Pressure vessels, piping and tankage made from Fiber Reinforced Thermosetting Polymer (FRP) have been in industrial service in chemical plants, refineries and other facilities since the 1950’s. Most service conditions will damage the FRP materials used for the equipment. This damage can impact the Fitness-For-Service (𝐹𝐹𝑆) of the equipment. As for most metal alloys, damage experienced by FRP is not always uniform and may be concentrated in localized areas. The situation is compounded because the damage that occurs is not detected using any of the inspections used in construction codes or other existing standards. There are no standardized codes to evaluate 𝐹𝐹𝑆 of in-service equipment made from FRP. In this Bulletin, we describe gaps between construction codes and damage; provide a technical basis for determining the extent of damage that has occurred to these materials; and show how to determine 𝐹𝐹𝑆. A methodology for determining 𝐹𝐹𝑆 will be presented that is independent of construction codes, specific materials, material tensile strength and normal service conditions. It is recommended that a part be added to API 579-1/ASME FFS-1 to incorporate this methodology.