undeerwater welding

TERM PAPER/SEMINAR on Title: Underwater Welding

Submitted to

Amity School of Engineering and Technology

Guided By: Submitted By: Mr. Shubham Sharma Omnish Singhal A2305413093 13093

AMITY UNIVERSITY UTTAR PRADESH
GAUTAM BUDDHA NAGAR

Declaration by the student
I, Omnish Singhal, student of B.Tech (MAE) hereby declare that the project titled “Underwater Welding” which is submitted by me to Department of Mechanical and Automation Engineering, Amity School of Engineering and Technology, Amity University Uttar Pradesh, Noida, in partial fulfillment of requirement for the award of the degree of Bachelor of Technology in Mechanical and Automation, has not been previously formed the basis for the award of any degree, diploma or other similar title or recognition.
The Author attests that permission has been obtained for the use of any copy righted material appearing in the Dissertation / Project report other than brief excerpts requiring only proper acknowledgement in scholarly writing and all such use is acknowledged.

Signature

Noida

Date Name and Signature of Student

Certificate by the Faculty Guide
This is to certify that Mr. Omnish Singhal, student of B.Tech. in Mechanical and Automation has carried out the work presented in the project of the Term paper entitle "Underwater Welding" as a part of First year programme of Bachelor of Technology in Mechanical and Automation from Amity School of Engineering and Technology, Amity University, Noida, Uttar Pradesh under my supervision.

Name & signature of the faculty Guide Amity School of Engineering and Technology, AUUP

INDEX
S.No.
Particulars
Page No.
1.

Introduction

6-7
2.

Classification Of Underwater Welding

7-9
3.

Arrangements For Underwater Welding

9-11
4.

Risk Associated With Underwater Welding

11
5.

Characteristics of a Good Underwater Welding

12
6.

Application of Underwater Welding

12

7.

Developments in Underwater Welding
13

8.

Underwater Welding- Future Scope of Research
13-14

9.

References
14-15

ABSTRACT
Welding is an unavoidable process of modern engineering. Underwater welding is an important tool for underwater fabrication works and installations. It joins metals and thermoplastics. The forming a pool of molten mass and allowing it to cool to become strong joints is called underwater welding .Since this welding is performed under water directly exposed to the wet environment .If damaged ships are to be repaired, underwater welding is the basic technology to be used. It is highly specialized profession- more employed in the oil or shipping industry and also in the defence operations.
My paper presentation deals with the welding parameters of Underwater Welding with Present Status and Future Scope. In this welding we have discussed about classification, operation principle, advantage, disadvantage and scope of further developments. Some risks are discussed in context to the existing welding techniques. In this section, a few welding techniques has discussed in detail. Finally, the scope of further research has been addressed.

1. INTRODUCTION
Welding processes have become increasingly important in almost all manufacturing industries and for structural application. Although, a large number of techniques are available for welding in atmosphere, many of them cannot be applied in offshore and marine application where presence of water is of major concern. In this regard, it is relevant to note that, a great majority of offshore repairing and surfacing work is carried out at a relatively shallow depth, in the region intermittently covered by the water known as the splash zone. This is predominantly because of the fact that the probability of failure is maximum at a shallow depth of water because of maximum collision probability between the ship and platform. Though, numerically most ship repair and welding jobs are carried out at a shallow depth, most technologically challenging task lies in the repairing at a deeper water level, especially, in pipelines and occurrence/creation of sudden defects leading to a catastrophic accidental failure.
The advantages of underwater welding are of economical nature, because underwater-welding for marine maintenance and repair jobs bypasses the need to pull the structure out of the sea and saves much valuable time. The main difficulties in underwater welding are the presence of a higher pressure due to the water head under which welding takes place, chilling action of the water on the weld metal (which might change the metallurgical structures and properties), the possibility of producing the arc mixtures of hydrogen and oxygen in pockets, which might set up an explosion, and the common danger sustained by divers, of having nitrogen diffused in the blood in dangerous proportions. Furthermore, complete insulation of the welding circuit is an essential requirement of underwater welding. In practice, the use of underwater wet welding for offshore repairs has been limited mainly because of porosity and low toughness in the resulting welds. With appropriate consumable design, however, it is possible to reduce porosity and to enhance weld metal toughness through micro structural refinement. Hence, welding in offshore and marine application is an important area of research and needs considerable attention and understanding where, many problems are still unsolved. In the present review, a brief understanding of the problems in underwater welding will be discussed in context to the existing welding techniques. Detailed description of a few advanced welding techniques has also been made. Finally, the scope of further research would be recommended.

