ANALYSIS OF SPECIALTY FLANGES FOR SUBSEA SERVICE

摘要

This report covers the model generation, error prediction, analysis, and stress classification of non standard flanges subjected to harsh environment and loading conditions. These proprietary flanges were used in hydrocarbon service in the main oil and gas lines from a major offshore production platform and facility to onshore gas and oil processing facilities. The flanges were to be in service 70 metres (219.5 feet) below the surface of the sea, were relatively large diameter, 0.935 metres (36.811 inches), and were to operate at pressures exceeding 14.9 MegaPascals [MPa] (2160 psig). These flanges were also expected to accommodate severe bending moments due to subsidence of the production field. Due to the proprietary non-standard design and harsh conditions, a rigorous method of analysis was required to satisfy the operator's safety/verification requirements and government regulations. Therefore, a rigorous finite element analysis was performed considering the worst case scenario and the resulting stresses determined; the peak stresses were removed from the analyses as the same contribute primarily to fatigue, and the resulting primary membrane plus bending stresses were compared with allowables set forth in ASME Section VIII Division 2. The justification and procedures for selecting the elements, type of analysis, stress classification, determining allowables, method of peak stress removal, and determining the model error prediction are the subjects of this paper and are described herein.