An LPG Tank Fails Where Nobody Is Looking

Walk past a bulk LPG installation and what you see is a painted vessel. If the paint is sound, the instinct is that the tank is sound. The parts that actually fail are the ones the walk-past never reaches: the underside of the saddles, the metal beneath the insulation, the vapour space at the top, and the fittings where the pipework meets the shell.

Where corrosion actually happens

At the supports. Where a tank sits on its saddles, water wicks into the gap between the steel and the support and stays there. Air and moisture, no sunlight to dry it, no coating maintenance because nobody can reach it. This is the single most common location for serious wall loss on horizontal vessels, and it is invisible without lifting or crawling under.

Under insulation. Corrosion under insulation is dangerous precisely because the insulation looks intact. Water enters at a damaged seal or an unsealed penetration, saturates the lagging and sits against warm steel. The cladding outside stays pristine while the shell beneath it thins.

In the vapour space. The top of the tank sees a different environment from the liquid-wetted lower half, and on tanks that have carried product with any moisture content, the vapour space is where internal attack concentrates.

The parts that are not the tank

• Relief valves, which must lift at their set pressure after years of sitting — the same drift problem every safety valve has.
• Pipework supports, where movement and vibration wear a line against a bracket.
• Bunding and drainage, which must contain a release and let rainwater out without letting vapour escape to a drain.
• Separation distances, which were right at design and may not be after a building was extended, a generator was sited, or a car park was added.
• Earthing and bonding, particularly at the fill point where static during transfer is the ignition risk.

What an assessment should produce

Not a pass or a fail, but a condition picture: wall thickness where it matters, the state of the coating and supports, whether the relief device has been tested, and a prioritised list of what to do and by when. Because LPG is heavier than air, that picture must also account for where a release would travel and collect — which is the part a tank-focused inspection tends to leave out.