Corrosion of heat affected zone.

[sftyvlv1]

Hi folks.
I'm a maintenance welder at a steel mill. We are having trouble with corrosion at the heat affected zone in the butt welds of the rolling solution piping on the cold rolling 4 stand.
The pipe is both A53/106B carbon and the welding process was SMAW with 6010 root and 7018 fill and cap.
We have since started replacing with 304L stainless and used the GTAW with 308L (purged) for root fill and cap.
Are we on the right track.

 

[Dhurjati Sen]

How long did the carbon steel piping survive?
What piping is used for the other rolling stands?
Without a proper failure analysis, simply upgrading the material is an expensive and low technical approach, but mostly works quite well.

DHURJATI SEN
Kolkata, India

 

[TugboatEng]

In carbon steels higher tensile strength means less nobility. The 60 and 70 ksi weld fillers will be anodic to the 36 ksi pipe.

Your best solutions are to make the fluid less corrosive or make the pipe more corrosion resistant.

304 may be an acceptable choice but it requires clean fluid with low chlorides for maximum life. 300 series stainless have minimum velocities that should be maintained for scouring and can be damaged by stagnant periods such as wet layups.

 

[EdStainless]

And for the reasons that TBE stated above you see many paper mills using 2205 duplex SS for nearly everything.
It is more pitting resistant than 316L, and much more cracking resistant.

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[sftyvlv1]

Thank you folks. Much appreciated.

 

[0707]

I am with, Dhurjati Sen.


regards

 

[Double-Edged]

Though using stainless you may consider passivation process to clean up any residuals.

 

[EdStainless]

If using SS your welds should be clean and bright (maybe just slightly golden) after welding with no clean up.
If not then fix your shield and purge gases.
Yes you can use pickling paste or electrochemical cleaning after welding for cleaner surfaces.
But that should be the detail between success and failure.

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P.E. Metallurgy, consulting work welcomed