From the above images:

1) The node you are trying to restrain is 10000.

2) If you add a restraint (anchor) at 10000, you have fixed node 10000 in global space.

3) If you add a restraint (anchor) at 10000, but define a CNODE (say 10001), then you have anchored node 10000 to 10001. So, what did you do with 10001? If the answer is nothing, then 10001 is free and therefore so is 10000. You must use 10001 as another node in your piping system, or apply displacements to 10001.