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stainless welding consumable for dish head forming 1

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submerged

Structural
Oct 4, 2015
10
Hi guys.

I have a project stainless Hooper, now for the dish head cap, i used welding electrode E308-17 and on the other weld side SW-308L CORED for flux core welding with complete joint penetration material 304L. after the weld process we undergo dye penetrant testing and it goes well. now ready for the dish head forming which will go massive pressure for forming and spinning, all the weld joint, CRACK.. can anybody tell me what happen, maybe due to the stress load of the process for the dish head forming or the consumable is the problem. thank you in advance...
 
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Not enough information to provide a meaningful response. First, where did the crack occur exactly? Do you have a picture of the crack or failure location? How did you ensure a full penetration weld joint? What is the thickness of the formed head?
 
And what NDT you did on the welds. With something that is going to be formed like this 100% x-ray might be a good idea.
Flux cored is not known for making the cleanest welds.
How thick is it?
What was the microstructure of the welds and HAZ?

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P.E. Metallurgy, Plymouth Tube
 
Thank you metengr. And edstainless. My apology not to mention the material thickness it is a 12 mm stainless plate 304L. Alongitunal crack occured it was a single bevel edge preparation 3mm root face 3 mm root gap 60 degree angle. We ust ndt. Dye penetrant and ultrasonic test to check if there are defects. But all weld joints pass the NDT test. Now my question is can the fluxcore welding process can hold the stress load of the dish head forming. Because i was advice by the machinery only welding electrode is advicble. Guys please any idea. Where do i start to locate the FAULT OR FAILURE.. please see attached photo. Thank you in advance.
 
 http://files.engineering.com/getfile.aspx?folder=38c6da1e-eac1-4497-b18c-062553c0771c&file=20151026_114932.jpg
Take it from an old head maker, nobody tortures welds like head manufacturers. The picture shows a centerline crack, which is indicative of lack of penetration. I know your UT report did not find any rejects, but head makers can find defects when UT or RT can't or don't show them as rejectable. Did you back gouge before welding the second side? If not the root fusion may not be sufficient.
 
I agree with the above post, you had a subsurface weld defect that resulted in rupture of the weld region under local bending stress. The welding processes or filler metal selection had nothing to do with the failure.
 
Sub, If you want to know for sure cut a cross section and look. But I am siding with my colleges, I bet that you don't have full penetration. Worse yet you may have a line of slag trapped in center of that weld. Back gouging works, I have even seen fabricators machine the back side before the weld pass to assure that they have sound metal and get good penetrations.
What was your UT standard? Take a piece of 12mm plate and drill a 0.25mm hole in the center in from one edge.
You also need to look at how the weld cools. Make sure that you don't have any center line shrinkage or cracking. What is your estimated FN of the weld?


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P.E. Metallurgy, Plymouth Tube
 
Submerged:
Where is the root of the weld, on the inside or outside of the formed head (in compression or tension during/from forming)? Was the root back gouged and rewelded? Is that crack essentially at the low spot/line btwn. two convex beads of weld? That’s a little bigger stress raiser than the unground (undercuts?) out near the outer edges of the two welds. How many passes was this weld? Let’s see a few more photos; two showing the next 12-16" of weld length to the left & right of the crack; and one showing the weld and crack location on the entire head; enough of the head so we can see its general location on the head.
 
Don56,metengr,edstainless,dhengr.

Guys thank you for the idea now probably i can now locate the root cause of this failure. The root weld is out side of the form head, so it is in the form of tension while the bevel is in form of compression. Does the root of the weld has effect facing in/outside the form head? yes back gouging is applied to the other side of the weld. UT test is standard using the 70 degree probe angle. anyway guys thank you so much for your time and response appreciated it much...more power.
 
I agree with the others that responded. The most likely culprit is incomplete fusion, failure to back gouge deep enough, slag, etc.

As mentioned, what acceptance criteria was applied and did the UT tech calibrate on a stainless steel calibration block? Passing UT does not mean the weld is a picture of perfection. There is no such thing as a perfect weld. The weld represent a metallurgical discontinuity. The mechanical properties of the weld may meet code imposed minimums, but they are still likely to be different than the base metal.

Having welded for more than twenty years before doing what I do now, I know that welders have a tendency to leave traces of the root intact while back gouging with the thought they will "burn it out" with the next bead. As a UT technician/Inspector, I can tell you that doesn't happen. Those traces of the root end up being traces of incomplete fusion by the time the joint is welded.

Best regards - Al
 
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