Thermoplastic materials used in long-term applications such as pressurized gas pipes or flexible offshore pipes have to withstand harsh conditions: The material is exposed to internal pressure, dynamic loads, and direct contact to an aggressive environment like hydrocarbons at elevated temperatures. During service, material of the inner barrier sheath can reach the free space in between the single elements of the pressure armors by, manufacture, swelling and creep, effectively forming polymer ingresses between steel components that have a free degree of relative movement. There, dynamic loads and stress concentrations in service caused by waves and production can act as potential starting points for crack initiation by squeezing the material. Subsequently, slow crack growth (SCG) under cyclic loading can occur, ultimately inducing a risk for premature failure in the field. While specific qualification approaches take SCG into account this investigation highlights that close to realistic in-situ testing might produce more robust results.