Offshore Structures Oil Rigs Offshore Platforms Stationed Platform - - PowerPoint PPT Presentation

Offshore Structures

Offshore Platforms

Wind Turbines Stationed Platform FPSO Oil Rigs Over bridges

Offshore Structure – Typical Layout

Atmospheric zone : Above splash zone, continuously exposed to air. Splash zone (0 – 5 m) : The zone alternately in and out of the water because of the tides, wind wave and waves Tidal zone (4 - 7 m) : Section between minimum low tide and maximum high tide. Submerged zone : The region below the tidal zone including sea water, sea bottom and buried mud zone.

Figure : Typical Corrosion rate of steel in offshore condition

Zone Thickness loss per year ( microns) Immersion 100-175 Splash 200-400 Atmospheric 75-175

Table: Offshore Corrosion rate in term of loss of thickness of steel per year.

Splash Zone : Difficult To Protect

• Sea water salinity
• Dry & Wet spell
• High Humidity
• O2 Concentration.
• Currently density of waves

Highly Corrosive Environment : Contributing factors

Splash Zone – Difficult To Protect

• Erosion: High & continual wave wind action

Temperature Fluctuation : Subzero to 35 – 40 °C Abrasion : Drill pipes and coatings, boat landing etc.

COATING SELECTION FOR OFFSHORE STRUCTURE

Resistant towards Offshore Corrosive Environment (The main environmental factors that affect the coating property are temperature extremes and thermal cycling, relative humidity, wet/dry cycling, PH extremes, Ultra Violet exposure, marine organism etc) Compatible With Substrate and Surface Preparation Compatible With Cathodic Protection Compliance With Regulatory Requirements (a coating system must not have any chemicals or pigment in its formulation that is banned to be used in offshore.) Cost

Splash Zone

 Any coating used must

be quite rugged and also quite resistant to aggressive environment.

 Since the part is exposed to dry and wet cycle, partially coated surface

can be exposed to sea water imparting high level of chlorides and wetness to the intermediate coat.

 Coating system therefore can be that which can be preferably applied

in a single coat for higher thickness and should have low curing time so that it cures fully before the wet spell attacks the member.

 Surface tolerant epoxies with thickness of around 400 microns.  Glass flake reinforced polyesters of around 750-1000 microns  Glass flake reinforced epoxy with total DFT of 800-1000 microns  Ultra-high build epoxies with total DFT of 2000-3000 microns  Thermal spray metallic coatings  Bituminus wrappings from which the wrapping material usually is

glass fibre. Befrore wrapping the steel is coated with a coaltar of bituminus primer.

Glass Flake Polyester Coatings

Isopthalic Based Polyester Coating 100% Solventless System Can be applied at 90% RH Applied on Sa2½ Blasted Surface Applied by Airless Spray for 800 um in one single coat. High Curing time. Both Surface preparation and application of coating can be finished in Low tide to High tide duration.

Advantage of this system

 Good tough & highly corrosion resistant.  Can be applied in single coat to a thickness more than 800-1000m.  Cures in less than 20 minutes in normal temperature of 30oC.  Can be coated in 90% RH  Has impact and abrasion resistance  Has UV and weathering resistance

Seashied



CLEANING



The area to be protected must be cleaned and be free from: Marine growth, Loosely adhering coating, Rust, Tight rust laminates



This may be achieved by using:

 Hand tools such as wire brushes, scrapers, etc  Air or hydraulically driven tools  High pressure water jetting  Wet abrasive blast cleaning



PRIMING THE SURFACE



All areas of exposed steel or concrete pile should be examined after

• cleaning. If the steel surface is pitted and the pits are more than 2mm in

depth the surface should be primed with Prempaste S105. Application can be achieved by gloved hand or by roller for larger areas.

SUB SEA APPLICATION

After Before

After 21/2 year

After 3 years After 6 years

Performance

• f

Jacketed Seashield

Protective coating System for Submerged Zone

 Coating and Cathodic Protection.  Initially for such a system coal tar epoxy was applied on

a Sa21/2 prepared surface up to DFT of 400m

 It has now been changed to epoxy system.

Coating system must have the tendency to displace the water from surface and adhere to it. One of the viable solution in maintenance coating is to apply amine adduct epoxy system with DFT of around 600 microns in two coats using good roller brush after removal of all marine growth and blasting the surface to get a minimum profile of 50- 75 microns. However, still underwater system are not giving desired service life and hence further development is required to achieve better properties when applied underwater.

Epoxy Diamine reaction

• Epoxy adhesion: Strong polar bond formation with surface in contact.
• Dry Surface: Polar bond displaces air
• Under water: Polar bond displaces water from the surface
• Hydrophobic hardeners preferred: Phenalkamines and Polyamides.
• Solventless (100% solids coatings) : Underwater curing
• No water miscible components
• No air or solvents required for curing process

Running Underwater Curing Products

Product Alocit 28.15 Epoxy coating Euronavy ES323 Chemco RA 500 Scubapox 1715 Chugoku Manufacturer Alocit Systems Euronavy ChemCO Scubapox Chugoku Marine Paints Colour Grey, White, black white Grey, Yellow Grey Blue, Grey, Black Mix Ratio 5:1 5:1 4:1 1:1 50:50:3 Coverage (250 mils) 1.35 m2 6.5 m2 5.7-6.3 m2 6.66 m2 0.60 l/m2 Curing Schedule (320C) Touch dry – 4 hours, Full cure – 7 days Touch Dry – 24 hours Touch dry -4 hrs hard dry-15 hours- Full cure – 7 days Hard dry - 7.5 hours Application Method Airless Spray, Brush, Roller Power Roller, Brush Airless Spray Brush , Trowel, Spatula Spatula , Trowel DFT application thickness 220 microns 200 microns per coat

• Min. 250

microns 300 -600 microns 600 microns

WHY TO MODIFY CURING AGENTS?

Curing agents are modified for a number of reasons. Some of these are:

• To lower viscosity,
• To increase compatibility with the resins,
• To increase the rate of cure,
• To get desirable pot life
• To minimize migration to the surface
• To avoid or minimize formation of carbamates or

bicarbonates (blushing),

• To increase toughness or plasticity.

For this amines are modified as:

• Amine adducts with epoxies
• Ketimines
• Mannich bases etc

UNDERWATER COATING Specification

• Underwater curing
• Surface tolerance properties
• Environmental friendly
• Fill surface irregularities
• Edge retention

Edge retention Diver applying coating underwater

Key Performance Parameters

MAINTENANCE ACTIVITIES

Diesel Tank below Helideck – Prior to Painting Diesel Tank below Helideck – After Painting

MAINTENANCE ACTIVITIES

Main deck to Cellar deck ladder – Prior to Painting

Main deck to Cellar deck ladder – After Painting

MAINTENANCE ACTIVITIES Underside Cellar deck – Prior to Painting Underside Cellar deck – After Painting

MAINTENANCE ACTIVITIES

Conductors from Cellar deck to Spider deck – Prior to Painting

Conductors from Cellar deck to Spider deck – After Painting

MAINTENANCE ACTIVITIES

Spider deck / Splash Zone / MSL Zone – Prior to Painting Spider deck / Splash zone / MSL zone – After Painting

MAINTENANCE ACTIVITIES

Unmanned Platform – After Painting

Helideck Underside – After Painting

MAINTENANCE ACTIVITIES

Group Headers – Prior to Painting Group Headers – After Painting

MAINTENANCE ACTIVITIES

Scaffolding of entire unmanned N 5 – Prior to Painting Generator Room – After Painting

Thanks