Structural
integrity assessment of pipes used in nuclear industry, oil-gas transmission
industry etc. is done by preforming fracture tests on small scale standard specimens
and full scale components. The crack growth data obtained from the fatigue and
fracture experiments are employed in determining various fracture parameters to
characterize the crack tip stress field. The unloading compliance technique is
a widely adopted technique to evaluate crack growth during fracture
experiments.  The pre-requisite for this
technique is the availability of equations correlating compliance measured
during experiments and crack length. ASTM E647-13 provides guidelines for
measurement of crack growth using compliance. ASTM E1820-11 provides the
necessary correlation between compliance and crack growth for standard
specimens namely Compact Test specimen, C(T), Disk shaped Compact Specimen,
DC(T) and Single Edge Bend specimen, SE(B). Van Minnebruggen (2011) et al. (2011)
validated the standardised test procedure described in ASTM E1820 to estimate
the ductile crack length extension from the experiments conducted on SENB
specimens made of pipeline material (Grade X65). However these correlations
cannot be used for evaluating crack growth on full scale piping components.
This is due to the fact that the equation should not only have crack length as
a function but
also the current deformation level/load level as a parameter*. Jan Džugan (2003)
proposed a modified approach using unloading compliance to estimate the crack
length in Charpy size specimens. The modification was made by introducing a function
of specimen size and specimen deformation to the compliance equation. Shen and
Tyson (2009) proposed compliance equations to estimate crack growth in Single
Edged notched Tension specimens, SE(T) incorporating the effect of rotation
during testing. Chattopadhyay et al. developed compliance correlations to
estimate crack growth in throughwall circumferentially cracked pipes subjected
to four point bending.  Compliance
correlations were derived by generating compliance versus crack length by
performing small displacement linear elastic finite element analysis. However,
it did not account for the large geometric deformation that might occur during
the loading of the specimen*. This paper studies the model proposed by
Chattopadhyay et al. and validates it by comparing the results with that of
preliminary experimental investigations on the fracture tests of four
throughwall circumferentially cracked straight pipes.