TANKER REPAIR AND LIFE EXTENSION FOR FPSO CONVERSION

Vessel Selection

The selected tanker shall not be too old as that will increase conversion cost and chances of failures will be high.The service life of the vessel can be in range of 15 to 20 years.For higher service life FPSO, its better to use new build hull.

Scope of Refurbishment Work

Refurbishment work required on the vessel's existing accommodation, fire fighting equipment, lifesaving equipment, structures, piping systems, machinery, control systems, and electrical equipment shall be carried out during the conversion period according to the following criteria:

Shop drawings, shipyard procedures, test and inspection procedures and plans, and any other fabrication/construction documentation required to perform the work shall be developed
Hull, marine, mooring, and safety systems shall be designed and built to Class rules.
Any additional classification is can be according to Marine guidance in "Role of Class for Offshore Floating Production and Offloading Structures."
Equipment identified with inherent problems or history of problems shall be replaced to ensure trouble-free operation during the design service life of the FPSO/FSO.
Existing spare parts used during the refurbishment shall be verified as supplied by the OEM and in new or as new condition.
Due consideration shall be given to which country's waters the vessel will be moored in. National content requirements, logistics, jurisdictional regulations, rules, and other specific requirements for FPSO/FSOs should be factored into decisions about repair/replacement of equipment and its future maintenance requirements.
All bulk parts/consumables for overhaul of systems shall be supplied and installed.
Equipment prone to wear down or corrode, through regular use or otherwise, shall be overhauled to "zero-time" maintenance running hours such that no major overhaul will be due during the first 3 years of the FPSO/FSO Operations.

Inclining Experiment

While alongside the wharf, with all debris, excess materials, Contractor tools, and equipment cleared from the FPSO/FSO and after all major equipment and systems are installed, inclining experiment using ballast water to simulate moment arms shall be performed.

After the experiment, following task shall be performed:

Revise existing trim and stability curves and provide a new Class-approved trim and stability book.
Prepare a revised loading manual and update the loading computer software from this data, with the appropriate Class approvals.

Dock Trial

Prior to leaving the yard,dock trial alongside a suitable wharf shall be performed; this is to verify that all ship machinery, auxiliary, control, and safety systems and equipment have been installed in accordance with relevant specifications and are safe and operable. Dock shall be suitable for testing of equipment (e.g., away from hazardous flammable materials).

Sea Trials and Inshore (Anchorage)

Sea trials undertaken shall include the following:

a)      Under full range of design operating conditions, run all main cargo pumps, ballast pumps, and sea water pumps.
b)      Stagger-test cargo tanks and ballast tanks.
c)      Test-run fresh-water generators.

Assigned Class Surveyor shall measure and mark new assigned load line for the FPSO/FSO per requirements from IMO
Vessel's ship-side shall be adequately protected from damage to the hull coating and structure while at the yard. Any damage sustained shall be repaired.
If the vessel's propulsion plant is to be used for transportation to site, a minimum 4 hour endurance test of the propulsion plant, shall be carried out.
All machinery and equipment shall be opened up, inspected, and overhauled to as-new condition or renewed.
Prior to deactivation of systems that will be retained for FPSO/FSO service or site transit, such systems shall be run-tested to identify any deficiencies in the performance or operation of the equipment. Samples of lubricating oils shall be taken for analysis and vibration readings shall be taken to assist in the evaluation of machinery condition.
Carry out a thermographic survey and megger testing of all electrical equipment. This survey and testing includes all motors and motor pot heads, switchboards, motor starter cabinets, distribution panels, etc. The megger readings shall be taken soon after equipment isolation to avoid inaccurate results.

Hull Steel Condition Survey

The inspection shall take place after appropriate blasting and cleaning to ensure that no defects are hidden by paint or scale. The scope of inspection shall cover the following items as a minimum:

Close-up visual inspection of the entire external hull structure.
Close-up visual inspection of the entire internal hull structure in all cargo, slop, ballast, fuel oil, forepeak, aft peak, pump room, engine room, and void spaces.
Close-up visual inspection of the toes of all transverse bottom webs and horizontal girders. Where these toes connect directly to an oil-tight bulkhead, they shall be tested by Magnetic Particle Inspection (MPI).
Close-up visual inspection and MPI of selective critical structural connections that may be prone to fatigue cracking. The critical connections shall be selected based on fatigue analysis results, experience with similar vessel configurations, and vessel's previous service history.
Close-up visual inspection of collar plates of all longitudinals passing through watertight or oil-tight bulkheads. A minimum of 30% of the welds shall be tested by MPI.
Ultrasonic Testing (UT) thickness measurements and close-up inspection of the entire main deck, entire keel and bottom plate, and two full-length wind and water strakes—port and starboard, particularly at ballast and fully loaded waterlines.
UT thickness measurements and close-up inspection of all horizontal stringers and longitudinal girders, including the centerline girder.
UT thickness measurements and close-up inspection of all transverse bulkheads.
UT thickness measurements and close-up inspection of three entire transverse girth belts in each tank.
Detailed measurements and pit mapping of all areas of significant pitting to side shell, bottom and main deck, and in cargo, slop, and ballast tanks, voids, pump room, and machinery spaces.
Close-up inspection of all erection welds and MPI of any suspect welds.
UT thickness measurements and close-up inspection of all seachests and bilge well plating.
Any additional tanks and structure as considered necessary by Class and Company.
On arrival in the conversion yard, all tank bottom plates, including the turn of the bilge, shall be fully blasted to Sa 3 or better and cleaned within 4 weeks of arrival to allow a detailed visual inspection and mapping of the condition of the bottom plating.

