UNDERWATER WELDING

Question
QUESTION: Dear Jeff,
In standard scuba gear, with standard tanks and air supply,
how deep could a diver go and come back without problems. I
believe this is a time issue so if time is minimized could
someone go deeper safely. If so, how deep and what are the
time constraints? Also, what equipment is needed to do
underwater carbon arc gouging? thanks
Sincerely, Dick Schlueter


ANSWER: It is both depth and time dependant, you can find examples of appropriate time / depth combinations in the US Navy Dive manual:

http://www.supsalv.org/00c3_publications.asp

Issues effecting depth and time at depth:

Gas in tissues / blood stream:
at 190 feet of sea water you have only 5 minutes counting the time it takes you to swim to depth before you would have to leave for the surface to remain inside of the no decompression limits. If you wanted to plan a decompression dive you could stay longer but you would have to spend time during ascent in the water column allowing some of the disolved gas to come out of solution.

Nitrogen narcosis:
Another issue to consider with standard SCUBA gear / gas mixes, nitrogen has a narcotic effect at depth. Depending on the depth of the dive you may need to investigate using a gas mixture (helium and oxygen or helium, oxygen, and air)

Central nervous system oxygen toxicity:
Oxygen is toxic in higher partial pressures, as a general rule divers do not use oxygen at a higher partial pressure than 1.4 atmospheres




Underwater cutting:
For underwater cutting exothermic or steel tubular cutting rods are normally used, both normally use a welding machine to ignite. Steel tubular rods actually cut with the current (similar to arc gouging but oxygen is used instead or air to move the material out of the curf)

There are also specialty tourches that run on compressed gasoline (petrogen) or special mixes (MAPP Gas) to utilize a torch flame.

Let me know if you have any other questions or need information on a specific project.

Jeff

www.rmediver.com

---------- FOLLOW-UP ----------

QUESTION: Jeff, assume I am on a submarine and have to perform an
underwater repair. what would the power supply be? I assume an oxygen tank will be needed to move the molten metal? ds...

ANSWER: You would use a DC welder running reverse polarity.

This would work for both starting your torch (exothermic) and for welding.

You would use O2 for the exothermic cutting.

---------- FOLLOW-UP ----------

QUESTION: Jeff, if the sum and the welder is underwater, where would the
DC power supply be located? is it water proof? ds...

Answer
No it would have to be mounted inside the sub or on surface - not waterproof.

If you are only doing underwater cutting then you could go with a battery ignition system, that could be submerged along with the O2 cylinder and leads for cutting. BROCO actually makes a system like this for smaller cutting operations, battery and O2 are mounted in a small diver carried pack.

I suppose depending on the amount of welding required it might be possible to build a battery bank that could deliver the required amperage as well...

If your submersable is surface tethered then you could run the welder at the surface to feed power. You will need to figure your loss (distance of leads) and ensure the welder is rated for above the demand required.

Jeff