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Welding diesel tank


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I have an integral diesel tank at stern- no access. 

 

There's some corrosion on the side of the tank caused by poor drainage design inside the stern deck.  Can this be welded with fuel in there or do I need to chop access and get it all out? 

 

If I have to chop access,  I'm guessing flying sparks are an issue? 

 

many thanks     

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Long ago when I worked for the NHS we had a fire safety course provided by the Fire Brigade. We dealt with a number of different fires including diesel. We were shown how difficult it is to get diesel to burn. Eventually the diesel fire in a tray was lit by the expedient of pouring a load of petrol on top and lighting that. There may be other ways but I came away with the knowledge that it's really hard to set diesel alight.

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11 minutes ago, George and Dragon said:

Long ago when I worked for the NHS we had a fire safety course provided by the Fire Brigade. We dealt with a number of different fires including diesel. We were shown how difficult it is to get diesel to burn. Eventually the diesel fire in a tray was lit by the expedient of pouring a load of petrol on top and lighting that. There may be other ways but I came away with the knowledge that it's really hard to set diesel alight.

I have a Dickinson diesel stove and you need some kind of wick to light it, waxed card works well or a match dropped on the edge of the diesel pool but not dropped into the diesel

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Most boatyards appear very happy to weld a diesel tank and are not too fussed about its state of fullness.

If your tank is seriously corroded then it might be a problem, would not be good if the welder hit a thin bit and blew a hole in it. ?

 

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

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Be very careful. Diesel vapours at normal temperatures fall outside the flammable range. But welding can take the temperature of  any,   even very small amounts of residual fuel into the explosive range. BANG, 

Gas cutting former diesel drums and empty diesel tanks have  resulted in the premature demise of far too many people.

Welding below,  fuel level should not result in an immediate explosion as the fuel will conduct the heat away  but may breach the fuel containment resulting in spill into a sensitive environment, or a fire, which if not immediately contained could lead to a subsequent explosion. 

You need an experienced operator with defined recognised  procedures, such as waterfilling, nitrogen or CO2 inerting,  and constant flammable gas testing, to undertake such hazardous work.

Water flushing and then draining will not reduce the fuel residues to safe levels if exposed to welding temperatures.

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The best way was shown on tomorows world pour soapy water in the drained tank and blow compresed air in to form bubbles that way no large volume of imflamabe gas. or fill the tank with fuel or water to reduce volume of gas which will go bang when you heat the tank up.

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Thought it might be tricky.

so the problem is the welding heating up gases in the tank. I’m not suggesting I’m going to pursue this but just looking at options

 

Let’s Say the boat yard wanted to weld with diesel remains in the tank

Will these be factors?

 

-does it make a difference if the weld is below fuel level? 
-the plate that’s being welded is of good thickness (4-5mm), would it be best to use mig for a shallower weld ( less heat) 

 

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3 hours ago, Polishicebreaker said:

Thought it might be tricky.

so the problem is the welding heating up gases in the tank. I’m not suggesting I’m going to pursue this but just looking at options

 

Let’s Say the boat yard wanted to weld with diesel remains in the tank

Will these be factors?

 

-does it make a difference if the weld is below fuel level? 
-the plate that’s being welded is of good thickness (4-5mm), would it be best to use mig for a shallower weld ( less heat) 

 

The problem is , as you say, the gas/diesel fumes above the fuel.  There aren't any fumes if the tank is brim full.  So, most  if not all yards will want the tank full so that any weld is not heating the fumes.

Mig is fine indoors.  Outside the gas shield tends to blow away in even the lightest breeze so you either turn the gas pressure up and use lots of expensive gas, or the weld is carp. In any event, if you are paying someone to do it, let them use their expertise and experience to choose how they do it.  You can act as welding sentry-looking to make sure the welding is not starting a fire inside and keeping an eye on the area round the welding (inside and out) till everything is stone cold again.

 

N

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3 hours ago, Polishicebreaker said:

Thought it might be tricky.

so the problem is the welding heating up gases in the tank. I’m not suggesting I’m going to pursue this but just looking at options

 

Let’s Say the boat yard wanted to weld with diesel remains in the tank

Will these be factors?

 

-does it make a difference if the weld is below fuel level? 
-the plate that’s being welded is of good thickness (4-5mm), would it be best to use mig for a shallower weld ( less heat) 

 

 

Are you intending to this yourself or use a boatyard/welder?. If you plan to use a boatyard then speak to a boatyard or two rather than asking on a forum where you get opinions from people who are not welders ?

 

You ask about MIG so maybe you plan a DIY job?. MIG certainly puts in less heat than oxy-acetylene, I would not recommend gas welding for a diesel tank ?. Most yards would likely choose stick welding rather than MIG.

 

.........Dave

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I have an integral tank built onto the baseplate. I wanted access to the very rear of this tank for sucking out samples/water/muck. I wanted a BSP boss welded to the top of the tank to achieve this, so this had to be done above the fuel level. Whilst in the drydock at a reputable yard I asked if they would do this.

