316L welded to Alloy 20 (20Cb-3)

[caper]

Any comment on welding 316L stainless to 20Cb-3. The application is in a powerplant in high temperature sulphuric acid . Previously it was welded with 309 rod. Would
309LMo be a better choice?

John

 

[Rich2001]

Welding
20Cb-3 (Carp-20) stainless have been satisfactorily welded by the shielded fusion and resistance welding processes. Do not try to Oxyacetylene weld, carbon pickup in the weld may occur. Since austenitic welds do not harden on air cooling, the welds should have good toughness. It is importance to keep the heat input and joint restraint to a minimum to avoid hot cracking. When a filler metal is required, use AWS E/ER320LR welding consumables. These "low-residual" consumables greatly improve the resistance to weld hot cracking, which can be a problem, especially with higher heat inputs and thicker sections. The alloy has been used in the as-welded condition; however, for elevated temperature service, a postweld stabilizing heat treatment should be considered.

I would also suggest that after each pass a dye penetrant test be performed.

 

[JLAU]

Hi,

Normally you would choose ER320LR for welding the 20Cb-3 due to the cupper content.

However, as 316 is not alloyed with Cupper, there is no reason to choose a filler with Cupper in the composition. It would be better to choose a filler with as few alloying elements as poosible without compromising the mechanical and corrosion protective properties. This minimises the risk of hot cracking.
Due to the Mo content in the 316 the filler should also contain Mo, so 309LMo seems to be a suitable choice.
Nevertheless, a proper welding procedure should be prepared and tested to proove the suitability.

JLAU