Introduction

Flanges play a vital role in pipeline systems. They connect steel pipes to pipe fittings or valves. So how do you choose the right flange? First, you need to know how to measure flange size. Of course, flange sizes are specified according to flange standards. Such as ASME B16.5 and DIN. If you need accurate sizes, you can measure them during use.

Why Measuring Flange Size Matters

Measuring flange size is important for proper installation because

1. Incorrect size may cause leakage.

2. Incorrect size measurement will cause welding failure with steel pipes.

3. Flange sizes of different standards are somewhat different.

4. The bolt holes of flanges of different standards must also be determined to correspond.

Key Dimensions for Measuring a Flange

When measuring a flange, pay attention to the following aspects:

1. Size standard

NPS: Nominal pipe size, mostly used in North America, expressed in inches.

DN: Nominal diameter, commonly used in international regions, mostly expressed in millimeters.

2. Outer diameter

The outer diameter size of the flange.

3. Bolt circle diameter

The diameter of the bolt hole is crucial to ensure that the flanges are connected correctly.

4. Number of Bolt Holes

Flanges have different bolt holes for different sizes according to different standards. There are usually three regular numbers of holes: 4, 6, and 8. When connecting flanges, in addition to ensuring the same size, the bolt holes must also be the same.

5. Bolt Hole Diameter

The bolt hole diameter also varies according to different standards. Usually it ranges from ½” to 1½”

6. Flange Thickness

In addition to the flange standard, the thickness of the flange is also related to the concave and convex surface. The thicker the thickness, the greater the pressure it can withstand.

Tools Needed to Measure a Flange

The commonly used dimensions for measuring flanges are: tape measure, caliper, and ruler.

Tape measure: used to measure OD and BCD.

Caliper: used to accurately measure the diameter of the bolt hole.

Ruler: used for plane measurement.

Step-by-Step Guide to Measuring Flange Size

Step 1: Measure the Outer Diameter (OD)

Use a tape measure or ruler to measure the dimensions of the outer edges of the flange. Usually in inches or millimeters.

Step 2: Determine the Bolt Circle Diameter (BCD)

The diameter of the bolt hole is usually measured with a caliper.

The distance between the two ends of the bolt hole.

Step 3: Count the Number of Bolt Holes

Check whether the number of bolt holes is consistent with the standard.

Step 4: Check the Flange Thickness

When measuring the thickness of the flange with a caliper, first exclude the concave and convex surfaces.

Step 5: Identify the Flange Pressure Rating

Generally, flange manufacturers will mark the size specifications on the flange. Such as CLASS 150 of ASME standard or PN16 of DIN standard.

Common Flange Size Chart

The following table is a common ASME B16.5 specification chart:

Measuring Flange Sizes for ASME vs. DIN Standards

ASME B16.5 (North America)

NPS pipe specification size, unit is inches.

Class standards: class 150, 300, 600, 900, 1500, 2500.

DIN European Standard

Use DN nominal size, unit is millimeter.

Pressure level: PN6, PN10, PN16, PN25, PN40

Common Mistakes to Avoid

OD and NPS are not clear, OD refers to the outside diameter, NPS refers to the inside diameter of the pipe.

The bolt holes are not aligned.

The pressure level does not match.

Summary

Correctly measuring the size of the flange is an important step in connecting the pipeline system. Correctly selecting the flange is the basis for ensuring the safety of the pipeline without the risk of leakage.

The above article introduces how to measure the dimensions of flanges of different standards, including inner diameter, outer diameter, thickness, bolt hole, and inner diameter of the hole. It also introduces how to use the tools that can be used.
I hope this article can help you understand the dimension measurement of flanges.