Miecz, whether or not this is standard is not really the point here.
The point is that this is a request for a change, a change order request, and, in this circumstance, it is the responsibility of the fabricator to show to you that the substitution is at least as good as your original callout. He has the burden of proof. He needs to show you the paper work. You do not need to do any investigative work here. This should be your normal "modus operande" here. (method of operation)
Cheers. Off the soapbox now.
Mike McCann
MMC Engineering