Galvanic Corrosion And Electric Insulation Between Different Materials Of Seawater Pipelines

Seawater cooling pipeline system which is called seawater pipelines for short is commonly used in shipping, seashore power plant and maritime oil field etc. At present, the former materials used in seawater pipelines are replaced by 90/10 Cu-Ni alloy with better corrosion resistance, galvanic corrosions between B10 and other materials are unavoidable. The galvanic corrosion and protection methods between 90/10 Cu-Ni alloy and other materials need to be researched urgently. Galvanic corrosion characteristic and galvanic effect of B10 couple with H62,Tup and TA2 are studied respectively under the conditions of different area ratios and different flow-rates seawater firstly in this article, then effect of resistance on galvanic corrosion and criterion of electric insulation was investigated using simulated electric insulate experiments contacting different resistances.The results of experiments about tested materials free corrosion in different flow-rates seawater show that corrosion potential series in diversified flow-rates seawater: TA2>B10>Tup>H62. The results of experiments about effects of area ratio of anode and cathode on galvanic corrosion indicate that galvanic effectγincreases with the increase of area ratio of anode and cathode; dezincification happens to H62 clearly; cathode and anode change to each other in short time when B10/Tup area ratio=5:1,10:1. With the increase of seawater flow-rate, galvanic effectγof B10-H62 increases, galvanic effectγof B10-TA2 decreases, galvanic effectγdecreases when B10/Tup area ratio=1:1, galvanic effectγis least in 3m/s flow-rate seawater when area ratio=5:1; corrosion rate of B10 in 1m/s flow-rate seawater is greater than free corrosion rate in the same flow-rate seawater when B10 couples with H62 and Tup respectively.The results of experiments about simulated electric insulation show that the technology of electric insulation is one of effective methods to prevent galvanic corrosion. With the increase of resistance, galvanic effectγof B10-H62 decreases; galvanic effectγof B10-Tup increases earlier, then decreases, it is greatest when B10 couples with Tup connecting resistance R=5KΩat area ratio=1:1 and connecting resistance R=1KΩat area ratio=5:1 and 10:1. B10 can be insulated with H62 and Tup respectively connecting a resistance R≥20KΩ, so 20KΩresistance can be considered the criterion of electric insulation, and there are no effects of area ratio, flow-rate and test time on it. Galvanic current density of B10-TA2 decreases with the increase of resistance, but galvanic current density is greater than the galvanic current density of both materials couple with each other directly when resistance R≤5KΩ; galvanic effectγincreases earlier, then decreases, the value is greatest when resistance R=1KΩ.B10 can not be insulated with TA2 connecting all tested resistances at all the tested conditions.In conclusion, tendency and effect of galvanic corrosion between B10 and other materials are very serious, they should avoid coupling each other directly when used in projects. The technology of electric insulation is one of effective methods to prevent galvanic corrosion, but the lowest resistance which can insulate B10 and other materials is different.