Question for 13mentaculus
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18-03-2011, 01:19 PM
Question for 13mentaculus
13mentaculus, you mentioned in another thread that you have a BS in physics. Now I must admit, I don't know what a BS is, and it just can't be short for what I first thought of! Tongue But I assume it involves something that makes you much more adept in physics then I am. So therefore I have a question for you.

I had a discussion with a colleague of mine a few days ago. He claims that if you have two pipelines of different diameters, say 2" and 4", then the 4" pipe needs to have a thicker wall than the 2" pipe in order to hold the same pressure. My position is that he is wrong. From what I remember from school its the pressure that matters, not the volume.

So who's right and who's wrong?

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18-03-2011, 01:50 PM
 
RE: Question for 13mentaculus
I'm sorry if i'm reading this incorrectly or if i'm just stupid, but it seems to me like you're wrong. If there's a 4" pipe to accommodate a certain pressure, if you get a smaller pipe that has to handle that same pressure, odds are, it needs a thicker wall.
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18-03-2011, 01:51 PM
RE: Question for 13mentaculus
If he means BSc, then its bachelor of science.

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19-03-2011, 12:11 AM
RE: Question for 13mentaculus
(18-03-2011 01:19 PM)ThinkingNorseman Wrote:  He claims that if you have two pipelines of different diameters, say 2" and 4", then the 4" pipe needs to have a thicker wall than the 2" pipe in order to hold the same pressure. My position is that he is wrong. From what I remember from school its the pressure that matters, not the volume.

I don't know about pipes and pressure, but when you double the height of a pillar you need to make it more than double its diameter to make it hold double the weight. Based on this my guess would be that he is right because there is more pressure on the larger pipe because there is more surface area inside the pipe.

I hope someone can verify the answer because I want to know. My best guess is still a guess.

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19-03-2011, 12:22 AM
RE: Question for 13mentaculus
(19-03-2011 12:11 AM)No J. Wrote:  I hope someone can verify the answer because I want to know. My best guess is still a guess.

My thoughts exactly. Thats why I'm asking the professional.
Once again confirming Daniel Dennet's argument that it is perfectly ordinary human behavior to get your information from a authority figure. Tongue

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19-03-2011, 04:08 AM
RE: Question for 13mentaculus
Can't we look up the equation for pressure in a physics textbook in electronic format ?

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19-03-2011, 08:32 AM
RE: Question for 13mentaculus
I know this isn't directed towards me, but I can't let an engineering question pass by Big Grin .

A larger diameter pipe needs to be thicker to hold the same pressure. Pressure is force/area, so if you increase the diameter, you increase the area and the overall magnitude of the force pushing outwards on the pipe is larger in the bigger pipe than the smaller one.

There is an equation for it, I can't remember it off the top of my head but essentially it's:

Thickness = Pressure (psig) * Diameter / (2 * {tensile stress + Pressure (psi)})

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20-03-2011, 02:39 AM
RE: Question for 13mentaculus
Thank you. I tried googling the question but couldn't find the answer there. Maybe it was in one of those charts that you need to be a certified plumber to make any sense of.

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21-03-2011, 07:34 PM
RE: Question for 13mentaculus
I'm just now seeing this thread.

I do have a degree in Physics, but I haven't taken a physics course since 2006 and I haven't used it all in the workforce, so almost everything that I learned is gone.

I have no idea. Your guess is probably as good as mine.

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22-03-2011, 12:45 PM
RE: Question for 13mentaculus
Good thing Glaucus saved the day then.
My colleague argued that there was a need for thicker walls in the pipe because of the overall pressure that was acting on it due to increased surface area. I argued that it also meant that there was more pipe wall to carry the load. oh well.. guess I was wrong again. He's going to love this when I tell him.

So Glaucus, what kind of an engineer are you anyway?

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