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Hi,

 

I have an ex-Black Prince probuild narrowboat which has the weed hatch apparently through the fuel tank. The hatch is secured by a bar across two steel loops welded to the tank.

 

One of these loops has failed ( maybe my fault over tightening weed hatch - appears to be ductile failure of one loop, see picture ). It seems to me that I will need a new loop welded in, but this is on top of the diesel tank.

 

I believe the diesel tank is integral with the boats structure - so does this mean the diesel tank need to be drained first and inerted before welding ? Does it then require pressure testing again ?

Any advice on practice here ?

 

 

IMG_20190601_165015.jpg

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3 minutes ago, Tim Read said:

Hi,

 

I have an ex-Black Prince probuild narrowboat which has the weed hatch apparently through the fuel tank. The hatch is secured by a bar across two steel loops welded to the tank.

 

One of these loops has failed ( maybe my fault over tightening weed hatch - appears to be ductile failure of one loop, see picture ). It seems to me that I will need a new loop welded in, but this is on top of the diesel tank.

 

I believe the diesel tank is integral with the boats structure - so does this mean the diesel tank need to be drained first and inerted before welding ? Does it then require pressure testing again ?

Any advice on practice here ?

 

 

IMG_20190601_165015.jpg

Surely the lid comes off and can be welded away from the boat. The boat shouldn't sink if the lids not on for a while.

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Sadly the loops are on the tank. I should perhaps have added a photo from further back which shows the tank more clearly.

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6 minutes ago, Tim Read said:

Sadly the loops are on the tank. I should perhaps have added a photo from further back which shows the tank more clearly.

Ok I understand now. :)

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Plenty around who would weld that with fuel in the tank, saying the diesel won’t burn without an oxygen supply. I wouldn’t want to be anywhere near though. 

 

Doesn’t have to be welded. Fix a new one on using big rivnuts.  

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It isnt a major problem When i rebuilt the back end of my boat I cut off the stern dollies and re welded them to ther top of the tank which is part of my rear dack, i also had to weld a new female spigot to a hole in the top of the tank to screw a new breather into, that was the bit i considered dangerous ... looking at the pic as the tank is remaining sealed you should have no problem as the vapours are contained.

 

Rick

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You must have been doing the weedhatch up pretty tight to rip that off! I stripped a thread once overtightening mine. If yours has neoprene on the inside of the flange then it shouldn't need doing up so tightly.

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Be very very careful. Welding closed vessels that have contained diesel is responsible for many fatalities. Using a  oxyacetylene torch to take the top off a 40gallon drum has killed far too many. In many cases this has been after water flushing but the remaining diesel film has provided enough fuel for the fatal bang. Diesel fuel vapours in a closed vessel at normal temperatures are below the lower flammable limit but there will be enough oxygen in the vapour space to support combustion. So if you dropped a match in the tank at normal temperatures nothing will happen. Kerosene tanks are another matter, as at normal temperatures the vapour space may well  be in the explosive range. There was once a multiple fatality when a fire prevention company demonstrated inerting a jet fuel tank using foam. The vapour space was in the explosive range and static electricity generated by the incoming foam provided the ignition.

The vapour space in petrol tanks would normally be too rich to support combustion. Do not attempt to verify this under any circumstances

Back to diesel, lube oil and bitumen vessels. Creating a hot surface by welding etc may well elevate the local vapour temperature enough to raise it to be above the lower explosive limit with dire consequences.

 

Prudent HS&E provision from both a safety and legal angle would require that the work be carried out by trained competant operators working to a define procedure and under a permit to work/ hot work, system. You may well find that this is a requirement of your marina, or boatyard. My guess is that a monitored inert gas inerting would be a minimum.

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Would it be possible to hammer the loop back into place and then make a new loop which fits over the existing one. Then drill and bolt the new one and the old one together through the upright sections?

