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20-09-2008, 10:56 PM
Post: #1
Underwater welding
Underwater welding refers to a number of distinct welding processes that are performed underwater.

The two main categories of underwater welding techniques are wet underwater welding and dry underwater welding, or hyperbaric welding.

In wet underwater welding, a variation of shielded metal arc welding is commonly used, employing a waterproof electrode. Other processes that are used include flux-cored arc welding and friction welding. In each of these cases, the welding power supply is connected to the welding equipment through cables and hoses. The process is generally limited to low carbon equivalent steels, especially at greater depths, because of hydrogen-caused cracking.

In dry underwater welding the weld is performed at the prevailing pressure in a chamber filled with a gas mixture sealed around the structure being welded. For this process, gas tungsten arc welding is often used, and the resulting welds are generally of high integrity.

The applications of underwater welding are diverse?it is often used to repair and construct ships, offshore platforms, and pipelines. Steel is the most common material welded. For deep water welds and other applications where high strength is necessary, dry water welding is most commonly used. Research into using dry water welding at depths of up to 1000 m are ongoing. In general, assuring the integrity of underwater welds can be difficult, especially wet underwater welds, because defects are difficult to detect.

For the structures being welded by wet underwater welding, inspection following welding may be more difficult than for welds deposited in air. Assuring the integrity of such underwater welds may be more difficult, and there is a risk that defects may remain undetected.

The risks of underwater welding include the risk of electric shock to the welder. To prevent this, the welding equipment ought to be properly insulated, and the voltage of the welding equipment should be controlled. Underwater welders must also consider the safety issues that normal divers face; most notably, the risk of decompression sickness due to the increased pressure of inhaled breathing gases.

posted by christina at 11:50 AM 0 comments
Underwater welding refers to a number of distinct welding processes that are performed underwater.

The two main categories of underwater welding techniques are wet underwater welding and dry underwater welding, or hyperbaric welding.

In wet underwater welding, a variation of shielded metal arc welding is commonly used, employing a waterproof electrode. Other processes that are used include flux-cored arc welding and friction welding. In each of these cases, the welding power supply is connected to the welding equipment through cables and hoses. The process is generally limited to low carbon equivalent steels, especially at greater depths, because of hydrogen-caused cracking.

In dry underwater welding the weld is performed at the prevailing pressure in a chamber filled with a gas mixture sealed around the structure being welded. For this process, gas tungsten arc welding is often used, and the resulting welds are generally of high integrity.

The applications of underwater welding are diverse?it is often used to repair and construct ships, offshore platforms, and pipelines. Steel is the most common material welded. For deep water welds and other applications where high strength is necessary, dry water welding is most commonly used. Research into using dry water welding at depths of up to 1000 m are ongoing. In general, assuring the integrity of underwater welds can be difficult, especially wet underwater welds, because defects are difficult to detect.

For the structures being welded by wet underwater welding, inspection following welding may be more difficult than for welds deposited in air. Assuring the integrity of such underwater welds may be more difficult, and there is a risk that defects may remain undetected.

The risks of underwater welding include the risk of electric shock to the welder. To prevent this, the welding equipment ought to be properly insulated, and the voltage of the welding equipment should be controlled. Underwater welders must also consider the safety issues that normal divers face; most notably, the risk of decompression sickness due to the increased pressure of inhaled breathing gases.

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21-01-2010, 06:49 AM
Post: #2
RE: Underwater welding
hello...can u provide me the download link.
the topic seems to be interesting and new
21-01-2010, 05:57 PM
Post: #3
RE: Underwater welding

Hi,
for more details read these articles:
http://www.statemaster.com/encyclopedia/...er-welding
http://www.freepatentsonline.com/3671707.html
http://en.wikipedia.org/wiki/Underwater_welding

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05-02-2010, 07:19 AM
Post: #4
RE: Underwater welding

.pdf  underwater welding.pdf (Size: 171.52 KB / Downloads: 1883)

.pdf  Underwater-Welding.pdf (Size: 27.11 KB / Downloads: 941)

