Audun S. KristoffersenPetroleum Safety Authority

Stavanger, Norway

Konstruksjonsdagen 2018

Petroleum Safety Authority

Structural Integrity in the

Barents Sea

Pre-study:

Establish the knowledge level relevant

for structural integrity for installations

operating in the Barents Sea

Phase 1 Phase 2 Main study:

Based on recommendations from

Pre-study

For installations operating in the Barents Sea

Simplified Risk Assessment

Events

Consequence

Uncertainty

RiskKnowledge Gaps

Workshop

Risk Assessment - Results

Risk Assessment - Results

1. Risers exposed to interaction with ice

2. Stability requirements and accidental flooding caused by ice impact

3. Uncertainty in modelling of ice loads

4. Uncertainty in factors used for ice loads

5. Uncertainty in local loads from ice

6. Ship collison with ice-strengthened vessels

• Outcome of Phase 1 was basis for Phase 2:

1.Glacial Ice Impact

2.Ice load factor calibration

Glacial Ice Impact

• Objective: Will the inherent capacity of a facility to withstand a ship impact be

sufficient to withstand an impact with glacial ice?

Performhydrodynamic

analysis

Perform Impactanalysis

Evaluate

Select Semi

Hydrodynamic Analyses

• Glacial ice and semi-submersible

Hydrodynamic Analyses

• Sea states

• Hs and Tp from a location in the Barents Sea

Hydrodynamic Analyses

Hydrodynamic Analyses

Area of impact

Impact Energy

• Impact energy reference value for requirements to ship impact assessments in

IMO MODU/NMA is 14 MJ

In present analysis ~0.94-0.98

From DNVGL-RP-C204

Impact Energy

Non-linear FE Analyses

Non-linear FE Analyses

Results

Non-linear FE Analyses

Results

Non-linear FE Analyses

Penetration

Summary

• Vertical extent of damage assumed for ship impact assessment is not

sufficient for glacial ice impact assessments

• The strengthened area may not be sufficient to withstand glacial ice impact

from the ice volumes studied herein

• Structural components assumed not exposed to ship impact may be exposed

to impact from glacial ice

• The horizontal penetration of damage may exceed 1.5 m which is the

minimum requirement for ship impact

• The pressure-area formulation used to assess glacial ice impact is associated

with uncertainty that should be considered in estimating glacial ice loads

Further Work

• Increase the understanding of ice motion in waves

• Further study components assumed not exposed to ice collision

Questions..?