Transverse and longitudinal sections of the coated pipe can be viewed under microscope. Corrosion test is necessary both under static and dynamic conditions

Either TEM or SEM could used to view the coated surface

Morphology and element compositions before and after coating will be good to characterize the sample using scanning electron microscopy and energy dispersive x-ray spectroscopy (EDS). You can also carry out corrosion test as suggested by Sefiu Bello. Good luck

XPS might be a good tool as well, adhesion test should be of interest as well.