Coefficient of Friction for Grit-Slime in Pipe
Coefficient of Friction for Grit-Slime in Pipe
(OP)
I have been researching a way to estimate a coefficient of friction for a pipeline system that is coated with a slimy grit. The flow is approximately 1 to 2% solids. The solid makeup is primarily small particulate silica cuttings from drilling and fine cement along with a small amount of flocculant (the slimy contributor). At this point they aren't adding enough or in the right manner for the floc to work as designed. I am not even sure if they bench tested the system to see if it was even the right type of floc for the material. The pipeline is made up of 4inch hose, 6inDR9 and DR11 HDPE, 8in DR11 HDPE and 8in Sch 40 LCS with numerous elbows, T's, valves and other assorted fittings. When the pipeline is broken apart at various connections, it shows a significant coating of the pumped solids material. It does become thinner in areas of higher turbulence in the system (T's, etc.). The thickness is generally estimated at 1/16in to 3/8in, but has not been actually measured or truly looked at in low velocity sections of the pipeline. I believe it has covered the material of the pipe sufficiently enough to significantly alter the COE from that of the standard COE normally attributed to standard pipe materials. The only information I have found refers to build up of grit/slime on gravity, half-pipe flow in sewage systems. It was determined that the added grit/slime significantly affected the COE and it did not matter as to the material of the pipe, etc. Also, I do not have any way to measure the flow or pressure on the line.
Does anyone have any experience in this type of problem?
Thanks for any help I am able to receive. Sherry
Does anyone have any experience in this type of problem?
Thanks for any help I am able to receive. Sherry





RE: Coefficient of Friction for Grit-Slime in Pipe
If the bore is signiciantly reduced the coefficient of friction is less significant.
I suggest that you need some rheological work undertaken to establish the type of fluid and its behaviour in a pipe. The solids could in fact help to break down eddies at the pipe wall. But this all depends on the velocity.
Without knowing the fluid rheology or behaviour it is difficult to comment. Is the pipe oerating in laminar, transition or turbulent regimes? Possible all three at different stages of the pipe?
The other reference I would suggest is Slurry Transport Using Centrifugal Pumps Wilson Addie Sellgren & Clift. This work has a great deal of knowledge from the Georgia Iron Works pump test rig included.
Flocculated slurries are difficult to model without laboratory information. The type of instrument used may impact the results. A Weissenberg rheogenometer or pipe rheometer is suggested. A simple rotating cup will give erroneous results.
Check out papers by Prof David Boger Melbourne University. He has done a lot of research on fine muds and ash transport. Also Dr Alan Thomas.
Why are you flocculating in the first place?
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