Stainless steel diesel fuel tanks?

[Kukri]

I am one of the many of us who watch the videos of Leo Sampson Goolden’s rebuilding of the Albert Strange gaff cutter “Tally Ho!”

Yesterday’s instalment included a section on diesel fuel tanks and a discussion of choice of material. He had ordered some welded plastic tanks which turned out to be faulty as the welds were defective.

There was then a discussion of what material to use for the new ones and I was rather surprised to watch him rule out stainless steel.

I understand that with stainless steel it is corrosion at the welds that is the problem, and the welding must be done properly, with the right grades of plate and rod, but lots of boats in the UK and elsewhere in Europe have stainless steel diesel fuel tanks.

I got the impression that in North America stainless steel fuel tanks are frowned on.

I’d welcome comments from those who know about this stuff!

 

[NormanS]

It seems a bit odd to condemn stainless steel for tanks, when it's clear that very few examples of failed stainless tanks exist, and these can be shown to have been incorrectly welded. By the same token, he should condemn plastic tanks.
All four of my 220 litre fuel and water tanks are stainless, built by a reputable company, more than 30 years ago, and have given no problems.

 

[Motor_Sailor]

Our yard in the States had a couple of guys doing nothing but replacing stainless steel fuel tanks, principally in power boats, but also a large number of sailing boats. All the usual problems of weld decay were compounded by the way they were mounted. They were usually either sat on rubber covered cross members with nylon tiedown straps, or foamed into place under the cockpit sole.

Even when designed properly with mounting flanges and water collecting sumps, stainless steel tanks are still the least predictable deisel tank material. TeK Tank plastic ones in the UK are a proven solution. Even plain steel with properly blasted and painted exteriors will give long, consistent service if there is a drain or pump-out tube to the low point to remove water. For the same money, I would rather have a properly designed mild steel tank with inspection port and drains, than a stainless one that had been 'simplified' to reduce cost.

 

[Wansworth]

No knowing the details of space available I would have gone for four separate tanks in steel built to be got at and large inspection hatches,maybe some fuel tanks up forward with a pump to a day tank

 

[Wansworth]

Two threads on tally Ho fuel tanks one here and one on scuttle but?

 

[doug748]

......................I understand that with stainless steel it is corrosion at the welds that is the problem, and the welding must be done properly, with the right grades of plate and rod, but lots of boats in the UK and elsewhere in Europe have stainless steel diesel fuel tanks.

I got the impression that in North America stainless steel fuel tanks are frowned on.

I’d welcome comments from those who know about this stuff!

I don't know much about the issue but they can corrode at the welds esp if there is water around. Not a dire problem if they are properly designed and maintained. My stainless tank coming up 45 years and still plugging on, which is probably all you can expect for any tank. The American attitude may well just be inertia in the industry, it happens; see the nearby thread about laying up at Safe Harbour.
My minds eye has always seen mild steel tanks a cost effective/cheap alternative for cruising boats.

In his place I would have looked at aluminium and cut down the designed capacity, for ease of removal, inspection and ventilation. I would also have looked seriously at innovation, esp using sealant on the inside of the alloy tank, after all this is how integral, aircraft fuel storage is arranged.

Not that I am dishing out advice, for it would be like offering Rembrandt painting lessons.

.

 

[vyv_cox]

Corrosion of the welds occurs by a process called sensitisation, in which carbon in the sheet metal or the filler rods forms chromium carbides in the heat affected zones, thus lowering the chromium content locally, making it susceptible to corrosion.

There are two principal ways of overcoming this:
1. Use the low carbon versions of the steel, 304L or 316L
2. Add preferential carbide formers to the filler rod, niobium for instance, with minimal carbon.
Rods for this duty are to 346 specification.

My diesel tank is made in stainless steel, now coming up to 40 years old. I know that there has been a small volume of water in it, the drain plug threads corroded, but the tank itself is good.

A very valid point made earlier is how the tank is supported and corrosion that takes place from outside in. My tank hangs on a bulkhead on brackets.

 

[Kukri]

Corrosion of the welds occurs by a process called sensitisation, in which carbon in the sheet metal or the filler rods forms chromium carbides in the heat affected zones, thus lowering the chromium content locally, making it susceptible to corrosion.

There are two principal ways of overcoming this:
1. Use the low carbon versions of the steel, 304L or 316L
2. Add preferential carbide formers to the filler rod, niobium for instance, with minimal carbon.
Rods for this duty are to 346 specification.

My diesel tank is made in stainless steel, now coming up to 40 years old. I know that there has been a small volume of water in it, the drain plug threads corroded, but the tank itself is good.

A very valid point made earlier is how the tank is supported and corrosion that takes place from outside in. My tank hangs on a bulkhead on brackets.

Thank you, Vyv. I confess that I was hoping that you would look in on this thread.

