[tekla]

Welds weakening the base metal is a myth that is disproven literally day 1 of any welding course. There are metals that don't like the heating and will weaken, but if the weld breaks before the base metal, someone fucked up real bad.

Of course shit welding can cause weakening of the material but thats true of everything. Anything that is worth welding that also is important will use metals that have strong welding properties that make the weld stronger than the base material.

[frognumber]

This is misleading or wrong. In general, the weakest part of a steel weld is the heat-affected zone. Not the rest of the base metal. Not the weld.

The heat-affected zone is caused by the weld. Ergo, welds to weaken the base metal.

In most cases, this also doesn't matter. I think all but one of the things I've welded, even a bad weld would have been way more than strong enough, and for many, even the tack weld would have held fine. Welds are very, very strong, and it's usually cheap and easy to use sufficiently strong materials that all of this is moot.

But for something like an ultralight bike frame, racing car, or airplane, it is something you do need to worry about.