the mystery of underwater welding

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http://awo.aws.org/2013/08/underwate...=2013%2BAWO%2B this is just something cool i saw on the aws"s facebook page
Reply:nice post
Reply:thanks, i heard that the helmet for underwater welding weights 25 to 30 pounds i couldnt believe it
Reply:The "SuperLite 17", termed the MK21 MOD1 SSDS for the uniformed warriors, helmet has an in-air weight of 29lbs.  The in-water weight is "neutrally buoyant".  How?  Key point.  The positively buoyant materials (~ items that float in water) and negatively buoyant materials (~ items that sink in water) comprising the helmet are in static equilibrium.  This balances of forces, vis a vis Archimede's Principle, makes the helmet weightless for the diver while subsea.+ buoyant materials include fiberglass, polyester resins, carbon fibers, polyurethane, oolycarbonate, Buna-N.- buoyant materials are all the ferrous/non-ferrous metallics built into the helmet.  Integrating the weld shield, fixed shade (flip-up) style, is the easy part.If you're interested in learning more about the pioneers of improved "heavy work" gear for divers, Bob Kirby and Bev Morgan, visit www.kmdsi.com.  For extra motivation, scan the SL17's O&M Manual (182pp) for a deep-cut on the system. "Discovery is to see what everybody else has seen, and to think what nobody else has thought" - Albert Szent-Gyorgyi
Reply:The helmet isn't neutral bouyant because the the weight of positively bouyant materials equals the weight of the negatively bouyant materials.  It is neutral bouyant because the helmet displaces a volume of water, the weight of which, equals the the weight of the helmet.Steel ships float because the weight of the water they displace is more than the weight of the ship and everything on it.  Submarines float, sink, or remain neutrally bouyant at whatever depth by adding water to the ballast tanks such that the weight of the submarine and the water in the ballast tanks is less than, greater than, or equal to (respectively) the weight of the volume of seawater that it displaces.
Reply:you wont catch me underwater welding maybe in a simulator but thats maybe
Reply:Displaced water's volume the key, not the weight.  Check.  Need to lay off the cerveza tonight. Ha!"Discovery is to see what everybody else has seen, and to think what nobody else has thought" - Albert Szent-Gyorgyi
Reply:career life expectancy:   Try to find hyperbaric welders in their forties... I don't know if things have changed but it used to be that people eventually had difficulty passing the physical once they were older.
Reply:I want to know how you scratch your nose with one of those on... you know it's happened before.Miller Dynasty 200DXMiller Spectrum 250DMiller Millermatic 200Bunch of old blue dinosaurs....
Reply:Question for you; rather of-topic but not by much. Why does the helmet not go negatively buoyant as the diver descends and air compresses?
Reply:ManoKai is right. It is all about volume,displacement of water weight. When you get ready to jump in on a normal shallow (under 60') your gear is over 100 lbs, but you are neutral in the water. A deep dive is more. I do a lot of rescue and commercial diving, but no underwater welding. I tried to learn it by myself in a tub once. All I can say is I should have stuck with playing with rubber duckies. I had no success. I used a WWII manual that just had one page on it. It said to dip 6011 rod in wax and jump in.  I'm sure it has progressed since then.
Reply:Originally Posted by jlamesQuestion for you; rather of-topic but not by much. Why does the helmet not go negatively buoyant as the diver descends and air compresses?
Reply:Ah ha. Thank you.
Reply:Originally Posted by PoptmThe helmet isn't neutral bouyant because the the weight of positively bouyant materials equals the weight of the negatively bouyant materials.  It is neutral bouyant because the helmet displaces a volume of water, the weight of which, equals the the weight of the helmet.
Reply:I just can't stop laughing. His answer reminds me of an old Danny Kaye skit in the Court JesterHope this works.
Reply:The helmet doesn't go negatively bouyant as the diver descends because they keep the air pressure in the helmet about equal (slightly above) the pressure at whatever depth the diver is at.  Those dive helmets are not "hard suits".   If they were it would get more negative the deeper it went due to the decreasing volume of the "hard suit" as it is compressed.
Reply:@ Poptm - "...about equal (or slightlly above) the pressure at whatever the diver is at..." is not correct. The low pressure feed to the helmet is however reduced for diver breathing.  The optimum overbottom pressure for dives shallower than 130 fsw is 135 psi, and for dives 130-190 fsw is 165 psi.  The minimum manifold pressure (MMP) supplied to the diver is the sum of the ambient pressure (0.445psi per fsw) and the overbottom pressure.Example.  The MMP for a diver to 180 fsw is calculated as follows........* Bottom pressure at 180 fsw = 180 fsw x 0.445 psi/fsw = 81 psig* Overbottom pressure = 165 psig* MMP = 81 psig + 165 psig = 246 psigNote:  The air pressure supplied to the diver, in this example, is three times the diver's ambient seawater pressure.  In the case of a dive to a depth of 50 fsw, say, the MMP would be seven times the ambient pressure.@ DSW - the SL17 (MK21) is an on-demand, open circuit, dive rig.  A cessation of air flow to the diver would eventually result in the diver becoming hypoxic.  Not stuffed up in the helmet a la the MK V of days past.  The prevent hypoxia and maximimize safety, dives of 60fsw or greater require the diver to use an EGS (emergency gas supply....come-home bottle....single Al 80).Last edited by ManoKai; 08-28-2013 at 07:05 AM."Discovery is to see what everybody else has seen, and to think what nobody else has thought" - Albert Szent-Gyorgyi
Reply:Some pretty interesting stuff that underwater welding; short life expectancy but I wonder how much money it pays.. Think you have to be a certified scuba diver though
Reply:I have a question.We all know that when you weld, you’re not suppose to quench your work piece with water after welding because it makes the metal brittle, and then things break and bad things happen.What happens when welding underwater. Wouldn’t you technically be constantly quenching your work piece causing it to become brittle?I know this may seem like a silly question, but I was just curious. kidtigger24  They think I’m crazy, but I know better. It is not I who am crazy. It is I who am MAD!
