309 vs 308 s/steel electrodes.

Date 07-21-2008 02:14

Hi my learnt friends of this educational welding site,last week we were installing a 3000 HLs capacity stainless steel tank,with a dia.of 3050mm on a concrete plinth with some(19mmx30mmx30mm) mild steel plates inserted (before casting)in the concrete so the base of tank can be welded to them.only to realize they did not have enough 309 electrodes for the job.They decided to use 308 electrodes which we had a large quantity of.I as the welder objected on the grounds of the finish weld structure.but those in-charge insisted that it can do the job.Do you all foresee any future problems with the welds or will it withstand the test of time.The tank will be used to store beer. The welding process was smaw. thanks in advance for your take on this.

By js55

Date 07-21-2008 13:39

Maybe. Maybe not. The basic idea of 309 in such dissimilars is that the higher alloy content can withstand greater dilution before you fall into the martensitic zone. If dilutions are held low 308 will work but it is not recommended (and I do not recommend it) especially with SMAW since the dilutions required are lower than what is common to SMAW (around 50% for beads on base metal).
Even 309 will fall into the martensitic zone if dilution is high. In fact, there will be a martensitic zone even with 309 its just that it will generally be so thin (and immediately adjacent to the fusion line) that it is predominantly rendered irrelevent. In fact, you can even get a very thin martensitic zone with nickel base alloys on carbon steel.
So, its not an absolute, but its risky with 308.
You need to consult engineering on this.