Shelf life is defined as the maximum period during which a material may be stored under specified conditions and still remain in a usable condition. API 936 emphasizes that materials such as monolithic refractories, when stored properly, should be used within their specified shelf lives to ensure they retain the required properties for performance.
Reference:API Std 936, Section 5.1.3 - Material Storage and Handling: "Refractory materials shall not be used beyond their stated shelf life unless verified by the manufacturer or appropriate testing."