Deep sea welding
- Thread starter karlj
- Start date
As a gas engineer I can confirm that yes it could explode, not necesarily would but there is a probability that it would from the static that would build up around the pipe that could cause a static discharge inside the pipe, in other words, boom, why most gas pipes have earth cables on them (Y) I helped 
That's petrol sr20
lol don't let me near a gas supply then :laugh:
first of all gasses are never piped with oxygen unless they are actually oxygenated such as N2O, but things like natural gas would be pure with no oxygen, and so it couldn't catch fire in the pipe. this is the same for spray cans, people often think that if you set fire to the spray from a spray can that it can go back inside the can, but thats not possible, if the fire was to enter the can it would starve itself of oxygen instantly and put itself out.
secondly if you were welding a gas pipe, i am pretty sure they would turn the gas off,
basically no there is no chance of a welder underwater blowing themselves up from welding a gas pipe.
secondly if you were welding a gas pipe, i am pretty sure they would turn the gas off,
basically no there is no chance of a welder underwater blowing themselves up from welding a gas pipe.
porkpie700
Buy & Sell Member
Some one has been watching a james bond movie i think :laugh:
Ah this is where I prove you wrong, welding creates alot of heat which would boil the surrounding area of water, this frees ups some oxygen mollecules from the water (not all of them just some) and presumably as there is welding going on it'd be turned off but let's assume it isn't (only because the question didn't specify ) welding would usually imply that there is a hole somewhere on the pipe so now you have the fuel, ignition and oxygen needed for combustion and the subsequent flame would be so intense that it would create more oxygenkeeping itself going. BOOM, essay answers for the masses
) welding would usually imply that there is a hole somewhere on the pipe so now you have the fuel, ignition and oxygen needed for combustion and the subsequent flame would be so intense that it would create more oxygenkeeping itself going. BOOM, essay answers for the masses
Ah this is where I prove you wrong, welding creates alot of heat which would boil the surrounding area of water, this frees ups some oxygen mollecules from the water (not all of them just some) and presumably as there is welding going on it'd be turned off but let's assume it isn't (only because the question didn't specify
but heating water doesn't cause it to separate into oxygen and hydrogen, if that was so then every time you boiled water you would have an insanely dangerous explosion risk. To separate water you need electrolysis, and you can't weld underwater with an electrical welder, you would need OxAc, the oxygen from the welder might be able to burn up any gas that comes in its path but you wouldn't notice it happening because the welder is already burning.
but lets say that there was enough oxygen around to allow it to burn, you wouldn't get an explosion so much, it would be more of a burn. so you have a small hole in a gas pipe, the gas is set on fire by the welder which then oxygenates itself from the water some how, it would simply make a jet of flame which would last for as long as there is gas and its length would be governed by the pressure in the system. but the flame would not be able to go into the pipe because there is no oxygen in the pipe, and the water wouldn't enter the pipe because the gas is at a higher pressure.
You're right and wrong Nex. They don't generally use Oxy Acetylene underwater, they use SMAW, aka stick welding. I imagine the arc and the heat (~4,500c) probably does split some water molecules but they either recombine immediately or diffuse harmlessly into the water .
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frank
Club Member
arc welded aint they http://en.wikipedia.org/wiki/Hyperbaric_welding
and they probably shut the length of pipe being welded and replace the gas with co2 inside that section ?
and they probably shut the length of pipe being welded and replace the gas with co2 inside that section ?
You're right and wrong Nex. They don't generally use Oxy Acetylene underwater, they use SMAW, aka stick welding. I imagine the arc and the heat (~4,500c) probably does split some water molecules but they either recombine immediately or diffuse harmlessly into the water
really they use arc? i thought it was only ever OxAc underwater? but yea in that case an arc would certainly create some oxygen, but probably not enough to start a reaction.
porkpie700
Buy & Sell Member
Alright i know how to settle this with a simple experiment. Someone jump into a swimming pool with a lighter, fart under water and try to light it. If you blow your ring peice inside out then the theory is true, if not then you'll just offend the other swimmers.
