Fuel Tanks

[Propnut]

4 year old fuel tanks that were built by a so called professional tank builder.Here's what i found when i opened the inspection ports.
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They used gasket material that was not compatible with diesel. You can see the gasket material in the bottom of the tank. It turned to mush. Now look at the pit in the bottom of the aluminum tank.
Has anyone ever seen a tank pit like this in 4 years? 200 hrs on the boat since the tanks were installed. So now I'm faced with pulling a new engine back out four years later to get the the tanks back out and put new tanks in. Any suggestions on the best tank builder on the east coast? I'm in North Carolina. When i contacted the builder, he said the gasket supplier must have sent him the wrong material. I think his aluminum supplier must have sent him the wrong aluminum as well. If crying would help, I'd boo hoo, but there's nothing to do but replace the tanks.

 

[O C Diver]

I would pull the tank out and cut the bottom off. After cleaning the walls, you might just be able to replace the bottom.

Ted

 

[Propnut]

That might be possible , but i'm done with these tanks. I had SP Tanks build a tank for a 49 Defever several years ago and they did a great job. I contacted them about building these tanks in 2019, but it was during height of the pandemic and they were not taking any orders.
I contacted them today and they are taking orders with a 2 week lead time.

In the past i have never added anything to my fuel. Has fuel changed any? Should i be adding a additive to the fuel? How often do y'all open up the inspection ports and clean the tanks?
Just trying to figure out what i need to do to avoid this nightmare again.

 

[O C Diver]

I really don't think the gasket and or adhesive caused that pitting. I use to inspect scuba tanks. You would be amazed at how a few drops of salt water will eat a pit in an aluminum tank in a year.

I don't know which alloys are used for fuel tanks, but I would hope they are as corrosion resistant at what they build aluminum boat hulls out of.

I would inspect the vent for the fuel tank where it goes through the hull. Some of the locations are begging for water intrusion. My guess on what caused the pit would be likely dissimilar metals. A copper penny would do that to aluminum. While salt water would do it also, it hard to imagine a small puddle staying there and not migrating to the side or a corner. Unless the pitting is directly under where the gasket was, I find it hard to imagine the adhesive caused the pitting.

Ted

 

[mvweebles]

.... When i contacted the builder, he said the gasket supplier must have sent him the wrong material. I think his aluminum supplier must have sent him the wrong aluminum as well. ....

Curious, did the builder offer any solution? Any effort to make it right?

Another question, what made you open the ports after just 4 years? Leak? Clogged pickups?

Sorry to hear this. If you believe the builder was incompetent or dishonest, suggest filing a case with the local Better Business Bureau. They aren't great, but after a few cases, tends to catch up with the business. If a future potential customer does a little checking, might warn them. Of course, online reviews with these pictures would help too. The mushy gasket and interior pitting is pretty damning.

Peter

 

[mvweebles]

I really don't think the gasket and or adhesive caused that pitting. I use to inspect scuba tanks. You would be amazed at how a few drops of salt water will eat a pit in an aluminum tank in a year.



I don't know which alloys are used for fuel tanks, but I would hope they are as corrosion resistant at what they build aluminum boat hulls out of.



I would inspect the vent for the fuel tank where it goes through the hull. Some of the locations are begging for water intrusion. My guess on what caused the pit would be likely dissimilar metals. A copper penny would do that to aluminum. While salt water would do it also, it hard to imagine a small puddle staying there and not migrating to the side or a corner. Unless the pitting is directly under where the gasket was, I find it hard to imagine the adhesive caused the pitting.



Ted

I had a friend who had a small diesel tank made for his 31 foot sailboat. Wrong alloy used and it didn't last 18 months.

The new tank builder might know.

Peter

 

[BruceK]

Tanks removed you should be able to get an expert opinion on failure. Supplied with wrong materials sounds BS. I wouldn`t want to let a 4yo tank failure go past without chasing the maker but views differ. He was your second(at least) choice, you now have a proven tank maker on the job.
My 1981 steel tanks were still good when I sold in 2020. 4 years is appalling. It`s not just "failure of consideration' for the value of the tanks, it`s the cost to remove and reinstall too.

 

[Comodave]

I would ask what alloy of aluminum was used in the manufacture of the tanks. I am not sure but I think that 5052 is one of the preferred alloys. The pitting is probably from some other metal or something that wasn’t done correctly in the manufacture. Sorry for your problems cause the tanks should have lasted at least 20 years or more.

 

[tiltrider1]

I had an aluminum fuel tank last only one year before leaking. The tank manufacture and I were unable to reach an acceptable solution. My best guess is that some sort of contamination was introduced during manufacture. Need less to say I took my business else where.

The last tank I had made used robotic welding and only aluminum was allowed in the building. That tank is now 15 years old and has always been issue free.

A month ago I did an inspection on a 35 year old aluminum diesel tank. It was spotless in side. However, I have never seen any water in the water separator. Leaky Deck Fills can be hell on fuel tanks.

 

[Iggy]

"WOW!"

Were its pitted. Can they weld a patch over it? Of is there more pitted areas to make it not worth it?

