1. NEW WELDING TRENDS
Under sea Welding process
Santhosh Kumar .S,
Venkatesh .S,
KARPAGAM INSTITUTE OF TECHNOLOGY
COIMBATORE
DEPARTMENT OF MECHANICAL ENGINEERING
2. Abstract
The process of joining together two pieces of metal-Welding is carried out by the use of
heat or pressure or both and with or without added metal-types of welding methods-under water
or under sea welding methods- 1.Dry welding 2.Wet welding. this welting process arise during
the last world war an urgent need was felt for salvaging vessels sunk into the deep sea and this
need raised the status of underwater welding from almost a pipe dream to a practical process.
Moreover international interests to develop and utilize ocean which covers 70% of the earth and
its resources such as development of offshore gas and oil field, fisheries multiplication, large
offshore construction and mineral resources, mining in sea bottom etc. have led to the
development of underwater welding. The interesting matter is an Underwater welder earns
$100,000 to $200,000.
3. Introduction How under water welding arise
Welding is a fabrication process that Russian metallurgist Konstantin Khrenov
joins metals or thermoplastics by using made the first underwater weld in 1930’s he
coalescence. Melting the work pieces and made simple experiments in his lab to bring
adding a filler material to form a pool of out the new method in welding process. The
molten material known as the weld puddle first under water welding was carried out by
that cools to become a strong joint describes British Admiralty – Dockyard for sealing
the process of welding. This is in contrast to leaking in ship rivets below the water line.
soldering and brazing which involves Underwater welding advanced through
melting of a material with lower melting World War II, particularly during Pearl
point material between the work pieces. Harbor salvage ops. Under water welding is
Welding process is many types such as Solid an important tool for underwater fabrication
state Welding-Resistance Welding- works. In 1946, special waterproof
Soldering-Oxyfuel gas welding-Brazing- electrodes were developed in Holland by
other process such as Induction welding; Van der Willingen. In 1970’s Whitey
electron beam welding, thermit welding, Grubbs and Dale Anderson of Chicago
laser beam welding and electro slag Bridge & Iron (CB&I) qualified an
welding. Other than this now there is an underwater wet welding procedure to
interesting topic that is underwater welding American Welding Society (AWS)
or undersea welding. Underwater standards. In recent years the number of
welding provides a means to assemble or offshore structures including oil drilling rigs,
repair underwater. This is a highly useful pipelines and platforms are being installed
technology available that allows repairs of significantly. Some of these structures will
ships damaged during hurricanes or wars. experience failures of its elements during
There are a couple of alternatives available, normal usage and during unpredicted
which include clamped and grouted repairs occurrences like storms, collisions. Any
and bolted flanges. However, these repair method will require the use of
alternatives do not always provide underwater welding.
satisfactory results and also introduces high
loading at offshore structures. This is a Under water Welding
highly specialized trade and most people are Hyperbaric welding is the process
employed in the oil or shipping industry and of welding at elevated pressures,
the military. normally underwater Hyperbaric welding
Underwater welding process can be can either take place wet in the water itself
classified into the following two categories: or dry inside a specially constructed positive
pressure enclosure and hence a dry
Wet Welding environment. It is predominantly referred to
Dry Welding as "hyperbaric welding" when used in a dry
environment, and "underwater welding"
when in a wet environment. The
4. applications of hyperbaric welding are welding procedures and production welding
divers. It is often used to repair ships, on materials with a relatively high carbon
offshore oil platforms, and pipelines. Steel is equivalent, up to 0.47%. The accepted
normal upper limit is 0.40% using ferritic
the most common material welded.
electrodes. The welding was carried out by a
Types of Underwater welding selected team of 20 coded wet welder divers,
who’s variety of skills and commitment to
There are two main categories in the the project was invaluable and who must be
underwater welding process which are; Wet commended. All of the wet welds were
subjected to 100% visual inspection and
Welding and Dry Welding. Wet Welding is
MPI by the client with a 100% pass rate.
performed underwater where the welding is
being done while being exposed to water.
