The direct connection of galvanized steel pipe to a brass valve is a near absolute guarantee of an advanced leak or failure.  This is due to the more aggressive attack of brass against the zinc protective finish of galvanized steel pipe.  Such events are far more common for open condenser water systems, but are common at domestic water systems as well.  Connecting copper to galvanized steel, such as might exist at a domestic water system as it trims out, produces a similar result.  The issue is less common for closed chilled or hot water systems, although the threat is always present.

The vulnerability of galvanized steel pipe to this form of corrosion is directly related to age, with decades older galvanized steel pipe often still providing acceptable service.  Given the far lower quality of today’s galvanized steel pipe, thread failures due to galvanic activity from a brass valve have been documented within 5 years or less.