Underwater welding is a type of welding which takes place underwater.In underwater welding, the environment around the welder is wet. and uses welding equipment which has been customized for wet environment,commonly use under water techniques are hyperbaric enclosure welding, wet Underwater-welding, high pressure water jet welding, other welding processes: friction welding, resistance welding, arc welding, tig welding, mig welding, oxyacetylene welding, electron beam welding, laser beam welding,and main risks for the welder performing Underwater-welding are the potential for electric shock,and the possibility of producing in the arc mixtures of hydrogen and oxygen in pockets, which might set up an explosion,and There are three main ways to perform Underwater-welding. One is to build an enclosure, a pit, around the place of repair and to pump away all the water: that amounts to prepare the conditions for normal welding in air, although the place may be deep under sea level. Another method of Underwater-welding consists in preparing an enclosure to be filled with gas (helium) under high pressure (hyperbaric) to push water back, and have the welder, fitted with breathing mask and other protective equipment, weld quite normally out of water but under pressure. The third is the wet Underwater-welding method, where no attempts are made to dry up the location of welding. Instead the power of the arc generates a bubble of a mixture of gases which lets metal melting and joining occur more or less normally, using specially covered electrodes to avoid that too much hydrogen be absorbed in the weld. The skilled welder must also be a diver, equipped for Underwater-welding, with all the extra equipment and protection a welder must use. There is also a less used method of Underwater-welding which features a special torch which sprays a cone of high pressure water, within which protective gas under pressure insulates the weld location from the water during welding.
for presentation of Underwater welding see http://www.ece.uwaterloo.ca/~ece434/Wint...tation.ppt
16-02-2010, 07:55 PM
Post: #5
RE: Underwater welding

.pptx  UNDER WATER WELDING.pptx (Size: 164.21 KB / Downloads: 1127)
INTRODUCTION

Underwater welding is an important tool for underwater fabrication works.
In 1946, special waterproof electrodes were developed in Holland by ËœVander Willingen'â„¢.
In recent years the number of offshore structures including oil drilling rigs, pipelines, platforms are being installed significantly.

CLASSIFICATION

¢ Under water welding can be classified as :
i. Wet welding
ii. Dry welding

WET WELDING

Key technology for repairing marine structure
Welding is performed under water directly exposed to the wet environment
Increased freedom movement makes more effective, efficient and economical
Supply is connected to the welder/driver via cables or hoses
Complete insulation of the cables and hoses are essential in case to prevent the chance for electric shock
MMA (Manual Metal Arc) welding is commonly used process in the repair of offshore platforms.

PRINCIPLE OF OPERATION

The work is connected to the positive side of dc source and electrode to the negative
The two parts of the circuit are brought together and then slightly separated
An electric current occurs in the gap and causes a sustained spark which melts the bare metal forming a weld pool The flux covering the electrode melts to provide a shielding gas.
Arc burns in the cavity formed inside the flux covering, which is designed to burn slower than the metal barrel to the electrode
Advantages

The versatility and low cost.
Less costlier than dry welding.
Speed with which it is carried out
No enclosures so no time is lost for building.

Disadvantages

Rapid quenching of the weld metal by the surrounding water.
Welders working under water are restricted in manipulating arc.
Hydrogen embrittlement causes cracks.
Poor visibility due to water contaminance.

DRY WELDING

A chamber is created near the area to be welded and the welder does the job by staying inside the chamber.
It produces high quality weld joints .
The gas-tungsten arc welding process is used mostly for pipe works
Gas metal arc welding is the best process for this welding.

Scope of further developments

Hyper baric welding is well established and generally well researched.
Research being carried out for welding at a range of 500 to 1000m deep.
THOR-1 (Tig Hyperbaric Orbital Robot) is developed where diver performs pipe fitting, installs the tracks and orbital head on the pipe and rest process is automated.

