Fixed tanks are generally safe from the sun, buried in the bowels of the ship. But jerry cans are often kept on deck, scorched by UV from the sun. They take a beating, hauled back and forth in the dinghy. Seams split and bottoms wear. Sunbrella covers can last for a decade at least, keeping the cans strong.
Gasoline cans pressurize and bulge. Specifically, the new ethanol formulations have greater vapor pressure than conventional gasoline, and left in the sun can reach unsafe pressures for tanks that have been weakened by the sun. Portable tanks should be stored out of the sun whenever possible. US Coast Guard regulations permit sealed cans below decks, though we don’t particularly like it.
Just for fun, we then tried repairing some cracks in badly sunburned jerry cans. The bottom line is that nothing worked, including welding, until we sanded through the sunburned material. Polyethylene just does not last forever in the sun. Think of it as an expiration date.
Polymer gasoline and diesel tanks cannot be repaired by any method. First, used tanks, and specifically used jerry cans, have generally been compromised in terms of material strength. Second, over the years, gasoline and fuel will have permeated the plastic to some extent. This internal oiliness makes it impossible to achieve a reliable and durable bond, even by plastic welding. This is true not only of polyethylene, but also of fiberglass fuel tanks, and as a result we do not recommend repair of any polymer tank.
