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fritcion factors, materials
2

fritcion factors, materials

fritcion factors, materials

(OP)
Hi there,

hope somebody could help me.
I have found and red several old posts concerning pressure drop and friction factors.
As a matter of fact, I am not able to find the difference between friction factors of following materials
- copper
- iron
- carbon steel
- stainless steel AISI 304
- stainless steel AISI 316
- stainless steel AISI 321 (by the way, is there an effective difference between friction factor of steels ?)
- aluminum

Please, can anybody help me ?

Many thanks

RE: fritcion factors, materials

I guess what you are looking for is values of absolute roughness, rather than values of friction factors. Once you have the absolute roughness you can calculate the relative roughness by dividing by the pipe diameter. The next step is to calculate the Reynolds Number and once you have that (Re) plus the relative roughness (e/D) you can use the Colebrook equation or a Moody Diagram to get the friction factor.

The absolute roughness is most often presented in a table like the one referenced by micalbrch, but the pipe fabrication method and the pipe's usage history are actually the more important factors. Drawn tubing (typically listed as copper, lead, etc in the tables) will be smoother than pipes made by welding bent plate. And even if commercial pipe starts off with a roughness of 0.05 mm, after a few years in a corrosive duty it can have a roughness of 1.0 mm or more.  On the other hand, in a non-corrosive duty it can actually get smoother with use.

Luckily for us, it is usually not too critical what roughness we use, so it is better to be a bit more conservative than the standard tables show.  It is not good to design a pipeline that works well at startup, and then becomes under sized as time goes on and the inner surfaces becomes rougher.

Katmar Software - Engineering & Risk Analysis Software
http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

RE: fritcion factors, materials

In addition to Katmar's excellent post, I use 150E-6 ft for commercial steel pipe which is the same as 0.05 mm.  

I've heard claims that several of the stainless steels were smoother than drawn carbon steel.  When I was doing gas measurement we got some SS meter tubes and we were afraid that they would be too smooth to meet the requirements of AGA-3 so we measured the surface roughness.  We got numbers very close to 150E-6 ft and all the tubes were in spec.  Since then I've used the same absolute roughness for all "steel pipe".

Copper and aluminium are both about 5E-6 ft.  The source I found for that claims that PVC and stainless are also 5E-6 ft.  I found another source that agrees with me that SS is the same as carbon steel and says copper and aluminium are 5E-6 ft.  You really have to do a "gut check" on anything you find on the interwebz.

At the end of the day, getting this wrong will be a second order error at best and if you are using the Moody Diagram instead of the Colebrook equation you probably will pull the same friction factor off the graph from using 5E-6 ft or 150E-6 ft (I never understood why the y-axis was Log, I generated my own version with a Cartesian y-axis and it is a lot easier to read).

David

RE: fritcion factors, materials

David, thanks for the feedback on what roughnesses are found in the real world.  I have always used the same numbers for SS pipe as for steel pipe, but this was based purely on gut feel and that the calcs seemed to check out ok when built. It's good to get confirmation from someone who has taken the trouble to actually measure it.

Katmar Software - Engineering & Risk Analysis Software
http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

RE: fritcion factors, materials

I've gotten down to 0.025 mm for a dry & somewhat sandy 20" CS pipeline 30 years old.  I attribute that to 1 of two things,

1) sand blasting effects made the routhness smoother, or
2) sand blasting effects made the inside diameter larger than what it should have been.

From "BigInch's Extremely simple theory of everything."

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