DEEP SEA CORROSION (not SRB) (1 Viewer)

[serge]

I saw a question like this in the 2002 paper...

I know most of the information about corrosion at different depths

except cold water having high oxygen levels... someone mentioned this
at school but i dont know if its true?

I know gases are more soluble at low temps, but would oxygen from the top of the ocean move lower because of the temperature getting cooler?

[if this does not occur then deep sea corrosion apart from SRB would be really
low, since very little UV light would make photosynthesis impossible,
hence very little, oxygen... but then again high CO2 from decaying fish, could
create a localised acidic area?]

any thoughts people?

 

[LostAuzzie]

cold water having high oxygen levels... someone mentioned this
at school but i dont know if its true?
I know gases are more soluble at low temps, but would oxygen from the top of the ocean move lower because of the temperature getting cooler?

As you mentioned, yes at lower temperatures the concentrations of dissolved gases increases. However, since the sources of dissolved oxygen are generally restricted to the higher 'layers' and no the dissolved oxygen generally doesnt migrate to lower depths due to the water being cooler. But some oxygen does enter the lower depths through ocean currents.

[if this does not occur then deep sea corrosion apart from SRB would be really low, since very little UV light would make photosynthesis impossible, hence very little, oxygen... but then again high CO2 from decaying fish, could create a localised acidic area?]

Yes Carbon Dioxide is one of the factors increasing the acidity of water at these depths. Others revolve around the Hydrogen sulfide produced by the SRBs (Hydrogen sulfide is an acid itself and the precipitation of active metals by Hydrogen Sulfide releases Hydrogen ions).
Acidic water accellerates regular corrosion because the standard reduction potential for oxygen is more positive in an acidic solution (there is a very small amount of oxygen at great depths). Acidic water also promotes the action of SRBs since these bacteria reduce sulfate in the presence of hydrogen ions to produce hydrogen sulfide and water.

Hope that helps!

 

[serge]

Acidic water accellerates regular corrosion because the standard reduction potential for oxygen is more positive in an acidic solution (there is a very small amount of oxygen at great depths)QUOTE]

yeh that helped alot...
so if SRB are not present and there is a very small amount of oxygen
then its safe to this deep sea (300m?) wreck will not be as corroded as a wreck
at a depth of say 5m?

 

[LostAuzzie]

There's still the slight acidity due to dissolved oxygen which would accellerate corrosion quite a bit. But probably not to the degree that it is more corroded than a wreck at a depth of 5m there is still not enough Oxygen and the inflow of oxygen carrying currents are at lower depths than this I believe. So to answer your question yes

 

[Haku]

just to clarify, the pH of sea water is 8 right? making it slightly acidic. While the increase in depts, decrease in pH occur due to the increasing carbonic acid concentration. is that true?

the book doesn;t say anything like that. On SRB create acidic environment around the ship due to its reduction of SO4, and making HS- which is acidic cause an acidic environment around the ship, accelerating corrosion.

 

[bmc]

basically there is less oxygen at great ocean depth but there is still sufficient there for corrossion to occur. as corrosion is where a metal loses electrons in reaction with oxygen and water the ingredients are still there for corrosion to occur

 

[serge]

just to clarify, the pH of sea water is 8 right? making it slightly acidic

no, and no

 

[Haku]

no, and no

...sorry the post was kinda wrong. meant to say pH 8, making it slightly basic

is that right?

but even at depts with higher presence of carbonic acid, it is still around 7-8 range. oh the HS- created by the SRBs cause a slightly acidic environment.

and no, oxygen do not occur at great depts that would cause much corrosion. and the temperature at the sea beds at depts is 4 degrees, so the temperature would cause a greater rate of corrosion.

 

[Captain Karl]

...sorry the post was kinda wrong. meant to say pH 8, making it slightly basic

is that right?

but even at depts with higher presence of carbonic acid, it is still around 7-8 range. oh the HS- created by the SRBs cause a slightly acidic environment.

and no, oxygen do not occur at great depts that would cause much corrosion. and the temperature at the sea beds at depts is 4 degrees, so the temperature would cause a greater rate of corrosion.

The overall pH at depths doesnt really change, but the water immediately surrounding the wreck becomes slightly acidic.
Dont know if you've worded it wrong again but generally a decrease in temperature corresponds with a decrease in corrosion rate because less have the required activation energy to react