4 each branch containing a valve 5 and 6 a series of annular electrodes 7 are held in pipe 2 and insulated from it by means of insulators 8 electrical contact to each annular electrode is made via leads 9 and insulating bushes 10 leads 11 and 12 respectively connect the electrodes and the pipe 2 to an electrical supply in operation electrodeposit 13 forms on each of electrodes 7 we have found see above that shear tends to reduce the efficiency of the deposition process however fig6 shows that at sufficiently low shear rates the efficiency is largely undiminished for example fig6 shows that 10 rpm had little effect on the deposition rate in our modified chan 35 oilfield rheometer 10 rpm corresponds to about 4 3 s u2212 1 for a pipe of diameter d the relation between wall shear rate wsr volumetric flow rate q and mean axial velocity v is wsr 16v 3d 64q 3nd 3 this sets an upper limit on v and q in order that the deposition process is not unduly lessened for example for d 0 1 m and wsr 4 3 s u2212 1 v 0 22 m s u2212 1 approximately which corresponds to about 100 l min u2212 1 the device operates as follows deposit is collected on electrodes 7 with valve 5 open and valve 6 closed pipe.