Metal vs. Plastic Fuel Tanks

[Sand crab]

They have been lining gas, diesel and all kinds of tanks with epoxy for a long time. One could just build an epoxy tank in place.

[a64pilot]

You can have plastic tanks custom made as easily as you can have metal ones and just as cheap. They are welded not rotomolded.
Tooling makes rotomoldimg way expensive for a one off job.

Bugs growing or not has nothing to do with fuel polishing, it has to do with whether or not the fuel was adequately treated. If treated correctly, there will be no snot growing in your fuel, ever.

[Singularity]

Originally Posted by zeehag

HAHAHAHAHA i was constantly underway. the plastic tank was pos. we not repeating bs issues.
we have stainless beauty .
condensation?? in tropics, not much. measured and monitored and racor is real.
theory and reality are different situations.
i am in reality.

ps...when water temps and air temps are same, there is no condensation issue.

As you have all the answers and a different interpretation of reality than most instrumentation known to humans, what specifically caused your biologic problem? How did the water persistently get into/remain in the tank?

The only reality that I'm aware of that would cause your previous situation was a dirty tank that was neither appropriately kept up in the first place, or appropriately cleaned and maintained thereafter. But if the tank was constructed of some highly porous material then this fact could contribute or even result in the woes stated. Then the lesson would be don't buy a crappy tank.

[zeehag]

Originally Posted by Singularity

As you have all the answers and a different interpretation of reality than most instrumentation known to humans, what specifically caused your biologic problem? How did the water persistently get into/remain in the tank?

The only reality that I'm aware of that would cause your previous situation was a dirty tank that was neither appropriately kept up in the first place, or appropriately cleaned and maintained thereafter. But if the tank was constructed of some highly porous material then this fact could contribute or even result in the woes stated. Then the lesson would be don't buy a crappy tank.

my sailing vs your desk work
i SAIL.
i sail TROPICS
my tank was NOT dirty., you have not been adventuring have you.
tank came with boat. was a bad choice by others before me.
i LEARNED from it, as you have not yet.
theory is merely theory. not all real time issues are as theoretical study shows.
try reality of sailing over desk jockey time.
i have encountered many with similar issues.
try real time not theory as your basis. real time trumps desk time every time
it is all good to understand the theories but they will not help you in real time issues.

[Singularity]

Originally Posted by zeehag

my sailing vs your desk work
i SAIL.
i sail TROPICS
my tank was NOT dirty., you have not been adventuring have you.
tank came with boat. was a bad choice by others before me.
i LEARNED from it, as you have not yet.
theory is merely theory. not all real time issues are as theoretical study shows.
try reality of sailing over desk jockey time.
i have encountered many with similar issues.
try real time not theory as your basis. real time trumps desk time every time
it is all good to understand the theories but they will not help you in real time issues.

You are correct on all counts.
I encourage anyone to review this person's blog before taking serious advice.

[thinwater]

Originally Posted by zeehag

HAHAHAHAHA i was constantly underway. the plastic tank was pos. we not repeating bs issues.
we have stainless beauty .
condensation?? in tropics, not much. measured and monitored and racor is real.
theory and reality are different situations.
i am in reality.

ps...when water temps and air temps are same, there is no condensation issue.

Why do you think the plastic tank grew more gook, as you put it? You must have a theory, since PE is inert toward hydrocarbons.


I don't doubt your experience, but I've inspected many thousands of tanks (licensed inspector--also real world, with many thousands of hours inside tanks) and that is the first time I've heard that one.

[thinwater]

Anyone ever have (or have intimate knowledge of) a modern (last 20 years) installed plastic tank leaking or otherwise failing?


Water tanks sometimes crack at fittings, but they are LDPE and low permeability fuel tanks are cross linked polyethylene; considerably different.

[Cheechako]

Originally Posted by thinwater

Anyone ever have (or have intimate knowledge of) a modern (last 20 years) installed plastic tank leaking or otherwise failing?


Water tanks sometimes crack at fittings, but they are LDPE and low permeability fuel tanks are cross linked polyethylene; considerably different.

