Diesel tank repair or replacement

[mullet]

My boat's has a welded ~45l stainless diesel tank, probably as old as the boat (pushing 40 years), and the welded seams are failing causing it to leak. I'm considering repairs vs replacement. Any consensus (ha!) on whether it is worth trying to repair a stainless tank, or would this be a case of throwing good money after bad?

The boat is a GRP Twister and the tank is in a cockpit locker, mounted on the locker's forward bulkhead; there are no other sensible locations elsewhere on the boat for a fuel tank the same size, but a replacement could be fitted in the same locker, potentially in a more practical way. Other factors/questions:

• The engine is a Beta 14 and gives decent boat speed at low revs, so it is not exactly a gas guzzler. A smaller tank plus supplementary fuel in cans could be practical.
• Internal inspection of the current tank is impossible (it is mounted horizontally, as high as possible on the forward bulkhead, to make use of the area of widest beam). And it has no fuel gauge. A lower installation would allow inspection access, offer a (small) CoG improvement and would not affect the engine (which doesn't need gravity feed). Any obvious downsides, beyond potentially needing an odd-shaped tank to maximise use of space?
• Plastic tanks. I am attracted by less condensation and no welds to fail. Any cons beyond being limited to manufacturers' sizes/shapes?
• The existing tank has flanges for bulkhead mounting. I've not seen this on any off-the-shelf tanks. If not bulkhead mounted, is there a recommended way of fixing the tank in place? Should I be looking at adding a shelf for it to sit on? Strapping it down?
• I am considering installing a diesel air heater (Eberspracher or similar) to the boat which might affect choices about the tank (size and location). The convenient location for the heater would be elsewhere in the same locker. Bad plan to put a combusting device in the same locker as the diesel or generally seen as acceptable? If a terrible idea I'll factor this out of considerations.

Any suggestions, advice, or pitfalls to avoid gratefully received!

 

[[70521]]

You don't say where you are. Find a good fabrication shop and get them to have a look at it and price the job up.

 

[mullet]

Good point. Medway, Kent.

 

[Crinan12]

Hi mullet i took my old steel tank (40 years old) out to clean a couple of years ago and the bottom of it was rusty so i just replaced it

The new plastic tank was only about £100 and it just didn't seem to make sense to consider repairing the old one

I fixed my tank in place with a couple of ratchet straps and some flat wrap just in case

There are loads of different sized off the shelf tanks so you should be able to get something to suit your space

I just have a beta 16 so i fitted a 40 litre tank and like you say have a couple of jerry cans as well.

Probably not much help to you, but that's what i did anyway!

 

[Wing Mark]

Personally, I'd consider getting it welded, maybe re-hashing it to a different shape, so it didn't have a flat bottom to harbour water.
Tig welding is not that expensive.
Stainless sheet is expensive.

I'm with Sandy, get it out, take it to a welding man and see what he says.
Maybe open it up to see if the inside is good or not?

The plumbing odds and ends add up too, So the total cost of changing the tank might spiral a little.

 

[Laysula]

If you do remove it to repair it,take the opportunity to put a drainpoint in to conveniently remove any water and also a second supply point for the eber.

 

[peteK]

I repaired a few pinholes in a leaking stainless diesel tank with jb weld,but could remove tank and clean inside and out.

 

[chrishscorp]

I did this repair earlier this year on my boat similar age. I took the tank to a chum who took one look and said its high ferric content stainless, scrap it not worth repairing.

I replaced with plastic, and strapped down. There may be availability issues on plastic tanks there was when i did the job as most off the shelf ones are made in Italy you will need to check availability.

 

[vyv_cox]

When the tank was built it was almost certainly made from 304/316 stainless steel, as the low carbon L version of these did not exist then. Over time welds in the non-L version corrode by a process known as sensitization, because the higher carbon content ties up chromium in the heat affected zone as carbides, reducing the Cr content of the alloy.

Weld repairs using low carbon filler rods and perhaps a new bottom sheet should last quite well, particularly if a small 'well' is included in the new bottom, allowing water to be drained periodically.