Speak to Adams on the Normandy's engineering deck. After Priority: Sur'Kesh, however, Mordin Solus and Eve will occupy the med bay, and Adams and the medical officer will temporarily reside in the crew quarters. In this case, Adams will only return to his station and request to speak with you after you have completed any two missions involving landing on a world (Leviathan and Omega missions count toward this).
Alternately, if you have already previously visited the Elkoss Combine Arsenal Supplies kiosk, head to the Normandy's Shuttle Bay and access the Alliance Requisitions terminal. You can purchase the item with a 10% surcharge.
If you speak to Adams right after purchasing the item, he tells you that they are performing modifications for the installation. When you visit him again after a period of time, he tells you that the thermal pipe has been successfully installed, thus, completing the mission.