   SEARCH HOME Math Central Quandaries & Queries  Question from Keith, a parent: What is the weight of 36 inch steel pipe 3/4 wall per foot in lbs. Hi Keith,

A 36 inch diameter piece of pipe with 3/4 inch walls can be seen as a 36 inch diameter cylinder of steel with a cylinder of diameter 36 - 1.5 = 34.5 inches removed. The volume of a cylinder of radius $r$ units and length $l$ units is $\pi \; r^2 \times l$ cubic units where $\pi$ is approximately $3.1416.$ You have asked for an answer in terms of feet so I am going to convert the pipe measurements in inches to feet by dividing by 12. Hence the volume of a 36 inch diameter piece of pipe with 3/4 inch walls and of length $l$ feet is

$\pi \left( \frac{18}{12}\right)^2 \times l - \pi \left( \frac{17.25}{12}\right)^2 \times l = 0.5768 \times l \mbox{ cubic feet}$

The density of steel depends on the grade or alloy of the material. The place where I normally look for densities is the SImetric site in the UK. Their densities of metals page gives the density of rolled steel as 7850 kilograms per cubic meter and the density of stainless steel between 7480 and 8000 kilograms per cubic meter. I will use 7850 kilograms per cubic meter to illustrate the procedure.

First to convert the density to pounds per cubic foot I used Google. I typed 7850 kilograms per cubic meter in pounds per cubic foot into the Google search window and received the response (7850 kilograms) per (cubic meter) = 490.059491 pounds per (cubic foot). Hence the weight of a 36 inch diameter piece of pipe with 3/4 inch walls is

$490.06 \times 0.5768 = 282.7 \mbox{ pounds per foot.}$

I hope this helps,
Penny     Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences.