CORROSION OF APPURTENANCES
A major advantage for using composite materials versus steel for the underground propane tank design is to eliminate the need for cathodic protection of the tank and the inspections associated with that protection. However, as the appurtenances used in conjunction with the underground propane tanks are also constructed of metal, we undertook a paper study evaluation of candidate appurtenance metals, and the likelihood of corrosion without cathodic protection of the tank. Unsurprisingly, some metals are more corrosion-resistant than others under these conditions, and results are described below.
Bonnet & body
Nozzle orifice, cylinder
Pressure Relief Valve
A review was conducted of the construction materials for tank appurtenances and the consequence of their interaction with an underground environment. The main sources of data for the materials of construction of the appurtenances were vendor catalogs and supplier information. The evaluated appurtenances included service valves, relief devices, level gages, regulators, and connection piping. Table 12 summarizes the alloys that are used in most of the appurtenances, and Table 13 lists the nominal composition of the alloys.
Table 12. List of Alloys Used in Appurtenances
Alternative Underground Propane Tank Materials, Phase II—Final Report
September 2009 Battelle and Lincoln Composites