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Old 12-17-2012, 09:30 PM   #124
Scraping Paint
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Originally Posted by RMoore View Post
What kind of maintenance is recommended for SS diesel fuel tanks?
Bob--- The five new tanks the PO had fabricated for our boat to replace the boat's three original iron tanks are stainless. When we had the boat surveyed these tanks were only a year old. The surveyor said that stainless tanks are not approved by the ABYC (this was in 1998). The reason he gave is that there is stainless and there is stainless. Even with the same alloy number the quality can vary greatly.

The same thing is true of the welds. Heating stainless in welding changes the steel's properties to the point where its "stainless" attributes can be reduced or go away entirely. So the quality of the welds is critical to the integrity and longevity of a stainless tank. Poor welds can lead to crevice corrosion and pin holing when the metal is deprived of oxygen as they are when the tanks sit full of fuel.

Because of all the variables possible with a stainless tank, the ABYC did not consider it an "approved" material for fuel tanks. I have heard this ruling has since been changed but I don't know for sure so don't assume I've heard right.

The surveyor said that as long as we moved fuel though the tanks regularly and the welds were exposed to oxygen periodically this would help hold weld problems at bay (if there were going to be weld problems).

He also said that while stainless was not a good choice for fuel tanks he was familiar with boats in the SFO Bay area that had had stainless tanks installed many, manay years earlier and were so far doing just fine. So it all depends on the quality of the metal and the welds.

So this plus not wanting to have fuel sit on the boat very long anyway prompted us to develop the fuel management procedure we have used since acquiring the boat.

All our tanks gravity feed from their lowest points so there is really no maintenance necessary to the tanks as nothing stays in a tank when it's emptied. We've never gotten any water or dirt in the bowls of the Racor filters the fuel runs through on the way to the engines. The tanks were made with large inspection ports but we have had no reason to remove them.

So maintenance-wise, I dunno. You can polish them if you like, I guess. We use bug killer and a fuel conditioner in our fuel, for what that's worth although neither one has any effect, good, bad, or indifferent, on the tanks themselves.

If someone was contemplating new tanks for a boat I would not recommend stainless for the reasons stated by the surveyor (at this point I'm assuming that what he told us is correct). If we had to re-tank our boat, or if someone asked us what to use for new tanks, I would recommend what Grand Banks themselves are now using for fuel tanks, which is composite.

Although an iron tank if properly made, protected, and installed can last a hell of a long time.
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