How to Measure the Diameter of a Flange?

Before you scoff at the notion of someone trying to tell you how to measure the diameter of a flange inside your piping system, take a moment to consider what’s at stake — the operation of your incredibly expensive equipment and the safety of your crew. After all, these are the two most critical components of your entire business.

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Think about the flange itself

This is just a quick review for those new to flanges. A flange is the circular piece used to connect two pipes. They can be made of a wide variety of materials such as stainless steel, galvanized steel, PVC and many others. They create a seal at the joint to keep fluids from leaking.

Although the dimension of the flange diameter is just one measurement used when identifying your flange, it is an incredibly crucial one when lining this piece up to your system.

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Getting started with measurement — the devil is in the details

There are three separate steps when discussing the measurement of the flange diameter. First, measuring the flange’s inside diameter, then across center of the flange and finally, the outside diameter.

Step 1 – Start by measuring inside the flange by simply measuring the center hole. This diameter lets you know what size pipe should be paired with the flange. If you have documentation that tells you the inside measurement of the flange and pipe, make sure you have the right documentation for the part. Papers can get mixed up easily, so it never hurts to take a quick measurement to verify independently.

Step 2 – Measure across the center of the flange. Make sure you find the exact center of the flange to get an accurate dimension. You’ll notice that the bolt holes around the flanges are distributed evenly. This will help guide you to the center.

Step 3 – Finally, measure around the outside diameter of the flange. If your system is squeezed into a tight space, a flange that is too thick may cause problems and some other pipes may need to be moved. Knowing the outside diameter will help you plan for this.

That’s really about all that needs to be done when measuring the diameter of a flange. However, it’s easy to acquire some false confidence and skip one or more of these steps. Be sure to watch the details, which will ensure a much better installation.

If you’re building a new system, this is an opportunity to buy the pipes and flanges specifically manufactured to fit together according to widely accepted standards. Obviously, this will eliminate chances for error.

Beyond the measurement, keep in mind what type of fluid will be passing through the system, the temperature of both the fluid inside, the working conditions outside, and of course, the material used to create the flange. Some pipe/flange materials will not play nice with the chemicals passing through. Make sure you understand the demands the system will create.


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