Method of making a tank

A method of making a metal tank for a liquid hydrocarbon comprising the steps of, forming a first tank wall terminating in a first flange, forming a second tank wall terminating in a second flange, said first flange being approximately twice the length of said second flange, applying a layer of adhesive means which is resistant to said liquid hydrocarbon as a layer thereof against one entire surface of said first flange, applying another layer of adhesive means against the surface of said first flange opposite from said one surface of said first flange, said other layer of adhesive means extending from the base of said first flange along roughly half its length, mechanically folding said first and second flanges to define an interlocking mechanical joint which cooperates with said layer of adhesive means to provide a liquid tight seal, said mechanical folding step comprising disposing roughly one half of said first flange and its associated adhesive means on one surface of said second flange and disposing the remaining portion of said first flange and its associated adhesive means on the surface of said second flange opposite from said one surface and bifolding said half length and adjoining structure during said mechanically folding step to define said joint having a plurality of six thicknesses.