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A Are the pipes coated or not? For uncoated piping, the distance of protection is about three pipe diameters, making CP impractical for the fowing conditions. Generally, the corrosion control (other than choice of material and coatings) is only on the outside of the piping. Internal corrosion rates are built into the life expectancy of the system, although the pH, etc., can be adjusted to make the water less corrosive to the materials already in use. A A length, and diameter depend on pipe diameter, water velocity, and distance from the rectifer. This is an interesting exercise if there is no facility for adjusting each anode current. A clue: go for a simple constant driving potential rectifer. A few more calculations are required for anode sizes, but there will be capital savings in the long run. There is no problem with using Mg anodes in potable water. Editor's Note: Additional MP Blog items appear in the individual technical sections: cathodic & anodic protection (p. 40), coatings & linings (p. 48), and chemical treatment (p. 62). It is my opinion that bare steel pipe should not be used in raw aerated water, let alone at a pH of 5.7 or less. Have you considered lining the pipe with a 100% solids, fastcuring polyurethane system? You can get coatings that will cure enough for immersion service in <5 min. No doubt you would need more than 0.5 h to do any signifcant amount of work when you consider the drying out and blasting necessary, but perhaps you could get the line shut down for a slightly longer period and just do it in sections. I was involved in the internal coating of a short section of replacement pipe that was installed inside a 48-in (1,220mm) line. The water fow was stopped for ~3 h. We could actually hear the water start fowing again ~20 km up the line as the painters were pulling the trigger. The pitch between the anodes is eight times the diameter for 25 Ω-cm saltwater. For any other diameter, adjust the pitch by the ratio of the resistivity. However, over time, the length of the anodes becomes greater than the diameter, at which point you would ask if CP was really necessary. Refer to the work done by Matthewman at the CEG Seawater Corrosion Lab in the early 1950s. He produced the fgure. Morgan did a lot of work while at Metlab Maple at about the same time, and I believe there is reference in his frst edition. The installation of useful zinc references should be considered with a means of calibration. The anode wiring, A NACE International, Vol. 52, No. 5 May 2013 MATERIALS PERFORMANCE 13