Hi gents. In Refinery Sea water heat exchanger we are using five galvanic anodes four is pencil type and one is large one at the half of the floating head and the other half is same. After five years I found the pencil anodes depleted and removed but the larger one half of it is gone. The coating ( coal tar epoxy) at the floating head is damage. My questions as the following: Is their any way to monitor these anodes using the test station to measure the potential? Is the coating failure due the overprotection and how to know it? The anode type is zinc. thanks Mark Corrosion Engineer