Built from proprietary aluminum alloy 6061-T6, Cycle-tested in excess of 100,000 cycles at service pressure, Minimum burst pressure tested to 2.5 times service pressure without failure. Cycle-tested in excess of 100,000 cycles at service pressure, Minimum burst pressure tested to 2.5 times service pressure without failure. Exterior Finish was Most Luxfer cylinders are painted with durable, premium-quality powder coatings Shot Blast and Brushed No Coat cylinders are not painted, making them ideal for rental, dive boats, etc. and Aluminum is highly resistant to external corrosion. Aluminum is highly resistant to internal corrosion is called interior finish.