When a constant stress is applied to a polymer or composite material, it may gradually deform over a period of time until a point is reached at which the material fractures or the product fails to meet its functional requirements. It is important for designers to be aware of this failure mode for permanent ancillary equipment, and that a material that can withstand a load in the short term may not be able to withstand this load in the long term. The time taken for the material to fracture depends on several factors, including the stress level, the ambient temperature, the type of environment, the component geometry, the molecular structure and the manufacturing method .
Source: API RP 17L2, Recommended Practice for Flexible Pipe Ancillary Equipment, First Edition, March 2013. Global Standards