An Investigation Into the Behaviour of Composite Repaired Pipelines Under Combined Internal Pressure and Bending

The repair of corroded pipelines with fiber reinforced composite materials has gained wide acceptance in the oil and gas transportation industry over recent times. It has been integrated into the ASME B31.4 and B31.8 pipeline codes, along with CSA Z662. A considerable amount of experimental research has been conducted on fiber reinforced composite repaired pipelines with external corrosion defects subject to hydrostatic internal pressure. However, the effects of the internal pressure, thermal loads and geotechnical loads create combined loading conditions on the buried pipeline that need to be considered. This paper aims to address the effectiveness of fiber reinforced composite repair systems on externally corroded pipelines under combined internal pressure and bending. For that, finite element analysis is conducted to examine the effects of various loading conditions on the effectiveness of the fiber reinforced composite repair system. Typical conventional commercially available fiber reinforced composite wrap systems are used for this purpose. Three loading conditions are considered on both conventionally repaired and unrepaired pipes subject to internal pressure, pure bending and combined internal pressure and bending. Results show that up to the stage of yielding of the steel in the defect region, the steel elastic stiffness counteracts most of the stress that is induced by the in-service loading conditions. Once the pipe is loaded beyond the yielding point of its material at the defect region, the composite starts to take effect, thus carrying a significant portion of the applied stresses. Essentially, by comparing the burst pressures of repaired pipes against unrepaired pipes, it is shown that the fiber reinforced composite system restores the minimum specified strength of the pipe to its value before the defects were applied. The results presented in the paper are believed to reveal the response of the wraps subject to realistic combined loading conditions that to our knowledge are nonexistent in open literature.