Welding a steel hull

Discussion in 'Metal Boat Building' started by Wynand N, Jun 23, 2008.

  1. lumpy bumpy
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    lumpy bumpy Junior Member

    Whats the repair procedure for a (stray) arc strike ?
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

    Well, depends which "standards" you are working too, appears some have non at all. But standard IACS quality method, which is the basis for all Class work, is:

    a) Remove the hardened zone by grinding
    b) Weld over a short bead over 50mm on
    the arc strike

    From IACS no.47 Shipbuilding and Repair Qulaity Standrad, dec 2004.
     
  3. rwatson
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    rwatson Senior Member

    I am referring here to the principle of hardening metal, the brittle or Martenzite zone


    I am referring here to information about failures of steek hulls due to bad welding practice.

    There have been NO examples provided by surveyors, litigants, steel boat owners and all the people who would normally have encountered them


    Thats good - since my guess that some welding jobs should be pre-heated, based on the mettalurgical info provided earlier, I have been given lots of examples which are of great interest to me.

    I will stop here and keep it simple, as some people are having trouble following my long dissertations.

    Once again - the info I am seeking is specific examples of sailing boat hull failures caused by bad welding practices. Thats it!
     
  4. Ad Hoc
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    Ad Hoc Naval Architect

    "..Once again - the info I am seeking is specific examples of sailing boat hull failures caused by bad welding practices. Thats it!.."

    Then i can only refer you to the post I made earlier, if that is all, post #168.
     
  5. rwatson
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    rwatson Senior Member

    I have one comment about that, but the moderators would delete the post.
     
  6. Ad Hoc
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    Ad Hoc Naval Architect

    Well, having been on both sides of such 'insurance' claims many times, defence and prosecution, i can assure you this happens far more frequently than you imagine! The rubbish fabrication/design i have seen which has been "passed" is shocking. But, despite having all this "evidence", it is in the hands of the lawyers....and as such, hidden from public viewing. Approx 90~95% are errors owing to manufacturing, and then down to, more often than not, sloppy amateurs who think they know better.

    Which is why new rules and procedures slowly change, owing to such failure's, which can never be high lighted publicly. Institutions and others are called for comments and analysis, and once the dust has settled down from the courts...new legislation and/or procedures follow to prevent the aforementioned "issue" again. (I'm on LR's technical committee, which does just this, reviews new rules for applicability owing to service experience feedback).

    But it doesn't bother me if you do not take my word for it...that is your prerogative. I'm just telling you how it is, from my own experience.
     
  7. Brent Swain
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    Brent Swain Member

    Let see. What you are saying is that the tiny amount of heat from a quick drag weakens the metal, but dumping a lot of heat on it by welding over it, or grinding it thinner , makes it strong again? Bit of a contradiction there? Sounds like fantasy to me. One would have to be pretty dense and gullible to believe that. Such welds in the middle of a plate would raise a ridge or worse. No wonder so many perfectionist boats need a lot of filler to make up for such screwups. The more you do to a piece of steel ,the greater the potential for distortion. Mine need absolutely no filler to make them fair.
    Not all hulls are insured, and thus subject to the secrecy of the insurance industry , yet I have still heard of none of the failures you claim. Sounds like you are grasping at straws, and making up stories ,to keep your feeble arguement alive.
    Give it up. You lost this one.
    Brent
     
  8. Ad Hoc
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    Ad Hoc Naval Architect

    Brent

    See this is where you are not doing yourself any favours. Notice the quote is not from me per se, but from IACS. Do you know what is IACS?

    If you do not, it is the organisation that effectively "runs" Classification societies. As such they formulate the "minimum" standards to comply with for all societies. This means if a welder is trained properly, if the welder is educated properly and if the welder is performing welds to a recognised Classification society and the welder is welding in a shipyard that has been audited by Class and if the welder has been 'approved' to weld certain types of weld for major structure, not minor stuff like tabs which does not require type approval cert etc, then said welder shall have to comply with the above.

    If the welder doesn't then said welder will be retrained or gently reminded not to keep producing substandard work or if continuously, kicked out of the yard or downgraded to minor work.

    So all you are saying above is that you have either no idea or simply do not care about quality in the same sense that others do and as such you clearly cannot be welding your boats to any accepted Classification standard for compliance and any international level of competency and hence quality, just your own. Since just your own, then obviously, like many on here, you can say what you like and do what you like. But it is in no way acceptable in any of the professional standards that exits worldwide, whatever your own thoughts or views are.

    The weight of experience and evidence for acceptance of professional standards worldwide is somewhat greater than your own personal views.
     
