Steel Welding query

Discussion in 'Metal Boat Building' started by JimCooper, Aug 17, 2005.

  1. JimCooper
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    JimCooper Junior Member

    A query to the welders

    If you are welding a steel deck from above, what can you use for a temp backing plate underneath to stop the puddle running away? Would some cement sheet do the trick? there'd be too much moisture in wood.

    I have seen stainless strips used this way on Al construction. Would like to know if anything works well for steel.

    Cheers
    Jim
     
  2. jehardiman
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    jehardiman Senior Member

    Stick or MIG? because my first response would be to improve your fitup, turn down your amps, and use a smaller rod.
     
  3. JimCooper
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    JimCooper Junior Member

    JE Hardiman
    Thanks

    I had some thick plate to weld with a bit of a gap a bit of rust and paint . I found by turning up the Amps (Using a big MIG) I could burn off the oil and rust and paint as I went but the welds are sagging and running away underneath so I wanted a backing plate to keep em in place.

    Made a few holes in my trousers too !

    Cheers
    Jim
     
  4. jehardiman
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    jehardiman Senior Member

    Jim, all you've done is set yourself up for a failure. Welding over rust and paint may work for farm equipment, but it causes embrittlement in the weld. So does too much energy input. In a steel hull, the deck takes a major portion of the bending load. Failure of a deck weld was a common cause of steel vessel loss in late 40's to early 60's (and I'll bet you have no arrester strake). For the safety of whoever goes to sea in that vessel, cut out all that poor weld and do it over.
     
  5. JimCooper
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    JimCooper Junior Member

    Thanks fella

    I'll give it to a boilermaker, and retire from the arena a defeated and broken man.

    Unless you want a holiday in Bonny Sunny Scotland.?

    Jim Out
     
  6. nero
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    nero Senior Member

    never tried it but was told copper flashing is an anti stick surface for welding on.
     
  7. jehardiman
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    jehardiman Senior Member

    Nero is correct, copper or brass can be used, but they can contaminate the weld. It it better, but more pricey, to use carbon arc rod if the throat is not too wide. Also you can try turning down the gas because it could be blowing the pool out, especially if you've got the amps way up.

    Jim, I'm not trying to rain on your parade, but this is one of the things we pound into the welders. Steel vessels rarely ever fail in the plate, they fail at the welds. Welds are stress and corrosion concentrators. The problem also is that they precipitously fail in tension. There is no warning until the BANG! At that point a crack has started and if the weld if brittle, it will zipper along the entire length of the weld. The hull girder will be crippled and water may begin flowing into the hull. Since this normally happens when the vessel is in a seaway, the vessel is usually quickly lost as the crack continues to propegate. Of course, no one can prevent the sea from overwhelming a vessel, but the idea is to do everything possible to prevent the vessel from breaking up in fairly benign conditions.

    If you wish to continue, there are fillers made for no-prep welding.

    http://www.lincolnelectric.com/knowledge/articles/content/20faq.asp#9

    http://www.jwharris.com/images/pdf2/70S6.pdf

    I'd also select one that meets ABS requirements.

    http://www.eagle.org/rules/downloads/consummables/27-APRVD-ApxB.pdf

    P.S. You need to move to the warm west coast. I lived for a year or two in Gourock, it's nice this time of year! ;)
     
    Last edited: Aug 22, 2005
  8. Wynand N
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    Wynand N Retired Steelboatbuilder

    Jim,

    An old boilermaker trick is the broken arc technique. In simple terms it means to start welding for a second or so, stop for a second, weld, stop...... With a little practice you will get the hang of it. The secret is to stop before the puddle burns through. You will end with a weld that is penetrated thoroughly and if you done it properly, it will looked if it was welded from the bottom as well.

    Low carbon welding electrodes are excellent in this regard, but it has to kept in an electrode heaterbox at about 180 C degrees to work properly and your welding machine needs an OCV (open circuit voltage) of at least 72 or more to weld it smoothly.

    Remember, practice makes perfect ;)
     
  9. JimCooper
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    JimCooper Junior Member

    JE Hardiman

    Ah... Inverclyde why on earth did you leave? Couldn't hae been the winters could it? Its a nice wee spot , I have been there often.

    I hae to ask looking back at your previos post; What's an arrester strake? sounds like something the Police carry in Glasgow!



    Thanks to Wynard and Nero for your correspondance too.

    Cheers
    Jim
     
  10. jehardiman
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    jehardiman Senior Member

    Well there is the joke about "little blue men" and swimming in the firth. I can't remember the sleet being more than an inch or two thick. And when did it become Inverclyde? When I was there it was Renfrewshire! Are you still using threepennies? I got some of those to spend! ;)

    Anyway, an arrester strake (or bar) is a riveted (old, early welded construction) or a notched thick strake (new, modern welded construction) right at the join of the shell and the deck. What it does is it acts as a crack arrester to keep any crack in the welds/plating from spreading from deck to shell or vice versa. Sometimes in construction it is now incorporated into the weld design of a thin decking to stringer plate or in the gunwale bar to shell attachments. It is important to maintaining hull girder strength in the event of damage and cracking.
     
  11. JimCooper
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    JimCooper Junior Member

    JE HArdiman
    Sorry you are of course correct I just asked my Sister (she knows such things) it is in Renfrewshire you'll have to forgive me its all a bit foriegn over there !

    Your thruppenny bits will have to be given to your grand-bairns.

    I think I have an arrester strake, there is a bar half inch by two that runs around the deck edge, it lies in the same plane as the deck plate, and is fully welded to all the frames and the hull plate that rises up past to become the Bulwark.

    The job is done...I called in a favour, an old welder, he ground and chopped and clucked and welded, his weld was true though he walked a random line down the lane.... what do Whisky fumes do to the weld properties ?

    Jim Out
     
  12. jehardiman
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    jehardiman Senior Member

    Most likely a gunwale bar. Good design practice is to make sure none of the deck plate welds line up with any butt joins of the bar.

    LOL, We were told by our landlord over there that the first rule was to never pay a tradesman for work until the job was finished. It seems there was wallpaper hanger hired to do the house we rented....and the paper had a vertical pattern....and you could tell which walls were done before and after lunch... :D .

    "Ooch, just a wee dram ta steady the hand...."
     
  13. MikeJohns
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    MikeJohns Senior Member

    Much brittleness is induced in large welds from the resulting crystalisation of the slow cooling mass. If you have to bridge then multiple runs will anneal the weld material and can be reasonable undertaken but only with MIG equipment and care.
     
  14. shugabear
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    shugabear jr member

    i like the way you think wynand i watched plenty of more expereinced boilermakers and learned alot when i apllied their tech to the ship building i do now it works more often than not and as a fitter i know that sometimes you cant always get that 3/16 gap or less and welding my own fit ups sometimes the stop start works really well with flux core but again to insure the best pentration your weld area has to be clean otherwise you dont get stregth so i agree completly
     

  15. lumpy bumpy
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    lumpy bumpy Junior Member

    Im afraid everyone is a bit of the mark with there welding advice .
     
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