Hull Steel Renewals

The following equation shall be used when determining the vessel's required steel renewal thickness, at time of conversion, that will result in achieving the required design life. Plate shall be renewed if its measured thickness is less than: Rule required thickness * (1 − 0.75 * allowable wastage)+ [(F(P)SO service life − X) * annual anticipated corrosion rate]
Bottom plating shall be renewed as defined by the steel renewal criteria, including wasted bottom plating in way of tank suction bell mouths. Repair of bottom plate pitting and grooving, etc. in cargo, ballast, and slop tanks may use a combination of steel renewals and weld repairs. The scope of work will typically cover, as a minimum, the Weld up all grooves.Gouge and re-weld external weld seams. Weld repair all remaining pitting that is distributed through the cargo and slop tanks and that is not repaired by bottom plate renewals.
In general, typical members requiring partial replacement include bulkhead horizontal stiffeners, bottom longitudinal face bars, horizontal stiffeners in way of bottom transverse web frames, webs of side shell and longitudinal bulkhead stiffeners, and longitudinal stiffeners and face bars, as well as ladders, platforms, and ladder handrails. Staging erected within the tanks for cleaning, close-up survey, and in preparation for blasting and coating applications shall be employed for steel replacements, where practicable.
In general, members requiring renewal typically comprise web frame face bars, web frame brackets, under deck longitudinal stiffeners, face bars on under-deck stiffeners, web plates of side shell and longitudinal bulkhead stiffeners, at drain holes, and flat bar stiffeners.
All pump and machinery foundations and deck plating shall be checked and renewed as required. The scope of work will typically cover, All pump and machinery foundations
Failure Modes and Effects Analysis (FMEA) shall be performed on appropriate systems to identify actions that could eliminate or reduce the chance of a potential failure (e.g., offloading system, DP system).
All known cracks shall be repaired in drydock during conversion. Repair of cracks is more difficult once the facility is producing.
All failed coatings shall be repaired or renewed.
Mechanical/electrical equipment, subsystems (e.g., Uninterruptible Power Supply [UPS], Distributed Control System [DCS], etc.) that cannot be supported by Manufacturer or approved Service Company, in the region where the vessel will be operating, shall be renewed.

Structural Steel

Application: Hull girder—deck plate, side shell plate, bottom plate, frames, girders, longitudinals, transverse and longitudinal bulkheads, major machinery foundations, and all other hull structural steel

All structural steel shall have the steel thickness forecast over the design life. Corrosion thickness forecasts shall be actual thickness, minus the assumed corrosion rate times the design life. Corrosion thickness forecasts shall consider plate fields, full plate, Hull Section Modulus, bands across structure, and any other combination relevant from a structural standpoint.
Assumed corrosion rates for all internal surfaces (including those to be coated during the conversion) shall be based on the mean of the range given for "General" rates for uncoated surfaces.

Deck plating, side shell plating within 3.0 m (9.84 ft.) of main deck, deck longitudinals, and deck webs (uncoated on tank side) shall use 0.2 mm/yr (0.00787 in./yr) as a minimum corrosion rate.
Side shell plating at least 3.0 m (9.84 ft) from main deck shall use 0.1 mm/yr (0.00394 in/yr) as a minimum corrosion rate.
The corrosion rates for single-hull vessels and double-hull vessels shall follow Class requirements.
Sampling of all major types of erection joints during the baseline inspection, with emphasis on erection joints incorporating "through bulkhead" stiffeners.
Inspecting specifically for groove corrosion along welds on longitudinal bulkheads and on transverse bulkheads where horizontally stiffened. The grooving is usually easily picked up on the non-stiffened side of the bulkhead, but can also be noted on the stiffened side.
Emphasizing any bulkheads previously exposed to ballast water.

Fatigue Life Issues

The fatigue analysis shall comply with the following:

For inspectable/repairable areas:

Utilize a minimum safety factor of 5 for critical structures .
Utilize a minimum safety factor of 2 for noncritical structures.

