NORSOK - U-009
Life extension for subsea systems
|Publication Date:||1 March 2011|
This NORSOK standard defines general principles for assessing an extension of service life beyond the original service life of subsea systems.
NOTE 1 This may require extension of the design life premised in the original design.
Sub-systems and components included within a subsea system are
• subsea trees (Annex B),
• manifolds (Annex C and Annex E),
• protection and support structures (Annex C),
• tethers and buoyancy aids (Annex H),
• valve stations (Annex D),
• subsea isolation valves (Annex D),
• interconnecting flowlines (Annex E),
• electrical, hydraulic, chemical and power umbilicals (Annex F),
• topsides control system modems/interface (Annex G),
• hydraulic/chemical lines (Annex E),
• subsea processing system.
The scope distribution is graphically shown in Figure 1.
NOTE 2 It should be noted that service life and design life are defined with some difference in identified standards.
Some examples are quoted here:
DNV-OS-F101:2007 Design life is the initially planned time period from initial installation or use until permanent decommissioning of the equipment or system. The original design life may be extended after a re-qualification.
ASME B31.8:2003 (Does not define a design life, but uses design life and service life as dimensional limits for design with respect to cyclic loading and cathodic protection systems).
ASME B31.4:2006 Design life is a period of time used in design calculations selected for the purpose of verifying that a replaceable or permanent component is suitable for the anticipated period of service. Design life does not pertain to the life of the pipeline system because a properly maintained and protected pipeline system can provide liquid transportation indefinitely.
The difference between service life and design life may be illustrated by the following example:
The design life of a system is 25 years. However, the system was intended to operate 15 years (limited by the reservoir predictions), and the operator applied for a 15 years permission - which becomes the original service life.
Later the operator wants to extend the service life by 5 years, for a total of 20 years. In this case the design supports the application for service life extension with respect to design life. The operator will still have to document acceptable system integrity to the end of the extended service life, and apply to the authorities.