According to and RD 10-249-98 section 5.1 and 5.2, the greater factor of initial elliptical cross-section is set
absence of data for actual initial ellipticity of bent pipe cross-sections
based on observation (for example,
during projection stage), two
analyses must be run: one with
a=0% and another with the greater value of a, based
on manufacturing specifications or according to the manufacturer
(see section 22.214.171.124).
Factor is used for:
bend wall thickness pressure analysis
bend stress analysis
considering the "bourdon effect" in bends (bend straightening under pressure)
mind that according to RD
10-249-98 section 126.96.36.199, initial ellipticity a should
be increased 1.8 times for low-temperature pipelines. This
is automatically taken into account when analyzing using RD 10-249-98 section 5.2.
In addition, according to section 188.8.131.52, if initial ellipticity is less than 3%, ellipticity is not considered in stress analysis. This is not automatically considered in START-PROF.