2. CLASSIFICATION
Underwater welding can be classified as
1) Wet Welding
2) Dry Welding

2.1 Wet welding
It is carried out directly at ambient water pressure with the welder/diver in the water using water-proof stick electrode and without any physical barrier between water and welding arc. Special precaution should be taken to produce underwater arc to protect it from surrounding water. Wet welding does not need any complicated experiment set up, it’s economical and can be immediately applied in case of emergency and accident as it does not need water to be evacuated. However, difficulties in welding operation due to lack of visibility in water, presence of sea current, ground swells in shallow water and inferior weld qualities (increased porosities, reduced ductility, greater hardness in the heat affected zone, hydrogen pick up from the environment) are the notable disadvantages of wet welding technique.
2.2 Dry welding
Dry welding in underwater may be achieved by several ways:
a. Dry habitat welding
Welding at ambient water pressure in a large chamber from which water has been displaced, in an atmosphere such that the welder/diver does not work in diving gear. This technique may be addressed as dry habitat welding.
b. Dry chamber welding
Welding at ambient water pressure in a simple open-bottom dry chamber that accommodates the head and shoulders of the welder/diver in full diving gear.
c. Dry spot welding
Welding at ambient water pressure in a small transparent, gas filled enclosure with the welder/diver in the water and no more than the welder/diver’s arm in the enclosure.
d. Dry welding at one atmosphere
Welding at a pressure vessel in which the pressure is maintained at approximately one atmosphere regardless of outside ambient water pressure.
e. Cofferdam welding
Welding inside of a closed bottom, open top enclosure at one atmosphere.
Underwater welding in a dry environment is made possible by encompassing the area to be welded with a physical barrier (weld chamber) that excludes water. The weld chamber is designed and custom built to accommodate braces and other structural members whose centerlines may intersect at or near the area that is to be welded. The chamber is usually built of steel, but plywood, rubberized canvas, or any other suitable material can be used. Size and configuration of the chamber are determined by dimensions and geometry of the area that must be encompassed and the number of welders that will be working in the chamber at the same time. Water is displaced from within the chamber by air or a suitable gas mixture, depending upon water depth and pressure at the work site. Buoyancy of the chamber is offset by ballast, by mechanical connections and chamber to the structure, or by a combination of both.
Dry welding requires a pressurized enclosure having controlled atmosphere. Weld metal is not in direct contact with water. Advantages of dry welding are improvement in stability of welding operation, reduced hydrogen problem, lower quench rate of the weld and base metal and restoration of weld strength and ductility. Dry welding may be carried out under high pressure, which consists of 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. Limitations of hyperbaric welding are the practical difficulties in sealing the chamber and increase in pressure as weld depth increases leading to problem which affects both the weld chemistry and microstructures.

3. ARRANGEMENTS FOR UNDER WATER WELDING
The arrangement for under water welding is shown.
For under water welding, DC machine is used as it is safer to use the AC. The voltage requirements for satisfactory welding are lower than for AC and if it is used, then it is difficult to maintain the arc under water. Therefore, DC equipment is readily mounted on the board ship. Negative polarity is preferred. This means that 65-75% of the heat is in the metal being welded. The weld pool is easier to handle and has enough fluidity to fill in undercut to a large extent. When DC is used with positive polarity, electrolysis will take place and cause rapid deterioration of any metallic components in the electrode holder. Current settings for under welding are commonly higher than for welding in air. The power source should be rated at 300-400Amps. Motor generated machines are most often used for wet welding. The welding machine frame is grounded to the ship. The welding circuit includes a positive type switch; usually a knife operated type on the surface and operates by the operator when the welder commands through the telephone. The switch in the circuit must be capable of breaking the full current and is used for safety reasons. The welding power should be connected to the electrode holder only during welding.
Special welding electrode holders with extra insulation against the water are used. Electrode holder utilizes a twist type head for gripping the electrode. It accommodates two sizes of electrodes.
Electrodes with special insulation are used for under water welding. A commonly used electrode type is AWS E6013 classification (American Welding Society). For become water proofing special coated with a layer of cellulose nitrate, wax or varnish. It is also done by wrapping the electrodes with a water proof type or by dipping it in special sodium silicate mixer and allows them to dry. During welding time, these coatings are easily dissolved. Commercial electrodes are available.
An essential requirement for under water welding is the complete insulation of the welding circuit so that the electrode cannot come in contact with the water. If the insulation does leak, sea water comes in contact with the metal conductor and part of the conductor current will leak away and will not be available at the arc. In addition, there will be rapid deterioration of copper cable at the point of leak. The work lead should be connected to the piece being welding within three feet (0.9m) of the point of welding.

4. RISKS ASSOCIATED WITH UNDERWATER WELDING
There is a risk to the welder/diver of electric shock. Precautions include achieving adequate electrical insulation of the welding equipment, shutting off the electricity supply immediately the arc is extinguished, and limiting the open-circuit voltage of MMA (SMA) welding sets. Secondly, hydrogen and oxygen are produced by the arc in wet welding.
Precautions must be taken to avoid the build-up of pockets of gas, which are potentially explosive. The other main area of risk is to the life or health of the welder/diver from nitrogen introduced into the blood steam during exposure to air at increased pressure. Precautions include the provision of an emergency air or gas supply, standby divers, and decompression chambers to avoid nitrogen narcosis following rapid surfacing after saturation diving.
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.