 

I suggested filling the tank with MIG gas, they said no need for that. They proposed to drill a hole then weld on the boss. I said welding the boss first then drilling the hole through the boss might be safer, they said they would do it that way but were happy to do it either way.

 

I did the prep to get to nice clean steel. They welded on the boss (supplied by me) in about 15 minutes and then drilled a hole in the top of the tank (they had a bigger better drill than me). I cleaned up then spent some time lifting swarf out of the tank with a little magnet. The welding cost about £15.

 

It was a tricky weld with limited access due to working through an access hole in the floorboards and right next to the propshaft. They did a very neat job, much better than I could have done.

 

Quite a lot of swarf and metal debris came out (despite greasing the drill bits), I reckon a lot had been in there since the boat was built.

 

They put a similar boss on the floor mounted skin tank at the same time so that I can drain that when required.

 

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

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2 hours ago, dmr said:

 

Are you intending to this yourself or use a boatyard/welder?. If you plan to use a boatyard then speak to a boatyard or two rather than asking on a forum where you get opinions from people who are not welders ?

 

You ask about MIG so maybe you plan a DIY job?. MIG certainly puts in less heat than oxy-acetylene, I would not recommend gas welding for a diesel tank ?. Most yards would likely choose stick welding rather than MIG.

 

.........Dave

Hi Dave, thanks for your comments. 
Wasn’t planning on doing it myself but wanted to get a bit of context before I go in to the yard. 
I did just manage to speak to a welder who said he’s done one under the fuel line with (lid off tank) used low amps and tried not to focus too much heat in one spot so that could be the way perhaps. 
In this case I wander if it’s best to fill the tank with fuel rather than empty it. 
 

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2 minutes ago, Polishicebreaker said:


In this case I wander if it’s best to fill the tank with fuel rather than empty it. 
 

Yes, you cannot set fire to diesel if there is no air. Even if you perforated the tank whilst welding, the fuel inside will not burn and the fuel spilled will not burn in the open air unless it is substantially heated or soaked into a wick of some kind.

 

Welded hundreds, never had a drama. Have a CO2 extinguisher to hand and feel confident.

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1 hour ago, Polishicebreaker said:

Hi Dave, thanks for your comments. 
Wasn’t planning on doing it myself but wanted to get a bit of context before I go in to the yard. 
I did just manage to speak to a welder who said he’s done one under the fuel line with (lid off tank) used low amps and tried not to focus too much heat in one spot so that could be the way perhaps. 
In this case I wander if it’s best to fill the tank with fuel rather than empty it. 
 

 

I reckon that a full tank is safer, as Tracy says you can't set fire to the diesel without air, but the bloke who did mine really did not care. Its my boat but it was his head next to the tank so I assume he was Very confident. I noticed that he did a very short weld, some chipping away of the slag, then another very short weld etc etc etc, though the difficult access likely made a long weld difficult.

 

There was a really good welder where I used to work, he would weld (with gas) right next to petrol fuel lines just by putting a wet rag over the fuel line.

 

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

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7 hours ago, dmr said:

  I said welding the boss first then drilling the hole through the boss might be safer, they said they would do it that way but were happy to do it either way.

 

 

Standard way of doing a hot tap of hydrocarbon lines.

 

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23 minutes ago, ditchcrawler said:

Standard way of doing a hot tap of hydrocarbon lines.

 

 

That's impressive, I particularly like the plugs that go round the corner.

 

So, my skin tank is on the floor under the engine. As I said I got a BSP boss welded on at the same time that they did the diesel tank. It was only last month that I finally got round to finishing the job and changing the antifreeze. Drained the engine, sucked as much water from the rubber hoses as I could then drilled "live" into the top of the skin tank through the BSP boss with a load of old towels surrounding the area. A lot easier than an oil pipeline ?.

 

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

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1 hour ago, Tracy D'arth said:

I used to hot tap cold water mains, the clever bit ( no pun intended ) is the drill and tap thread cutter in  water tight box that then lets you fit the stop tap without getting soaked.

With gas it  was a case of dropping the pressure as the steel wouldn't take the working pressure at weld heat. Also you can pressure test the welded stub and valve without pressure testing 30 miles of pipe

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34 minutes ago, ditchcrawler said:

With gas it  was a case of dropping the pressure as the steel wouldn't take the working pressure at weld heat. Also you can pressure test the welded stub and valve without pressure testing 30 miles of pipe

 

I suppose the welder would turn into a very spectacular flame cutter ?.

 

..........Dave

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  • 6 months later...
12 minutes ago, waterworks said:

You cannot safely weld a Diesel tank unless it's been properly purged, no serious welder would even think of it, it's totally against H&S. 

 

 

 

 

 

True for petrol but I think you may be mistaken as regards to diesel as all of the guidance says it can be totally safe -

If you are welding above the level of diesel than it is possible to get the fumes heated up, but if below the fuel level then the fuel removes the heat sufficiently - fill the tank with diesel and weld away.

 

I know of several boat yards that are more than happy to weld a tank in situ and containg diesel.

 

 

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