Page 287 - Pipelines and Risers

260 Chapter 15

The Bilby-Cottrell-Swinden Dislocation Model is for an embedded crack in an infinite body.
For other geometry and crack shapes, it is necessary to introduce the elastic compliance
factor, Y (or called geometry function Y). Rearranging the equation and introducing Y as
described by Heald et al. (1971), stress intensity factor (SIF) K can be written as:

(15.9)

In this chapter, geometry functions for a surface crack in plates by Newman and Raju (1981)
are used. For the wide plate under combined tension and bending, the stress intensity factor K
is the sum of tension and bending terms:
F F 6M
+ H---;-& (15.10)
fit

where factors F, Q and bending correction factor H are given by Newman and Raju (1981).

Solutions for bending moment M and uniaxial tensile stress (T in a dented pipe are given by
Shannon (1973). These complex functions can be approximately represented by the following
relationships:

(15.11)

M=0.85~~tDd (15.12)

where:
OH = nominal hoop stress
Dd = dent depth.

Substituting (T and M into Equation (15.10), we get:

(15.13)

Therefore, the geometry function, Y, can be expressed as:
+5.1 H (+))
Y = -y 1.(%) (15.14)
1-
I6

The material fails when the following critical condition is satisfied
K=K,t (15.15)

in which Kmt is related to the Charpy energy C,.