Monthly Archives: December 2012

Almost all building materials undergo some sort of dimensional change when exposed to different environments. In the case of piping, this happens most noticeably when the temperature rises or falls substantially above or below the installation temperature.

This can be detrimental to your piping system if it is installed without taking this dimensional change into account. This usually happens when pipe expansion or contraction is restricted by improperly designed piping systems or pipe support. So how can one account for this dimensional change? The answer involves a little math.

There is a formula some engineer or other brainiac type came up with to figure out the extent a pipe might expand or contract. It uses what is called the coefficient of linear expansion.

Here are the coefficients for PVC and CPVC:

This coefficient comes into play with other factors – like the temperature range your pipe will endure and the length of pipe you are calculating. Here is the full expansion formula:

Change in Inches = [Y(T₁-T₂) /10] x [L/100]

Y = Expansion Coefficient

(T₁-T₂) = Temperature change in degrees between the installation temperature (temperature at which the pipe was installed) and either the max or min temperature it will endure. Choose either the max or min temperature based on whichever is furthest from your installation temperature.

L =Length of straight sections of pipe (ft.)

Looks confusing doesn’t it? The expansion formula upon first glance looks very complicated, but it’s actually pretty simple when you’re putting in real world numbers. Let’s look at an example problem.

Example: How many inches of expansion should I expect on my 500 foot straight section of PVC if the min temperature is 20°F, the max temperature is 110°F, and the installation temperature was 80°F?

Change in Inches = .360 (80-20)/10 x 500/100 = .360 x 6 x 5 = 10.8 inches

Now that you know how much your pipe is expected to expand or contract, you can adjust your design accordingly. Most well-designed piping systems use special configurations to accommodate for dimensions change.

This includes things like loops and direction changes in the pipe. Before beginning a piping system it is important to understand factors like dimensional change. Details like this make the difference between a quality system install and a hack job.

Adequate pipe support is essential for a durable and properly functioning piping system. Without the support it needs, piping systems incur stress and sag that lead to degradation and break down.

There are a number of factors that go into calculating the amount of support each system needs. There are all kinds of formulas and techniques used to determine the amount of support required. You’ll find that your support needs vary from system to system based on configuration, pipe size, load, and temperature.

There are also other things to keep in mind when planning your support. Valves and other points of extra load should be supported separately from your pipe spacing. You should also consider how much your pipe will expand or contract in different atmospheric conditions. Apply any clamps or supports with this fluctuation in mind.

There are a number of helpful reference guides designed to assist you in determining the proper spacing for your PVC pipe system. These guides are only a general estimate, and they are usually based on a several assumptions. The chart below, for example, assumes you are using un-insulated pipe to carry fluids of a specific gravity no greater than 1.0. This chart should only be used as a general guide.

As we’ve pointed out, there are various factors that contribute to support requirements that you will need to take into account for each system you create. If in doubt, more than enough support is always better than inadequate support.

Keep in mind, liquids of a higher specific gravity will require greater support. Usually this means making supports closer together. All of these measurements assume your piping system will be horizontal. Spacing for vertical systems should usually be about two times the intervals in the table above.

If you are working on an inspected job, you will also need to be aware of any specific code requirements for pipe support in your area. Supports should at the very least be compliant with all codes and regulations you will face. Have more advice or suggestions for pipe support? We'd love to hear your comments.