0027/nd guidelines for Marine Lifting and Lowering Operations

19.12 
SUBSEA STORAGE TANKS 
19.12.1 
Requirements for towage or transportation to the installation site are covered in 0030/ND, Ref. [5]. 
19.12.2 
Any major compartment, whose buoyancy is required for intact or damaged stability, shall be 
pressurised to a minimum of 0.34 bar (5 psi). Compartment pressures shall be monitored for a period 
of three days prior to sailaway, immediately prior to sailaway and immediately upon arrival at the 
installation site. The method of monitoring the pressures shall be stated.
19.12.3 
Careful attention should be given to the design of the primary and secondary flooding and venting 
systems to minimise the risk of premature flooding of the main and trimming tanks. The damage cases 
considered shall include the effects of any valve failing to open or close (or stay open or closed) at any 
relevant stage. 

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GUIDELINES
 
FOR
 
MARINE
 
LIFTING
 
&
 
LOWERING
 
OPERATIONS 
0027/ND Rev 11 
 
Page 76 of 84 
19.12.4 
A dynamic lift analysis shall be carried out to identify the limiting seastates for lowering and hence 
establish the associated DAFs (Dynamic Amplification Factors). 
19.12.5 
Ideally the lowering system should be reversible though this may not be feasible for deballasting 
through the splash zone. The system should be designed to allow the storage tank to be repositioned 
on the seabed if the initial position is out of tolerance. 
19.12.6 
The floating stability and reserve buoyancy of the storage tank shall be analysed for the floating 
phases and from submergence through the splash zone to landing on the seabed. The effects of any 
cranes, winches, floating buoys and/or heave compensation systems used to control the descent 
should be considered in the analyses. The effects of the loss of any one lowering line or flooding of 
any one compartment at any stage shall be determined. If any such loss or flooding would lead to loss 
of the tank then suitable mitigation plans should be presented to GL Noble Denton for approval and be 
the subject of risk assessments to show that the risks are acceptable. 
19.12.7 
Tug movements shall be given careful consideration to reduce the probability of tank damage during 
tow or operations afloat.
19.12.8 
Initial ballasting of the storage tank will typically be carried out with the tank held in position by tugs 
about 50 to 100m away from the installation vessel. This distance selected should be sufficient to 
avoid contact but close enough for monitoring. 

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