Is copying methods from a paper from the same group plagiarism? I just wanted to see what people think about a possible plagiarism issue. I found a new article which, as far as I can tell, uses data first shown in an older publication from the same group but with a different first author. This may be irrelevant but I thought I'd mention it anyways; this new article's only novelty is to analyze the old data with a model developed in another group. 

To the point: this new article has many (more than 8) sentences taken from the older article from the same research group. These sentences describe the experimental setup. It's clearly the same setup as the older article.

Is this plagiarism? I've been taught that it is but I've talked to another academic who says it's not since there are only a limited number of ways that methods can be explained.
Experimental and methodology sections are increasingly being recognized as "exceptions" from plagiarism, for reasons of practical necessity. For instance, I use the same basic technique to study different problems in engineering and material science. One of the sentences in my methodology section is:


  We use the SHAKE algorithm to constrain the bonds in water molecules [citation].


There are only so many ways to write this statement, and at the same time, I can't ignore this information, because it would imply a change in method. Is it plagiarism for me to reuse the same wording as in an earlier paper? If it is, I'm in big trouble. Similarly, if I were an experimental group, how many ways are there to say:


  We used chemical X from vendor Y as received.


For this reason—because often methodologies are very similar to previous methodologies within a research group–many journals now do not consider such so-called "self-plagiarism" of the methodology section to be a problem.