72 are mounted thus when fitting is done from outside the tank the inside of the tank shell 13 is generally welded first when a seam has been fit from inside the tank the outside of the seam is generally welded first automatic vertical welding equipment such as that described by christensen et al u s pat no 2 794 901 arnold et al u s pat no 3 210 520 yadron et al u s pat no 3 255 944 or rainey u s pat no 3 444 349 can be used to improve the quality and productivity of vertical seam welds when the surface of the vertical seam on one side of the tank shell 13 has been welded key plates 72 and finger bars 81 can be removed from the opposite side to facilitate welding of that side when this method is used weld shrinkage causes the shell plates to wrap tightly around the inside key nuts 45 at the desired inside circumference completing all vertical seam welding in the first ring helps prevent ovaling or flattening of the shell however with the present invention it is not necessary to complete all vertical seam welding in the first ring before beginning to hang plates in the second ring 21 fig8 shows the outside surface of a second ring shell plate 130 just prior to its placement at.