A Glass Reinforced Epoxy (GRE) fire water header, installed on a Liquefied Natural Gas (LNG) jetty, comprises DN700 pipes and is subjected to seismic accelerations. Due to the jetty’s structure, the seismic accelerations provided by the client vary significantly along its length. The fire water header must be evaluated for both Operating Basis Earthquake (OBE) and Safe Shutdown Earthquake (SSE) seismic loads. Given the failure mechanism of GRE, the analysis focused on the more critical SSE earthquake.
Analysis
The pipe stress analysis was conducted using the CAESAR II software package, adhering to ISO 14692 standards. Flange assessments were performed following the equivalent pressure method. The specified seismic loads included varying accelerations along the length of the system. Both scenarios—with and without friction—were analyzed to ensure the inclusion of the most critical conditions.
Due to the high support loads resulting from seismic accelerations, a special support shoe was designed. The stress check for this support shoe was performed according to ASME Section VIII, Division 2 (ASME VIII-2).
Results
The supporting layout was significantly modified to minimize stresses in the system and reduce support loads caused by seismic accelerations. Additionally, pipe reinforcements were required at multiple locations.
“High seismic support loads necessitated the design of a special support shoe.”
With the proposed modifications, the system complies with all stress and load requirements.
