The TEMA Standards specify the maximum unsupported span that heat exchanger tubes may have.
Some tubes are supported at every baffle hole, with the unsupported span equal to the baffle spacing. But the tubes passing through the window are only supported every second baffle, so the unsupported span is equal to twice the baffle spacing. The maximum unsupported spans allowed by the standards for different
tube materials and diameters are shown in Table 6-2.