I’m not dismissing sabotage, although I think the risks for the US are higher than any potential gains, so that leaves Russia or a third party...... but a plausible theory for it being an accident, has been put up. I can’t even link to the website, as the blog on which it was discussed has been hit with a bot-attack, but the theory goes like this.
Both Nordstream pipelines were left for some time full of Natural Gas and under pressure. Normal procedure for a pipeline that will not be in use is to empty it and refill with nitrogen. This is done because under some conditions, Natural Gas that has not been scrupulously dehydrated, will form methane hydrate. Methane hydrate looks, behaves and weighs like ice, and can plug pipes.
Unplugging pipes plugged with MH requires lots of patience. The pipeline must be depressurised slowly and from both ends. If the depressurisation is not done evenly, you may have a chunk of ice weighing a tonne, with a differential pressure of well over 1000psi from one end to the other. Yes... it behaves just like a bullet in a gun-barrel, and velocities approaching 300kph have been observed.
Ask yourself what happens when a mass of that size, travelling at that speed, meets an obstruction such as a valve or bend in tge pipe? Look up the industry literature on Hydrate Plugs.
Now the speculation is that when you have Politicians wanting to turn gas on and off as it suits them. A management who do not expect to feel the pain if something goes wrong, and engineers in a culture where you “Do as you are ordered“ . It seems possible that someone in the hierarchy issued orders to have the pipelines ready, and the order was passed down the chain with enough “emphasis” that an engineer with a few shots of Vodka under his belt, said the Russian equivalent of “The Hell with it”, and pushed the wrong buttons.
Telling the Germans at the other end of the line doesn’t enter into it if you are institutionally paranoid, know you are possibly doing the wrong thing... and that kind of communication was not included in the orders.
Brought to you by the same engineering culture that gave us Chernobyl, the Kursk and one or two other disasters.
Just a theory, mostly derided by those who know how things “should” be done, but gaining some traction amongst pipeline engineers with experience in the field... and experience working with Russians. Or so they say.