Assessment of Existing Structures and Repairs - Offshore Structures: Design, Construction and Maintenance - page 476

TABLE 7.10 Effect of Change in Morison Coefficients on

the Average Reliability Index, Based on HSE

Date of Code Average Reliability Index

1970 - 1972 1.45

1972 - 1981 1.8

1981 - 1994 2.25

RP2A was first introduced. The maximum difference in the average reliability is
between a reliability index of 2.25 for the twentieth edition and a value of 2.32
for the eleventh edition.
To illustrate the importance of environmental loading, Table 7.10 shows the
effect on average reliability index of changes in the Morison coefficients. The
table shows that the platform reliability for the platform design in 1970 was
1.45, but it changed to 2.25 for design after 1981, so there is an increase of
about 55%. For the purposes of the table, the designs have been based on the
latest resistance formulations in the twentieth edition, and all that have been
changed are the drag and inertia coefficients.
In general, component reliability is most sensitive to environmental loading,
particularly extreme wave height.

7.7 FAILURE DUE TO FIRE
The deck of an offshore structure platform in the oil and gas industry may be
exposed to fire. So in most cases, after a fire, an assessment of the deck is
requested to determine if the deck can be used or if it needs strengthening.
There are many studies of the reduction on steel structures exposed to fire.
The analysis of catenary action in steel beams under fire conditions is based
on the field test done by Yingzhi Yin from Manchester University in 2003.
The large deflection behavior of steel beams at elevated temperatures is
what was studied.
The parametric study investigated uniform temperature effect in lateral and
axial restraint, in axial restraint only and without any restraint axially or later-
ally. According to European code EC3, steel strength will soften progressively
from 100 ° C to 200 ° C. Note that only 23% of ambient-temperature strength

remains at 700 C.

The EC1 (ISO 834) standard fire curve is shown in Figure 7.5 , which pre-
sents a different EC1 time-temperature curve.
Fire resistance times are based on standard fire tests based on ASTME84-05, not
on survival in real fires. Based on fire load and compartment properties (

°

100 m 2 )is
presented. The differences between hydrocarbon fire and external fire are shown in
Figure 7.6 .

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