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Back of the envelope, SI units.

13 × 10^-6 thermal expansion coefficient of steel

45 - -40 max temp difference

570k length of tube in meters

line1 × line2 × line3 = 629m (~1890') of thermal expansion over a 570 km tube.

Did I read it right that they will take out all that expansion at the ends? To get that down to say 30m between pylons you have to have about 30 expansion joints. Can they go full speed through an expansion joint?

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They are taking it out at the ends. Assume a fixed point in the middle, and you have some 1000' of movement at either end. That should be feasible, but the tube needs to be designed for very significant longitudinal movement through the pylons, and the design needs to take into account the possible lateral loads on pylons from having to bend the tube away from the geometry it has at the baseline temperature.

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