Welding Technology In Offshore Structur

WELDING TECHNOLOGY IN OFFSHORE
STRUCTURE

NURUL HUSNA BINTI MAHAYUDDIN
SITI AISYAH BINTI MOHD YUSOF
NURFAEZAH BINTI MOHD HASSIM
AIDA BINTI ABD WAHIT
AQMAL ARIFFIN BIN ALIAS

2011127493
2011180123
2012248558
2011295216
2011255028

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Recently, oil and natural gas are being more actively developed throughout the world to cope with the increasing demand. A rapidly growing number of offshore structures are being built, for example, in Southeast Asia, Korea and China.
Offshore steel structures :welded structures made of homogeneous steel materials whose qualities remain stable on a lasting basis. However they require suitable measures to prevent corrosion of the steel members.
It is necessary to apply highly reliable corrosion-preventive treatment to offshore steel structures used in extremely corrosive marine environments such as splash zone and tidal zone. It has been common practice to apply corrosion-preventive organic material to them.
There are cases where corrosion-preventive metallic sheathing is applied to an offshore steel structure which is required to withstand use for an extremely prolonged periods, for example from 50 to 100 years. When this method is used, the steel structure seldom needs repair and hence, the cost of maintenance can be cut significantly. The application of metallic sheathing has been limited because the cost of the material and fabrication are higher than those of the conventional corrosionpreventive methods.
Minimizing the lifecycle cost of an off shore structure used in a highly corrosive environment, practical use metallic sheathing technology using a highly reliable and economic sea water-resistant austenitic stainless steel sheet.

1. Jacket
Function:
Stable platform for oil and gas production facilities
 Structure:
Deck supported by a steel tubular structure having its feet on the sea bed
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2. Gravity Based Structure (GBS)
 Function:
Base which supports several vertical columns which supports a deck carrying production facilities.

 Structure:
- Large reinforced concrete bottom mounted structure which uses its weight to resist environmental loads, not attached to the bottom with piles.
- Easy to adapt for oil storage since the base is large.

3. Spar
 Function:
Vertical floating oil platform typically used in very deep water which supports drilling and production activities.  Structure
 Consist of large-diameter, single vertical cylinder supporting a deck
 The family of spar consists of cylindrical, truss and cell spar.

1. Jack-up rig
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Function:

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Mainly used as exploratory drilling platforms and offshore and wind farm service platforms.

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Designed to move from place to place and anchor themselves by deploying the legs to the bottom of the ocean using a rack and pinion gear system on each leg.

 Structure
- Consist of buoyant hull fitted with a number of movable legs, capable of raising its hull over the surface of the sea. - The hull is raised to required elevation above sea surface on its legs supported by sea bed.

2. Tension Leg Platform (TLP)
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Function:
- Vertical moored floating structure or offshore production of oil or gas
- Connected to the sea bed by vertical tendons

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Structure:
- Consist of tubular steel members called tendons
- Group of tendons is called a tension leg
- Fully buoyant and restricted below floating line by mooring elements

3. Floating Production,
Storage and Offloading
Facility (FPSO)
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Function:
- Processing of hydrocarbons and for storage of oil
- Receive hydrocarbon produced from nearby platforms, process them and store oil until it can be offloaded onto tanker / transported through pipeline.

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Structure:
- Can stand in critical environmental conditions.
- Easy to install

4. Semi – Submergible Rig (SSR)
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Function:
- offshore drilling rigs
- safety vessels
- oil production platforms
- heavy lift cranes

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Structure:
- Consist of lower hulls, column, braces, decks and derricks.
- Operating deck located high above sea level
- Structural column connect to pontoons and operating deck

Main structural components of SSR

Comparison of deepwater semi-submersible and drillship

5 . Drilling ship
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Function
- Use in exploratory offshore drilling of new oil and gas wells
- scientific drilling

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Structure
- Have functional ability of SSR
- Kept stationary for long period
- Carry large pay load than SSR
- Greater mobility in contrast to SSR

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Heat generated by an electric arc to fuse metal together in the joint area.