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4 hours ago, DandV said:

Be very very careful. Welding closed vessels that have contained diesel is responsible for many fatalities. Using a  oxyacetylene torch to take the top off a 40gallon drum has killed far too many. In many cases this has been after water flushing but the remaining diesel film has provided enough fuel for the fatal bang. Diesel fuel vapours in a closed vessel at normal temperatures are below the lower flammable limit but there will be enough oxygen in the vapour space to support combustion. So if you dropped a match in the tank at normal temperatures nothing will happen. Kerosene tanks are another matter, as at normal temperatures the vapour space may well  be in the explosive range. There was once a multiple fatality when a fire prevention company demonstrated inerting a jet fuel tank using foam. The vapour space was in the explosive range and static electricity generated by the incoming foam provided the ignition.

The vapour space in petrol tanks would normally be too rich to support combustion. Do not attempt to verify this under any circumstances

Back to diesel, lube oil and bitumen vessels. Creating a hot surface by welding etc may well elevate the local vapour temperature enough to raise it to be above the lower explosive limit with dire consequences.

 

Prudent HS&E provision from both a safety and legal angle would require that the work be carried out by trained competant operators working to a define procedure and under a permit to work/ hot work, system. You may well find that this is a requirement of your marina, or boatyard. My guess is that a monitored inert gas inerting would be a minimum.

 

A friend of mine who built shells for a living use to happily weld up leaks on full diesel tanks occasionally. I mentioned this to my (now departed) father-in-law who was a fuels chemist/engineer at BP, who said something similar to the above and advised me to be nowhere near during such a process. 

 

F-I-L also commented he would prefer to stand next to a tank of petrol being welded than a diesel tank. I can't clearly remember the reason for this.

 

ISTR my shell builder friend saying the diesel tank needs to be full rather than empty before welding commences, and poo-pooing my F-I-L's concerns. 

 

 

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Have you any scope for a redesign of he clamping arrangement?  I was thinking in terms of a pair of uprights from the sides, or front and back, of the hatch, with holes in them for the clamp-bar.  It of course depends on how wide the flange area is, plus the top plate would need notching to accomodate the uprights.

 

p.s. only the lucky ones tell you it is safe to weld diesel tanks.  We sent them away to specialists.

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1 minute ago, Grebe said:

p.s. only the lucky ones tell you it is safe to weld diesel tanks.  We sent them away to specialists.

They used to be called asylums (or locally - 'the nut-house')

 

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1 minute ago, Mike the Boilerman said:

 

A friend of mine who built shells for a living use to happily weld up leaks on full diesel tanks occasionally. I mentioned this to my (now departed) father-in-law who was a fuels chemist/engineer at BP, who said something similar to the above and advised me to be nowhere near during such a process. 

 

F-I-L also commented he would prefer to stand next to a tank of petrol being welded than a diesel tank. I can't clearly remember the reason for this.

 

ISTR my shell builder friend saying the diesel tank needs to be full rather than empty before welding commences, and poo-pooing my F-I-L's concerns. 

 

 

When I was a junior oil company engineer I saw a  new branch stab welded into a 8" diesel wharf line once. Line left full of diesel. They did have a load of fire fighting equipment available but it was a wet sack that was used each time the diesel ignited. The permitting and supervision was by an old hand installation superintendent. In those days that some diesel escaped into the soil, was not perceived as a problem. The advice not to be any where near is sound, but if you are going to do it, a flooded tank is safer because the fuel will take the heat away and exclude the air with it's necessary oxygen. 

 

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Welded on lots of tanks but only diesel never with petrol.

Better if its full, less air space for gasses. The tank is not sealed, it has the breather.

If you don't penetrate the tank its not so bad but I always fill the tank with carbon dioxide from a fire extinguisher first for safety.

Never had one light up or go bang. Else I would not be typing here!

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3 minutes ago, DandV said:

In those days that some diesel escaped into the soil, was not perceived as a problem.

 

I once did some work for an oil company site engineer who told me diesel fuel spilled into the sea was not regarded as a polluting event as diesel will evaporate and disappear in two or three days causing no harm, unlike the heavier fractions of distillate.

