leaking fuel tank

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tyce

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it appears that some where on the bottom weld of my stainless tank, there is a hole, unfortunately in a senior moment by parkers, they made the tank bigger than the hatch it has to come out through.
so before smashing it in to a smaller shape and fitting a plastic one, does anyone know if there is any magig repair available.
i suspect there is not but worth a try
 
The short answer is "no", unless you can weld it, but have you tried filing it and smearing epoxy (e.g. plastic metal) over the wound? Obviously it would have to be empty first but maybe it is already? /forums/images/graemlins/crazy.gif It worked for me on some oil lines on our Yanmar 1GM, for several weeks, although I hesitate to offer it as a permanent fix.
 
I once made a temporary repair (lasted about 6 months) on a car fuel tank with some stuff from Halfords. Can't remember what it was called, "petro patch" or some such. It consisted of a roll of fabric bandage and some red stuff in a tube covered in "don't touch" warnings. The solvent was Xylene IIRC. It looked a bit dubious but, as I said, it did the trick. When the tank leaked again it was further spread of corrosion / structural failure in the steel; the patch still seemed OK.
 
Parker were not the only ones to have 'senior moments'. The Moody 33 has the sam problem. It was a steel tank and when I bought the boat had obviously been leaking for a long time. I had to pump ot the diesel and then cut it into 3 pieces. Interestingly it looked as though some sort of liquid epoxy? had been poured in but it obviously didn't cure the leak! I used a 'reciprocating' saw from a local hire company and it cut through it a treat - but not sure how it would work on stainless....... Replaced with a plastic Plastimo tank of 20 gallons.
 
I have a small inverter type welder I use for welding stainless with a small argon gas bottle which would allow the tank to be welded inside even your small yacht providing you could get to the leek. I am positive some one in the UK close to you would have a simular setup. This would do the job correctly.

I would do it for you but I am a bit too far away.
 
Stress corrosion cracking.

Heat of welding stresses weld locally when it cools storing energy locally in weld. Presence of chlorides in seawater help to make SS brittle in minute cracks .Cracks and stored energy due to stressing initiate zip effect and hey presto small hole created when energy dissipated
 
Yep thats the process. It can be overcome by heating to about 350 400 C and leaving to soak at the temperature for a while which will releave the stresses induced by the welding.

Cliff will know the details better than me
 
Had a similar problem with a mild steel tank that would not come out of the hatch. Welders (understandably) would not touch it. In the end, I managed to turn the tank over in the locker, cleaned up round the hole very carefully and glued a steel patch with epoxy (which claimed to be impervious to diesel). I then glassed over the repair. It has held well with no sign of lifting round the edges or any other deterioration.
 
I doubt very much if the leak is due to SCC for a number of reasons.

Chloride stress corrosion cracking (SCC) can occur in chloride-containing solutions at elevated temperature, normally above 50 degrees C, when tensile stress is present. It particularly affects austenitic stainless steels, and a common failure observed in the field is cracking from the outside of tanks or pipes carrying hot fluids. For example, if a water leak occurs into insulation on the outside, chlorides can concentrate through evapouration, and SCC can take place because of the tensile stresses present in the outside surface of pipes and tanks.

Intergranular corrosion (IGC) is preferential attack at the grain boundaries of a stainless steel and is commonly associated with welding and would be the favourite cause of welds leaking.

If stainless steel is heated to the sensitising temperature range, such as can occur in the heat affected zone of a weld, then chromium can combine with carbon in the steel to form chromium carbides in the grain boundaries. Such a stainless steel is said to be 'sensitised'. Around each chromium carbide particle is an area low in chromium so that, when the material is placed in a corrosive environment, attack of these low-chromium regions can occur. This is called IGC.

The most common way today to avoid IGC is to specify a low carbon 'L' grade of stainless steel when welding, such as Type 304L . In the past, when it was difficult for mills to achieve low carbon levels, titanium (Ti) or niobium (Nb) were added since these elements preferentially combine with carbon and so leave the chromium unaffected. Grades containing these additions include Type 321 (S32100) containing Ti and Type 347 (S34700) containing Nb.

Heating to the tank to 350~400°C will have little effect except to cause sever distortion. Fuel tanks are so thin the effects of weld shrinkage are minimal except for causing distortion if a proper weld technique and sequence is not used. Water lying in the bottom of the Diesel tank can cause accellerated IGC (old name was weld decay) but using an "L" grade 304 or 316 reduces the chromium depletion at the grain boundaries hence reduces IGC.

If there is access to the leak it may be possible to grind out the leaky material with a slitting wheel and reweld - these little inverter powered GTAW (TIG) units are great /forums/images/graemlins/grin.gif
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Thanks for the very detailed metallurgical explanation. As a mechanical design Engineer I never got to that detail in material science.

My comment about was based on stress releaving the assembly, but take your point that being of thin material and having stressed built up in the material due to the working of the base material and the stresses induces due to welding the distortion would be more than possibly acceptable.
 
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