I have watched a construction company build a million gallon fuel storage tank. Over time, I saw the steel rust to a horrible looking orange. I was aghast at the sight of it. I am confident now that they applied a serious rust converter product on it before applying paint, as it ended up with a perfect finish which has survived a salt spray environment for several years since then.
I will be doing some work at that facility soon, so I will ask about their process.
I think I can explain.
They would have had to sand or water blasted the tank before applying a zinc/epoxy/urethane system.
The zinc is a sacrificial coating used to show yellow/rust streaks once exposed to moisture. The idea being that it was a visual indicator that the topcoat had failed. This "indicator" gives the asset owner time to inspect and assert a repair process as deemed necessary. They key point here is that the actual tank (or asset) was not failing, but rather the top coat had failed causing the zinc to stain.
It's a very effective way of assessing the condition of the asset without losing the integrity of said asset.
The rusting tank during construction is expected and dealt with accordingly. The amount of rust on it during this time would be unsightly for sure, but not detrimental to the overall integrity of the asset. Some new modern coatings technology has replaced sand blasting in these cases with a water blast which is cheaper and creates far less dust to clean up.
