Generally yes, although it depends greatly upon the type of coating, and if whether multiple coats of paint have bonded strongly enough to each other to transmit sound.  Since any paint or coating is of far less density than any metal, the movement of sound through it slows dramatically to trick the instrument into interpreting a longer length of travel through a much thicker pipe or tank wall.  The results is a falsely heavier wall thickness measurement exceeding the true thickness of the subject metal and paint itself.

In order to eliminate the need to scrape away the paint or coating, as well as potentially damage the pipe itself, we employ a feature of our Olympus instrumentation called “echo-to-echo,” which essentially negates the coating thickness.  This method may not be possible for heavier and especially rubberized coatings, or for very old pipe or metal surfaces where the paint is cracking and peeling.

An alternate method is to physically remove the coating in the areas tested which not only requires significantly greater effort, but also adds later work to the maintenance staff in re-painting the pipe.  A common shortcut to measure the thickness of the paint coating and deduct this value from all readings made across both paint and metal introduces potentially significant error into the investigation since paints and most coatings are applied unequally.