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An arc is truck between the tip of the electrode and the workpiece and the core wire begin to melt. 

The coating of the core wire provides a protecting gas to shield the weld pool from the surrounding air.

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It is done semi-auto by handled gun. It uses shielding gas such as argon, carbon dioxide and carbon dioxide mixture, argon mixture with oxygen or helium. It uses electrode. 

Heat generated by a DC electric arc to join metals together.

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The arc is struck between a continuously fed consumable filler wire and the workpiece.

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The filler wire and workpiece are both melted in the process.

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Heat generated by an electric arc.

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The arc is struck between a non-consumable tungsten electrode and the workpiece to join them together.

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The process may be operated without filler wire or the filler wire is added by a consumable wire rod to the weld pool.

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Use arc struck between a continuously fed electrode and the workpiece. 

The metal is melted in the process and an additional filler metal is provided by a granular flux. 

The arc is submerging under the molten flux and it provides protection to molten metal against the atmosphere. ADVANTAGES

Allows easy access to restricted areas which cannot be accessed by dry underwater welding.
 Welding support equipment can be easily mobilized to site.
 Repair operations are easily planned and carried out due to welder accessibility. 

DISADVANTAGES

Reduction in ductility, impact strength and increase in porosity and hardness; surrounding water causes rapid quenching of the weld metal.  Poor visibility and the welder cannot weld properly.  Presence of large amount of hydrogen and causes embrittlement. 

ADVANTAGES
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Welder/Diver Safety; Welding is performed in a chamber.
Good Quality Welds; This method has ability to produce welds of quality comparable to open air welds because water is no longer present to quench the weld and H2 level is much lower than wet welds.
Surface Monitoring; Joint preparation, pipe alignment,
NDT inspection, etc. are monitored visually.

DISADVANTAGES
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Requires large quantities of complex equipment and much support equipment on the surface. The chamber is extremely complex. Cost is extremely high.
Work depth has an effect; at greater depths, the arc constricts and corresponding higher voltages are required.
Cannot use the same chamber for another job, if it is a different one.  Process of welding at elevated pressures,

normally in underwater.
 Hyperbaric welding can either take place wet

in the water itself or dry inside a specially constructed positive pressure enclosure and hence a dry environment.

 The applications of hyperbaric welding are

diverse—it is often used to repair;
 ships
offshore oil platforms
pipelines
 Steel

is the most common material welded.

 Used a dry hyperbaric welding which is done

in the chamber by the well-trained welder.
 at a pressure equal to the hydrostatic head at the depth of the weld.
 most hyperbaric welding is dine using saturation diving techniques.The weld are made in the dry chamber

DRY HYPERBARIC
 Exposed to the toxicity of the gas will caused to the hard-breath
 The chamber can explode if no proper safety guidance WET HYPERBARIC
 Easy to get electric shock

Offshore steel structures are welded structures made of homogeneous steel materials whose qualities remain stable on a lasting basis. They have a number of advantages over structures made of other materials, such as plenty of leeway in design and short construction period. On the other hand, they require suitable measures to prevent corrosion of the steel members.
 Corrosion-preventive coating must be repaired or renewed as required to maintain their long-term durability
 Structure builded must strong enough to overcome the environment effects such wind, wave, ice and snow, water depth and variation of sea level, current, temperature and also marine growth  The selection of steel type and its grade is important in designing the offshore structure
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Material used should have high withstand to environment conditions, should withstand force applied and should have high weldability to obtain a longer structural life
 Structural steels for offshore application can be welded by the following welding processes, SMAW (Shielded Metal Arc
Welding), GMAW (Gas Metal Arc Welding), FCAW (Flux core
Arc Welding), GTAW (Gas Tungsten Arc Welding), and SAW
(Submerged Arc Welding)
 In producing the offshore structure, excellent skilled workers are needed
 The welding processes are an important process to joint the metal permanently at a surface or in the water using various techniques 