In AWS D10.10 Table 3 for B31.1 & Table 4 for B31.3 the heat band requirements for piping under 6" has quite a difference. If the SB is slightly different and the same formulas are used then the HB1 & HB2 listed width's are incorrect. I created a spread sheet to automatically calculate the required SB, HB & GCB which works excellent but the 6" Pipe or less under B31.3 does not compute. I have gone through both the AWS  and the ASME Code books but can find no reason for the excessively wide HB requirements. Could someone please enlighten the reason for the wider HB or was a mistake in inital calculations to blame