For non-inspectable/non-repairable areas:

Utilize a safety factor of 10 for critical structures
Utilize a safety factor of 5 for noncritical structures and for FPSO/FSO turret/mooring attachments.

Include evaluation of low-cycle fatigue.

The fatigue analysis shall identify areas where structural details require a higher level of inspection.

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Critical structures are those that, in the event of failure, could lead to loss of structural integrity, loss of life, or significant hydrocarbon release.Structure and details that do not satisfy the fatigue life requirements shall be modified and/or renewed as necessary to obtain the minimum fatigue life.

All Pipe Systems

Prior to departing the yard, pressure tests shall be performed to 1.5 times the Maximum Anticipated Working Pressure (MAWP) that reflects the likely operating scenario or per Class requirements. For example, the offloading line, crude oil wash line, and slop lines shall all be pressure tested at the same time, if procedures allow them to operate concurrently.
The existing pipe material and wall thickness shall be evaluated against field life. For an extended field life, in-service repairs may be necessary; however, this shall be avoided during peak production period.

Pipes, supports, and couplings that fail or show excessive deformation shall be repaired/renewed.

· All main deck piping shall be renewed.

Any cargo lines that transition through a ballast tank shall be rerouted.

Diesel Engines

Application: Generator drivers, emergency generators, fire pumps, etc.

Crankshaft deflections shall be recorded prior to commencement of work and on completion of all work, with vessel in a similar ballast/empty condition.
External visual inspection shall be conducted.
Review of maintenance history shall be performed.
Review of Manufacturer's maintenance schedule, based on running hours, shall be performed.
Internal visual inspection of all running surfaces, crankcase, gears, turbo chargers, and air coolers, etc., shall be conducted.
Calibration of all components (e.g., pistons, liners, valves, running gear, bearings) shall be performed.
Calibration, setting, and testing of safety devices shall be performed.
Inspection of governors shall be conducted.
Alignment and load tests shall be conducted.
Vibration test shall be conducted.
Confirmation that all specialized tools are available and in good condition shall be provided.

If any part, sub-unit, or assembly does not satisfy Manufacturer's recommended tolerances, then the part, sub-unit, or assembly shall be replaced.
All consumable items (e.g., "O" rings, gaskets, piston rings, valve plates, springs, bearings, seals, gland packing, flexible hoses) shall be renewed.
Vibration test results shall be within Manufacturer's or ISO 8528 recommended criteria, whichever is the most stringent.
If spares are not available from original Manufacturer or reputable Supplier, then the unit or sub-unit shall be replaced.
Resilient mountings shall be renewed.

Turbine Equipment

Application: Cargo and ballast pump drivers, auxiliary generators, feed pumps, inert gas fans—not including main propulsion turbines

External visual inspection shall be conducted.
Review of maintenance history shall be performed.
Review of Manufacturer's maintenance schedule, based on running hours, shall be performed.
Internal visual inspection of all turbine casing, gearbox, gears, etc. shall be conducted.
Calibration of all components, turbine blades, nozzles, seals, bearings, gear backlash, etc., shall be performed.
Calibration, setting, and testing of safety devices shall be performed.
Confirmation that all specialized tools are available and in good condition shall be provided.
Measurement and submission of all turbine and bearing clearances shall be provided
Prior to closure of casings, all drain holes shall be proven clear
Inspection of governor and synchronizing motor shall be conducted, if applicable.
Vibration test shall be conducted.
Alignment and load tests shall be conducted.

If any part, sub-unit, or assembly does not satisfy Manufacturer's recommended tolerances, then the part, sub-unit, or assembly shall be replaced.
Vibration test results shall be within Manufacturer's or ISO 7919 and ISO 10816 recommended criteria, whichever is the most stringent.
All consumable items (e.g., "O" rings, gaskets, piston rings, valve plates, springs, bearings, seals, gland packing) shall be renewed.
For generators, the steam regulating valve oil cylinder, linkages, and cam shaft shall be overhauled to new condition.
If spares are not available from original Manufacturer or reputable Supplier, then the unit or sub-unit shall be replaced.
Turbine Blades shall be replaced according to the following criteria:

If a blade's diminution is 20% or greater of original blade thickness, the blade shall be replaced.
If 30% or more of the total number of blades require replacement, then a total blade replacement shall be required.

Main Propulsion

Application: Diesel or turbine

As required by Classification Society, if Project Design Basis does not include that the vessel will be towed to site.
If main engine is not needed, then the engine block may remain, but all piping and ancillary equipment shall be removed.

Single Hull Cargo and Ballast Tank Corrosion Rates

1)      The individual wastage allowances are acceptable, provided the hull girder section modulus (SM) is not less than 90% of the hull girder SM required.
2)      Corrosion rates are total rates for plating or members exposed from two sides.
3)      The corrosion rates shall be used in the equation above to determine the vessel's required steel renewal thickness, at time of conversion, that will result in achieving the required design life.