Firwin FAQ – What is the relation between insulation blanket size and the pipe size?

Rectangular Insulation Blanket and Corresponding Pipe

It is important to keep in mind that the actual size (length and width) of an insulation blanket can be somewhat larger than might be expected for a given pipe diameter. This is because when determining the actual size of an insulation blanket, the thickness of the blanket must be taken into account.

This is best illustrated by the following example. First, some basic mathematics – as most of us can remember from high school, the circumference of a circle is the circle’s diameter x PI. So, let’s say you have a pipe that needs insulating, that is 4″ diameter, and 10″ in length. Calculating the pipe’s circumference as 4 x PI, gives you approximately a 12.5″ circumference.

Pipe Diameter with and without insulation blanket illustration

Now here’s the tricky part. If your conclusion is that the blanket size for this application would be 12.5″ x 10″, you would be incorrect. That is because the insulation blanket thickness essentially increases the oustide diameter of the pipe.

In our case here, to arrive at the ‘insulating diameter’, you would need to increase the pipe diameter by the blanket’s thickness at each end of the pipe. So for a 1″ thick blanket, our 4″ diameter pipe becomes a 6″ diameter pipe. The resulting insulation blanket dimension would then be 6 * PI, or 18.75″.

“We find that this is a fairly common mistake”, said Brett Herman, Firwin’s V.P. of Sales and Operations. ” A customer will submit a request for specific size blanket, say 12.5″ x 10″, thinking that this will be sufficient to wrap a 1″ thick insulation blanket around his 4″ diameter pipe. Without taking into account the insulation thickness, the resulting blanket will be approximately 6″ too small and will not fit around his pipe diameter.”

To prevent this from occuring, Firwin always tries to determine what the application is that the client is trying to insulate, and what are the dimension of the components. “It’s easy just to go ahead and make the blanket to the customer’s specifications. But our experience shows that people do not always realize how to take insulation thickness into account. So before we proceed and manufacture a blanket, we try to determine what the customer is trying to acheive. If he says he wants to wrap an 4″ diameter pipe with a 1″ thick insulation blanket, then we know what the blanket size he submitted is not correct, and we are able to advise the customer and prevent a problem from occuring”, added Brett.