Why a white bloom is rarely a failing weld, how flux, condensation salts, coolant and aluminium each leave a different mark, and when the residue proves nothing.
The difference between dry carbon and an oily film, how to tell oil from unburnt fuel, what the breather contributes, and how to clean a tip so the next read counts.
What a driven section has already been through, the properties that do not come back, why clamps and gaskets are consumables, and when reuse stops paying.
How a flange goes out of face, reading the gap with a straight edge, cutting the weld instead of the flange, re-facing or replacing, and closing without force.
Why a bend is the worst place to cut, what the section loses there, moving the cut onto a straight, and holding the curve when there is nowhere else to cut.
Preparing a joint before going underneath, purging a fitted run, working overhead without losing the line, shielding what sits above, and inspecting from below.