Incidentally at this time in another thread, but a water tank. It surprised me though.: http://www.cruisersforum.com/forums/...-a-214743.html

[zeehag]

Originally Posted by thinwater

Why do you think the plastic tank grew more gook, as you put it? You must have a theory, since PE is inert toward hydrocarbons.


I don't doubt your experience, but I've inspected many thousands of tanks (licensed inspector--also real world, with many thousands of hours inside tanks) and that is the first time I've heard that one.

tropics.
plastic is nasty stuff. grows slime mold and reeks of that. also holds odors.
i prefer stainless as it is easier to clean and keep cleaner than that plastic thing that used to be in this boat. plastic doesnot dissipate heat as well as stainless .... that featur is important when water under boat is more than 85 degrees f, which is always the case in many of the areas in which i travel. mazatlan is 75-100 f water temps, this past year has been colder..may to may ... may is when the current that defines our weather changes to hot or cold or neutral each year.

[wsmurdoch]

Originally Posted by thinwater

Anyone ever have (or have intimate knowledge of) a modern (last 20 years) installed plastic tank leaking or otherwise failing?


Water tanks sometimes crack at fittings, but they are LDPE and low permeability fuel tanks are cross linked polyethylene; considerably different.

I have a (PE?) 10 gallon water tank in my 1981 Tanzer 22 that cracked at its threaded discharge fitting when the 1/2" male hose fitting was over tightened into the female fitting (half coupling) on the tank. I did it. It was my fault. Patched with a hose clamp to hold the crack together, it has been fine for decades.

Over the years, I have had several 3 or 6 gallon red outboard fuel tanks turn yellow, crack, and leak from (I suspect) UV damage. I have also had the same occur in red plastic 2 to 5 gallon jerry jugs. Protection from sunlight solves that problem.

Bill

[thinwater]

Originally Posted by wsmurdoch

I have a (PE?) 10 gallon water tank in my 1981 Tanzer 22 that cracked at its threaded discharge fitting when the 1/2" male hose fitting was over tightened into the female fitting (half coupling) on the tank. I did it. It was my fault. Patched with a hose clamp to hold the crack together, it has been fine for decades.

Over the years, I have had several 3 or 6 gallon red outboard fuel tanks turn yellow, crack, and leak from (I suspect) UV damage. I have also had the same occur in red plastic 2 to 5 gallon jerry jugs. Protection from sunlight solves that problem.

Bill

Exactly. But neither applies here.

[wsmurdoch]

Originally Posted by thinwater

Exactly. But neither applies here.

Yup.

Bill

[ATC]

Being in the business of cleaning fuel tanks we see indicators that are consistence with fuel quality and tank longevity.


First fuel quality - The diurnal temperature change is the biggest issue with vented fuel tanks. This applies to boat gasoline and diesel.

In gasoline tanks, the lite ingredients start to evaporate beginning at -400 degrees F. This will continue until there is a varnish deposits on the bottom an empty fuel tank. With ethanol blended fuel and water will reduce the quality of the fuel. Once the water reaches 0.05% by volume and nears 60 degrees F the ethanol is pulled out of the fuel and leaves a very low quality fuel. Usually unacceptable for most engines.

In diesel fuel tanks the degradation begins with moisture. Due to the diesel engines where fuel is pulled from the tank, sent to the engine and a return line going back to the fuel tank. It is this return line that can return diesel fuel near the operating temperature of the engine into a less than full tank. When the hot returned fuel enters the tank, it warms up the ullage area and creates condensation. This is one way moisture enters the fuel system.

In both cases, proper maintenance must be maintained.

Now what we see in poly tanks vs aluminum tanks - There appears to be a greater contamination issue with poly tanks for diesel fuel. Again the hot fuel return may be the fault here where the poly tank does not dissipate the heat. Aluminum tanks seem to fare better with boat gasoline and diesel.


Tank Longevity - We look for corrosion / pitting in the area of the fuel sending units. As with any electrical system, the path has to get there and get back. We see improper bonding / grounding to be the cause of most tanks failing. This holds true with both poly and aluminum. Of course a poly tank we not fail the same way as an aluminum tank but the failure is in the embedment's that are attached to the various fittings.


I think I have addressed the few issues that we see during the last eleven years and nearly 4000 tanks.

