Hi,
Buggles, for analyses of very large piped systems, shells are inefficient, though they can provide you with a LOT of data, especially in local areas.
However, in order to study the behaviour of an antire system, I'd stay on PIPE16: it can handle everything you need. The usage of this element saved us, where I work, more than once from situations where a hand-calc would have suffered from unacceptable simplifications in order to be solved. Once you have solved your system with "line-elements" (in 3D, however), you can use the elem / nodal loads in order to input the correct BCs for local analyses with shell or solid elems.
Before looking for other software, I suggest having a thorough reading of the Manual about this element. Only if you find it has unacceptable "weaknesses" for what you must do, then look elsewhere...
Regards