Round tubing is used in non-brazed, mechanically assembled in form of U-Bend hairpins. Aluminum hairpins provide requisite formicary corrosion protection and have the majority market share for indoor application. Outdoor application requires more stringent corrosion protection, smaller diameter tubing and larger coils. This makes applying this tubing in outdoor environment an engineering challenge. Developments in long life 3000 series alloys, hairpin lubrication, processing and coil fabrication may open up a limited outdoor market, and make the indoor market more attractive. Alloy development has focused on refinements/composition that alter failure mode from pitting to general lateral corrosion, increasing tubing’s corrosion performance.