Civil Engineering Reference
In-Depth Information
Design is intended to be based on the wave period within the recommended
range producing the worst effect.
7.3.9 Deck Air Gap
In the early editions of the HSE code, no detailed guidance was given on air
gap, other than where the second and third editions stated that the maximum
crest elevation from the 50-year wave was required for calculating the clearance
height of the superstructure.
However, the fourth edition has a subsection devoted to the topic. The notes
state that the air gap should be based on an assessment of the probability of encoun-
tering extreme wave crests of return period greater than 50 years, but the air gap rela-
tive to the design extreme wave crest elevation should never be less than 15 m.
Further guidance is given for structures with large-diameter members that diffract
waves (D/L
>
1/5) and that may increase the maximum crest elevation.
7.3.10 Historical Review of Major North Sea Incidents
Knowledge of major offshore incidents serves a precautionary function in design.
The Piper Alpha disaster had a major effect on the development of offshore
design, particularly in the North Sea. The repercussions following any major inci-
dent inevitably lead to changes in design guidance and practice. Where fatalities
occurred, as on Sea Gem, Alexander Kielland and Piper Alpha, the changes in
practice have been far-reaching.
Table 7.3
summarizes the major incidents.
TABLE 7.3
Major Incidents for Fixed Offshore Structures
Date
Platform
Type of Incident
1965
Sea Gem
Jack-up collapse due to brittle fracture; fatalities
1974
Auk A
Collision damage to platform
1976
Heather A
Jacket damaged by pile driving
1978
Transworld 58
Semi-sub fatigue damage to critical member
1980
Alexander
Kielland
Semi-sub capsize because of loss of column resulting from
fatigue damage; fatalities
1984
Ninian
Damage due to fabrication defect in primary structure
1984
Claymore
Damage due to fabrication defect in subsea brace
1988
Piper A
Platform collapse due to fire and explosion; 167 fatalities
2003
Various
platforms
Platform damage and some failures in GoM due to Hurri-
cane Lilli
2004
Temsah
Platform collapse and fire
Search WWH ::
Custom Search