Pipe bend radius and erosion due to turbulence
Pipe bend radius and erosion due to turbulence
(OP)
Hello all,
I have some sea water cooled heat exchangers being installed and afew of the bends in the stainless steel piping are extremely tight. I have brought this up with the engineers but I am making no headway with them. I have done a fair bit of searching on the internet but mostly get information on the effects of bend radii on the material of the pipe, not the flow of fluid in the pipe.
Is there a rule of thumb that will give a guideline for the radius of a bend, given the fluid velocity in the pipe, to reduce turbulence at the bend?
If anyone could point me in the right direction to where I could read up on the subject that would be great.
Thanks,
Gareth
I have some sea water cooled heat exchangers being installed and afew of the bends in the stainless steel piping are extremely tight. I have brought this up with the engineers but I am making no headway with them. I have done a fair bit of searching on the internet but mostly get information on the effects of bend radii on the material of the pipe, not the flow of fluid in the pipe.
Is there a rule of thumb that will give a guideline for the radius of a bend, given the fluid velocity in the pipe, to reduce turbulence at the bend?
If anyone could point me in the right direction to where I could read up on the subject that would be great.
Thanks,
Gareth





RE: Pipe bend radius and erosion due to turbulence
http://virtualpipeline.spaces.msn.com
"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain
RE: Pipe bend radius and erosion due to turbulence
http://virtualpipeline.spaces.msn.com
"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain
RE: Pipe bend radius and erosion due to turbulence
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdoweb/
RE: Pipe bend radius and erosion due to turbulence
Regards, John.
RE: Pipe bend radius and erosion due to turbulence
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdoweb/
RE: Pipe bend radius and erosion due to turbulence
From the replies it seems that erosion corrosion will only be an issue if the sea water is very high pressure and velocity. Also the fact that stainless doesn't rely on the protective oxides of carbon steel reduces the problem further.
What I don't understand is BigInch's comment on Reynold's number. Even if the Reynold's number for a particular flow predicts laminar flow in a straight pipe, surely that flow could become turbulent at a bend, then return to laminar flow after the bend. The calculation for Reynold's number doesn't take into account the shape of the pipe.
Gareth
RE: Pipe bend radius and erosion due to turbulence
http://virtualpipeline.spaces.msn.com
"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain
RE: Pipe bend radius and erosion due to turbulence
density p = 1000 kg/m3
viscosity u = 0.001 PaS
diameter D = 0.05 m
v = (R * u)/(D * p)
= (2000 * 0.001)/(0.05 * 1000)
= 0.04 m/S
4 cm per second? That's so slow, I was expecting the transition to turbulence at a much higher velocity. This means that fluid in all the pipes in the system are well within the turbulent region.
There is something that bothers me about the Reynold's number calculation and it's probably just evidence that I'm in over my head, but I'd like to understand more about it. According to the formula, an increase in pipe diameter increases the Reynold's number for a given velocity. Now the turbulence is caused by the effect of the pipe walls on the fluid as it passes by, so surely a larger pipe means that a lower proportion of the volume of fluid is affected by the pipe walls as it moves, so there should be less turbulence. Why does a larger pipe diameter make it more turbulent?
RE: Pipe bend radius and erosion due to turbulence
http://virtualpipeline.spaces.msn.com
"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain
RE: Pipe bend radius and erosion due to turbulence
If this is within 'reasonable normal velocities' for similar exchangers, I do, as others, not belive this to be the most critical issue.
More critical for designing will be the quality and origin of the seawater. Seawater in the Red Sea will not be equal to North Sea, Mexican Gulf or brackish water - different properties and temperature can alter the chemical and corrosive properties considerably. The higher (outgoing) temperature more crtical than the entering.
Every North Sea offshore material engineer will know this, and oil companies offshore often do not allow SS for seawater handling at all, even if this is commonly used in shipbuilding. If SS is selected, material quality will be most important, and have to be of proven for seawater from the area and similar applications.
Also consider in the practical use that all sand and shell rests should to be filtered from the seawater, abrasion from this do probaly do more for the bends tah Reynolds at normal velocities, and think about inside growth in exchanger pipes and cleaning methodes for pipe inner wall.
Outside cleaning?
If you want to use pigging for the exchanger the sharp bends may limit your choice of pig type.
Also to be considered: how critical the application is and the required lifetime length. If critical you might want to exchange the material specification to exotic.
RE: Pipe bend radius and erosion due to turbulence