In my experience tracer dyes work best on materials and intensities that are easiest to visually inspect at 10x.
Even if our customers require us to use one, we still look at the part under magnification. High intensity peening on a hard part will result in more of the tracer coming off the part than just the impact area. Some materials will literally soak up the tracer making it very difficult to remove by peening. If peening alone is done to remove the dye, then the part in all likelihood will have several times 100% coverage. Doing so could potentially debit the fatigue life of the part. In my opinion tracer dyes are great tools for original set up to see if your process is peening the correct areas. But there is no substitute for visually inspecting the part at magnification of 7x - 10x.
