Some Aspects of the Corrosion Of Tin Plate by Prunes

Abstract

The mechanism of corrosion of tin plate in cans has been investigated by the prune pack method. Evidence is presented which indicates that, in prunes at least, tin corrodes at a constant rate without the evolution of measurable quantities of hydrogen. Hydrogen evolution in canned prunes is related directly to the solution of the iron of the steel base. Above a certain minimum tin coating weight, this minimum being dependent upon the character of the steel base, increased tin coating weight, up to at least 1.5 pounds per base box, results in increased pack life. The improvement in pack life per increment increase of tin coating weight is the same for all types of steels investigated. Experiments are described which illustrate that tin affords cathodic protection to steel in contact with prunes. The more corrosion resistant the steel, the more effective is the cathodic protection. These tests indicate that porosity of the tin coating is not an important factor in the corrosion of plain (unlacquered) cans by prunes. These conclusions do not necessarily apply to other food products packed in plain tin cans or to food products packed in lacquered cans.