Structural integrity

The structural integrity of offshore installations underpins the safety of all offshore workers. All the surface equipment and processes are mounted on large towers (mainly of a lattice nature) most of which are underwater and are pinned to the seabed. Other floating structures also are used. The surface equipment (including accommodation) is housed in large structures which sit on these towers.

The structural integrity has to be designed to withstand:

• large waves (in excess of 25m in the northern North Sea)
• impact from vessels
• earthquakes.

Structural integrity must be maintained throughout the lifetime of the installation by an appropriate management system of inspection, analysis and repair.

• Structural integrity strategy
  Sets out the OSD five-year strategy (2008-2013) in relation to the major hazards threat to the safety of offshore installations from loss of structural integrity.
• Technical policy relating to foundations and geotechnics for offshore installations in the UKCS
• Technical policy relating to extreme weather hazards
• Technical policy relating to seismic event hazards
• Technical policy relating to behaviour under explosion hazards
• Technical policy on safety case assessment relating to structural integrity
• Technical policy relating to structural integrity management (fixed structures)
• Technical policy relating to structural degradation and deterioration (including aspects of ageing)
• Jack-up (self-elevating) installations: rack phase difference
  (Offshore Information Sheet 4/2007) Draws the industry's attention to previous findings on rack phase difference (RPD) in truss legs of jack up (self-elevating) installations.
• Ageing semi-submersible installations
  (Offshore Information Sheet 5/2007) Deals with the ageing processes that affect the structure of semi-submersible installations. Some of these processes will also apply to marine systems.
• Technical policy relating to structural response to ship impact
• The role of an offshore metocean adviser
  (Offshore Information Sheet 1/2008) Meteorological and oceanographical matters concerning offshore installations and operations. The sheet gives one example of good practice in how dutyholders can deal with these matters, by the setting up of an appropriately informed role referred to in this guidance as a 'Metocean Advisor'.
• Jack-up (self-elevating) installations: review and location approval using desktop risk assessments in lieu of undertaking site soils borings
  (Offshore Information Sheet 3/2008) guidance on when a desk-top risk assessment may be undertaken in lieu of a detailed geotechnical site investigation. It also details the requirements for such an assessment.