Wet Welding is most effective as it provides Wet Welding indicates that welding is
the freedom of movement for the welder, performed underwater, directly exposed to
because of this wet welding is efficient, the wet environment. A special electrode is
economical and the most utilized choice for used and welding is carried out manually
just as one does in open air welding. The
repair work underwater.
increased freedom of movement makes wet
welding the most effective, efficient and
Wet welding
economical method. Welding power supply
Hydroweld and Underwater Technical is located on the surface with connection to
the diver/welder via cables and hoses.
Services pooled their technical and
Power Supply used: DC
administrative skills to successfully Polarity: -ve polarity
complete a contract for DML (Devonport
Management Ltd), which carry out work on Principle of Wet Welting
behalf of the MoD (Ministry of Defence).
The process of underwater wet welding
The project, the first ever of its kind,
takes in the following manner:
required the wet welding of over 40 The work piece to be welded is connected to
blanking plates to the ballast tanks of a one side of an electric circuit, and a metal
submarine, the largest being 2.6 x 1.2 electrode to the other side. These two parts
meters. The contract was completed on time, of the circuit are brought together, and then
in budget with no lost time accidents and at separated slightly. The electric current
a fraction of the cost of dry docking. jumps the gap and causes a sustained spark
(arc), which melts the bare metal, forming a
All of the wet welding was completed
weld pool. At the same time, the tip of
using Hydro weld FS wet welding
electrodes, which are the only underwater electrode melts, and metal droplets are
welding electrodes have been approved, by projected into the weld pool. During this
the MoD, for permanent and temporary operation, the flux covering the electrode
repairs to war ships. This project further melts to provide a shielding gas, which is
proved the electrodes capabilities and used to stabilize the arc column and shield
welding techniques used by Hydroweld,
the transfer metal. The arc burns in a cavity
through the successfully completion of wet
formed inside the flux covering, which is
5. designed to burn slower than the metal come in contact with the metal parts. If the
barrel of the electrode. insulation does leak, seawater will come in
contact with the metal conductor and part of
the current will leak away and will not be
available at the arc. In addition, there will be
rapid deterioration of the copper cable at the
point of the leak.
We prefer Wet Welting method for
When DC is used with +ve polarity,
Wet underwater MMA welding has now
electrolysis will take place and cause rapid
been widely used for many years in the
deterioration of any metallic components in repair of offshore platforms. The benefits of
the electrode holder. For wet welding AC is wet welding are: -
not used on account of electrical safety and 1) The versatility and low cost of wet
difficulty in maintaining an arc underwater. welding makes this method highly
The power source should be a direct current desirable.
machine rated at 300 or 400 amperes. Motor 2) Other benefits include the speed. With
which the operation is carried out.
generator welding machines are most often
3) It is less costly compared to dry
used for underwater welding in the wet. The welding.
welding machine frame must be grounded to 4) The welder can reach portions of
the ship. The welding circuit must include a offshore structures that could not be
positive type of switch, usually a knife welded using other methods.
switch operated on the surface and 5) No enclosures are needed and no time
commanded by the welder-diver. The knife is lost building. Readily available
standard welding machine and
switch in the electrode circuit must be
equipments are used. The equipment
capable of breaking the full welding current needed for mobilization of a wet
and is used for safety reasons. The welding welded job is minimal.
power should be connected to the electrode We oppose Wet Welting method for
holder only during welding.
Although wet welding is widely used for
Direct current with electrode negative underwater fabrication works, it suffers from
(straight polarity) is used. Special welding the following drawbacks: -
1) There is rapid quenching of the weld
electrode holders with extra insulation
metal by the surrounding water.
against the water are used. The underwater Although quenching increases the
welding electrode holder utilizes a twist type tensile strength of the weld, it
head for gripping the electrode. It decreases the ductility and impact
accommodates two sizes of electrodes. strength of the weldment and
increases porosity and hardness.