APPLICATIONS

Offshore construction for tapping sea resources
Temporary repair work caused by shipâ„¢s collisions, unexpected accidents
Salvaging vessels sunk in the sea
Repair and maintenance of ships
Construction of large ships beyond the capacity of existing docks

CONCLUSION

Alternatives which include clamped and grouted repairs (which may introduce unacceptably high loading on offshore structures) and the use of bolted flanges for the tie-ins are not necessarily and are not always satisfactory
20-03-2011, 12:07 AM
Post: #6
RE: Underwater welding
Hi,this is anil from Bangalore i am requesting to you to send full report of under water welding...


Thanking You
26-03-2011, 01:11 AM
Post: #7
RE: Underwater welding
hi i need full report
26-03-2011, 10:13 AM
Post: #8
RE: Underwater welding
Presented by:
CLIND M.B


.pptx  UNDER WATER WELDING.pptx (Size: 608.87 KB / Downloads: 253)
UNDER WATER WELDING
What is under water welding?

 Under water welding is the process of welding at elevated pressures, normally underwater.
 Under water welding can either take place wet in the water itself or dry inside a specially constructed positive pressure enclosure.
TYPES OF UNDER WATER WELDING
RISKS INVOLVED
SAFETY MEASURES TO BE TAKEN

 It is unsafe to operate the torch without the flash arrestor in place. To do so may cause injury and destroy the torch.
 Do not attempt to speed up the welding by creating a fire deep inside the metal. Such a situation can lead to an explosion.
 NEVER bring a cutting torch into a cell with the oxygen on or with the welding generator running.
 Never put down or carry an electrode holder while the power is on.
 Never allow any metallic part of the diving dress to touch the work.
Advantages of wet welding
 1) The versatility and low cost of wet welding makes this method highly desirable.
 2) Other benefits include the speed. With which the operation is carried out.
 3) It is less costly compared to dry welding.
 4) The welder can reach portions of offshore structures that could not be welded using other methods.
 5) No enclosures are needed and no time is lost building.
 6) Readily available standard welding machine and equipments are used.
Disadvantages of wet welding.
ADVANTAGES OF DRY WELDING
1. Welding is performed in a chamber, immune to ocean currents. The warm, dry habitat is well illuminated and has its own environmental control system.
2. This method has ability to produce welds of quality comparable to open air welds as no water is present to quench the weld.
3. Joint preparation, pipe alignment etc can be monitored visually.
4. Non-Destructive testing is also facilitated by the dry habitat environment.
DISADVANTAGES OF DRY WELDING
1) The habitat welding requires large quantities of complex equipment and much support equipment on the surface. The chamber is extremely complex.
2) Cost of habitat welding is extremely high and increases with depth. Work depth has an effect on habitat welding.
3) At greater depths, the arc constricts and corresponding higher voltages are required. The process is costly $ 80000 charge for a single weld job. One cannot use the same chamber for another job, if it is a different one.
Scope For Further Developments
 Dry Hyperbaric welds are better in quality than wet welds. Present trend is towards automation. THOR – 1 (TIG Hyperbaric Orbital Robot) is developed where diver performs pipefitting, installs the trac and orbital head on the pipe and the rest process is automated.
 Developments of diverless Hyperbaric welding system is an even greater challenge calling for annexe developments like pipe preparation and aligning, automatic electrode and wire reel changing functions, using a robot arm installed.
 This is in testing stage in deep waters. Explosive and friction welding are also to be tested in deep waters.
31-03-2011, 12:44 PM
Post: #9
RE: Underwater welding
Principles of Operation - An extract from Underwater Welding - A Welder's Mate
Manual metal arc welding (MMA) is still one of the most important fusion welding processes, for both surface and underwater welding in today’s construction industries. American terminology refers to it as Shielded Metal Arc Welding (SMAW). The definition of fusion welding, as stated in BS 499: Pt 1 1991 states, “any welding process in which the weld is made between surfaces brought together to a molten state, without hammering or pressure”. Any arc-welding system in which the electrode is melted off to become part of the weld is described as metal-arc. Briefly, the process takes place in the following manner. The work to be welded is connected to one side of an electric circuit, via means of a cable. A flux-coated electrode is attached to a holder, also connected via a cable, both being attached to a power source. When the electrode makes contact with the work, an electrical contact is made. The electric current jumps the gap and causes a sustained spark (arc), which melts the base metal and the covering of the electrode forming a common weld puddle.
