# Pipes and tubes

## Main Question or Discussion Point

what are the principles regarding pipe OD, thickness & strength as well regarding round and square which one is more stronger. This matter came up becoz there are certain sizes of OD not available in HR but only available in CR, on the other hand there are certain sizes which we can convert form round to square to save material or increase strength. Pls note that we have to find out the following regarding Pipes -

1. If we make a Hollow Round Tube of 15.88mm OD and 1.2mm Wall Thickness, means a weight of 470gm per mtr. Keeping the same weight per mtr, if we make Holow Tube of 19.08mm OD then its thickness will be 1.0mm.

Now our question is, which Hollow Tube will be stronger? Which will bend less when put same pressure on same length? The Tube with 15.88mm OD or with 19.08mm OD as the material used in both of them is same?

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1. If we make a Hollow Round Tube of 15.88mm OD and 1.2mm Wall Thickness, means a weight of 470gm per mtr. Keeping the same weight per mtr, if we make Holow Tube of 19.08mm OD then its thickness will be 1.0mm.

Now our question is, which Hollow Tube will be stronger? Which will bend less when put same pressure on same length? The Tube with 15.88mm OD or with 19.08mm OD as the material used in both of them is same?
Stronger in what sense? Generally when we speak of the 'strength' of a pipe, we're refering to its ability to resist internal pressure. But we might also be thinking of using a pipe to make some kind of framework in which it must resist a bending moment.

For the case of internal pressure, a thicker wall and smaller diameter is stronger because there is more material to resist the forces that tend to split the pipe (ie: lower force per unit area of material).

For the case of a bending moment in a pipe, the thinner wall and larger OD is stronger (up to the point where buckling becomes the primary failure mechanism) because there is more material farther away from the point of bending (called a 'neutral axis) and this allows for larger moments to be resisted in the same way that less force is needed on a longer lever arm to produce the same moment around a fulcrum.