Agreed with garnet1. From a due diligence perspective, when I'm in this position as an engineer (and I'm there frequently) I consider myself responsible to make sure the existing owner's equipment I'm tying in is safe. Not to the point where I review design calcs, but if I notice a PSV missing, leaking flanges, improper gasket & bolting materials, etc. I advise in writing of the risks associated with what I've seen. Beyond that, as garnet1 said, it's between you and the owner.