Your wet-pipe sprinkler system may not be as filled with water as you expect it to be. A bubble of air may migrate to the highest point in the system, creating a very vulnerable location for internal pipe corrosion. That’s why NFPA 13 now requires that all new wet sprinkler systems be fitted with an air vent at the system’s highest point. This is a good investment for both new and existing systems. The UNITED Fire Systems Model AR-1 automatic air release device is Factory Mutual (FM) Approved for just this function. See here for more information, and take action to prevent damaging corrosion.