It is not any thing more than a factor for anticipating cracks in piping joints!it is equal and greater than 1,this factor increase calculated stress.
first time "in piping" it achieved by markle experiments by applying cyclic bending moment on different piping parts.
it is different from scf which is a geometrical coefficient and is not valid in piping material(it is valid for realy brittle material).
but actually there are too many things around it.
regards