The water into O2 point is correct but not quite as extreme as i think people are first imagening. Think about fish; they live in water and breath O2 which is contained in the water. Just as if you submerge a plate of iron into a glass of rain water it'll still rust because it will react with the O2 in the water (yes i've tried it lol), why do you think the titanic is rusted to hell. Water is quite good at disolving and holding onto things, including gasses.
Has anybody actually done a search to see if an underwater explosion has happened ever? I'm sure it probably has at some point in history, but as for the present day, with all the health and safety hysteria (that may very well one day make it illegal to masterbate without wearing suitable eye protection, yes ####ing glasses) i feel pretty confident in betting that they most likely do shut off the gas supply and purge the pipes with a non-reactant gas such as CO2 before letting anyone near them.
That's enough geeky #### from me *geek*
The water into O2 point is correct but not quite as extreme as i think people are first imagening. Think about fish; they live in water and breath O2 which is contained in the water. Just as if you submerge a plate of iron into a glass of rain water it'll still rust because it will react with the O2 in the water (yes i've tried it lol), why do you think the titanic is rusted to hell. Water is quite good at disolving and holding onto things, including gasses.
Has anybody actually done a search to see if an underwater explosion has happened ever? I'm sure it probably has at some point in history, but as for the present day, with all the health and safety hysteria (that may very well one day make it illegal to masterbate without wearing suitable eye protection, yes ####ing glasses) i feel pretty confident in betting that they most likely do shut off the gas supply and purge the pipes with a non-reactant gas such as CO2 before letting anyone near them.
That's enough geeky #### from me *geek*
I have not heard of an underwater pipeline explosion, leaks yes but not explosions. Although the chances are minimal I would think that it would be more likely that the possible reason for an underwater explosion would be attributed to a pipeline overpressure which lead to a pipeline rupture, not as a result of combustion of pipeline gas. The only explosions I have ever heard of are all subsurface pipelines.
There is a risk of explosion through welding but that is mainly attributed to the formation of hydrogen and oxygen at the welding arc point not an explosion from the gas contained within the pipeline itself. There is a major reason why this would be extremely hard to achieve which i will leave you to figure out.
CO2 is not really the best gas to purge the line either and most of the time it is not the wish of the operator to shutdown the pipeline as this is a major financial penalty to bare in lost revenue, which run into huge numbers, especially if you were looking at the 40's pipeline for example.
MMA welding is commonly used Nex but that has risks to the diver in the form of electric shocks, although minimal with the right precautions and would be overall a safer option in a dry welding envoronment for the lack of supplied 02. Both wet and dry methods are employed in subsea welding, dry normally using Helium as the vacation gas. CO2 is not a good gas to use as it could cause issues with the welds depending on the material being welded, Cr steels for one do not react well in the presence of CO2 and can cause embrittlement of the weld. In fact CO2 itself is not a simple gas to transport through a pipeline......that however is a completely different subject.
In summary, yes there are explosion risks associated to subsea welding but not to the extent suggested here.
There is a risk of explosion through welding but that is mainly attributed to the formation of hydrogen and oxygen at the welding arc point not an explosion from the gas contained within the pipeline itself. There is a major reason why this would be extremely hard to achieve which i will leave you to figure out.
CO2 is not really the best gas to purge the line either and most of the time it is not the wish of the operator to shutdown the pipeline as this is a major financial penalty to bare in lost revenue, which run into huge numbers, especially if you were looking at the 40's pipeline for example.
MMA welding is commonly used Nex but that has risks to the diver in the form of electric shocks, although minimal with the right precautions and would be overall a safer option in a dry welding envoronment for the lack of supplied 02. Both wet and dry methods are employed in subsea welding, dry normally using Helium as the vacation gas. CO2 is not a good gas to use as it could cause issues with the welds depending on the material being welded, Cr steels for one do not react well in the presence of CO2 and can cause embrittlement of the weld. In fact CO2 itself is not a simple gas to transport through a pipeline......that however is a completely different subject.
In summary, yes there are explosion risks associated to subsea welding but not to the extent suggested here.
