I took my second weld test. I failed due to porosity. Passed my first test, but this one hurt.
It passed all visual inspections. Failed at the bend test ( 2 out of 4). Tig root, hot pass, and fill to half the wall thickness then stick with 7018.
I was told that the porosity was in the 7018 portion of the weld.
Next time I'll weld the 7018 hotter. I'll get more comfortable.
I feel that I need to improve my start and stops.
ANY suggestions on the best technique for tie-ins with 7018 would be appreciated.
Also What is the best way to come out of your tacks to prevent fish eyes?
for your tacks while tig welding christmas tree them sort of and the pull the fish eye up the side of the wall... while capping with tig christmas tree and then pull out, if you pull out too slow youll get porosity out there where you dont have any shielding gas.. hope i could help.. fish eyes are more of a problem on stainless than carbon.
Thanks for the suggestions. I'll try it. Where is the filler wire when starting the x-mas tree? Should I give it a little bump before i pull it out of the puddle?
Another welder suggested that to me to prevent a key hole at my tacks.
while starting the tree your wire will already be pulled out because you have already tied into the other tack. dont really understand what you mean by giving it a little bump. but you dont need to, every welder has a different way, just have to find out which one works best for you.
By mightymoe 
Date 07-07-2008 13:08
Edited 07-07-2008 13:49
I was talking about the original tacks. If I come out of them slowly it tends to key hole a little bit.
From tack to tack it looks good, I feather the tacks back, then take my time and make sure they break down. The root looks good. No fish eyes.
I need to try the method you reccommended to prevent fish eyes in my innital tacks.
I'm no expert but I had the same prob with 7018 and an old hand told me that when you first strike off your lohi there is no shielding so there is always porosity in your start. You have to start about 3/4 to 1/2 inch above your stop and then move to the stop, then as your coming up you burn out the porosity as you run back up over it. Hope that helps.
I am over in the UK and I specialise in heavy wall , the biggest being 41/2".
The porosity may be caused by a few factors
1-damp or cold rods(need to preheat or use fresh vacpac)
2-A breeze or draft where you are welding.
3-holding rod to far from the weld pool(you have to keep a tight arc)
4-As another gentalman said burn off the tip , start the rod higher on the but and come down so when you weld up you burn the drag strike out.
5-Make sure all stop/starts are ground.
You mentioned using a higher amperage, be carefull there as if you go to hot it is possible to get piping in the weld core
Some people get very on edge when doing a test, at the end of the day it is just another but thats being bombed,
If your failing on the bend test try using smaller rods, as this will give you more layers in the weld structure of the butt,
Also are your cutting the pieces for the bend test ,if so draw file the edges and radius the corners ,this wont give so much of a peak when there bent and less likely to cracking.
hope this is of some use good luck Brooksy
Thanks BROOKSY
All good reminders.
There are a few things I'll do different next time.
I had not welded in 6G position since my last test, and smallest pipe I had been on was 4". So I need to get more comfortable, brace myself off better. I know this contributed to some long arcs, and irregular weld beads.
I'll grind all start and stops. I didn't do this on my first test and passed, but that was X-rayed.
I used 3/32 7018 for fill and cap. It got hot. I was spending time waiting for it to cool down ( under 500 F.). It took me all of 5 hours to do. The last 1/2 hour I didn't even check the temp. Had to get it done. Would 1/8 help in that it would fill it up faster?
I set my amperage at 80. I ran a bead on some scrap metal and adjusted it to reduce splatter ( save time cleaning ), I feel this was a mistake. I feel I should have run 4 or so amps. higher. It would have helped burn the drag stike out.
The rods were kept in an oven the whole time. I drew a handfull at a time.
Weld test was in a nice shop. No breezes.
I had no part in the cutting or bending testing of the weld.
I have another weld test lined up this week.
Thank You for the help.
The fisheye often come from a rapid cooling of the weld metal when you pull the arc out. When I tack, fisheyes are not a concern because when I tie into my tacks, they are completely remelted.
BUT I still have other stops to be concerned with. One thing to minimize this is to reduce your current slightly that you are welding with, when you get to the end of the bead or tack, remove (or don't) the wire and carry the puddle up the bevel of the pipe. Do this quickly and lengthen the arc as you are doing it. This should give an appearance of a tapering down in width to a point.
Another key point is where you start and stop. ASME specifies where the bend specimens must come from . Try to avoid starts and stops in this area. If the inspector does not mark the top on the coupon, he is probably just guessing.
For porosity at the starts, I strike the are an inch or so ahead of where I am actaully starting. I get the arc established, get my orientattion and move to the place I am starting. This keeps me from having a built up start from waiting to burn out anoy porosity. Machines with hot starts can also help this. In that case, I just fire up where I want to start.
My tie ins for 7018 are done the same way, strike the arc in front, get you bearings, move to the cleaned crater of the previous bead, let it fill and move on.
Hope this helps
Gerald
Thanks I'll use that.
At this point I think I need to increase amps. To burn out that 1/2' to 1" drag . When welding on 2" pipe 1" ahead can put you up hill a little ways. Should that be a concern for me?
The testing supervisor didn't like fish eyes in my tacks, but he let me continue. He told me test was over if they were still there after root pass. After my root pass ther were no more fish eyes.
I'll find out the cut locations for my next test, I'm sure that will help me.
That drag is done is so quickly that little metal is deposited. In addition the arc is a little long. Pausing long enogh at the start will alos work but sometimes increases the buildup.
You make it sound so easy.
That is one of the things I need to improve on. My starts are more slow motion than quick.
thanks.
you'd be suprised, but you might just buff your welds a little better, i've seen some damn good welders fail the exact same test(including yours truly) because they overlooked a little bit of slag, and make sure you don't cut your stops & starts in any straps
also i noticed where a few others suggested starting about an inch above your starts, i agree. that flux is what burns any slag out and the tip of a use rod obviously doesn't have the flux left so that can help.
Thanks for the input. All the help has been great.
don't take it too much to heart. I can make anybody bust a test if I grind the test strap. There is a right way and wrong way to grind straps. Grind the straps across and don't round up the edges and you can crack every time. Always grind lengthwise on the straps and round the edges. If the straps were cut with a torch there could crack due to HAZ along the strap edges. Bent alot of tests and seen alot bent , seen alot of guys test break because they ground them wrong.
Scrappy,
You are very correct. Proper preparation of a test piece, IMO, can indeed mean the differance between pass or fail.
I have seen test pieces fail with a corner crack that, again IMO, resulted from the lack of proper preparation for bending.
jrw159
