Weld Quality
Posted: Tue Jun 06, 2017 2:59 am
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. 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?
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. 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?