In particular, Kelly could help a bullpen that has struggled mightily getting to closer Craig Kimbrel.
The hard-throwing righty has been phenomenal in relief for Pawtucket, posting a 0.56 ERA while notching 25 strikeouts and walking only two in his last 13 appearances.
For the 27-year-old Scott, this will be his first trip to the Major Leagues. He has pitched 32 games at Triple-A this season, six of them starts, going 4-3 with a 2.54 ERA.
Hanigan, who has been out with peroneal tendinitis in his right ankle, will give Boston a third catcher behind Sandy Leon and Bryan Holaday.
The Red Sox will likely have more September callups after the Minor League season ends on Monday.
Ian Browne has covered the Red Sox for MLB.com since 2002. Follow him on Twitter @IanMBrowne and Facebook. This story was not subject to the approval of Major League Baseball or its clubs.