Aluminum Fuel Tanks
January 2, 2015Neil Haynes
For those of you who now own or intend to buy a vessel with aluminum fuel tanks, here are a few things to ponder. There are lots of things that contribute to aluminum fuel tank failures: materials, construction, installation, environment, corrosion and for gasoline powered vessels, fuel quality and additives. The National Technical Information Service did a fairly comprehensive study in conjunction with the U.S.C.G. on aluminum fuel tanks causes of failures. The bottom line is that most aluminum fuel tanks will not last as long as the vessel they are installed in.
Here are some of the pertinent facts reported in this study for your consideration:
Tanks failed in recreational boats from three to 27 years old, both in fresh and salt water.
There were no common problems connected to the reported failures.
Based on the wide range of data, it was not possible to make a realistic determination of the average life of aluminum tanks.
Tanks are prone to failure for a number of reasons, even when installed as required by federal regulations.
Boats of any size are susceptible to tank failures.
75% of boats with failed tanks had inboard engines.
If a problem occurs, it is difficult to detect and repairs will be complex and expensive.
The most alarming fact was 23% of the owners of gasoline powered boats continued to operate them after a problem was detected.
Most of the corrosion failures were due to corrosion on the bottom of the tanks. Aluminum tanks can be affected by pitting, crevice and galvanic corrosion.
55% of these problems involved removing permanent structures to access below deck fuel tanks.
The repairs ranged any where from a few hours to several months.
92% of reported failures were due to corrosion.
Fatigue fractures were mostly confined to tanks with a minimum thickness of .090.
45% of the subject vessels were purchased new.
Only 16% of the cases received any form of help from the manufacturer after a problem occurred.
45% of the cases reported using a fuel additive, like octane booster.
When tanks were replaced, shops generally recommended a thicker .125 inch tank with a chromate primer coating.One really interesting fact revealed in this study was the misconception that storing boats with fuel tanks full actually contributed to corrosion problems due to the concept of “heat capacity of a surfaces.” The large mass of a full fuel tank results in a lower heating and cooling rate for the lower surface of a tank. This large mass means that any condensation which forms on the lower surface of the tank will be retained for longer periods of time as this surface will be the last to respond to ambient temperature. The retention of condensation on the lower surface of the tank will prolong the activity of any corrosion cells which may be present, thus tending to propagate the corrosion process.So what does all this mean to all of us, your prospective as a potential buyer or owner and me a as an inspector?
Here is my take. I have seen lots of tank failures with lots of reasons. A screw through a bulkhead touching a tank; $15,000 repair cost. Poultice corrosion due to pop off inspection covers degrading and tank top debris holding moisture; $ 4,000 repair cost. Cracked weld on a high end sport fisherman due to improper support: $10,000 repair cost. We had to cut two windows in one vessel’s transom and remove tanks out the stern as the most cost affective solution. Cause was improper support as builder used moisture absorbent gasket material causing severe corrosion: $ 5,000.00 per side repair cost. A 1997 fuel tank that pit, corroded from the inside and failed after three years usage and cause was not confirmed.
As an inspector of lots of different types of vessels, I can only inspect what I can see, and it is what we can’t see that bothers me. If you own or intend to buy an older vessel, 12-15 years old, especially a gasoline powered vessel, be prepared for what we see on a frequent basis, the necessity of fuel tank replacement. The older the vessel, the more likely you are to have problems with tanks and usually these problems are costly. One notable tank manufacturer only warrants their tanks out one year. Don’t depend on your insurance company to solve your problem, as most policies will not cover corrosion.
Lots of the folks I come in contact with don’t have pockets deep enough to barely own the boat, much less plop out thousands of dollars for a tank replacement. My advise to prospective buyers, don’t bite off more than you can chew. If you own an older vessel, especially gasoline powered, frequent inspections of fuel components and visible tank surfaces will help to advert disaster.
Use your nose and practice safe recommended fueling practices. A gas fume detector is good equipment to have on board for gasoline powered vessels. If you suspect a fuel tank problem, cease operation immediately and turn off AC and DC power and contact a respectable repair facility. If you have to replace a fuel tank, insure that your chosen repairer knows how to comply with Federal regulations (CFR 183.501-183-590). Also a good understanding of American Yacht and Boat Council recommended practices H-24 for gasoline fuel systems.
Leaking fuel tanks can lead to possible heavy federal fines, so don’t postpone action. Many insurance companies have spill clauses, so investigate coverage clauses with your agent or carrier. Be prepared.
We once pressure tested a suspected diesel tank that held adequate pressure for 24 hours, only later to discover the fractured weld was sitting atop a gasket. A pressure test is not an appropriate diagnostic procedure in my opinion, especially on a thinner older tank as you may burst the tank or a corrosion cell in the process. A global visual inspection is the only way to really know what problems may exist on the outer surfaces of a tank.
Here’s hoping that your fuel stays where it belongs, in your tank. And remember, the Lord loves boaters.
©Neil K. Haynes March 9, 2005
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