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# Pipe Fitting

## Pipe Fitting

(OP)
A section of 4.5 inch standard weight, seamless steel pipe, has a wall thickness of .355". When the pipe is bent into a 90° turn, the length of the outside edge of the curve will exceed the length of the inside edge of the curve by how many inches.

This is a question from the USCG Merchant Marine Chief Engineer Exam. Can anyone help with a formula?
Replies continue below

### RE: Pipe Fitting

Hi Chief!

CAUTION:  This reply is from an electrical/math guy who just had to take a stab at it -- please wait for confirmation from one of the piping experts in this forum!

The way I see it, the radius of the outer edge of your ell will be greater than the inner radius by the inner diameter of the pipe plus twice the wall thickness (ignoring deformation during the bending process).  Since the full 360-degree circumference of the circle would be 2*pi*r, one fourth of that (90 degrees) would be 0.5*pi*r.  You're looking at the difference in two radii (4.5+0.355+0.355) so the difference in the arc lengths would be 0.5*pi*(5.21) or 8.184 inches.

I'll be interested to see if there are deformation factors that need to be applied -- let's see who else posts an answer!

Kindest regards to all,

Old Dave

### RE: Pipe Fitting

(OP)
Old Dave thanks, your right on the money 8.184 is the correct USCG answer.

I'm writing a help file for a Merchant Marine chief engineer exam CD, (hawsepipe.net) taking question by question, writing a page on why the answer is what it is.

Thanks again

### RE: Pipe Fitting

dieselchief...

Is't this kind of a wacky question for an exam for a Mechant Marine Chief Engineer ?

I can fully understand why this would be on a shipyard pipefitter's exam........ Why on earth would the chief engineer be interested in this issue ??

MJC

### RE: Pipe Fitting

MJC,

Talking as an ex diesel chief when youre in the middle of the atlantic and your cooling water pumps fail and the ship looses all power a shipyard pipefitter is unlikely to be available.

### RE: Pipe Fitting

(OP)
As a Merchant Marine engineer you are the welder, machinist, pipefitter, electrician, diesel mechanic, air conditioning, refrigeration, hydraulic, and electronic technician. Did I leave anything out? When something brakes, WHAT EVER IT IS they call “CHIEF”, come to think of it there should be a Merchant Marine Chief on the space shuttle.

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