STATOIL - SIRI PLATFORM
North Sea, Danish Sector - 1999-2000

Platform
The Siri platform sits in the Danish sector of the North Sea in 180 feet of water. The platform is a purpose built jack-up structure, set on a steel storage tank and installed in 1998.

Challenge
Siri is a high-consequence, low redundancy platform. The three legs are 11.5 feet. in diameter with circumferential girth welds every 10 feet and jacking holes along their length. The legs were fabricated using a high strength steel with low fracture toughness. The wall thickness ranges from 2.5 to 4.5 inches with the transitions on the inner surface. The girth welds are ground to ensure a smooth outer surface. The presence of a sprayed aluminum coating on the outer surface of the leg hinders the use of MT inspection. Access to the inside is prevented by equipment therein. With these restraints the challenge faced by Statoil is how and when to inspect the structure.

MSL Scope
MSL is retained by Statoil as structural consultants for the Siri platform.

Platform Assessment:
MSL has undertaken ultimate strength and fatigue assessments of the platform. Fatigue life predictions are used to identify those welds requiring inspection.

  

 

 

     Siri Platform (left) with Drilling Rig

 

Reliability-based Inspection Planning:
A fracture mechanics reliability analysis model was used to predict the reliability levels of girth welds as a function of time. The inspection interval reflects a target reliability level and can be updated based on future inspection data and the POD associated with the inspection tool.

Development of the Inspection Tool:
MSL is assisting Statoil in developing an inspection tool to meet the challenge of the platform girth weld inspections.

Benefits
MSL is assisting Statoil in meeting the regulatory requirements and in developing a rational inspection plan which minimizes the life cycle cost of the facility without compromise to safety or the environment.