Pipe pressure change due to seismic acceleration
Pipe pressure change due to seismic acceleration
(OP)
I have a question that may lead to interesting discussions.
Can seismic acceleration lead to transient pressure fluctuations in a pressurized pipe? Any hint or insight could be useful.
Thanks.
Can seismic acceleration lead to transient pressure fluctuations in a pressurized pipe? Any hint or insight could be useful.
Thanks.





RE: Pipe pressure change due to seismic acceleration
A tanker truck going around a curve, or stopping, produces accelerations that act upon the fluid, which may change the level of the fluid inside the tank, thereby also changing the pressure against the walls of the container.
These internal fluid pressures generated from small seismic accelerations would normally be small in relation to the typically large internal pressure stresses of a typical pipeline, hence such effects from seismic loads are typically ignored. Seismic loads generally are assumed to cause axial, lateral and vertical relative displacements between points of a pipeline as the seismic waves move along or across a pipeline. These are the stresses that are usually being analyzed in the seismic design of pipelines.
Independent events are seldomly independent.
RE: Pipe pressure change due to seismic acceleration
Let me explain further. We have a large pipe that runs horizontally around 250 meters straight before a 270 degree bend. The seismic acceleration is as high as 0.6g. The operating pressure of the line is ~550 kPa and the line class maximum allowable pressure is 1000 kPa. The pressure increase due to seismic axial acceleration is ~1500 kPa, which could lead to instantaneous pressure of ~2000 kPag at the bend for this pipe.
Should we considering changing the line class to be prepared for the instantaneous pressure increase in this pipe?
RE: Pipe pressure change due to seismic acceleration
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Pipe pressure change due to seismic acceleration
I calculated the additional pressure due to seismic acceleration using the rho X acceleration X height equation. In this case, it will be 1000 x 6 x 250 = 1500 kPa. Does it make sense? This pressure could be instantaneous (maybe a small fraction of a second) but I do not know if from a stress point of view, the pipe will withstand it or not. Do you have anything to add to it?
RE: Pipe pressure change due to seismic acceleration
RE: Pipe pressure change due to seismic acceleration
Independent events are seldomly independent.
RE: Pipe pressure change due to seismic acceleration
If the pipeline is flowing freely, then I speculate the acceleration of the elbow won't appreciably accelerate the water within, and the earthquake wouldn't contribute to a significant surge.
RE: Pipe pressure change due to seismic acceleration
Sorry, not buying any of that.
Independent events are seldomly independent.
RE: Pipe pressure change due to seismic acceleration
RE: Pipe pressure change due to seismic acceleration
Independent events are seldomly independent.
RE: Pipe pressure change due to seismic acceleration
RE: Pipe pressure change due to seismic acceleration
Can a seismic event accelerate a 250m pipe at 0.6 g? Yes, Northridge and other events had that much ground acceleration, and the typical wavelength for those waves was on the order of 5 km, so it's possible.
Could the pipeline rupture due to such events? Well, you'd have to exceed the burst (or collapse pressure) of the pipe (which if you do your homework correctly, ought to be 2x to 3x of your design pressure, no?), and do so before ground motion caused the pipe to seperate anyway, so it ought to be pretty rare. But it does happen, again see rconner's link, specifically the two slides he pointed to (slide 35 shows a clear rupture, slide 36 shows a vacuum collapse).
There was a large wooden water pipeline, approx. 30 miles long and 400' or so of elevation drop, near my house where I grew up (seismically active area). Spaced every half-mile or so were surge towers, designed to relieve such pressure events. They did work, as we never heard of this line rupturing, and it survived at least two or three Magnitude 5 or better events.