mylexicon
Mechanical
- Dec 16, 2005
- 43
I have tried to simulate, using CAESAR II software, a pipeline undergoing lateral displacement at a fault crossing. The pipe that I am looking at is API 5L X52, 36" in dia with 0.625" wall thickness carrying heavy crude.
The civil engineer in charge has suggested differential ground movements of about 30" at this fault crossing perpendicular to the longitudinal axis of the pipe. He has also produced a drawing showing the Special Detail for Fault Crossings. The pipe is placed in a ditch cut 2.3 meters deep into the ground and 3 meters wide. The trench filled with very soft soil or sand to accomodate for expected movements during seismic activities and to reduce the restraining effect of soil around the pipe. This special trench detail is supposed to be implemented along 440 meters of the pipeline, within 220 meters before and after the fault line.
I am pretty confident about my model, but 30" of vertical movement?!! No pipe will be able to withstand such abrupt ground displacement, deflection / rotation.
When modeling the soil springs, I have taken into consideration that along the pipe within 200 meters of the fault crossing the pipe is surrounded by soft sandy soil with minimal cohesion. But still there is no way the stresses will be within allowables of ASME B31.4. even with higher pipe schedules.
Can someone tell me what happens in real life? I honestly do not think I can come up with back up calculations showing that the pipe stresses are within code allowables. I haven't seen this anywhere, but is plastic deformation of the pipe acceptable?
any pipeline experts out there? how do you guys handle these fault crossings in real life?
we'll be glad to hear from the members.
regards,
drno
The civil engineer in charge has suggested differential ground movements of about 30" at this fault crossing perpendicular to the longitudinal axis of the pipe. He has also produced a drawing showing the Special Detail for Fault Crossings. The pipe is placed in a ditch cut 2.3 meters deep into the ground and 3 meters wide. The trench filled with very soft soil or sand to accomodate for expected movements during seismic activities and to reduce the restraining effect of soil around the pipe. This special trench detail is supposed to be implemented along 440 meters of the pipeline, within 220 meters before and after the fault line.
I am pretty confident about my model, but 30" of vertical movement?!! No pipe will be able to withstand such abrupt ground displacement, deflection / rotation.
When modeling the soil springs, I have taken into consideration that along the pipe within 200 meters of the fault crossing the pipe is surrounded by soft sandy soil with minimal cohesion. But still there is no way the stresses will be within allowables of ASME B31.4. even with higher pipe schedules.
Can someone tell me what happens in real life? I honestly do not think I can come up with back up calculations showing that the pipe stresses are within code allowables. I haven't seen this anywhere, but is plastic deformation of the pipe acceptable?
any pipeline experts out there? how do you guys handle these fault crossings in real life?
we'll be glad to hear from the members.
regards,
drno
