Not logged inAmerican Welding Society Forum
Forum AWS Website Help Search Login
Up Topic American Welding Society Services / Certifications / bend test finishing
- - By ctacker (****) Date 10-05-2008 22:13
What kind of finish is required for doing bend tests?
Parent - - By michael kniolek (***) Date 10-06-2008 00:36
I didnt see a set surface finish but when i did bend tests i would radius the corners 1/8  max and polish the faces a bit to prevent any tearing.
Parent - - By ctacker (****) Date 10-06-2008 00:43
I have not seen anything either, but I know you can't torch cut a strap. It would be nice to have a spec to go by.
I would like to know how everyone else is doing it, I think even a bandsaw would make it too rough, but have never tried it!
Parent - By jon20013 (*****) Date 10-06-2008 01:27
ctacker, there are no surface finish requirements per se but the advice by Michael given is good.
Parent - - By aevald (*****) Date 10-06-2008 02:20
Hello Carl, quite some time ago there was a thread referred to as (A "Heartbreaker"), if you go back to that post I had included some examples of test coupons that I had prepared by sawing them first and then using a belt sander to prepare them for final bending. All of the sanding marks run the length of the test specimens and the edges all have a slight radius to prevent unwarranted edge cracks. There are also a number of different testing machines included by others. Like you and others have already included, I don't believe there is a specific surface finish that is stated in D1.1 and likely other codes. Just a little something more for consideration. Best regards, Allan
Parent - - By 803056 (*****) Date 10-06-2008 03:06
Saw cut edges and use a disk grinder to remove face reinforcement and the remnants of backing should be sufficient for most carbon steels and austenitic stainless steels. As mentioned by Allen, be sure the grind marks run the length of the test piece, not parallel to the transverse groove weld. Break the edges with a file just to remove the sharp edge.

When performing side bend during training sessions, I don't remove the face reinforcement or the backing. If there is any problems with fusion in the area of the root or along the toes, it becomes very evident. If the weld is good it will bend just fine with the backing still attached and the face reinforcement in the as welded condition. As I said, I only do this during training sessions.

If you do elect to torch cut the samples, you should remove the HAZ before bending.

Best regards - Al
Parent - - By ctacker (****) Date 10-06-2008 04:12
Allen, I remember that thread well, but it didn't address the finished surface.

I have access to quite a few machines that can put a machined surface, belt sanders and wet grinders, etc. I am trying to get the company to start doing bends instead of forking out the money for RT on our welder quals and would like all the info before I make the proposal.

I figured it would be hard to keep the thickness at 3/8" especially if you saw cut and used a disk grinder to remove the reinforcement(and backing).
most of our bends would require side bends on 1" plate. I should have mentioned that.

I think I will stick with my original thought and cut +1/2" peices and machine to 3/8" for side bends.

I cannot figure out why our foundry down the road doesn't do our PQR's either. the have all the equipment even for charpy's but my QA manager would rather spend 1 grand to test at a lab. we supposedly have one of the largest x-ray machines in the western US also.
You would think coorporate would want to keep all that stuff in house and stop paying another lab!

