1/2" sch10 6061 6-G pipe test

By Blaster (***)

Date 11-02-2010 01:22 Edited 11-02-2010 01:42

Wow, that sounds pretty challenging.

I am not experienced with aluminum pipe butt joints, though I have welded a fair bit of aluminum.

I have a former pipe fitter friend who was telling me that J edge preps were the hot ticket on aluminum pipe. Don't know what size range he was refering to though.

For more consistant results, my first instinct would be to get a purge in there.

By aevald

Date 11-02-2010 01:49

Hello Blaster, aluminum full-penetration pipe welding has some inherent difficulties. One of the biggest being a lack of cleaning action on the part of the arc on the inside of the pipe since only the outside surface is the one that has direct contact with the arc. Outside surface oxidation can be dealt with readily by proper initial cleaning and use of decent welding parameters/machine settings. The internals present a whole new set of issues. Since the aluminum is subjected to oxidation immediately following any cleaning regimen you will not see the same internal results with a purge on aluminum as say stainless steel. Since there is no bombardment of the internal surface by the DC+ side of the arc there will be a certain level of oxidation on the internally penetrated surface, in other words you'll still have a "skin" effect on any internal weld build-up/penetration. I realize my explanation might be a bit crude and others can certainly describe it much more technically correct, but I believe I have fairly accurately described the challenge. As to the OP's experiences on his particular welding challenge, I don't envy him any at all. Coming up with consistent "penetration" on such a small bore thin-walled pipe/tube would definitely be a challenge. I wonder if there are any "orbital" offerings for aluminum? This may sound a bit far-fetched but maybe an internal backing ring(yea really small) might fit the bill if there is no internal restriction issue in his application and he is essentially looking to maximize the strength of the welded joint. A little bit for consideration and thought. Best regards, Allan

By Blaster (***)

Date 11-02-2010 04:19

Hi Allan

Makes sense, thanks. On sheet, we do open root butts and outside open corners with a bit of temporary copper or aluminum backing clamped on the backside of the joint, clearanced so it won't touch the weld. We weld slightly uphill so the torch argon runs through the keyhole and under the weld as it goes in. The backing holds the argon against the back of the weld. When done right the backside of the root looks perfectly clean, shiney, and wetted in. I suppose in this instance the EP cleaning action is able to do its thing through the keyhole, preventing the skin.

Even if the weld is not open root, I wonder if the groove angle was opened up a bit, and enough heat brought to open a keyhole, with a purge, if that may be workable?

Anyhow I look forward to learning more about how to best make this weldment. I have done melt through welds on aluminum and the skin on the back always seems to be a nuisance. In a 6G position I can see how good consistancy could be tough.

By aevald

Date 11-02-2010 04:55

Hello Blaster, shortly after my post and reading your reply, I thought about the open root situation that you describe for your butts and corners, I believe a back-hand progression might help as well, do recall having similar results on some joints of that type, open key-hole(I believe) being the key to getting the "clean" backside condition. Also know that Lawrence, Al, and likely a couple of others here on the forum will have some useful contributions to add, I just sit back in anticipation and sometimes bait the question with my ignorance. But, that is the way that I often learn. Best regards, Allan

By Lawrence (*****)

Date 11-02-2010 04:18

It's gonna have to be hot and very fast..

Perfect prep inside and out, done right before hotwork...

Consistant penetration relates directly to two things for the most part... Travel speed and torch angle..

If you slow down or change torch angle.. The heat will go where you don't want it.

Don't ball your tungsten... Go 3/32 with a blunted tip. Not a long slim taper, but a radical one. Think about 7 to 8 on the balence control.

Forget purge... If it's a test you don't have the luxary.. Besides it really doesn't have an effect on penetration.

If you have the lattitude... consider a small root face rather than a knife edge prep.. It will help you avoid overpenetrating from keyholing.

Like the others say... Thats a tough test.

There are many things to do to make production more consistant.. But that won't apply to a test.

Welcome to the forum!

By Root Pass (***)

Date 11-02-2010 23:25

How about a super-mini chill-ring?

By 803056

Date 11-03-2010 01:11 Edited 11-03-2010 01:13

You didn't mention what welding standard governs your work. It does make a difference.

If you are qualifying the ASME Section IX you stand a better chance of passing because the visual acceptance criteria is so lax. You don't even need to be able to pass helium through the bore for ASME Section IX.

If you are welding to an AWS, military, or aerospace welding standard you have my heart felt sympathy. The visual criteria is the same for the small diameter as it is for large diameters. You didn't mention the position, or if you did I missed it. You stand a fighting chance if you can use a positioner and you can weld the piece in the flat position and roll it as you go.

I have little to add to the advice already offered. The only thing I would offer is the possibility of welding with DCEN so you can focus the arc more so than is possible with AC. That being said, if you have a machine with variable frequency AC, you have the potential of varying the frequency to accomplish a similar effect as the DCEN with the added advantage of cathodic cleaning (with the AC).

You can reduce the root face to something on the order of 0.030 inch to minimize the amperage needed to obtain joint penetration. A cover pass can be used to complete the fill if it is needed. Clearly the filler metal diameter has to be 0.030 or so to minimize the currant required.

Clean, clean, clean, and then clean again, both the base metal extrenal surfaces and inside diameter as well as the filler metal. Clean gloves are a must. Clean work surfaces are a must. Wash everything down with isopropyl alcohol. Yes, it can ignite, so use the appropriate precautions.

Good luck.

Best regard - Al

By 46.00

Date 11-04-2010 21:33

Hi TK!

What you are trying to achieve is very difficult but far from impossible!
At the moment we are manually welding 32mm OD aluminium pipe with consistant xray results and very predictable root penetration! We also weld using orbital technique (polysoude and AMI) which are also very acceptable, both to B31.3 standards and AWS standards!
Keep practising!

By ssbn727 (*****)

Date 11-08-2010 02:11

Hi TK!

Are you sure you're talking about 1/2 " diameter - schedule 10 pipe??? What is the wall thickness of this pipe?
I ask this because schedule 10 pipe has a nominal wall thickness of .109"
What is the actual groove joint configuration??? Is the joint a "U" groove, or a "V" groove instead and if it is, then what would the radius be on each "J" groove if it is a "U' groove being welded together???

Al does make perfect sense to reduce the size of the root face to what he suggests in order to achieve consistent penetration along with the other suggestions given by Lawrence also. Al also hit the nail right on the head regarding cleanliness when welding Aluminum... Finally as Lawrence mentioned earlier, the joint configuration must be precisely prepared prior to welding since it is more critical with Aluminum than with steels. ;) Btw, what are your welding machine settings (Volts, Amps, type of tungsten&prep, gas flow rate, etc.)???

Respectfully,
Henry