Weld testing

  1. Hitch

    Hitch Moderator Staff Member

    Posts: 10,231
    Somerset
    I know its not important for most of you, but i thought id give you a little insight into the various methods for weld testing....
    Besides just hammering it to death!!



    There are a lot of ways to test welds, but some are specialist and expensive, such as xraying etc.
    They are generally set into two categories, 'Non Destructive', and 'Destructive'

    A very rough way of testing is just to knock it about for a while, held in a vice. Great for first time welders that want to make a noise!! This would be a destructive weld test!

    Root bend.
    A slightly more technical way is a 'root bend' test. Do a weld, then cut a portion out of it, say 40mm wide. Then bend it between 2 blocks in a press, with the root facing down.
    If its okay it will bend nicely without the underside of the weld cracking.

    Dye Penetrants.
    Dye penetrant testing is another simple way to check for cracks and holes that you cant see.
    Its a three part kit, a cleaner, dye (flawfinder) and a developer.
    First clean the weld area, then sprya on the dye. Allow it to dry then clean of the surface. Then spray on the developer, this reacts with the coloured dye and make it very easy to see and defects.
    Can be handy to use before sending stuff for xray.

    Magnetic powder.
    The area is magnetised with an electromagnet, then the powder is spread on the surface. Any defects are shown up by concentrated areas of the powder.

    Xraying/Radiographic.
    Xray or Gamma ray testing is used on a lot of things, the defects will show up as light areas on the film.

    Ultrasound.
    Works in very much the same way as an ultrasound in a hospital.
    The waves are reflected back at varying frequencies, allowing you to build up a picture of what is being tested.

    Macro Etc.
    This test allows you to see how the weld material is deposited onto the parent metal. A slice is taken through the weld, then polished. When the surface is smooth, a mixture of Nitric acid and alcohol is then wiped onto the surface. This darkens the weld material, allowing it to stand out fromthe parent metal. Good for checking penetration.


    :welder:
  2. malcolm

    malcolm Administrator Staff Member

    Posts: 8,220
    Bedford UK
    What do you reckon for hobby weld testing? You've listed techniques that will find cracks, inclusions, and check penetration, but the bits and pieces required to do the testing are a bit expensive.

    One hobby method is a (low cycle) fatigue test. Weld two bits of metal together, clamp one end in a vice, and bend the other backwards and forwards until it breaks off. If the parent metal breaks not the weld it's a good-un. Problem with that is it's really just a penetration test - doesn't check for undercutting or cracks in the actual weld itself.

    What other methods are there that hobby folk could do?
  3. JBweld Amatuer welder

    That's really helpfull........doin' loads of test weld at the moment. If I find how to post images, I'll organise some...

    Cheers, JB...
  4. Hitch

    Hitch Moderator Staff Member

    Posts: 10,231
    Somerset
    One of the best methods will be experience and visual inspection, if its fails a visible inspection, it will most likely fail any other testing method. And if there is a crack in the weld you should be able to see it to be honest.

    Perhaps we could get some pics of badly undercut welds to use as an example.
  5. Drains

    Drains Yeah, nah.

    Posts: 7,672
    Soggy Sefton, NZ
    Dye penetrant testing is cheap, just a few quid for the cleaner, dye and developer. Useful on runs where you need to know there are no cold laps or no penetration, which you can get easily enough in the wrong circumstances.

    If I were JBWeld i'd certainly have some tins lying around....! It revealed a couple of very well concealed cold laps on my boat which might have caused leaks. John, you should really do all welds below the waterline with dye pen. It's quick and easy and non destructive.
  6. JBweld Amatuer welder

    Thanks si, probably end up using dye penetrant.......I'll be needing to pressure test the diesel tank, so will probably use it in this area as well...
  7. Drains

    Drains Yeah, nah.

    Posts: 7,672
    Soggy Sefton, NZ
    What pressure you testing the tank to? I went up to 10psi and it all got a bit bulgy...
  8. Hitch

    Hitch Moderator Staff Member

    Posts: 10,231
    Somerset
    How big are the tanks then, 10psi isnt a lot.

    Perhaps a few baffles could have been put in?
  9. JBweld Amatuer welder

    dunno si, haven't got that far.......psi I understand but this is in kfc's or something:laughing:
  10. Drains

    Drains Yeah, nah.

    Posts: 7,672
    Soggy Sefton, NZ
    The tanks are hull integral. My diesel tanks largest panel is about 8'x4'. It's framed and baffled. I may have gone a bit over 10psi, but from memory the spec is about 5, maybe 7. I'll have to go and check my Boat Safety Scheme book, but it's on the boat.

    The most important requirement is adequate ventilation for the tank so that theres no pressurisation during filling. In service they should be at atmospheric. The pressure test is an opportunity to get the bubbles out, + put a gauge on and walk away for an hour or two. If the pressure stays the same and there are no bubbles, its time for a celebratory cuppa!
  11. Drains

    Drains Yeah, nah.

    Posts: 7,672
    Soggy Sefton, NZ
    Where do you put the bucket of chicken wings then?
  12. Haze

    Haze is it can be hugs tiem ?

    Posts: 640
    West London
    i guess u mean kilopascals, which I THINK is the same units as feet head
  13. madkayaker

    madkayaker Pro sparkey Pro Welder

    Posts: 13,726
    Cumbria
    I know this is an old thread but where can i get a dye test from?
  14. irondarren Member

    BOC i believe sell the kits
  15. madkayaker

    madkayaker Pro sparkey Pro Welder

    Posts: 13,726
    Cumbria
    thanks any ideas of online suppliers?
  16. Sparkey

    Sparkey still sitting in my corner of the forum

    Posts: 5,038
    France
  17. Hitch

    Hitch Moderator Staff Member

    Posts: 10,231
    Somerset
  18. madkayaker

    madkayaker Pro sparkey Pro Welder

    Posts: 13,726
    Cumbria
    thanks Hitch What do i need Dye, Developer, Cleaner?
  19. snowcat

    snowcat back in black Staff Member

    any decent welding supliers will sell it (3 cans your need) Im sure DIY welding would as well....
  20. Hitch

    Hitch Moderator Staff Member

    Posts: 10,231
    Somerset
    Cleaner, penetrant and developer
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