The Adaptive Total Focusing Method (ATFM), which can be applied to an irregular surface, has been attracting attention in the field of phased array ultrasonic testing for power plants and chemical plants, and its introduction into ultrasonic testing for plants is being considered. When ATFM is applied to an irregular surface, such as a weld cap of piping in a power plant, a gel acoustic coupler is promising from the viewpoint of workability in the field. Segmented Polyurethane Gel (SPUG), which is like water in sound velocity and density, is beginning to be used in ultrasound imaging in the medical field. This paper discusses the use of SPUG as a material for acoustic couplers in the field application of ATFM, and examines the behavior of SPUG in contact with water, machine oil, glycerin paste, and epoxy resin, and shows examples assuming the wall thickness measurement of steel structures and delamination inspection of glass fiber reinforced resin.