# Specifying Bend Angle in Round Pipes

Specifying Bend Angle in Round Pipes

A maintenance guy needs to replace a curved pipe elbow in his factory.

He calls up and says “I need a round pipe with a 120 degree bend”.

Sounds OK, except he is looking at a pipe like this… and this is NOT a 120 degree bend!

The “Degree of Bend” (D.O.B) or “bend angle” is actually 60 degrees in this sketch.

The bend angle is actually the supplement of 120 degrees (180 – 120 = 60).

Maybe if he said “120 degree long radius elbow” we might understand.

But it is best to clarify.  Otherwise, the pipe will probably arrive like this.

My high school geometry teacher, Mr. Oliver, would say “it’s a compliment to be 90 instead of 180” to help us distinguish between complementary and supplementary angles.  “But don’t forget the spelling is different: in geometry it is spelled with an ‘e’, like ‘complete’.”

He also allowed me to pull my grade out of the cellar with a ten page paper on pi (no, it wasn’t just the number pi to 10,000 decimal places).