Formation of icecap around gas pipelines
Formation of icecap around gas pipelines
(OP)
It is possible that gas pipeline at certain operating conditions could develop a icecap due to Joule-Thompson cooling of the gas in the pipeline.
Has anybody heard of this phenomena and if this ice-formation if cyclic and combined with melting/freezing could lead to the pipe beeing "pushed" towards the surface as is seen with e.g. stones in countries where the surface will freeze during winter?
Best Regards
Morten
Has anybody heard of this phenomena and if this ice-formation if cyclic and combined with melting/freezing could lead to the pipe beeing "pushed" towards the surface as is seen with e.g. stones in countries where the surface will freeze during winter?
Best Regards
Morten





RE: Formation of icecap around gas pipelines
above frost line, this may explain some problems i've had will shallow lines moving a lot.
RE: Formation of icecap around gas pipelines
Th JT is about half a degree / bar pressure loss
A pipeline trenched slightly below sea bottom will rapidly reach ambient temperatures about 3-4 deg as a worst case and the the cooling will continue from there. The gas temperature will asymptotically approach a SS temperature some deg. below ambient. If this ambient is close to zero as it could be where I live then the SS temp could be below 0 deg C.
RE: Formation of icecap around gas pipelines
But if you could somehow induce cooling/freezing, the frozen zone around the pipe would be essentially radial, thus would be less likely to form ice lensing (which causes frost heave), and would not tend to move the pipe in any direction.
The effect you mention (ojects being pushed up, "boulder heave")is more likely to happen to discrete objects in a natural frost zone, with a fairly level, downward moving freezing interface. Even in areas with large seasonal frost depths (10' +), upward jacking of pipes in the frost zone does not happen. Most pipes here in Alaska are installed in the seasonal frost zone.
Carl
RE: Formation of icecap around gas pipelines
Best Regards
Morten
RE: Formation of icecap around gas pipelines
Just a thought.
RE: Formation of icecap around gas pipelines
I would suggest that the salinity will also lower the freezing point.
RE: Formation of icecap around gas pipelines
Best Regards
Morten
RE: Formation of icecap around gas pipelines
I'd be surprised to see a problem in your situation unless you are operating in a shallow artic zone. In that case you could have conditions where the sea freezes (at a very low temperature) all the way to to ocean floor. However, your biggest concern then is not pipeline heave, but rather mechanical damage from the shifting ocean ice. I know that the Northstar project (N. Slope of Alaska) was very concerned about this phenomenon and they went to great lengths to armor the pipeline.
Good luck with your project.
RE: Formation of icecap around gas pipelines
If you have access to a common process simulator such as HYSYS try to make a "standard nataural gas" (90% c1 and a mix. of c2-c5 for the rest of the 10%) and set up a +200 km pipeline module with an inlet P of approx 140 barg and select heat exchange with environment (wet sand). Then see it for your self.
Best Regards
Morten