Compare the two diagrams in Figure 1 and you will notice a couple of differences for the wet welding one, namely; DC current only, the use of a knife switch and the double insulated cables. The polarity, which is generally DCSP (-), although can also work quite satisfactorily on DCRP (+), otherwise, the basic circuit is the same.
After the arc is moved or discontinued, the metal solidifies so the previously melted metal has now fused into one piece. This melting action is controlled by varying the amount of electric current which flows across the arc, and by changing the size of the electrode. Typical temperatures that exist within the arc plasma can reach over 5000ºC. As the electrode melts, metal droplets are projected into the weldpool. This common pool of molten metal is called a puddle. This puddle solidifies behind the electrode as it is moved along the joint being welded. The result is a fusion bond and the metallurgical unification of the workpieces. ~
Now, metals at high temperature are active chemically with the main constituents of air, oxygen and nitrogen. Should the metal in the molten puddle come in contact with air, oxides and nitrites (instant rust) would be formed, which upon solidification of the molten pool would destroy the mechanical properties of the weld joint. For this reason, the various arc-welding processes provide some means for shielding the arc and the molten puddle with a protective shield of gas, vapour and slag. This is referred to, as metallic arc shielding, and such shielding in MMA welding is accomplished by the flux covering of the electrode. The slag even after the weld has solidified still has a protective function, as it minimises contact of the very hot metal from the air, until the temperature lowers to a point where any reaction of the metal with air is eliminated.
The arc itself burns in a small cavity formed inside the flux covering, which is designed to burn slower than the metal barrel of the electrode, thereby, assisting in protecting and controlling the metal droplets that leave the electrode. This barrel is called the cup or barrel length. For wet welding this particular function is very important, for without this mechanism the production of acceptable weld deposition would be difficult, as it greatly assists a constant and controlled arc length to be maintained. Therefore, even in poor visibility, all the diver need do is exert a slight downward pressure on the electrode to maintain a constant feed rate, which keeps the flux chipping and burning away without the need for any arc length control, as such.
Now, for underwater welding the arc does not behave as in air. The activity of the gas bubbles being particularly important, as this tends to create a rather unstable arc condition, compared with surface welding, together with a somewhat more confusing weld puddle, which must be mastered by the diver before successful welding can take place. Apart from this, with regard to the actual physical principles of operation, there is no difference between surface MMA welding and underwater wet-stick welding. Both processes use basically the same equipment with the exception of necessary waterproofing for the electrodes and certain other safety equipment.
17-08-2011, 03:30 PM
Post: #10
RE: Underwater welding
hey can u plz give me some gud seminar file on underwater welding @
rahulpansare555[at]gmail.com
18-08-2011, 10:05 AM
Post: #11
RE: Underwater welding
To get more information about the topic "Underwater welding " please refer the link below
http://www.seminarprojects.com/Thread-un...er-welding

http://www.seminarprojects.com/Thread-un...2#pid54822
02-02-2012, 07:41 PM
Post: #12
RE: Underwater welding
pls provide to download
03-02-2012, 11:09 AM
Post: #13
RE: Underwater welding
To get more information about the topic "Underwater welding " please refer the link below
http://www.seminarprojects.com/Thread-un...er-welding

http://www.seminarprojects.com/Thread-un...2#pid54822
14-10-2012, 01:28 AM
Post: #14
RE: Underwater welding
i want the full seminar report on underwater welding.
25-12-2014, 06:01 PM
Post: #15
RE: Underwater welding
give me the full report
26-12-2014, 10:17 AM
Post: #16
RE: Underwater welding
To get full information or details of Underwater welding please have a look on the pages


http://seminarprojects.com/Thread-underw...2#pid54822

http://seminarprojects.com/Thread-underwater-welding

http://seminarprojects.com/Thread-underw...elding-ppt

http://seminarprojects.com/Thread-underw...ding--9768


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