Join Date: Apr 2002
Location: Montréal (Québec)
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The answer is a definite "it depends". The best sign of rims that need to be replaced is when the rim surface is concave (i.e. rounded in, caved in) instead of flat. On a well used up rim, you will see a nice, smooth well-polished groove that goes all around the rim. No dent, no fine line (unless there were a few rocks grooving their way), but rather a groove that looks like ruts on some forest roads. At some point, the groove is deep enough that the rim isn't thick enough and will split apart. The minimum safe thickness depends on tire pressure and some rims have a wear indicator in them.
In your case, it's either a severe bump that flattened your rim or an improperly made rim junction. Or maybe your rim is so worn out (see paragraph above) that the seam is the only section that's rigid enough. In the latter case, replace the rim ASAP. In the two other cases, it's your judgment call.
BTW, there are some techniques by which one "de-bulges" a bulge with pliers and a block of wood, or sands a rough section, but in my humble opinion, these are at best temporary stop gap measures that are fine on a tour, but nothing else.