weld failure heat treating 1

[gnzlezgonz]

good afternoon sirs
question Aluminum tubes 5.25 od 1/8 wall and machined Flanges both 6061 T-6 welded using ER5356
.045 filler wire ac at 140 to 180 amps argon 15cfh helium 10cfh
evrything was cleaned tube flange and filler rod with alcohol sst wire brush washed
of with alcohol and let them air dried no compressed air
the weld prep was 30 degree 60 degree combined bevel X .05 depth +.025 penetration
per customers drawings
tubes were leaked checked with helium leak detector to
1X10-9 sent out for heat treating (anneling)
tubes were machined and leaked checked again no leaks
customer gets them they leak
question
would 550 for 3 hrs then air cool be enough heat to crack the welds
end use theres no heat on tubes there water cooled
they just have to hold Vacuum
apreciate your coments thanks
gonzo

 

[tbuelna]

gnzlezgonz,

Some suggestions:

1) Try purging the internal volume with shielding gas during welding.

2) Double check to be sure that all of your parts are the 6061 alloy that you think they are.

3) Although it's hard to tell from your sketch, it appears that there is some significant change in local section thickness between the two mating parts in the joint. If so, this would likely produce some residual strains in the weld zone. So make sure that your post weld heat treatment first includes a thorough stress relief cycle.

4) If you continue to have cracking after suggestions 1, 2 & 3 above, ultrasonic NDI, macro-section, or x-ray a sample of the weld joint area to check for weld defects.

Hope that helps. Good luck.
Terry

 

[racookpe1978]

Basic question, but it needs to be asked: Are you "sure" it is your tube welds that are leaking?

How was the test done the first two times? How did the customer do the test the third time?

How was the leaking point(s) verified? Could the gas be coming out of another part of the (customer's) machine?

 

[mfgenggear]

All the above suggestions are very good

Some of my experience

I second purging the tubes using helium or argon mix
make caps each end, except one end add a fitting to allow
the purging. The caps expand in the tubes or bolt through
if accessible.

Secondly, helium leak testing is a tricky business,
I would take a trip to your customer to verify their technique. There are so many variables.

In addition to leak testing, you must do Penetrant & X-ray.
for detection of cracks.

Pre heat aluminum prior to welding to prevent cracks.

It is possible the cracks are opening up from residual stress, from my experience & observations.

Welding Aluminum can be very difficult from my experience.
If the conditions or procedures are not optimum cracks are issues.

 

[mfgenggear]

just wanted to discuss about the weld prep.

It is from my experience
It is so important that all oxide, & any debri is remove
& clean within a short time before welding.

there can be major issues with this not been done.

An experience weld engineer & welders is of course required.

 

[gnzlezgonz]

thank you sir's for reply to my problem
I have taken the tubes that were leaking to get them re-checked by the company that certified them leak thight
we're good on the welds
once the customer gets the tubes they go out to get
media blast with Garnet crystal 50 to 60 mesh
so I had them check one with out the blasting good
second one blasted leaks
I welded them to customer specs everything was good untill they blasted them ,Now I have to machine out the old weld (no coolant)make new weld prep(100 degree's combined x .100 deep
with a weld reinforcement of .050,so will see how this works tubes have a bolt pattern and 0ring groove
machined to size so now it's going to be a shrinking detail that I'm going to have to resolve once againg sir's thank you for you help
Gonzo

 

[mfgenggear]

gnzlezgonz

take X-rays of the welds or/& helium leak test & mark the cracks/leaks.
it is possible to mark the location & just drill out the cracks & spot tig weld then retest for leaks.
repeat until all the cracks (leaks) are gone.

if you do need to cut off the end caps then there will be welding shrinkage it may be wise to start with
new details (Tube or end cap).
Allow excess on the new detail to allow for the extra length needed.

are you using a weld fixture to tack the assembly before welding, setting your envelope for final assembly fit up.

well any way
good luck