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CompoSimmonite
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Welded a few petrol tanks and never had a problem. With filler neck upright fill to brim with water and leave at least overnight.
Jelly_Sheffield
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Effectively the big trap (and significant difference to most industrial tanks/vessels) seems to be the fact that it's extremely hard to get a sufficiently large amount of the residues out, to prevent clean tanks rapidly returning to the 0.6-1.3% vapour concentration required to explode again.
So summarising the advice:
• If at all possible find an alternative way to do the job. [Substitution]
• If unavoidable:
– Remove the bulk of vapours and liquid residues by repeatedly filling with hot, detergent laden water until the tank overflows, with the tank oriented so that there's no "headspace". Three times seems to be a consensus. [Hazard Reduction - Fuel Source]
– Purge with a constant flow of steam to further remove any residues in nooks or crannies. [Hazard Reduction - Adsorbed Fuel Source]
– Partially refill with water to minimise the headspace to only that necessary for a dry area behind your weld. [Hazard Mitigation - Reduce Volume of Potential Fuel-Air Mixture]
– Connect a 5 lpm flow of inert shielding gas to the tank, and allow to run through as a constant sparge for at least 30 min before welding. [Risk Reduction - Eliminate Oxidiser Source]
– Weld immediately once the system is "inerted". [Risk Reduction - FA Mixture Recurrence]
Based on experience doing this kind of thing with other systems, the advice given makes sense, and pure "decontamination" based approaches that could be successful would both take far longer, be much more energy intensive, and be difficult to "prove".
It occurs to me that if using a Gas Purge Only, using a Drager tube to "prove" the Hydrocarbon and Oxygen levels in the exhaust of that purge, would give piece of mind worth at least the £30 in testing tubes.
So summarising the advice:
• If at all possible find an alternative way to do the job. [Substitution]
• If unavoidable:
– Remove the bulk of vapours and liquid residues by repeatedly filling with hot, detergent laden water until the tank overflows, with the tank oriented so that there's no "headspace". Three times seems to be a consensus. [Hazard Reduction - Fuel Source]
– Purge with a constant flow of steam to further remove any residues in nooks or crannies. [Hazard Reduction - Adsorbed Fuel Source]
– Partially refill with water to minimise the headspace to only that necessary for a dry area behind your weld. [Hazard Mitigation - Reduce Volume of Potential Fuel-Air Mixture]
– Connect a 5 lpm flow of inert shielding gas to the tank, and allow to run through as a constant sparge for at least 30 min before welding. [Risk Reduction - Eliminate Oxidiser Source]
– Weld immediately once the system is "inerted". [Risk Reduction - FA Mixture Recurrence]
Based on experience doing this kind of thing with other systems, the advice given makes sense, and pure "decontamination" based approaches that could be successful would both take far longer, be much more energy intensive, and be difficult to "prove".
It occurs to me that if using a Gas Purge Only, using a Drager tube to "prove" the Hydrocarbon and Oxygen levels in the exhaust of that purge, would give piece of mind worth at least the £30 in testing tubes.
Trevorleach
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You are over thinking it, many trucks/boats/rvs use standpipes on their main fuel tanks, we had one on our old petrol boat, never blew up in the 6 years we owned it, it was 25 odd yrs old back then.
Not sure drilling tin is classed as hot works? and if it is lightly spray the drill bit with water whilst drilling the hole.
Jelly_Sheffield
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It's mostly that I think the underside of underside of a Landrover is going to be pelted with spray and periodically immersed, which is probably more than a standard bulkhead fitting is designed to deal with, so I'd rather use a proper threaded or gasketed flange connection where I can get a decent seal.
I think it depends who you ask and where it is, because the term isn't precisely defined...
Certainly for the purposes of all the COMAH sites and Vessels I have worked on drilling metal would need a hot works permit if done in a "Zoned Area" around flammables.
But done on a gate in the car-park, I doubt anyone would insist on a fire watch for 30 minutes after drilling.
Old Dog
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Standpipe fuel supplies go in from the top of the tank not underneath which is far better than welding a threaded port into the side or bottom of the tank which is prone to cracking.
Jelly_Sheffield
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I found the reference document (from back when the HSE still published such useful practical guidance) I was after when I originally wrote this post.
Guidance Note CG15 - The Cleaning and Gas-Freeing of Tanks Containing Flammable Liquids
To summarise, for small (<60m³) tanks, there are several acceptable methods:
To Gas-Free:
1) Steaming with dry steam at 2 barg, maintaining temperature (131°C) for 30 minutes or until the condensate is free of hydrocarbon residue, whichever is the longer.
2) Complete immersion in a boiling mixture of water with caustic soda (or detergent for aluminium) for 30 minutes, which it recommends as most suited to vehicle fuel tanks.
3) High-Velocity Steam-Jet cleaning followed by gas-testing of the internal atmosphere once cooled.
Inerting:
4) Filling with water completely, leaving no ullage.
5) Purging with an excess of low-velocity Nitrogen or another inert gas over an extended period until no vapour is detected in the gas exiting the tank.
In practice for most welding purposes outside an industrial environment, 5) is going to be the most practical approach, followed by 2) for smaller tanks.
