Questions about inspection/code from my students.

By Lawrence (*****)

Date 02-09-2016 04:29

Welcome to the forum Dew.

I just happen to be in the built-up beam business and prior to that taught at a tech college, so I know about the student questions and I have a couple of answers too :)

The "optional" unlimited thickness test (Fig 4.30) is a single bevel rather than a V-groove... This test assembly presents a couple of special challenges.

If you think about it,,, The welder is being tested on a groove and a fillet, both on the root pass !

Special attention needs to be paid to gun angle, with the arc energy of the electrode wire pointed directly at the root of the fillet at the bottom of the assembly, The beveled edge at the top will fuse easily enough because it is thin.

The root opening is 1/4" and it's pretty critical that it is not more or less... Any wider and you will need to run a split root, any thinner and there is a tendency for the root pass to bridge.

Arc length is also critical with MCAW and this joint... A long "silent" arc, a weld with no crackle, has a tendency to be too wide and hard to control. You want an arc that is as short as possible without causing spatter... Start at 27 volts and adjust up or down by half volt increments until you get that nice short arc. (crackle but no spatter)

You will hear other opinions... But I advise a 10 to 15 degree push gun angle for each pass... Do not whip the gun back and forth at all.. Nor side to side.. Straight stringers that lay in and look like caulking.

Also,, to get the best cover pass you really should fully employ the use of run-on and run-off tabs... Not just on the root, but also on the top beveled edge and the square bottom edge... The code does not prohibit this, and most smart builders allow this in both testing and production when necessary.

By welderbrent (*****)

Date 02-09-2016 04:59

Dew (and students),

WELCOME TO THE AWS WELDING FORUM!!

Lawrence gave great advice as usual but I would like to add a couple of thoughts.

Keep the heat down. Take a short pause between passes to 'inspect' your work thus allowing the coupon to cool somewhat. Not too much but keep that heat down especially as you get to the cap passes.

Besides Lawrence's point about the joint used the students should realize that in production a single bevel groove will be easier once mastered since the bottom square cut will help support the weld and not let it roll out as much as a V groove would and it means less weld going in which keeps time and heat down in the joint, both for testing and production.

Because of the difference in bending strength, yield, toughness, between a single bevel and a V groove the single bevel will slip more easily in the bender. It takes some added care and maybe even some American Ingenuity to fixture the coupons so they won't slip. Think about it gang. You come into, or go out of, the bevel side more smoothly but the stress change is more sudden and resists bending at the square edge. With a V groove you have the easy transition of forces on both sides instead of just the one.

You won't find anything about your questions in the codes. They just call it, if they tried to fully explain everything D1.1 would take up my entire bookcase instead of being just one volume.

Good luck.

He Is In Control, Have a Great Day, Brent

By jwright650 (*****)

Date 02-09-2016 12:04 Edited 02-09-2016 12:07

#1) Fabricators test in the 2G position usually because everything can be turned (by hand or with a crane) and welded in either 1G/1F or 2G/2F positions, the 2G test qualified a welder for all of these positions.

#2) The reason the coupon slips off center while bending is the single bevel, as the coupon is stretching around the die it favors more to one side due to the asymmetric shape.

#3) With 2G, I had lots of students struggle with the cover passes drooping and rolling over once they were out of the groove and there was nothing to help hold the puddle up. I had them practice running stringers across a flat bar that was held in the same position as the coupon. We welded a 1/2" thick plate to the work table, drew a line across the plate with soapstone and they ran passes across the plate and practiced stacking the beads(basically padding the plate) until they could run caps/cover passes with confidence. When you don't have the ledge to lay on, you have to move your hands a bit quicker as the plate starts heating up and the puddle wants to droop down.

Lawrence has good advice about utilizing stringers without whipping forward/back or any side to side weaving, all that does is add heat. These types of puddle manipulations are good to have in your welder's tool box for a few instances where fit-up or material thicknesses that aren't ideal for the diameter of electrode that is being used, but for testing, they need to leave them in the toolbox and use straight smooth stringers for more consistent results.

Edit* and yes use run on/off tabs, that is a good practice to get into as a new welder testing for a fabricator. When splicing a flange, the run on/off tabs ensure the flange thickness is maintained across the entire width of the flange.

By 803056

Date 02-09-2016 16:49 Edited 02-09-2016 17:14

Good advice.

I would add that the welding parameters should be based on the manufacturer's recommendations. I encounter a lot of situations were the welder's set the machine by the "feel" and encounter problems as a result. Often the problems that are being experienced can be remedied by using the manufacturer's optimum parameters.

The other thing is that the way the information is presented can be confusing. I find that a graphic presentation is easier for the welder to follow. In short, listing the voltage 25 to 20, welding current 120 to 220, wire feed speed 120 ipm to 250 ipm is of little use to the welder. The one parameter often overlooked is the electrode extension or contact to work distance (nonstandard terminology). Varying the electrode extension has a major influence on the welding current. I typically put black tape of the ammeter so the welder has to set the machine using WFS. If one thinks about it, the three constants in any semi-automatic process is arc voltage set at the power supply, wire feed speed set by the welder at the wire feeder, and electrode extension set by the welder as he moves the nozzle closer to or further from the work piece. Welding current - it varies as the welder moves the gun toward and away from the weld pool.

I am always amazed by the number of welders that do not understand the relationship between the electrode extension and welding current. It is an easy demonstration that I shown too many times to recount. "I never know that." is what I usually hear. Once the welder knows how important it is, he is aware of the relationship and holds the electrode extension the proper distance.

I will try to attach a graphic presentation I used for one of my WPS. The parameters are for a specific FCAW electrode. The graph has to be specific for the electrode based on the manufacturer's recommended parameters. What works for one does not necessarily work for the same electrode classification made by a different manufacturer, or even brand because of the variations in flux components, volume of flux, and thickness of the sheet metal used.

I can't seem to get the file to embed, instead it is an attachment. An extra step, but Oh so worth the effort!

Best regards - Al

Attachment: WFSvsAMPE71T-MJH420-Aug-2014Model1.pdf (41k)

By Lawrence (*****)

Date 02-09-2016 17:24

Here is another illustration that speaks to what Al is trying to convey.

By 803056

Date 02-09-2016 17:43 Edited 02-09-2016 17:45

I was?

Nice sketch Lawrence. Can I steal the concept for my presentation?

Doesn't the same logic hold true for welding with SAW using AC?

Best regards - Al

By Lawrence (*****)

Date 02-09-2016 17:48

Steal away Al,

I'll send you a few PowerPoint's if you would like, you can just sanitize any proprietary stuff and have at it... As long as you don't use it for my direct competitors :)

There are a large fraction of AC SAW users who take advantage of CC current delivery rather than CV, therefore rendering the above scenario rather inaccurate.

By 803056

Date 02-09-2016 20:15

Excellent!

Thanks - Al