 

[mvweebles]

QUESTION to OP: I see the mushy gasket, but what is the yellow-ish muck and sludge on the bottom? Possible you have multiple problems, not just an improperly fabricated tank?

Peter

 

[Propnut]

I have no idea what the sludge is. I assume it's water and dissolved gasket material. Guess I've been lucky for the past 35 years of boating to have never had a problem like this. Funny thing is, I removed the two 30 year old steel tanks that were not leaking just to avoid having a problem. I figured these tanks would outlast me. Anyway , now I'm gun shy and just want to do everything possible so this doesn't happen again.

 

[Nick F]

QUESTION to OP: I see the mushy gasket, but what is the yellow-ish muck and sludge on the bottom? Possible you have multiple problems, not just an improperly fabricated tank?

Peter

+1

 

[Pete Meisinger]

Whoever built those tanks did one thing right, they gave you great access to the inside of the tanks through large inspection ports.

Those tanks can be easily repaired through any number of ways. The best would probably be to get a good aluminum welder to look at them.

pete

 

[dannc]

Marine grade aluminum is 5000 series with 5086 and 5083 being more common than other alloys for use in trawlers. Short of sending a sample off to test, I don't know how one would really know that alloy that was used. The OP could as, the builder but the answer will have to be taken with a grain of salt.

Another possibility is the corrosion caused by the shop using grinders/brushes to clean the AL that had been used on steel, in other words was there cross contamination.

Is there is pitting under the yellow junk, the yellow stuff could have prevented the AL oxides from protecting the metal, or the maybe the yellow stuff had a contaminate in the gaskets that reacted to the AL.

Some of the pitting appears to be on the side of the tank. If that is the case, I would question how the gasket goo would have caused the issue, unless the yellow stuff got stuck to the tank side or some gasket had a chemical that reacted with the AL.

What a mess.

Later,
Dan

 

[SteveK]

Whoever built those tanks did one thing right, they gave you great access to the inside of the tanks through large inspection ports.

Those tanks can be easily repaired through any number of ways. The best would probably be to get a good aluminum welder to look at them.

pete

Those large inspection holes makes me think these are recycled tanks, not new built.

 

[DDW]

You want 5000 series aluminum, may have gotten 6000 (much more commonly available). You could shoot the tank with an xray spectrography gun, many scrap dealer have them and you'd know in 30 seconds.

While the wrong allow may have contributed to the early failure, I'd certainly look into what is causing all that junk in the tank - that isn't normal.

If I was having new tanks made, I'd make sure the bottom had a slope, and sloped in both directions towards an inspection port. That way all the water, debris, and sludge ends up where you can easily suck it out. Flat bottom tanks are often a time bomb.

 

[Comodave]

Steve D has a couple of great articles on his website about how to do a proper installation. Make sure you do things correctly with the new tanks.

 

[Barking Sands]

ABYC fuel tank material list for reference.

TABLE 3 - Metallic Fuel Tank Material and Fabrication Requirements MATERIAL 1 SPECIFICATION MINIMUM NOMINAL SHEET THICKNESS in (mm)

Nickel-Copper ASTM-B127-98 Class A 0.031 (0.79)

Copper-Nickel ASTM-B122/B 122M-00 0.045 (1.14)

Copper ASTM-B152/B 152M-00 Type E.T.P. 0.057 (1.45)

Copper-Silicon ASTM-B96/B96M-01 Types A, B & G 0.050 (1.27)

Steel Sheet ASTM A653/A 653M-02A 0.0747 (1.90)

Aluminized Steel ASTM A-463/A 463M-02a 0.0478 (1.21)

Aluminum Alloy 5052 or 5083 or 5086 0.090 (2.29)

Stainless Steel 316L or 317L 0.0747 (1.9) 0.031 (0.79) 2

That can definitely be repaired in several ways. But I understand that you likely don't have a warm and fuzzy regarding construction and material type at this point. Many times aluminum material type is imprinted on the sheet every so many feet. If you look around..inside or out you may be able to spot the details of the material. If you get a new tank made ask to see the invoice and PO of the purchased material to confirm type prior to fabrication. It would hopefully be purchased for the job and separated and not hauled out of a stack of unmarked sheet lying out in the yard. When we purchase material the type comes marked on the sheet and the PO is written with sharpie upon receipt in various places on each 4x8 sheet and all PO and documentation is retained so we can match it up and provide the customer the required documentation that gives traceability of the materials all the way back to its manufacturer.

 

[Propnut]

Another point of interest is I chose to pull fuel directly from the bottom of the tank rather than from the drop tube 1/4" off the bottom. My thought was any contaminants on the bottom of the fuel tank would be pulled out and caught by the off engine fuel filters.
I have no idea how the crap got into the tanks. I will have the tank material tested to see what it actually is. I'm also wondering if the 1/4"gasket material and glue that was used to hold the gasket to the covers could have had some chemical reaction to the aluminum . There were pieces scattered over the bottom of the tank. When i tried to pick them up , i couldn't .
They were just mush. Had to use paper towels to get them up.
I can't believe that water could have caused that bad of corrosion in less than 4 years . Nothing left to do but remove the engine and pull the tanks.
Let the fun begin!

