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Hill Engineering at Pipeline Pigging & Integrity Management Conference

Hill Engineering gave a presentation about fatigue analysis of pipelines at the 2018 Pipeline Pigging & Integrity Management (PPIM) Conference in Houston, TX. PPIM is the industry’s only forum devoted exclusively to pigging for maintenance and inspection, as well as pipeline integrity evaluation and repair. Hill Engineering’s presentation, titled “Is the Paris Fatigue Crack Growth Relation the Only Model Appropriate for Pressure Cycle Fatigue Analysis of Pipelines,” included an overview of various fatigue analysis models for pipeline fatigue crack growth assessment. The abstract text is presented below.

Fatigue is the progressive cumulative damage that structures experience during cyclic operation. In-service fatigue failures of energy pipelines typically occur due to the cumulative effects of operational pressure cycles driven primarily by internal pressures that are less than the Maximum Operating Pressure (MOP) or Maximum Allowable Operating Pressure (MAOP). Fatigue loading is known to be a driving force to the formation and growth of cracks from corrosion sites, dents, welds and other internal, external or embedded discontinuities.

While it is challenging to establish the conditions and predict the time for cracks to initiate in pipelines, their growth rate and behavior can be reasonably predicted by applying a fatigue crack growth model supported by experimental fatigue crack growth testing derived from engineering Fracture Mechanics principles. Fatigue crack growth modeling is generally derived from standardized fatigue testing of samples taken from the material and structure of interest. Therefore, a fatigue crack growth model should carry the measured effects of the environment, temperature, loading frequency, stress ratio and mean stress for the loading spectra. The choice of a fatigue crack growth model will directly affect the final fatigue life prediction of pipelines with cracks and the determination of the next integrity assessment interval.

This paper reviews the most common fatigue crack growth relations developed by the aircraft industry and applicable to the energy pipeline industry when modeling fatigue crack growth. These relations are Paris, Forman, Walker, NASGRO and a tabulated form. The stages of fatigue life and the fundamental principles of fatigue crack growth analysis will be presented and discussed within the context of and applicability to energy pipelines.

If you are planning to attend the conference please stop by to discuss Hill Engineering’s capabilities in fatigue analysis and design and residual stress measurement. Please contact us for more information.