PT
PT turns up in 2 fields: welding, concrete. Here is what it means to the people in each one.
PT in welding
Penetrant testing: revealing surface-breaking cracks by drawing colored or fluorescent dye out of them.
Liquid penetrant testing applies a thin dye to a cleaned surface, lets it soak into open flaws for a dwell time, often 10 minutes or more, removes the excess and applies a white developer that pulls the dye back out as visible indications. It works on any nonporous material, including stainless, aluminum and titanium, but finds only discontinuities open to the surface, and the surface must be thoroughly cleaned first.
"Do PT on the stainless root after grinding, red dye, ten-minute dwell, then developer."
PT in concrete
Post-tensioning: reinforcing concrete with steel tendons that are stretched tight after the concrete hardens.
Post-tensioning places high-strength strand in sheathing or ducts before the pour and jacks it to high tension once the concrete is strong enough, squeezing the member into compression so it spans farther with less depth and cracking. US building slabs and parking decks mostly use unbonded monostrand tendons, while bridges and heavy structures use bonded, grouted multistrand systems. Cutting or coring a PT slab without locating the tendons first can release a strand with lethal force.
"It's a PT deck, so nobody drills, cores or shoots a pin into it until the GPR guy marks the tendons."