 

[ean_p]

Another issue with SS tank construction is its easy to skimp on the use of expensive shield gas on the inside of the tank which 'burns' the steel in the weld zone. A good builder would have the tank flooded with gas, but its not cheap!

 

[Mudisox]

No problem from two s/s diesel tanks except no drain off tap. had to cut an access hole to clear the sludge. Not bad really for 40 years.

 

[Refueler]

My two tanks of 1970's vintage are :

Truck 80ltr mild steel diesel tank of typical black exterior coated. Bolted to glassed in mounts under stbd fwd bunk.

RV 70ltr stainless steel oval water tank. Bolted to glassed in mounts under port fwd bunk.

Both still in excellent condition .....

 

[PetiteFleur]

My original tank was painted mild steel and was leaking king when I bought the boat. I replaced with a Plastimo plastic tank which has not given any problems. 91L so more than adequate for my 25hp engine. The original tank was much larger so fitting a smaller tank gave me space to fit the calorifier alongside it thus freeing up a galley cupboard.

 

[Wansworth]

Almost all the fuel tanks I have seen whilst looking for a yacht have been hidden away and difficult to get to,whatever the material.Frankly if I was designing from scratch proper access to the tank and it’s cleaning would be a good idea as so many engine problems stem from the fuel…..and it’s tank.pp

 

[RivalRedwing]

I've a stainless tank on a '78 Rival 34 secured to the underside of the cockpit. The tank is still sound but one of the securing tangs has failed (not a great design from that perspective!) its now benefitting from supplementary support via a ratchet strap as it would be an engine out job to replace it.

 

[garymalmgren]

There are two principal ways of overcoming this:
1. Use the low carbon versions of the steel, 304L or 316L
2. Add preferential carbide formers to the filler rod, niobium for instance, with minimal carbon.
Rods for this duty are to 346 specification.

There is a third method that hasn't been mentioned yet.
Soft soldering .
Make a tank with ample overlaps on internal baffles and end pieces.
Use a modern flux and solder combination and you will have a strong corrosion free joint.
I did this when I made a large eutectic plate years ago and was surprised at how easy and strong it was.
The expansion and contraction that it was subjected to would be far greater than the static and sloshing in a fuel tank.

Yes, I know that a fuel tank will be subjected to heavy loading. That is why I suggest large flange overlaps.

gary

 

[RobbieW]

I have 2 x c.225l SS fuel tanks in a Rival 41. One started to weep from the bottom corner about 10 years ago, I could just (fingertip) reach the seam from the inside. I used epoxy filler then POR15 to seal it from the inside, its been dry so far

 

[rotrax]

There are two principal ways of overcoming this:
1. Use the low carbon versions of the steel, 304L or 316L
2. Add preferential carbide formers to the filler rod, niobium for instance, with minimal carbon.
Rods for this duty are to 346 specification.

There is a third method that hasn't been mentioned yet.
Soft soldering .
Make a tank with ample overlaps on internal baffles and end pieces.
Use a modern flux and solder combination and you will have a strong corrosion free joint.
I did this when I made a large eutectic plate years ago and was surprised at how easy and strong it was.
The expansion and contraction that it was subjected to would be far greater than the static and sloshing in a fuel tank.

Yes, I know that a fuel tank will be subjected to heavy loading. That is why I suggest large flange overlaps.

gary

The pre war HRD Motorcycle fuel tanks were two piece, mild steel with soldered in bright polished S/S sides. As an antique motorcycle specialist I can say I have never seen a leaky one that had not suffered severe crash damage. The soldering was fine in long term use.

IIRC, the flux took some development by HRD before being satisfactory.

 

[Hoolie]

I know it's a bit different from a fuel tank, but earlier this year we had a major leak in one of our 210 litre SS water tanks from a sprung seam weld. We recently had it welded up and the guy was rather puzzled that it appeared to have been exacerbated by impact damage.

A few years ago the boat fell off its cradles in high winds on to its port side - exactly where our defective tank is installed! Sadly it's far too late now to add to the insurance claim.

 

[Caer Urfa]

I have used plastic tanks quite a few times from https://www.tek-tanks.com/ and never had a problem with them and they do various sizes/shapes 'and custom made ones'.
Leo diplomatically did not show it but I think he must be privately fuming that unfortunately he chose a cowboy outfit to make the tanks as they should never have left the factory in that condition
I have followed his website since he bought Tally Ho and its a pleasure watching every Sunday a masterclass in boat building and at least he always asks and makes time to listen to other peoples advice not like some web site with so called restorers

 

[penfold]

Stainless steel is an excellent material for tanks but will fail at welds if it's not done properly and unsuitable installation can expose it to salt water and low oxygen conditions conducive to corrosion, e.g. plonking tanks onto a plywood shelf or mounting with pads of absorbent material.