FIllet Weld Cracking

[abangbikerz]

We fabricate a pressure vessel using SS304 material. Stiffener ring is welded on the outside of the vessel using carbon steel plate. The ring is welded intermittently along the shell using 309l electrode(SMAW process).

Lots of cracking found at the centreline of the fillet weld. We dont know why it happens. But after that we change using fcaw process and the problem solved. no more cracking happen.

Anybody had any experience with this kind of problem??

 

[kingnero]

Centerline cracking often means contaminants in the weld, leading to hot cracking. In DMW, there might be other causes (like differential thermal expansion). Can you provide more info or pics?

 

[Tmoose]

What shape were the welds that cracked? Convex or concave?

http://www.lincolnelectric.com/en-us/support/process-and-theory/Documents/weldcracking.pdf

 

[metengr]

Yes. Similar to groove welds, the problem relates to deposited weld profile (excessive concavity) versus throat depth of the fillet weld.

 

[Tmoose]

It was kind of heartbreaking for me to learn that a nicely concave fillet which looks to be "better" with lower stress concentration is really so bad as a result of vicious stress during solidification. But the toe of the weld is really the worst place for stress concentration, which I guess explains the existence of wash welding the toes with TIG to created a gentler profile.

 

[abangbikerz]

Here are the pics of the crack. Looks like the crack starts from the crater and propagated longitudinally. We never have this problem before when welding pno8 to pno8 stiffener ring even using smaw process. But in this case crack found on almost every weldment.

 

[racookpe1978]

How thick are the two pieces of baseplate metal?
How thick is the intended fillet?

Why intermittent weld on the stiffener?
Why that choice of that particular length of intermittent fillet?

 

[metengr]

I would go back and check the filler metal composition and ferrite content. It looks to me that is hot cracking from lack of ferrite in the weld metal.

 

[abangbikerz]

racookpe the shell is 10mm thickness the ring is 18mm thickness. The length of weld is 2 inch based on ASME VIII. Stiffener ring should not be continously welded as to allowed the vessel to expand and contract during service esp for high temp vessel.( from my understanding)

metengr thanks for that. will do some research. It could be the SMAW electrode problem as we are not using the high end brand.

 

[gtaw]

The cracks most likely initiated in the concave weld crater. Concave welds (or craters) tend to crack as the weld cools. Once the crack is initiated, it is rather easy for the crack to propagate. Considering the difference in the coefficient of expansion and contraction between the carbon steel and the austenitic stainless, it is easy to see why the welds cracked.

The easiest way to mitigate the probability of cracking is to have the welder fill the craters to the full cross section by reversing the direction of travel when he terminates the weld. This is true regardless of the welding process. Concave unfilled craters are the surest way of initiating a hot crack.

Best regards - Al

 

[weldstan]

Weld appears to be concave from the photo. What is the appearance of the FCAW weld? Convex?

 

[Tmoose]

The cleanliness of the surroundings is not helping matters any.
How do you store your electrodes? They need to be kept dry, and that usually mean warmer than surroundings
When SMAW welding did the electrode get real hot when half used up?

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http://www.millerwelds.com/resources/articles/smaw-stick-arc-welding-tips-techniques/

http://www.lincolnelectric.com/en-u...to/Pages/high-quality-stick-welds-detail.aspx

http://www.thefabricator.com/article/arcwelding/cracking-down-on-weld-cracks

 

[Guest102023]

You needed to move from SMAW to FCAW anyway, so the result is a bonus!

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"