Page 275 - Pipelines and Risers

248 Chapter 14

Bursting Model
The burst strength formulation is expressed as
Mburst(t) = APp (t) - AP- (t) (14.45)

where Apmx(t) is the annual maximum operating pressure, Ap,(t) is the pressure resulting in
bursting in year t.

The annual maximum occurring pressure in year t is expressed as a function of the operating
pressure:
AP-tt)= X~p,-A~mtt) (14.46)

where, xAp,- defines the relationship between annual maximum pressure and the average
operating pressure.

The bursting capacity of the pipeline depends on the degree of grooving corrosion, and is
modeled as:
(14.47)

where Apf is the burst pressure for uncorroded pipe, AREAo is the original area prior to metal
loss due to corrosion L. AREA is the exact area of the metal loss due to corrosion in the axial
direction of through-wall thickness. y is the factor of safety, M is the Folias factor, Q is the
spiral correction factor.

The burst pressure Apf for uncorroded pipe is:
APf = ; (14.48)
20 "wt

where D is the pipe diameter and t is the pipe thickness.

The flow stress is defined by Tresca or von Mises yield criterion as:
%ow = Xf[[*) +(3"')" (14.49)
n+ 1

where, Xf is the model uncertainty for predicting the burst capacity, n is the hardening index,
0, is the ultimate stress.