Areas covered
Inspection approach
Propeller
Visual inspection of propeller blade, propeller boss, stern tube.
Check for damage, corrosion, erosion/cavitation, oil leakage, cracks etc.
Rudder
Attachments of rudder (if applicable) to be cleaned and examined.
Visual inspection of welding, rudder blades, attachments, paint, bearing
Units permanently on location may be exempted from measuring the clearance of the rudder bearing.
Moonpools and turrets
The extent of the survey in the moonpool area should be clearly identified showing any areas that are inaccessible for survey
4.5 Self-elevating units/Jack-ups 4.5.1 Introduction This section starts by introducing the two separate surveys as DNV GL has defined to cover the bottom survey. Subsequently the scope of each of these is detailed further. Conclusively, the section defines how to proceed for units for a period more than 5 years on location.
4.5.2 Separate surveys Different from floating units, the hull (deckbox) of a jack-up structure is elevated above sea and fully accessible for inspection during operation. At the same time the legs are available when the jack-up is in transit mode with legs fully elevated. With due regard of this specific situation, DNV-GL has organized the bottom survey in two parts (ref OSS-104, Pt. 7, Ch. 3, Sec. 2.3): 1) Bottom survey; covering external hull/deckbox 2) Spudcan-leg survey; covering spudcans and the underwater areas of legs, together with their connections The separation gives more control in planning and execution of the survey, at the same time provides a clear overview of the unit’s (inspection) status. It is underlined that these surveys taken together complement the statutory bottom survey as defined by the different regulations as defined in 2.1.
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In a typical situation on location, the separate bottom survey can be completed while the spudcan/mat is partly or fully obscured below mud line. In this situation, the separate bottom survey can be completed (and credited) where the spudcan-leg survey remains pending.
With acceptance from the Flag, drydock in line with Section 3.3 and the referred OSS-104 paragraph, the spudcan-leg surveys shall postponed till the next rig move1,2.
4.5.3 Hull/Deckbox The deck box bottom and side surfaces are normally subject to general visual inspection when the jackup is in elevated mode. Alternatively the bottom survey may be carried out dry during transit if the jackup is placed on a barge or in water by divers when in floating mode, ref. requirements given in Table 7. The following areas of the structure and the following scope shall be carried out during the survey:
Table 7 Normal Bottom survey of self-elevating units Areas covered
Inspection Approach
Visual inspection of hull, external
Visual inspection of the deck box from boat or adjacent platform.
plate areas
Alternative inspection by divers when in floating/transit mode.
Corrosion protection (CP)
Visual check of the anodes, since the upper hull is usually out of the water the CP system is usually inoperative.
Sea valves
These can normally be opened from inside while the rig is in operation.
Legs down to the splash zone
Full closing of valves is to be checked.
Visual survey from the hull.
4.5.4 Leg and Spudcan Leg and spudcan become available for inspection when the unit is in transit mode and is therefore normally inspected separately from the hull when lifting the legs. Table 8 specifies the scope of this survey.
1
The next due date taken from the date when the survey was due
2
For all clearness, it is noted that the interval of the spudcan-leg survey is equal to the traditional bottom survey, i.e. two times in any five (5) year period, with an interval not exceeding three (3) years between examinations. Page 15 of 17
Table 8 Normal Survey Scope Leg and Spud Can Survey Areas covered
Inspection Approach
Legs
General visual inspection of legs d uring jacking operation.
Connections between vertical chords and braces/diagonals are checked together with racks and rack plate welding.
Spudcans
Around the pin holes in cylindrical legs
Leg-well structure
Jacking gear support structure
ROV/diver inspection of the underside of the spudcan to look for gross deformation.
Visual inspection around piping penetrations
Visual inspection of the spudcan from the outside, alternative check of spudcan bottom from the inside, if access from outside is not possible
Legs – lower part
Spudcan and mat internal structure in way of leg support
The lower part of the leg, i.e. up to level 4 (in way of the
Leg / spudcan connection
lower/upper guides in transit) and leg / spudcan connection is to be visually surveyed.
Corrosion protection
Visual inspection of galvanic (sacrificial) anodes above sea level when in transit condition
Visual inspection of a representative amount of galvanic (sacrificial) anodes by diver or ROV when in other than transit condition
Alternative - potential measurements to evaluate efficiency of the cathodic protection system when in elevated mode.
To be taken at different levels and sides of the leg to confirm sufficient coverage.
4.5.5 Long-term operation at location Self-elevating units planning for long term operations on location beyond 5 years shall be designed as permanently installed self-elevating units for the site specific environmental and soil conditions in accordance to DNVGL-OSS-104, Pt. 7, Ch. 6. A separate approval process for UWILD applies for this condition.
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APPENDIX A
EXAMPLE OF PLAN DOCUMENT - TABLE OF CONTENT
The following figure represents a table of content of a plan document to be used for UWILD planning.
1. Introduction 1.1. Main Project/Vessel Particulars
Vessel Name:
Vessel Type:
Flag:
Class:
Vessel Owner / Operator:
Field:
Field Operator:
Vessel Location
Vessel Summer Draft
Water Depth:
Project Launch Date:
2. Survey Procedure & Scope 2.1. General Short description of scope, DNV GL’ s role/supervision, use of vendors 2.2. Planning 2.3. Hull Conditions Damage/leaks/corrosion/coating 2.4. Weather/sea condition limitations 2.5. Cleaning methods hull/sea-chest 2.6. Use of Support vessel/Divers/ROV/CCTV etc. 2.7. Diving/ROV company 2.8. Items to be inspected 2.9. NDT methods to be used if required 2.10.
Recording of survey and findings
2.11.
Approval of vendors to be used
3. Project Team Responsibilities 4. General 4.1. Client /OIM/etc. Description of equipment/tools to be used Procedures to be used to ensure safety during inspection Risk assessment Project Procedures & Reference Documents - o0o -
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