From Guild Wars 2 Wiki
Some items are always Soulbound:
Items may also become Soulbound in several ways:
- Applying an upgrade to an item
- Damaging or breaking armor will soulbind it until it is repaired
- Equiping masterwork or better quality equipment (with the exception of Ascended equipment)
- Equiping items with an upgrade component already applied
- During the first BWE, items were known to lose their Soulbound status, usually by being repaired by an armor vendor after breaking.