It depends of the current and voltage you will use to weld. The aim is that the Heat Altered Zones of the welds not to be in touch with each other. When you homologate the welds, the HAZ must be under 350HV, anyway, it is always higher than what you can measure inside the weld. If the second HAZ from the second weld touches the first one, it will heat-treat again the first HAZ, and you might have higher hardness than 350HV, and it will lose the mechanical properties of the base metal. If you have fatigue type stresses, it will result in cracs. But I also don't know clear specs for minimum distances. It is about your good sense, where would you place the welds, and also if the welder has the necessary space to get there to make those welds.