TBH id have expected Porosity to be the big issueWe made a batch of acid fume fans two years ago. We noticed that MIG welding with pure 1050 wire, the old reels (10+ years old) caused far more birdsnests and burnback problems, in spite of looking fine to the naked eye, and being a respectable brand (Murex IIRC). in the end, we hoyed it all out to scrap and ran new reels only, and suddenly, no more problems.
We'll have the same problem in a few years time I suspect, as we run through it in batches, but infrequently.