What are the paramaters that go into the calculation of the Bend SIF.Why is my SIF and Flexibility factors changing on the introduction of pressure.Consider this case of mine.

A 6" sch 40 pipe ,1.5D radius elbow.I checked the SIF using the "review SIF facility " the following were my observation

SIF Inplane = 2.26
SIF Outplane=1.888
Flexibility Factor = 6.59

The above check was with zero pressure and B31.3 as the code.Next I added a pressure of 2000KPa

SIF Inplane = 2.205
SIF Outplane = 1.837
Flexibility Factor = 6.435

I checked the following things in K-aux to be certain
a)Pressure Stiffening is None
b)Bourdon Effect is None

My Questions

1)Why is my SIF and Flexibility Factors changing on the introduction of Pressure.There is some sort of stiffening occuring?.
2)If I am correct Pressure Stiffening and Bourdon Effect settings in the K-aux do not affect the i and k values?.
3)The pressure stiffening in the config set up affects the i and k values .Maybe this is the missing link , how does it affect?.
4)SIF and Flexibility factors for a elbow are dependent on the radius of the pipe , bend radius and thickness.That means a 45 Elbow and 90 Elbow having all these paramaters same have matching k and i values?.
5)Lastly , increasing the elbow radius decreases flexibility (Loads increase) and decreases SIF (Stresses come down).

Thanks in Advance