What makes one fail a PhD viva? I do not ask about special cases, e.g. supervisor does not approve the thesis, there is rivalry between the supervisor and the examiners and so on.
Is there any general standard for viva, e.g. one needs to be able to answer 2/3 of the questions, etc.

I'm waiting for my viva, and I'm only worried about questions about related work. For example, my thesis only addresses a problem on deterministic programs, do I need to know all approaches to the same problem on probabilistic programs? (at the moment I don't).



UPDATE

I would like to emphasize again that I do not ask about special cases, e.g. plagiarism, wrong methodology etc. I believe theses cases are extremely rare. I just want to ask about a normal case where one managed to publish some papers, and advisor (happily) approved the thesis.
No, there are no general worldwide standards, other than "the examiners should be satisfied".

Your advisor is probably the best person to answer questions like this for your specific case.