Reply:Your right ManoKai.  I ain't a diver.  Just used to pressure tests some of those helmets and the tests were never at a very large number (way below the pressure at maximum depth).  So I just assumed that pressure in them was only at or slightly above ambient sea pressure.  Boys at work as well as you straightened me out though.  Thanks for that.KidTigger.  There are two types of underwater welding (that I am familar with)... wet welding and welding in a chamber which is dry (with the exception of the high humidity).  The wet welds are done right in the water and as such are, for lack of a better term, substandard from a structural point of view with respect to naval vessel welding criteria.  And as such there use is very limited.  They are full of micro cracks. Wet welds are therefore used on items where that kind of defect can be tolerated.  Welds made in a chamber are of a quality similar to those made on dry land.We used to mainly use, when wet welding, 1/8" or small waterproofed mild steel electrodes on steels when the carbon equivalent of the steel was below a certain limit and nickel waterproof electrodes 3/32" when the carbon equivalent of the material was above the limit.
Reply:Wow. A lot of equations that seem to make the whole thing seem really complex. Being a SCUBA Instructor (but not an underwater welder), I would like to add my 2 cents worth in attempting to simplify what happens underwater.The pressure of 1 gravity at sea level is 14.7 psi.The weight of salt water as depth increases is 1 gravity every 33 feet. Fresh water is 1g/34 feet.The human lungs are not that strong. If you were using only a snorkel to supply air from the surface, you would not be able to draw air in as little as 3-4 feet of water.  This is because the weight of the water is compressing the air spaces in the body (sinuses, lungs, ears, etc.). That is why the SCUBA regulators deliver air to the diver at a pressure that is about 1/4psi above the pressure at depth.So, at 33 feet depth of salt water, the regulator on a typical 80cu ft SCUBA tank is delivering air at 1G surface plus 1G at depth, or 2G. At 66 ft, the diver is getting 3G of air pressure and so on.The reason diving mixes are used at depth is because of what is called the partial pressures of gasses. SCUBA tanks are typically filled with normal air which roughly is a 20/80 mix - 20% O and 80% N. As depth increases, the Oxygen intake increases. Every person is different, but at somewhere between 160 and 180 feet, the O content delivered to the diver becomes toxic. That is why other gasses are mixed. Typically, Helium is used. By adding another gas, the percentage of Oxygen (partial pressure) is reduced, therefore, increasing the depth at which a diver can go before it becomes toxic.The problem with deep diving is the Nitrogen intake. The higher N content and extreme pressures causes it to get into the bone marrow. The risk is high and eventually, bones will get extremely brittle. A typical saturation diver can not do this type of job for more than a few years. That is why pressurized suits are needed. They allow the diver to maintain a much lower pressure within the suit compared to the pressure at depth.If any of you welders are considering this type of career, be aware of the extremely high risks to your health. Sport diving has an industry recognized limit of 130 fsw. Anything beyond this depth is considered to be commercial in nature. Even at depths of 80-90 feet, Nitrogen Narcosis is a concern. It gives the diver a euphoric feeling and sometimes leads to poor decisions. PADI Instructor #37718.Happy bubbles.
Reply:Originally Posted by jlamesI just can't stop laughing. His answer reminds me of an old Danny Kaye skit in the Court JesterHope this works.
Reply:Evidencing the effects of Nitrogen Narcosis!
Reply:I enjoyed it, thanks for posting! I hate being bi-polar it's awsomeMy Heroes Have Always Been Cowboys
Reply:Hi, the question previously..."what does it pay".....this is so typical for those that do not value living and can tolerate poor health to the point of being completely comatose for the rest of their lives.Welding, with all the attached hazards of fume inhalation and arc flashes not to mention UV exposure and cancer related symptoms, is a very real health hazard which not taken seriously can make you a patient in the intensive care for the rest of your short life.Now it's exciting to go welding in an environment so hazardous that getting paid extra to do it is a good prospect.......just don't expect to see your grandchildren grow up around you.Ian.Originally Posted by blackbartManoKai is right. It is all about volume,displacement of water weight. When you get ready to jump in on a normal shallow (under 60') your gear is over 100 lbs, but you are neutral in the water. A deep dive is more. I do a lot of rescue and commercial diving, but no underwater welding. I tried to learn it by myself in a tub once. All I can say is I should have stuck with playing with rubber duckies. I had no success. I used a WWII manual that just had one page on it. It said to dip 6011 rod in wax and jump in.  I'm sure it has progressed since then.