Rusting stainless

[Hitch]

could be....should be neutralised with a mild alkali after pickling

We use neutralising paste very occasionally.
A rub with a bit of scotchy, then a good going over with a power washer does the trick usually.

It's a job usually left for apprentices/lower skilled guys, but you have to keep your eyes on them. If you get a lacklustre lad washing stuff off, it usually ends up like that. Then next day you get them back outside washing it off with superbright and a bucket.