As a possible problem with brasses in service it is restricted to aluminium brass of abnormally high phosphorus content in service in sulphide-polluted water. Pitting corrosion Pitting corrosion, which some years ago was a rather common cause of failure of copper water pipes in some districts, is not a serious problem with brasses.
Alpha brasses inhibited against dezincification can however suffer pitting under some circumstances.
As in copper, the pitting produces very localised attack often in approximately hemispherical form beneath a small adherent mound of green corrosion product. If this mound is carefully removed, crystals of red cuprous oxide can usually be seen in the cavity. Figure 8 shows lists a number of common metals and alloys in their order of nobility in sea water and may be used to give some indication of the possible galvanic corrosion effects of coupling brasses to other metals. In general the further the other metal is from the brasses in the electrochemical series the greater the effect will be. The relative positions of the different metals indicated in Table 29 are different in a different environment or even under prolonged stagnant conditions in sea water, where the passive films on stainless steels could break down and sulphide films could form on the copper alloys.