5. CHARACTERISTICS OF A GOOD UNDERWATER WELDING
The characteristics of a good underwater welding process are:
(a) Requirement of inexpensive welding equipment, low welding cost, easy to operate and flexibility of operation in all positions.
(b) Minimum electrical hazards, a minimum of 20 cm/min welding speed at least.
(c) Permit good visibility.
(d) Produce good quality and reliable welds.
(e) Operator should be capable in supporting himself.
(f) Easily automated.

6. APPLICATION OF UNDERWATER WELDING
The important applications of underwater welding are:
(a) Offshore construction for tapping sea resources.
(b) Temporary repair work caused by ship’s collisions or unexpected accidents.
(c) Salvaging vessels sunk in the sea.
(d) Repair and maintenance of ships.
(e) Construction of large ships beyond the capacity of existing docks.
(f) Maintenance of the pipe lines deep inside the water.

7. DEVELOPMENTS IN UNDER WATER WELDING
Wet welding has been used as an underwater welding technique for a long time and is still being used. With recent acceleration in the construction of offshore structures underwater welding has assumed increased importance. This has led to the development of alternative welding methods like friction welding, explosive welding, and stud welding. Sufficient literature is not available of these processes.

8. UNDERWATER WELDING – FUTURE SCOPE OF RESEARCH
Considerable research effort has been made to improve process performance and control strategies for the various underwater welding processes over the last half century. However, there are still many problems to overcome. The major efforts on research and development should be focused on the following topics:
(a) Automation of the underwater joining and inspection of the welded structures.
(b) Mechanized underwater welding for actual usage of very large floating structures.
(c) Investigation of the potential of using a robot manipulator for underwater ultrasonic testing of welds in joints of complex geometry.
(d) Application of advanced welding technique, like friction, laser welding and understand the behavior of materials after the welding and process optimization.
(e) Invention of new welding techniques and explore the possibility of its application in underwater welding.
(f) Generation of research data book on weld ability of materials during underwater welding

9. REFERENCES
1. Blakemore, G. R. (2000): Underwater Intervention 2000 – Houston, Jan 24-26.
2. Chen W, Zhang X, et al. (1998): Proc SPIE, Vol. 3550, pp. 287–297.
3. Khanna, O. P. (2004): A Textbook of Welding Technology, Dhanpat Rai Publications (P) Ltd., N. Delhi, India.
4. Oates W. A. (ed.) (1996): Welding Handbook, Vol. 3, American Welding Society, Miami, USA
5. Shida, T., Hirokawa, M. and Sato, S. (1997): Welding Research Abroad, Vol. 43, No. 5, pp. 36.
6. Duley W. W. (ed.) (1999): Laser Welding, John Wiley & Sons, Inc., N. York, pp. 1
7. DuttaMajumdar, J. And Manna, I. (2003): Sadhana, Vol. 28, pp. 495.
8. Farson D, Ali A, Sang Y. (1998): Weld Res Suppl., Vol. 77, No.: 4, pp. 142–148.
9. Haddad, G. N., Farmer, A. J. (1985): Weld. J., Vol. 64, No. 12, p. 339-342
10. Hugel H, Matthias G, Muller G, et al. (1999): Proc SPIE, Vol. 3571, pp. 52–60
11. Chen HB, Li L, Brookfield DJ, et al. (1993): Multifrequency fiber optic sensors for in-process laser welding quality monitoring. Proc NDT E Int., Vol. 26, No. 2, pp. 268–274.
12. Dawas, C. (ed.) (1992): Laser Welding, Mc. Graw-Hill, N. York.
13. Kruusing, A. (2004): Optics and Lasers in Engineering, Vol. 41, pp. 329–352.
14. Lancester, J. F. (1987): The Physics of Fusion Welding – Part I: The Electric Arc in Welding, IEE Proc., Vol.134, pp. 233-254
15. Ogawa Y, Irie T, Ono Y, et al., (1998): Proceedings of the 17th OMAE

References: 2. Chen W, Zhang X, et al. (1998): Proc SPIE, Vol. 3550, pp. 287–297. 3. Khanna, O. P. (2004): A Textbook of Welding Technology, Dhanpat Rai Publications (P) Ltd., N. Delhi, India. 4. Oates W. A. (ed.) (1996): Welding Handbook, Vol. 3, American Welding Society, Miami, USA 5 6. Duley W. W. (ed.) (1999): Laser Welding, John Wiley & Sons, Inc., N. York, pp. 1 7 8. Farson D, Ali A, Sang Y. (1998): Weld Res Suppl., Vol. 77, No.: 4, pp. 142–148. 9 10. Hugel H, Matthias G, Muller G, et al. (1999): Proc SPIE, Vol. 3571, pp. 52–60 11