Matching filler and over-alloying are both defensible and only one is right for a given joint. How dilution, ferrite balance and hot cracking decide the answer, and what the drawing should state.
Sustained heat and steady load deform a thin section slowly without ever exceeding yield. Why brackets and shields move before the pipe does, and how support spacing is really a material decision.
Colour on a weld is an oxide thickness reading, and the thickness records what the shielding did. How to read the sequence on titanium and stainless, and why the layer has to come off before the next arc.
Coastal stainless fails by pitting and crevice attack rather than by bad material. How chlorides concentrate as a hot surface dries, why the top of a pipe can go first, and what molybdenum genuinely buys.
One process removes contamination and the other removes metal. Why passivating a tinted weld achieves nothing, what the depleted layer under the colour actually is, and how to specify finishing so the part resists corrosion.
Welding locks elastic strain into a part, and the real question is whether it matters. Where residual stress causes trouble, why most tube never needs a furnace, and how titanium changes the answer entirely.
A hot exhaust is longer than a cold one and the growth has to go somewhere. Why flange faces and shell seams fail before the tube does, and how support layout and compliance points decide what survives.
Two metals only corrode each other when an electrolyte joins them. How area ratio and drying cycles set the rate, where the couple appears on a real car, and the isolation and drainage choices that keep it predictable.
