What Does Waster Mean?
Waster is a sacrificial material that is used to protect the system from corrosion. Waster pieces or zinc anodes are used in piping alloys to protect against galvanic corrosion in sea water. The thick-walled waster pieces have a high corrosion allowance and are positioned in a manner physically separating and protecting dissimilar piping materials.
Corrosionpedia Explains Waster
Seawater cooling systems are designed to reduce flow-induced erosion of the piping system. The piping systems, where possible, have geometry or sizing to minimize turbulent flow. The waster pieces are bi-electrodes positioned between the cathodic and anodic pipes and generate a potential gradient opposing the galvanic potential gradient, thus eliminating galvanic corrosion.
Waster pieces or zinc anodes have been used successfully for protecting sea chests of saltwater piping systems. When the sea chest is steel and the valve is nonferrous, a waster sleeve of mild steel is recommended as additional protection. Mixed ferrous and nonferrous systems should be designed to include a waster piece of extra-heavy galvanized steel on the nonferrous section, connected in such a way as to afford easy removal.
The most common causes of galvanic corrosion problems of aluminum in ships are placement of an aluminum deckhouse on a steel support and attaching steel or copper-based alloys to the hull or the piping, or both. These more noble metal fittings should be electrically insulated from the aluminum; even so, the waster-plate practice is recommended.