LDON Traps reset, so it is possible to set them off multiple times. My clc has the first set of spells to detect, disarm, and then open chest/boxes, and I have discovered that you can NOT disarm a trap unless you first detect it. You can skip the disarm part if your detect is successful and indicates that the chest is not trapped. Note that there are 3 different types of trap (mechanical - rogue/bard, cursed - clerical, and magical - casters) and you must have the matching ability to open the chest if trapped - clerical line will not disarm or open a mechanical trap in other words, only rogue/bard can.
BTW, most chests I have opened have fairly minor treasure - no drop potions for example, or a gem or such.