There is no straigthforward answer.
Firstly, the mixture lime / water is highly non newtonian, pseudoplastic, so there is no simple definition of what viscosity is.
The following data is extracted from a technical paper
for a commercially available lime milk
23.5% wt (shear stress Pa shear rate s-1):
(0 0) (20 40) (31 200) (40 900) at 20°C
Secondly, a commercial paper displays significant differences, depending on the kind of lime. I do not know to what extent the information is reliable, but the graph shows viscosity going way up at 300 g/l (as ca(oh)2) when prepared by slaking CaO, and the "limit" is 700 g/l when prepared from hydrated (ca(OH)2). The paper states that the lime milk remains "liquid" for less than 200 g/l Ca(OH)2 if prepared from CaO, and less than 500 g/l if prepared from hydrated lime.
Hope this helps, I have quoted here what I found, but would not be overly confident on the above data
One paper is a technico-commercial paper of september 1996 from BUXTON lime, and is about the properties of their propriatory KALIC lime milk.
Another is a brochure from the LHOIST group
You dont mention in your post whether 30% is by weight or volume?
I have successfully used PVC tube (plasticised) fully supported in cable ladder. The reason for this is that scale formation and then blockage occurs. With flexible tube one can shake it, hit, move it etc to unblock & descale the line.
Lime slurry would be one of the most difficult fluids to work with.
I have also seen a half pipe (PVC_U) used in a gravity situation. This was for lime dosing in a sewage treatment plant. The half pipe was run over the sedientation tank. Any blockage resulted in an overflow into the tank. No big deal but no difficult spillage to clean up.
