308L weld fracture with heat tint 1

[98RedRANG]

Has anyone seen a stainless 308 weld fracture with a heat tint inside the weld? Weld is joining 304.
This weld was pulled open after a PT inspection revealed a leak from a tight crack.
The weld was part of a cooling water piping system.
The fracture itself (confined to the weld bead) and the heat tint is interesting.
The plate is about 0.425" thk. This a repair weld that was service 3 months.
Has anyone seen a similar type failure before (solidification cracking?) through a weld bead.

 

[TugboatEng]

Once the crack forms crevice corrosion begins. This is not heat tint.

 

[EdStainless]

I am with TBE, looks like lack of penetration to me.

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P.E. Metallurgy, consulting work welcomed

 

[98RedRANG]

The weld was specified as a fillet weld, but its the fracture face that seems unusual and how would colored oxidation IN a stainless weld in a closed water system occur. the failures of stainless welds usually have a fatigue or ductile overload look (when they do happen through weld bead) not this inter solidification grain look.
Im not sure how one would even recreate such a fracture face.

 

[TugboatEng]

This has a general description of the problem.

https://www.ssina.com/education/corrosion/pitting-and-crevice-corrosion/

Stainless steel require oxygen to stay corrosion resistant. Pinholes and cracks are breeding grounds for crevice corrosion as they can't get proper exposure to form their passive layer.

 

[kingnero]

Filler metal is 308, but what is the base metal?
I don't like the general appearance of the cross section you've shown. Is this a dynamically loaded joint?

 

[98RedRANG]

Weld is joining 304 to make a box connection for the cooling water. This area is under stress and vibration, but I don't see any macro fatigue striations. The whole fracture has this appearance.

 

[blacksmith37]

Have you verified that it is not chloride stress corrosion ?

 

[98RedRANG]

The water in the system is very clean and is carefully monitored with a nitrogen blanket. Both Cl and SO4 was found to be under 0.5ppb with low O2 under 100ppb.
this weld broken in the same place a previous weld did and we know its a very stressed joint, but I have not seen a Stainless weld fracture like this before.

 

[hbk_mnm]

looking at the linearity of the shade, it seems there was some issue when that particular bead was being welded. Weld might not have been properly cleaned during the run or maybe improper 308 electrode. And also the weld joint breakage and that tint looks like two different issues.
Just my wild guess.

 

[0707]

Maybe a improper electrode to join 308 with 304ss. As this area is under stress and vibration although the photo is not quite clear, I would bet in a fatigue failure.

luis

 

[TugboatEng]

308 is the standard electrode for joining 304 stainless.

 

[blacksmith37]

A few micros are more reliable evaluation of chloride SCC than water analysis.