Thanks guys, Carl
Parent - By aevald (*****) Date 10-06-2008 04:28
Hello again Carl, I do a lot of side bends on 1" materials as well. We have a DoAll C916 horizontal band saw that I use for cutting. I will try to include some pictures of the set-up that I use, I can generally get to within 1/32" of the 3/8" thickness if I take a little bit of care. So this essentially leaves very little additional removal to be done. I do not believe you need to go to such lengths as machining the coupons to thickness to meet the requirements of testing. I do understand your concerns for finishing requirements, yet whether you have a mirror finish or just have a finish that resembles a brushed SS finish, any discontinuities that show up will be seen in a similar fashion and be able to be measured very readily. Just a hunch of mine, but the vagueness of the code here may be due to an attempt to avoid a lot of litigation and challenges and thus leave that part up to the testing labs or inspectors/testers disgression. Best regards, Allan  
Parent - - By aevald (*****) Date 10-06-2008 19:32
Hello Carl, I have a series of pictures that somewhat show how I go about setting up and cutting straps from some of the weld test plates that I process, these are some plates that I looked out so they are very rough in the actual welds that can be seen.
     I start out by checking to see how the plates fit face to face against one another and if required I grind to ensure a good fit and then tack them together. I also stamp a series of V's on the vertical plate on one end of it so that I can identify the two plates from one another.
     Once I have determined that they fit well I line up one edge of the end of both plates and then tack the two plates together on all four corners, I also put a small stitch weld in the center of both ends of the plates to keep the pieces together after I have cut various parts off. Before going on to sawing anything I carefully check to see that there isn't any spatter or anything that would prevent them from siting squarely in the saw vice.
     Our saw has a fixed vice face and a swivelling vice face, I use an adjustable spacer to ensure that the plates are gripped tightly and squarely against the fixed vice face. The fixed face is where I set the end of the plates that have been lined up. This ensures a good flat surface that will rest squarely against the saw vice while all the cutting is taking place.
     I place the plates in the saw and measure off the correct trim cut and proceed to cut this material off. Since the corners are tacked this trim piece comes off in one piece and doesn't shift any. Next I position and measure the correct width for the actual test coupons and lock them in place. As they are cut they will come off one at a time and will not have any weld tacks to interfere with their cutting, they will also have the end stamped as to which one is the vertical strap and make the two easily distinguishable.
     After cutting the straps from one end of the plate I will flip the test over in the vice with out changing it's other orientation, meaning the evened up end will still be resting against the fixed vice face. I then proceed with cutting this end of the test pieces in the same manner as I did with the first end.
     You will end up with four straps that can easily be prepared for the rest of the bending process. I will likely get some flak on this one, but I remove the backing bar by placing the bar portion in a vice and using a crescent wrench to gently twist off the backing bar using a slight back and forth motion to shear it from the back of the coupon. Since the tensile of the weld metal is slightly higher than the backing bar it will usually remove the bar by tearing material from it as opposed to removing material from the back of the plate coupons.
     I will try to use a chronological order to show the process. Best regards, Allan
Parent - By ctacker (****) Date 10-06-2008 21:54
Thanks Allen, all the straps I have seen have had a machine finish(highly polished). one of the reasons for this post was to find out how everyone was doing it, I know alot of shops don't have access to a machine shop as I do. I know a band saw can leave a rough edge. so I was unsure about needing a highly polished finish or not. I couldn't find anything in the codes to verify anything. thanks for taking time to post!

Regards, Carl
Parent - - By pipewelder_1999 (****) Date 10-06-2008 10:39
I have bent leftover straps on face/root bends bends that have been torch cut and left as-is with no noticeable failures resulting from the finish.

These were all on .218" wall crbon steel with GTAW roots and 7018 fill and cap. No reinforcement was removed on either face and the only open area was a corner crack at the toe of the weld on the cap.  Because of the reinforcement, the coupons don't bend the same across all the length.

It was just an experiment after watching guys spend more time cutting and prepping straps than they did welding the coupon.

I cut them with a torch, grind the torch marks out, grind the face that will be in tension, and bend them.
Parent - - By Mikeqc1 (****) Date 10-06-2008 18:19
I use a doall saw too like it was said earlier a little care and you can cut them damn close, i set my test plates vertical and cut them, so there was less material for the blade to walk during the cut .
the way some of my guys break in the saw blades, I would need to change it out for every test. :)
They put a new blade on and let er rip! even after explaining the break in cycle of a new blade it doesnt help.
Parent - - By spots (**) Date 02-05-2009 13:38
I am a green CWI with a background in NDT/QC and the only welding I've done was in high school.

I have been having issues with small surface cracks in the base metal HAZ when bending welder qualification coupons in my bender named "Widow maker". We are using 3/8" A36 steel and doing root/face bends. The face bends have more cracking. The welders claim the surface cracks are grinding marks, so I shine them up with a tiger paw and show them the cracks have some depth. I have asked them to orient their grinding marks with the length of the plate, most do some knuckle heads don't.

AWS D1.1 says in "The convex surface of the bend test specimen shall be visually inspected for surface discontinuities..."

