I want to make your clear that most of the SGW applications runs over the UDP protocol. UDP ports 2123 and 2152 are used for control and data respectively. As per my knowledge SGW has following three interfaces.
S11 -Interface with MME which is primarily used for session/bearer establishment.
S5 - Interface with Home network PGW
S8 - Interface with Visited network PGW
Only the interface towards PCRF which is based on Diameter uses TCP/SCTP. SCTP is better than TCP in many terms that's why it is used as transport protocol. Diameter uses 3868 standard port for communication with its peer.