There is another option which is being discussed in Norwegian media now - that the Russians have used the pipelines essentially for storage of excess gas (Seeing as the pipelines are basically, combined, a 5M cubic meter pressure vessel)
That would go a long way towards explaining how several ruptures happened in relatively short succession - pipes being loaded up with too much gas (after all, the more gas stored, the more money in the bank for later on!)
Once the first one burst, someone probably re-evaluated that idea, but letting off gas in sufficient quantities fast enough may not have been possible.
Of course, if this was indeed the case, I assume it will very soon be very evident - I can't imagine that the rupture caused by an external force will be indistinguishable from that of it rupturing due to overpressure.
...but that would require flow, right? (that is, closing of the flow too fast will basically lead to a shockwave rupturing the pipe).
In this case, the pipes were basically being used as pressure vessels (I believe it was quoted in the media that pressure in one of the pipes was 105bar/1,500psi or so before the leak sprung).
With nothing but static pressure, I have a hard time seeing how such a pipeline may be sabotaged in SW alone - doubly so as it, as far as I can tell from media reports, really is the proverbial dumb pipe - valves and thingamajigs at either end, but the pipeline itself is essentially just a pipe with no shutoff valves throughout. (Which, in itself I find hard to believe, so I probably had better dig a little bit more!)
That would go a long way towards explaining how several ruptures happened in relatively short succession - pipes being loaded up with too much gas (after all, the more gas stored, the more money in the bank for later on!)
Once the first one burst, someone probably re-evaluated that idea, but letting off gas in sufficient quantities fast enough may not have been possible.
Of course, if this was indeed the case, I assume it will very soon be very evident - I can't imagine that the rupture caused by an external force will be indistinguishable from that of it rupturing due to overpressure.