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The Marine Growth Sensitivity Study (MGSS)

THE MARINE GROWTH SENSITIVITY STUDY (MGSS)

The structural benefits associated with marine growth control are dependent on the platform configuration, environmental loading, engineering practice and various other factors.

Studies have generally shown that hard fouling increase drag force and subsequently the overall wave force / hydrodynamic loading. However, there are no specific studies in quantifying the structural benefits of controlling marine growth on offshore platforms.

What are the direct structural benefits in controlling marine growth on offshore platforms?

With the aid of an international design house, IEV conducted a ‘Marine Growth Sensitivity Study’ (MGSS) to quantitatively establish the local and global structural benefits, namely base shear, axial load, fatigue life and reserved strength ratio (RSR), of controlling marine growth on offshore structures.

The MGSS was conducted for three typical jacket configurations, tripod, 4-legged jackets and 8-legged jackets; actual surveyed growth profiles attained from (respectively) Thailand, Vietnam and Indonesia, were considered in the study.

BASE SHEAR
The analysis for the four-legged jacket shows with complete removal of marine growth from the first bay of all structural elements including conductors, the base shear force is reduced by up to 16%.

PILE AXIAL LOAD
Pile loading on the 4-legged jacket is reduced by 6% with the removal of marine growth from the first bay of conductors and by 13% with the removal of marine growth from the first bay of all members.

For the 8-legged jacket, the pile axial load reduction range from 2% (with marine growth removal from first bay of the conductors) to 5% (with marine growth removal from the first bay of all members).

FATIGUE
Fatigue assessment conducted for connections at the wave zone and mudline shows that with complete removal of marine growth from the first bay of all members, the fatigue life of the respective connections improved by up to 60% and 100%.

Should removal of growth be extended to the second bay, the fatigue life of the connections is enhanced even further; i.e. up to 110% and 180% respectively.

SUMMARY
The results show that there are direct structural benefits of preventing marine growth on offshore platforms and other marine structures such as jetties. It also showed that removal of marine growth by diver is less effective and the reduction in environmental loading (i.e. base shear) achieved is far less compared to IEV’s marine growth control technology.


PILE AXIAL LOAD REDUCTION

MGR Cases Reduction in Pile Axial Load 
4 Legged 8 Legged
1st Bay – Conductors 5.5% 2.4%
1st & 2nd Bay – Conductors 8.8% 3.8%
1st Bay – All Members 12.9% 5.3%

 

RESERVES STRENGTH RATIO IMPROVEMENT

MGR Cases RSR Improvement (%)
Tripod 4 Legged 8 Legged
1st Bay – Conductors 11% 7% 4.2%
1st & 2nd Bay – Conductors 18% 11.1% 7%
1st Bay – All Members - 17.0% 8.7%

 

1ST BAY MGR TRADE OFF BENEFITS

MGR Case Jacket Configuration Allowable Increment in Growth Thickness
Operating Storm
1st Bay of Conductors

Tripod

4 Legged

8 Legged

65%

35%

38%
67%

35%

42%
1st Bay of All Members 4 Legged

8 Legged
105%

125%
105%

130%