A "singular stiffness matrix" means you have "rigid body motion", which is numerically unsolvable. It means you have a "zero stiffness" value for one of the terms on the diagonal of the stiffness matrix (which will sooner or later be used as a divisor).

This happens when you don't adequately restrain the model, or you have element connectivity problems. In your case, your model only has +Y supports. The other 5 degrees of freedom are not restrained - hence rigid body motion.

The terminal points of your pipe runs have to connect to "something", if these represent nozzles, a first pass approximaton could use anchors at these locations.