One of the methods of Non destructive testing I do

I am getting ready to head up to Port Huron, Mi to do some testing on the blue water bridge. The funny thing is, I will drive two and a half hours to do a half hour of work. I love it...anyway, I will be doing Magnetic Particle testing, this method involves putting a magnetic field into a weld and applying a fine iron powder to the area. What this does is identifies cracks in the weld or base metal. What happens is the magnetic field is put into the steel using a "Yoke" which is an electro magnet. After the field is applied if there is a crack or other break in the steel, The leakage of the magnetic flux will attract the iron powder that was applied and thus the crack is identified. Amazing, Its kinda like Mr. Wizard but I get paid for it.....