Single wall exhaust pipe

Inspected a 50 yr old house with a gas water heater that was replaced in 1988. Still had the original single wall exhaust pipe, would the B-vent pipe have been the standard in 1988?

If it ran through the attic, or there are clearance issues, it should be a B-vent, even in 1988.

Single-wall vents are perfectly acceptable under the appropriate circumstances.

Thank you. This pipe was in unconditioned space. It was double walled at penetration thru ceiling.

Single wall metal pipe, or single wall transite pipe?