Enhancing your equipment from +1 to +3 has no revert when upgrading fails, only the enchanting material will be consumed. From +4 to +10, every fail degrade the item by 1. And from 11 to 13, unsuccessful upgrade revert the item to +9. Still, enchanting materials will be consumed.
Success rates are depended on the enchanting material you are going to use. Materials that are dropped from monster give lower success rate than materials that can be purchased in the item mall.
Upgrade Bonus:
Equipments - Increase base attributes: HP, MP and Defenses
Weapons - Increase Physical and Magic Attack
Highly upgraded weapons also form a special kind of glow.
+7 Blue Glow
+9 Yellow Glow
+11 Purple/Pink Glow
+13 Red Glow
Success comes in random chances depending on percentage of failure and chance of success when upgrading a certain item. However, gamers tend to have their own way of doing things to have better gaming experience.