[Ike]

Anyone ever have (or have intimate knowledge of) a modern (last 20 years) installed plastic tank leaking or otherwise failing?

Interesting thread and lots of good info here. This is a subject that I spent many years on while working in the Coast Guard Office of Boating Safety. Yes I have seen a few plastic tanks fail, but it wasn't the tank. It was usually either a gasket that leaked, or someone (usually the boat owner) accidentally punched a hole in the tank with a screw or drill while installing something else.

Most of what I will say here only applies to gasoline tanks. Actually Cross linked Poly tanks were introduced in the 70's. My first encounter with them was while investigating boat fires in the late 70's. Not one of those were in any way due to a leaky plastic tank and quite a few involved metal tanks. In the 80's we started a research project to test the tanks for permeation and it's affects on the tanks. After soaking them in gasoline in a controlled environment, for five years, the differences in weight, permeation and fire resistance were zero. We also tested them for the affects of alcohol. Again, no change. What does all that mean?

First realize that plastic gasoline tanks have to meet the same safety standards as metal tanks. They have to resist a fire for 2 1/2 minutes without leaking. They are submitted to the fire and then pressure tested at a max of 3 psi, and cannot leak or they fail the test. The same test is true for metal tanks.

Also the USCG had a pretty lose standard (according to the EPA) on permeation, but our concern was not environmental. We didn't want boats blowing up because vapors permeated through the tank walls, so our standard was set to keep it below the Lower explosive limit. All the tanks we tested met this standard, but that is also why you could smell fuel vapors. Your nose is very sensitive to even tiny amounts of gasoline vapor.

In the late 80's we had UL do a long study of issues with aluminum gasoline tanks. I helped with some of the investigations of fires involving boats with aluminum tanks. A lot of information came out of that study.

Aluminum tanks on average last twenty years if properly installed and maintained. We had some fail in less than a year and some that were over 30 years old. But the average was 20.

The most common failure was pinhole leaks in the bottom. This was almost always due to moisture being trapped under the tank with no way to dry out. As an addendum to that we began to see a lot of aluminum tank failures due to phase separation of alcohol from the gasoline in boats that were stored with partially filled tanks. (one marina had over 40 boats with failed tanks in one winter)

In the early 2000's the EPA got into the act and started proposing changes to evaporative emissions and exhaust emissions. I was the liaison officer from the USCG to the EPA on that project for 3 years. The major thing that changed was the construction of PE tanks. The industry had to make them less permeable. They do this several ways but the easiest is a hard liner. The hose people used the same idea on fuel hoses. The added benefit is they permeate far less and don't stink (at least not to my nose)

But to answer the question in the quote, there are boats running around with plastic tanks that are 40 years old or more. I don't know if my boat came with a plastic tank but it got one somewhere in it's life and I have had it 11 years. The boat is going on 47 years old. The previous owner had it 10 years and he said the tank was already there. So that's 21 years or older.

As far as diesel goes I have seen every type of material used for tanks. When I visited Hatteras Yachts in 1985 all their diesel boats had Fiberglass tanks. I have seen aluminum, steel, stainless steel, monel and others. By the way, terneplate has been banned for gas tanks in boats for over 40 years and I have never seen one in a Diesel boat That doesn't mean there aren't some but they are few and far between because of serious corrosion issues.

The primary issue is installation, installation, installation. If the tank is installed right, so that it is kept dry on all sides (including the bottom and top), is inspected regularly and pressure tested annually it may outlast you. Check gaskets and fittings. Accident statistics show that most fuel leaks are at fittings. With diesel, scrubbing the fuel can help considerably and virtually eliminate things growing in the tank.

[AlanWilson]

I've had stainless for 12 years: no problems & no smell. But good thick polypropylene also seems to work.
One point: get it made with a sump and a drain cock at the lowest point, but also take the outlet pipe to the filter from the lowest point (ie the sump), not an inch or so above.
The reasoning for taking the outlet an inch above the bottom is to not suck up crud (sorry - technical term - water, muck & bug), but that is a mistake. The crud is thereby left in the bottom, to get stirred up when you have heavy weather & get sucked into the filter in bulk and block it. Better to suck up crud as soon as it appears and let the filter do its job, keeping the tank clean.