Guidance Note CG15 - The Cleaning and Gas-Freeing of Tanks Containing Flammable Liquids
To summarise, for small (<60m³) tanks, there are several acceptable methods:
To Gas-Free:
1) Steaming with dry steam at 2 barg, maintaining temperature (131°C) for 30 minutes or until the condensate is free of hydrocarbon residue, whichever is the longer.
2) Complete immersion in a boiling mixture of water with caustic soda (or detergent for aluminium) for 30 minutes, which it recommends as most suited to vehicle fuel tanks.
3) High-Velocity Steam-Jet cleaning followed by gas-testing of the internal atmosphere once cooled.
Inerting:
4) Filling with water completely, leaving no ullage.
5) Purging with an excess of low-velocity Nitrogen or another inert gas over an extended period until no vapour is detected in the gas exiting the tank.
In practice for most welding purposes outside an industrial environment, 5) is going to be the most practical approach, followed by 2) for smaller tanks.
I think you've got the sequence wrong.
Caustic or steam clean, then fill with gas or water.
If you have concerns about internal corrosion being porous and holding fuel then after the first caustic wash use citric acid, preferably with it's ph buffered back to 6-7 range and a surficant.
Caustic or steam clean, then fill with gas or water.
If you have concerns about internal corrosion being porous and holding fuel then after the first caustic wash use citric acid, preferably with it's ph buffered back to 6-7 range and a surficant.
Fazerruss
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Jesus there are a lot of people over thinking this. I repair motorcycle fuel tanks.
Just fill with hot soapy water a few times and rinse out. Then steam out with a wallpaper stripper. If you want to be extra safe you can purge with exhaust fumes.
Then it will be fine.
I do this and haven't blown myself up yet.
Just fill with hot soapy water a few times and rinse out. Then steam out with a wallpaper stripper. If you want to be extra safe you can purge with exhaust fumes.
Then it will be fine.
I do this and haven't blown myself up yet.
Last edited:
addjunkie
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Youve been fine, as have I, but many have got it wrong, needing a new tank and underwear or worse. Nothing wrong with fully considering the hazards and potential substitutions / mitigations to reduce them. Its a mind set learnt in a working environment, but-the concept of thinking things through is very beneficial, comes as part of the PPPPPP.
However I think dreager tubes etc are a bit OTT for a landrover tank…..if really worried after cleaning and water filling, flame on a long stick, see if it ignites. With the reduced ullage risk is minimal.
Drilling in a hazardous area is normally considered hot work due to the spark potential, but drilling into a water filled tank in a non hazardous area is fine. If worried as said lubricate the bit with water. In a working environment all these things would or should be covered by PTW procedures and site safety standards. I was once the man who said yea or nay on a COMAH site by my signature!
Jelly_Sheffield
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I was just repeating the HSE guidance, who consider any one of the 5 techniques listed as acceptable.
I would note that 30 minutes of continuous dry steam flow at 2 bar is a very aggressive clean, and passing through a small tank is going to result in an exhaust that would itself be really very dangerous.
sako243
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@Jelly_Sheffield you could take a leaf out of a friend of mines book. He put a small 3l catch can in the return line of the fuel tank (Rover 4.6V8), that 3l provides enough to run his Eberspacher for 48h.
Return from engine in the top, return to tank out the top, heater pickup down the bottom. Never runs the risk of running the tank dry and to refill simply start the vehicle up and it refills quite quickly.
Return from engine in the top, return to tank out the top, heater pickup down the bottom. Never runs the risk of running the tank dry and to refill simply start the vehicle up and it refills quite quickly.
Pete.
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Whenever I weld the aluminium tank on my bike I empty out the fuel, leave it in the sun for a while then weld it. Before striking an arc on it with the tig the first time I stick my mapping torch around the filler at arms length to make sure there's no build up of vapour.
Petrol has quite a narrow lel/uel range 1.3 - 7.1%. 1.3% is going to have quite a strong smell.
Petrol has quite a narrow lel/uel range 1.3 - 7.1%. 1.3% is going to have quite a strong smell.
Which way is the opening pointing, during the leaving out in the sun bit? Downwards would seem best, because fuel vapour is heavier than air.
Pete.
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Ah well the integral pump is mounted on a large plate about 7" diameter so it has a pretty big hole to verify t out of.
Jelly_Sheffield
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This is it exactly it, and the mindset just slowly takes root in your thought processes, as a young man I was a little cavalier and willing to take significant personal risk to get the job done.
In my day job I gained increasing responsibility to keep others safe, and ran a couple of really spicy projects where real harm to real people whose wives and children I really knew, was foreseeably a direct consequence of me making bad decisions or people not listening...
That changed things for me, because I saw that to ensure others were safe I had to lead from the front and personally embody those behaviours.
Fair, it's the very far end of the spectrum of control measures, and wouldn't be a solution anyone would reach for unless they already knew about them and used them...
Ooooh, controlling RAMS, PTW, & MoC can be a thankless task, but probably one of the most meaningful in terms of keeping people safe.
In spite of that, I am very happy to now be slightly removed from having to deal with grumbling contractors and irate production managers directly.
prepman
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Steaming out was a method I have heard of but never used.
