With an aim to increase the heat exchanging efficiency, It's usually to extend the surface area (or internal surface area) by adding fins onto a tube,  which,  through this manufacturing process,  would greatly improve and upgrade the heat transferring efficiency of heating tube, it's called Finned Tube or Fin Tubes.

♦ Welded finned tubes

♦ Extruded finned tubes

♦ Welded helical solid finned tubes

♦ Welded serrated finned tubes

♦ Welded helical serrated finned tubes