<p>Varying electric resistance welding (ERW) techniques and heat treatment procedures have been used since the 1920s to make longitudinal seam welds on pipes and tubes. These different ERW weld types and heat treatments can have dramatic effects on pipeline mechanical and corrosion properties. Pipeline owners/operators may not have sufficient records that document the ERW technique and heat treatment used during the fabrication of their vintage pipe from several decades ago. Further, studies that correlate the effects of heat treatment process on weld microstructure evolution are very limited in the open literature. In this work, ERW and base material from a vintage pipeline installed in 1952 was examined before and after normalizing heat treatments. Selected pipe samples were also heat treated at lower temperatures or cooled from normalizing heat treatment temperatures at controlled rates. Each microstructure was documented using optical and scanning electron microscopy to create modern, high-resolution reference images for a range of ERW conditions. Microhardness testing results are also presented for certain conditions.</p>