 

 

 

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There is a stub of the clamp loop still attached to the tank top. Is there enough metal there to drill a hole and another in the other side of the break and bolt/rivet a strap across? Might need taping, iether in to the loop, or strap, rather than nut/bolting if there is a clearance issue with the clamp bar. Countersunk bolt head could also help with clearance.

Jen

See pic below:

strap.jpg.e26558c48a00d1dd30bb1d3f9e90aade.jpg

Edited by Jen-in-Wellies
  • Greenie 2

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Welding fuel tanks is  a fools game if you don't take proper precautions. Don't take a chance on it without considering a foolproof way to do it. If you take yourself back to school and remember the science class where they taught you the triangle of fire.  1/ fuel 2/ air/ 3/ heat (ignition source). With all these present the chances of a spectacular end to your day is very likely indeed. I have fond memories of a colleague attempting to braze a leak off pipe connection back into a Lister fuel tank on a dumper.  He used all the dodgy justifications for excessive risk too. The resultant bang and cloud of smoke and flame was spectacular indeed. The scorced face less so. It was a blessing that he had his goggles on.

However these days its easy to provide an easy remedy to your problem by breaking the triangle of fire by removing one or more of the elements. Personally I would empty the tank, it's an opportunity to clean it out anyway. Ensure that the filler cap is securely shut and remove the tank vent. Use that connection to connect up the regulator hose from an inert gas bottle. Nitrogen would be my gas of choice but I have used the Co2 hose from a mig welder before. Add gas from the gas bottle at  very low pressure and  fill the tank with it. No fuel, no air, no bang. Weld away.

 

Dont forget that if you do manage to start a fire and hurt yourself or damage something the insurer will call it misadventure and probably not pay out.

 

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Hi,

I would have thought the best way was remove old bracket, make new one, drill, tap and bolt this in position, using sealant to complete the repair. 

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1 minute ago, LEO said:

Hi,

I would have thought the best way was remove old bracket, make new one, drill, tap and bolt this in position, using sealant to complete the repair. 

 

This loops us back to my suggestion to do this but using Rivnuts in Post 5. I suggested this because we don't know the thickness of the top of the diesel tank. Quite possibly only 3mm.

 

 

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The trap with welding or flame cutting  vessels that have contained combustible, as distinct from flammable, materials is that when cold a flammable gas detector will give a nill reading. This can give inexperienced operators a false sense of security. As soon as heat is applied any previous readings are no longer valid, and the generation of the flammable vapours up to hazardous levels may well be faster then any detection technology.

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9 minutes ago, Mike the Boilerman said:

 

I once did some work for an oil company site engineer who told me diesel fuel spilled into the sea was not regarded as a polluting event as diesel will evaporate and disappear in two or three days causing no harm, unlike the heavier fractions of distillate.

 

 

 

Society's perception of pollution has changed markably in a short time. I agree with the now emphasis on concentrating resources into prevention. So now I could neveragree that a diesel spill could not be regarded as a polluting event. But if a spill occurs a considered approach is required. If on water,  diesel will evaporate and for small spills this may be environmentally more friendly then spraying it with detergent where it will spread its effect beyond the surface. However politics will generally dictate the detergent solution. 

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The thought of welding a used fuel tank fills me with horror!

I think rivnuts or drilling and tapping is the way to repair this and welding being the last resort,and then only done by a qualified person with proper equipment,inert gas.fire fighting gear etc.

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Take the boat to any good boatyard with an experienced welder and they will weld it for you. If you are worried you could fill the top of the tank with inert gas, but the boatyard welder would not bother to do this.

 

.................Dave

  • Happy 1

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2 hours ago, Mike the Boilerman said:

 

I once did some work for an oil company site engineer who told me diesel fuel spilled into the sea was not regarded as a polluting event as diesel will evaporate and disappear in two or three days causing no harm, unlike the heavier fractions of distillate.

 

 

 

I was told exactly the same when a diesel bowser sank near Tower Bridge.  It  dragged down a tug which was moored alongside and caused, in my eyes, a massive stretch of polluted river.  Sure enough after a few tides it had all disappeared.

sunkboat 056.jpg

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