressure classes require more bolts for proper sealing.

5. Bolt Hole Diameter

Size of bolt holes. Standard clearance is 1/16″ to 1/8″ larger than bolt diameter.

6. Flange Thickness

Increases with pressure class. Affects flange weight and structural strength.

7. Hub Dimensions

• Hub diameter at base (B)
• Hub diameter at weld (for weld neck)
• Hub length (for weld neck)

Sample ASME B16.5 Class 150 Dimensions

Chỉ số hài lòng của khách hàng (NPS)	OD	BC	Bu lông	Hole	Thick
1/2 inch	3.50″	2.38″	4	0.62″	0.44″
1″	4.25″	3.12″	4	0.62″	0.56″
2″	6.00″	4.75″	4	0.75″	0.62″
4″	9.00″	7.50″	8	0.75″	0.81″
6 inch	11.00″	9.50″	8	0.88″	0.94″
12 inch	19.00″	17.00″	12	1.00″	1.12″

Sample ASME B16.5 Class 300 Dimensions

Chỉ số hài lòng của khách hàng (NPS)	OD	BC	Bu lông	Hole	Thick
1/2 inch	3.75″	2.62″	4	0.62″	0.56″
2″	6.50″	5.00″	8	0.75″	0.81″
4″	10.00″	7.88″	8	0.88″	1.06″
6 inch	12.50″	10.62″	12	0.88″	1.25″
12 inch	21.50″	17.00″	16	1.12″	1.75″

How to Use Dimension Charts

1. Identify NPS: Match your pipe size
2. Select Class: Based on design pressure and temperature
3. Check OD: Verify space constraints
4. Verify BC: Ensure mating flange compatibility
5. Confirm Bolt Pattern: Match bolt count and size
6. Review Hub: Ensure proper pipe fit for weld neck

Important Notes

• Dimensions in inches (multiply by 25.4 for mm)
• Tolerances specified in ASME B16.5
• Class 150 and 300 share same OD for NPS 1/2 to 12
• Higher classes have larger OD and more bolts
• Blind flanges have same OD and bolt pattern but no hub

Những sai lầm thường gặp

• Confusing NPS with actual pipe diameter
• Mixing pressure classes (bolt patterns differ)
• Not accounting for gasket thickness in assembly
• Overlooking hub dimensions for weld neck fit-up

Always refer to the latest ASME B16.5 standard for complete dimensional data and tolerances.

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