Modelling miter welds along a pipeline

Question

I'm currently performing a study to check the stresses in a fabricated expansion loop which has a 1.5&deg; - 3&deg; miter weld between two pipe joints. 
 I'll like to know how it should be modelled in AutoPIPE. Can it be, for example, a 1.5&deg; deviation in the second pipe joint from the original alignment of the first pipe joint which causes a kink, or is there any other approach i'll have to consider? 
 Any advise is greatly appreciated.

Ross Sinclair · Accepted Answer

For two common codes, consider the following: 
 B31.1 104.3.3 Miters 
 A widely spaced miter with theta < 9*SQRT(tn/r)deg shall be considered to be equivalent to a girth butt-welded joint, and the rules of this paragraph do not apply. 
 B31.3 304.2.3 Miter Bends. 
 An angular offset of 3 deg or less (angle in Fig. 304.2.3) does not require design consideration as a miter bend. 
 This means that for B31.1 you need to calculate the value for your particular wall thickness and radius. 
 For B31.3 it is simply any change in angle up to 3 degrees (with a single cut). 
 For these geometries, they can simply be modelled as kinks in the pipe.