 

[BruceK]

If possible, engineering a small sump with drain cock below the base level of the tank might be better if drawing from the bottom of the tank. That way the water and debris can be drained off periodically and don`t become a burden for the filter/water trap.
From memory, Nigel Calder is a fan of the drainage sump method.

 

[motion30]

The 5000 series Aluminum. Is used not because it is more corrosion resistant. It is used because it is not a heat treatment material and does not lose much strength when well. The 5000 series aluminum is strained harden. 6061 is actually a stronger metal but not as suitable for welling as it is he treated

 

[Insequent]

I'd suggest making the new tanks out of steel. Properly primed and then coated with epoxy paint and you wont have any further problems.

 

[rslifkin]

Well made aluminum fuel tanks can last just fine. Mine hold gas, not diesel, but at 37 years old they still look good from the outside and the limited interior inspection I've been able to do on them showed no concerns either.

 

[Portage_Bay]

I'd suggest making the new tanks out of steel. Properly primed and then coated with epoxy paint and you wont have any further problems.

Agree. Many of us here have boats 30+ yrs old with steel tanks, some failing, most not, proving that the lifespan can be quite long when installed and maintained correctly. One key thing is to keep water away from the tanks, fill fittings, deck leaks etc. Mine are 40 yrs old and still going strong. In one sense it becomes a question of how old is the boat and how long is it's estimated remaining useful life? Another 30 yrs? If steel is cheaper than aluminum or stainless and you can find a competent tank builder then steel could be a good choice.

When I say steel tanks can age well I'm also talking about what is called Black Iron. See posts #3 and #5 in the thread Black Iron Fuel Tanks. DavidM, the author of post #3 is a very knowledgeable poster.


An excellent article on fuel tanks
Fuel Tank Design by Steve D'Antonio

 

[sunchaser]

I've seen Al tanks in this condition. One thing to check very carefully is how they are bedded so bottoms and sides stay dry. Are you bilges totally dry?

With a suspect bonding system, non-Al metals in contact with the tanks or bad wiring somewhere electrical induced galvanic corrosion can occur internally. How are the tank fills and draw tubes connected to the tanks and what material are they? Any salt water exacerbates the corrosion via the Cl ion.

Some years ago Larry M had new Al tanks made, his advice may be forthcoming on materials of construction, bedding and stray currents.

 

[Comodave]

If you go with steel tanks it may hurt resale value. Most people don’t want steel tanks due to the history of rusted out tanks, whether a real problem or not that is the perception.

 

[DDW]

When we purchase material the type comes marked on the sheet and the PO is written with sharpie upon receipt in various places on each 4x8 sheet and all PO and documentation is retained so we can match it up and provide the customer the required documentation that gives traceability of the materials all the way back to its manufacturer.

If concerned (or even if not) I'd ask for a material certification for the aluminum used in the tank. If the tank manufacturer can't give that to you, find one who can - any reputable aluminum supplier provides this for nothing with the order.

If possible, engineering a small sump with drain cock below the base level of the tank might be better if drawing from the bottom of the tank. That way the water and debris can be drained off periodically and don`t become a burden for the filter/water trap.
From memory, Nigel Calder is a fan of the drainage sump method.

I did this when we made the tanks for the sailboat. Small sump (only about 6 x 6 x 2" deep) at the low point in the tank with the pickup tube directly above it at tank bottom level. That ensures that the tank can be sucked completely dry (except for the very small sump volume), all the water and debris ends up in the sump and stays there until you clean it out, and if something collects there that causes corrosion, that small sump can be cut out and replaced at minimum cost.

The 5000 series Aluminum. Is used not because it is more corrosion resistant. It is used because it is not a heat treatment material and does not lose much strength when well. The 5000 series aluminum is strained harden. 6061 is actually a stronger metal but not as suitable for welling as it is he treated

The strength of even 6061-T0 (fully annealed) aluminum is perfectly adequate for a tank. It is the corrosion resistance of 5000 series you are after.

I'd suggest making the new tanks out of steel. Properly primed and then coated with epoxy paint and you wont have any further problems.

No way in hell I'd use steel. Not a matter of IF it will corrode, only WHEN. On something you can see and maintain, OK, but not on a tank. There are better materials.

 

[Barking Sands]

It just occured to me....why doesn't the Marine industry treat the bare aluminum with Alodine and then coat with epoxy primers? Every wet airplane wing i have ever worked on was coated in this way and I have seen some as old as 50 years that looked just fine. This internal wing is around 25 years old.

 

[DDW]

View attachment 136966

View attachment 136967

It just occured to me....why doesn't the Marine industry treat the bare aluminum with Alodine and then coat with epoxy primers? Every wet airplane wing i have ever worked on was coated in this way and I have seen some as old as 50 years that looked just fine. This internal wing is around 25 years old.

Unfortunately, no. In the marine industry, bare aluminum is just left that way. These days, alodine is being outlawed as a dangerous substance. Bare 5000 series hulls are common in salt water though, and don't have rapid corrosion problems under normal circumstances.