Infrared scanning of the wall of a pipe or tunnel can show information about any changes in the wall condition or the condition of the ground immediately outside the pipe or tunnel. Such changes may include the presence of annular gaps, delaminations, exterior voids, presence of localized groundwater flow, etc. These changes can affect the wall surface temperature because they change the heat flow characteristics in their vicinity. The method works best when a temperature change is induced in the interior environment of a pipe or tunnel for a long enough period to allow the condition of the pipe wall or ground to clearly show differences in surface temperature. For instance, the low thermal conductivity across a localized delamination or annular space will cause the pipe wall in that area to have a higher temperature than in an adjacent area where the heat transfer direct to the ground is greater.