General welding questions that dont fit in TIG, MIG, Stick, or Certification etc.
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Coldman
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I've been turning over in my mind, in recent times, comments made in recent intertwined posts, some welding engineer remarks made to me during code welding college, and and some ideas of my own. I'm gonna ramble on here for a while before I get to a clear point.

The first post that comes to mind is the chap using 7018 for a root pass but finding it hard going and questioning why it is done at all when 6010 goes in better.

Several times in the last few years the question has been asked why is a hot pass called a hot pass. Some say it is just an old term that stuck, others says its just another term for second pass.

Some also mentioned graininess of filler bead and this also brings to mind heat treatment.

So the welding engineer told me that each pass of a weld heat treats the preceding beads, interesting.

So with in reply to the 7018 root pass, everything we do in professional welding (and codes) is designed (whether we know it or not) to minimise the risk of hydrogen cracking in our welding - our number one enemy. In Australia, all SMAW (MMAW) certification procedures are done with 7016. No 6010/11/13/14. These rods contain hydrogen. (And no 7018 just to make it harder). In the field 6010/11 is used because sometimes it's the best way due to contamination, big gaps, etc.
Many of us (I am sure) may have seen video of hydrogen diffusing out of welds and the longer the bead stays hot the more hydrogen diffuses out. So here is my first point, maybe the term "hot pass" really means keeping the root pass hot while hydrogen diffuses out thereby making it a valid choice of rod without fear of future cracking.

My second point is that if each bead heat treats the previous bead/s, does that mean grain refinement is also going on. It kind looks that way in some of my requal macros.

So I thought I would put it to the test. I prepped up a 60* single bevel butt joint on a 10mm 3/8" plate and tigged 4 passes. Took a slice at each pass for macro inspection to see how grains develop and refine. Here is the result.
Macros.jpg
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1st Pass - root, appears to be grainy.
2nd Pass - "hot pass" - appears to be grainy but the root pass is not so grainy anymore.
3rd pass - fill - appears grainy but the previous two passes appear to be finer grained.\
4th pass - cap - maybe not so grainy but previous three pass don't look grainy. Maybe the increased mass at this point kept it hot long enough to refine the grains a little. I did rush the cap, should have been a multi bead cap but weaved two 3/32" twin wires to get it done in one cause I was interested in layers only to prove the point.

Anyway that's the way it looks to me. So my conclusions are:
- multiple beads heat treat each other resulting in fine grain strong welds.
- multiple beads allow hydrogen diffusion giving strength to welds no matter which filler is used.
- single pass 6010/11 beads could be brittle and prone to cracking. Maybe we should test this. Who's up to testing a single pass 6010 bead and comparing to a single pass 7018 with the BFH?
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motox
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Coldman
i do not do not do any code work but i like my welds to be as strong as my knowledge
and ability allows. your post was a complete study of what makes up a proper
weld and just what happens in the process. thanks you for this info.
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- single pass 6010/11 beads could be brittle and prone to cracking. Maybe we should test this. Who's up to testing a single pass 6010 bead and comparing to a single pass 7018 with the BFH?
This had been done and the 7018 wins easily because of its higher ductility.
image.jpeg
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Dave J.

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Coldman
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Thanks for that Dave, good info.

Still wouldn't mind seeing a down and dirty test one day. Always been told cellulose welds were brittle and had to be finished with other filler/cap rods. Never saw any crack or fail. I remember long ago on a construction job, journeyman plumbers were fully welding out 6" and 8" chilled water pipes with 6010 whereas the metal worker guys (boilermakers) on industrial and workshop jobs were filling and capping mostly with 6013 at that time. I was intrigued and asked them about the practice. Never did get an answer cause in those days it didn't take much to ruffle the pleats of a journeyman plumber's skirts and they threatened strike if I questioned their work. I think they viewed my question as a challenge to their political bent or demarcation when all I was interested in was learning about an alternative method.
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Poland308
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Coldman wrote:Thanks for that Dave, good info.

Still wouldn't mind seeing a down and dirty test one day. Always been told cellulose welds were brittle and had to be finished with other filler/cap rods. Never saw any crack or fail. I remember long ago on a construction job, journeyman plumbers were fully welding out 6" and 8" chilled water pipes with 6010 whereas the metal worker guys (boilermakers) on industrial and workshop jobs were filling and capping mostly with 6013 at that time. I was intrigued and asked them about the practice. Never did get an answer cause in those days it didn't take much to ruffle the pleats of a journeyman plumber's skirts and they threatened strike if I questioned their work. I think they viewed my question as a challenge to their political bent or demarcation when all I was interested in was learning about an alternative method.
Good to see some things are the same here as they are there. :D
I see lots of pipe here that was put in from the 50's to the 80's that was welded all the way out with 6010. I recently ran across a bunch of underground brine piping for an ice rink ( brine temps are about 13F returning to the chiller) that was put in in the early 90's by a company out of Canada that I think is 6013 all the way out. I've not seen any cracking but the 6013 is starting to turn to Swiss cheese. Think that might just be a from the calcium chloride they use for the brine. Some of the existing chiller lines were from the 80's that were 6010 are rusted from the same environment but aren't springing leaks the same way dispite being in service 10 years longer. I made some repairs with 7018 but I'll need another 30 years to make an accurate comparison.
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Josh
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Pipeline buddy of mine does 6010 root and either a 6010, 7010, or 8010 fill and cap. But he also said about 3 weeks ago that they are planning on switching to 6010 root and 7018("low hydrogen electrode always actually what he said so I just assumed). And then I made a joke about carrying around a rod oven. So maybe there is failure on certain pipes that is causing a change or it could be a desire to switch to 7018 just to do it. And then at the same time he will go and do some oxy-fuel welding over at the power plant so...
A student now but really want to weld everyday. Want to learn everything about everything. Want to become a knower of all and master of none.
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Nick
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