DZR explained

Vyv Cox busts the myths surrounding the use of dezincification-resistant (DZR) seacock materials

- Vyv Cox

Until the relatively recent arrival on the market of plastic seacocks, these essential fittings in boats of all types have been made from three principal metal alloys: stainless steel, bronze and brass. Stainless steel is less common due to both cost and corrosion difficulties; instead, one of two copper alloys is the first choice of most boatbuilders. This article focuses on these two, with particular emphasis on the most recent form of brass, dezincification-resistant brass or, as it is most commonly known, DZR.

Bronze is an alloy of copper and tin, at one time containing 10% tin as gunmetal, but as the cost of this metal has increased, its content has reduced to 7% and 5% in LG4 and LG2. Valves in these materials should be ideal for seawater service if it were not for two practical problems: the alloy can only be cast, an expensive manufacturing process, and the ball inside the valve, being difficult to manufacture in bronze, is most commonly produced in chromium-plated brass, which tends to pit and corrode in service, leading to seizure. Hence, most valves, skin fittings and hose tails in boats are made from brass.

Makeup of brass

Brass is an alloy of copper and zinc, varying in composition from 95/5 to 60/40 (Cu/Zn). 70/30 brass is ductile at ambient temperatures and is widely used as sheet, wire and tubing, but its ductility is less than that of 60/40 at higher temperatures, making it less suitable for high volume production methods. Fittings for boats are manufactured in 60/40 brass by a process known as hot forging, in which a billet is heated to a temperature between 680°C and 750°C before being pressed with great strength between dies to form its shape. Seacock and domestic fittings made from 60/40 brass dominated the market until it became apparent that failures due to corrosion were occurring in certain waters.