In my opinion surface cracks, even small ones without much depth, are a bust.

It is also my opinion that they are putting too much heat into their test pieces and making the metal brittle which causes the metal to crack/tear rather than bending.

Can anyone shed some light on this matter?
Parent - By jwright650 (*****) Date 02-05-2009 14:02
3/8" thick A36 is pretty dang hard to screw up(via too much heat input from welding).....however if the welder is welding with the machine too cold, you can have coupon problems when welding with wire.

In my experience the grinding marks can start or initiate the cracks that you see, so just because they are deep doesn't rule out that they didn't come from the improper grinding direction. Coupon preparation can make or "break" the welder's test. Also the heat from improper grinding can cause surface cracking.
Parent - - By aevald (*****) Date 02-05-2009 14:19
Hello spots, there are a number of things which could possibly give the indications that you are seeing as you have described them. First off, are you certain of the grain of the test pieces? If the grain is running the same direction as the weld joint you may see some "cracking" and in some cases you might even find some serious fractures. As you mentioned additionally, the grinding lines/marks, if they are ground with the marks in the same direction as the weld joint you could see additional possible indications/fractures. If the test pieces are being made from plate and the direction of rolling isn't apparent/known you could very well have issues come from this that aren't the fault of the tester. If you are using flat bar, even if it is correctly oriented it may exhibit some of this surface tearing due to the manufacturing process, in some cases, due to the size of the bar it will be subjected to a more rapid cooling rate than plate would be and this can have an effect on how it might bend or it's level of brittleness (a possible contributor to surface cracks).
     There are some of the folks on the forum that have done some testing concerning arc strikes and such and have polished up bars with arc strikes on them and shown the effects of these problems regarding tearing (if you have seen arc strikes outside of weld zone, these would very likely show up as discontinuities and would justify a break-out), there have been others that have bent pieces with the grain going the wrong direction, I have bent pieces that I have ground the wrong way and found issues, I have also scribed lines across pieces and found issues with cracking related to that practice and many of these pieces didn't even have a weld in them they were simply a piece of flat bar of the same size as a test piece. I would leave you with one final thought, consider that cracks outside the area of the weld deposit are typically not an indication of the welders level of electrode application and manipulation skills. If there are cracks that are there due to excessive heat/incorrect prep and such then these might be due to not following the WPS that has been provided, this might lead you to question their skills with following this document and might justify a break-out. Personally, I tend to disregard indications outside of the actual weld zone as long as I can determine that they aren't related to the fusion line between the weld metal and the parent metal or have anything to do with an arc strike. Even though you are using A36 material, I wouldn't allow or get used to doing any rapid cooling of the test pieces, in other words I wouldn't dunk them in water. Technically speaking this shouldn't effect the test pieces due to their relatively low carbon content, yet, I believe you will find this to not always be the case. In D1.1 I believe there is a statement that speaks to cracks that don't exhibit any slag or lack of fusion and allows an additional coupon to be taken. So depending on your interpretation of this you might take this into consideration as well. I believe you will be receiving additional comments on this topic so stay tuned and make your best call after you have considered all of them. My $.02 Best regards, Allan
Parent - By spots (**) Date 02-05-2009 15:35
If I am reading what has been posted correctly, it is unlikely that the indications are a result of the welding process and my test plates are suspect.

Grinding direction and technique are issues I will have to address. The test plates are supposed to be saw cut from 3/8" X 7" flat bar. This latest batch were flame cut poorly and at an improper angle so some grinding to get the correct bevel is required in addition to removing the HAZ. We are supposed to be getting some replacements soon.

I hope that there is more discussion on this topic. Failing someone needlessly is a waste of time and money for the welder and the company.

Thank you for your time gentlemen.
Parent - By Mikeqc1 (****) Date 02-05-2009 15:14
I would verify that your "widowmaker" has the right dia rollers / plunger.
Make sure that the bender has no defects that could cause the "cracking tearing"
I would polish these coupons before bending them.
For heck of it bend a coupon with no weld see what happens.
Up Topic American Welding Society Services / Certifications / bend test finishing

Powered by mwForum 2.29.2 © 1999-2013 Markus Wichitill