The electrode types used conform to AWS 2) Hydrogen Embrittlement – Large
E6013 classification. The electrodes must be amount of hydrogen is present in the
waterproofed. All connections must be weld region, resulting from the
thoroughly insulated so that the water cannot dissociation of the water vapour in
6. the arc region. The H2 dissolves in X-ray and code requirements. Most welding
the Heat Affected Zone (HAZ) and processes can be operated at hyperbaric
the weld metal, which causes pressures, but all processes suffer a
Embrittlement, cracks and reduction in capability and efficiency results
microscopic fissures. Cracks can as the pressure increases. Hyperbaric
grow and may result in catastrophic welding, using MMA (SMA), TIG (GTA) or
failure of the structure. FCAW, is the preferred process for high
3) Another disadvantage is poor integrity welds, particularly for deep water
visibility. The welder sometimes is welds, including tie-ins in pipelines and
not able to weld properly. risers in the oil and gas industries; however
GTA is the method most commonly
Dry welding method employed for hyperbaric welding
Hyperbaric Welding is the process operations.
in which a chamber is sealed around the
Risk of Dry welding
structure to be welded, and is filled with a There is a risk to the welder/diver of electric
gas (commonly helium containing 0.5 bar of shock. Precautions include achieving
oxygen) at the prevailing pressure. adequate electrical insulation of the welding
The hyperbaric welding may be one of two equipment, shutting off the electricity supply
immediately the arc is extinguished, and
types:
limiting the open-circuit voltage of MMA
A) Mini-Habitat welding - makes use of a (SMA) welding sets. Secondly, hydrogen
small, easily portable, gas-filled, often and oxygen are produced by the arc in wet
Plexiglas enclosure, which is placed over the welding.
joint by a diver. Water is displaced by an Precautions must be taken to avoid the
inert gas or air supplied from the surface. In build-up of pockets of gas, which are
potentially explosive. The other main area of
this instance welding is performed at
risk is to the life or health of the
elevated ambient pressures. Depending on welder/diver from nitrogen introduced into
the size of the enclosure, the diver is the blood stream during exposure to air at
partially immersed in water (only the diver's increased pressure. Precautions include the
hands and the welding torch are inside the provision of an emergency air or gas supply,
habitat). This method requires adequate stand-by divers, and decompression
chambers to avoid nitrogen narcosis
visibility and is limited to areas with clear
following rapid surfacing after saturation
access. The diver/welder welds with each of diving.
several MMA electrodes, positioned in For the structures being welded by wet
advance through the flexible port. underwater welding, inspection following
B) Large Habitat welding - a specially welding may be more difficult than for
designed chamber is built and positioned welds deposited in air. Assuring the integrity
around the intended weld and the of such underwater welds may be more
welder/diver enters the chamber in order to difficult, and there is a risk that defects may
undertake the work. The habitat is sealed remain undetected.
and water is excluded by introducing an
appropriate gas. Hyperbaric welding
produces high-quality weld joints that meet
7. 4) Non-Destructive Testing (NDT) –
NDT is also facilitated by the dry
habitat environment.
We oppose Dry welting for
We prefer Dry welding for 1) The habitat welding requires large
quantities of complex equipment and
1) Welder/Diver Safety – Welding is much support equipment on the
performed in a chamber, immune to surface. The chamber is extremely
ocean currents and marine animals. complex.
The warm, dry habitat is well 2) Cost of habitat welding is extremely
illuminated and has its own high and increases with depth. Work
environmental control system (ECS). depth has an effect on habitat
2) Good Quality Welds – This method welding. At greater depths, the arc
has ability to produce welds of constricts and corresponding higher
quality comparable to open air welds voltages are required. The process is
because water is no longer present to costly – a $ 80000 charge for a single
quench the weld and H2 level is weld job. One cannot use the same
much lower than wet welds. chamber for another job, if it is a
3) Surface Monitoring – Joint different one.
preparation, pipe alignment, NDT
inspection, etc. are monitored
visually.
8. Concluded as
Even through under water welding is more advantageous, there are more risk factor faced
by the workers. 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.
under water welding has it scope; Developments of diver less Hyperbaric welding system is an
even greater challenge calling for annexes 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.
