Something we have long noticed at PS is that gasoline and diesel control samples in our aging and corrosion studies never really age much. Only when the samples include metal samples do they generate gum and discolor. One explanation is refinery stability treatments, but the primary difference is that copper and zinc ions are powerful catalysts for polymerization. Shore-side fuel storage systems do not experience this type of break down because copper tubing, brass fittings and galvanized pipe are forbidden by code . The following requirements are quoted from standards groups and OEMs.