  9. welder/fitter
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    welder/fitter Senior Member

    Arc strikes can change the granular structure on the surface layers of the plate, yet not alter the other layers through the thickness of the plate. When one welds the thickness of plate found on a steel sailboat hull, energy from the arc is sufficient to create a more uniform - through the thickness - alteration in granular structure, both during the welding - increase in temp/expansion of granular structure - and afterward - decrease in temp/reduction in granular structure, providing the steels lower critical point has not been surpassed. The change in granular structure begins to occur - when temp. is increasing - at 212Degrees(F). This is taught in the most basic of welding programs and most basic of metallurgy courses. Ask any "C" level welder & he/she should recall it.
     
  10. rwatson
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    rwatson Senior Member

    So, there would be some technical reference available about the effect of arc strikes, on say 5mm steel ?

    Sorry, I was able to find the answer to my own quiestion thorugh the magic of the internet.

    "research by S. H. Van Malssen, published in the AWS Welding Journal, July, 1984, pages 29-37, demonstrated that in conventional construction steels, arc strikes do not cause cracks"

    http://www.steelstructures.com/StlInspNews/NEWS arc strikes.htm

    Article Name: The Effects of Arc Strikes on Steels Used in Nuclear Construction
    Author: S.H. Van Malssen
    Page: 29
    Date: Jul. 1984


    Sounds like this might apply to boats ?
     
    Last edited: Aug 10, 2009
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  11. Ad Hoc
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    Ad Hoc Naval Architect

    geeesssss..this goes round in more circles that an American Oval racing car!
     
  12. welder/fitter
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    welder/fitter Senior Member

    So, if I follow correctly, you are suggesting that a steel boat is a static, not dynamic structure? That there is no fatigue loading, especially with the method used to construct the "origamiboats"? Aside from the apples/oranges comparison, my understanding of the consideration is that it is for one simple strike, not several, and not dragging a rod across the plate - once again, on a structure that is static. No, imho, this does not apply to boats.
     
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  13. Ad Hoc
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    Ad Hoc Naval Architect

    It also looks like he is saying that ICAS is wrong and the TWI is wrong and IIW is wrong and all those other bodies around the world involved with shipbuilding/design etc are all wrong.

    I think you had better email them that report very quickly as their whole MO is wrong! I'm sure they will be very grateful that you have pointed out this error which has missed everyone by....thank heavens for the Internet eh!
     
  14. rwatson
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    rwatson Senior Member

    No - it doesnt say anything of the sort. You obviously didnt read the article in full.

    If you cant be bothered looking up the info, i will reproduce a few basic points for you.

    "The arc strike is similar to a very small weld, one made without preheat and certainly smaller than the minimum weld size required to reduce the risk of cracking. The arc strike cools very rapidly, leaving a very small but very hard surface and heat-affected zone (HAZ). A high-hardness HAZ increases the risk of brittle fracture, hence an arc strike may serve as a crack initiator. The significance of a crack found at the surface also exceeds that of a crack below the surface.

    Crack propagation requires a combination of high stress, adequate crack size and low toughness in the steel. Fatigue from cyclic loading certainly increases the likelihood of crack propagation. "

    and

    "For fatigue applications, bridges and such, arc strikes certainly should be ground to remove the hard HAZ. This is reflected in the AWS D1.5 - Bridge Welding Code. This code also calls for magnetic particle testing (looking for cracks that should not be there in conventional bridge steel) and for hardness testing of the region of the arc strike. These provisions apply to members in tension and in stress reversal. "

    The big question is this one
    "His study agreed that the hardness level of the HAZ is increased because of the carbon content of the steels. However, because the stress levels generally remain in the elastic region, and because the loading is non-fatigue, the HAZ should not affect performance. "

    So, it is clear that arc strikes are potential problems in high loaded areas (bridges, high stress) , but in many cases, strikes will not cause a problem.

    So, the question only remains, are there any areas in a typical boat hull that would be candidates for severe cracking and failure due to an arc strike. Brent says he has never struck any, I cant find any surveyors, boatbuilders or boat owners reporting any incidents ....
     

  15. Ad Hoc
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    Ad Hoc Naval Architect

    I'm sorry but with respect, you're missing the point again.

    "..So, the question only remains, are there any areas in a typical boat hull that would be candidates for severe cracking and failure due to an arc strike..."

    Please reread post #227 and #233, since it HAS been determined to be detrimental hence the formal procedure issued by endless bodies around the world,, if one is doing professional quality welding for Classification approvals.

    Since if it were NOT a problem, why do they all insist this? Why do turbine blade manufacturers reject ALL items that have one single arc-strike on them?? It is all one single simple word which has been repeated endlessly on this thread by many.

    If you fail to grasp this, then there is nothing more i can add. You arguments are circular which suggest your comprehension on the subject is lacking.
     
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