Here is a link to a recent paper, with an algorithm, for fitting arc splines to NURBS:

https://www.researchgate.net/profile/Xunnian_Yang/publication/3845146_Approximating_NURBS_curves_by_arc_splines/links/594ca7eb458515e70348b782/Approximating-NURBS-curves-by-arc-splines.pdf

- Brian