The new contract is for construction of a hydrochloric acid dosing plant, including installation, tie-in, pre-commissioning, and commissioning support.
Contract value was not disclosed.
Last year Total used Costain for engineering procurement and construction (EPC) services for a condensate mercury removal unit (CMRU) and subsea control unit (SCS) at the plant.
The SGP project provides facilities for handling and processing natural gas and associated condensate fields to the west of Shetland.
Costain oil & gas sector director Frazer McKay said: "We are delighted to have been awarded this additional scope at SGP. It demonstrates the value that Costain can add and the ongoing development of our relationship with Total. We look forward to integrating both projects at SGP to achieve a safe, successful and cost efficient delivery."