SCHOOL OF MARITIME STUDIES Form no : 08/02
Date : 15/02/2012
VELS UNIVERSITY Issue no : 02/12
THALAMBUR Rev. no : 00
WELDING TYPES, DESTRUCTIVE AND NON-DESTRUCTIVE TEST ON WELDED MATERIALS
AIM:
To study about Welding types, destructive and non-destructive test on welded materials.
WELDING :
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing
fusion, which is distinct from lower temperature metal-joining techniques such as brazing and soldering, which
do not melt the base metal. In addition to melting the base metal, a filler material is often added to the joint to
form a pool of molten material (the weld pool) that cools to form a joint that can be as strong as the base
material. Pressure may also be used in conjunction with heat, or by itself, to produce a weld.
MANUAL METAL ARC WELDING
Shielded metal arc welding (SMAW), also known as manual metal arc welding (MMA or MMAW), flux
shielded arc welding or informally as stick welding, is a manual arc welding process that uses a consumable
electrode covered with a flux to lay the weld.
An electric current, in the form of either alternating current or direct current from a welding power supply, is
used to form an electric arc between the electrode and the metals to be joined. The work piece and the electrode
melts forming the weld pool that cools to form a joint. As the weld is laid, the flux coating of the electrode
disintegrates, giving off vapors that serve as a shielding gas and providing a layer of slag, both of which protect
the weld area from atmospheric contamination.
Because of the versatility of the process and the simplicity of its equipment and operation, shielded metal arc
welding is one of the world's first and most popular welding processes.
Shielded metal arc welding equipment typically consists of a constant current welding power supply and an
electrode, with an electrode holder, a 'ground' clamp, and welding cables (also known as welding leads)
connecting the two
GAS TUNGSTEN ARC WELDING
Gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG) welding, is an arc welding process
that uses a non-consumable tungsten electrode to produce the weld. The weld area is protected from
atmospheric contamination by an inert shielding gas (argon or helium), and a filler metal is normally used,
though some welds, known as autogenously welds, do not require it. A constant-current welding power supply
produces electrical energy, which is conducted across the arc through a column of highly ionized gas and metal
vapors known as a plasma.
GTAW is most commonly used to weld thin sections of stainless steel and non-ferrous metals such as
aluminum, magnesium, and copper alloys. The process grants the operator greater control over the weld than
SCHOOL OF MARITIME STUDIES Form no : 08/02
Date : 15/02/2012
VELS UNIVERSITY Issue no : 02/12
THALAMBUR Rev. no : 00
competing processes such as shielded metal arc welding and gas metal arc welding, allowing for stronger,
higher quality welds.
The equipment required for the gas tungsten arc welding operation includes a welding torch utilizing a non-
consumable tungsten electrode, a constant-current welding power supply, and a shielding gas source.
GAS METAL ARC WELDING
Gas metal arc welding (GMAW), sometimes referred to by its subtypes metal inert gas (MIG) welding or metal
active gas (MAG) welding, is a welding process in which an electric arc forms between a consumable wire
electrode and the work piece metal(s), which heats the workpiece metal(s), causing them to melt, and join.
Along with the wire electrode, a shielding gas feeds through the welding gun, which shields the process from
contaminants in the air. The process can be semi-automatic or automatic. A constant voltage, direct current
power source is most commonly used with GMAW, but constant current systems, as well as alternating current,
can be used. There are four primary methods of metal transfer in GMAW, called globular, short-circuiting,
spray, and pulsed-spray, each of which has distinct properties and corresponding advantages and limitations
To perform gas metal arc welding, the basic necessary equipment is a welding gun, a wire feed unit, a welding
power supply, a welding electrode wire, and a shielding gas supply.
FLUX-CORED ARC WELDING
Flux-cored arc welding (FCAW or FCA) is a semi-automatic or automatic arc welding process. FCAW requires
a continuously-fed consumable tubular electrode containing a flux and a constant-voltage or, less commonly, a
constant-current welding power supply. An externally supplied shielding gas is sometimes used, but often the
flux itself is relied upon to generate the necessary protection from the atmosphere, producing both gaseous
protection and liquid slag protecting the weld. The process is widely used in construction because of its high
welding speed and portability.
SUBMERGED ARC WELDING
Submerged arc welding (SAW) is a common arc welding process. The molten weld and the arc zone are
protected from atmospheric contamination by being "submerged" under a blanket of granular fusible flux
consisting of lime, silica, manganese oxide, calcium fluoride, and other compounds. When molten, the flux
becomes conductive, and provides a current path between the electrode and the work. This thick layer of flux
completely covers the molten metal thus preventing spatter and sparks as well as suppressing the intense
ultraviolet radiation and fumes that are a part of the shielded metal arc welding (SMAW) process
SAW is normally operated in the automatic or mechanized mode, however, semi-automatic (hand-held) SAW
guns with pressurized or gravity flux feed delivery are available. The process is normally limited to the flat or
horizontal-fillet welding positions (although horizontal groove position welds have been done with a special
SCHOOL OF MARITIME STUDIES Form no : 08/02
Date : 15/02/2012
VELS UNIVERSITY Issue no : 02/12
THALAMBUR Rev. no : 00
arrangement to support the flux). Deposition rates approaching 45 kg/h (100 lb/h) have been reported — this
compares to ~5 kg/h (10 lb/h) (max) for shielded metal arc welding. Although currents ranging from 300 to
2000 A are commonly utilized, currents of up to 5000 A have also been used (multiple arcs).
ELECTROSLAG WELDING
Electro slag welding (ESW) is a highly productive, single pass welding process for thick (greater than 25 mm
up to about 300 mm) materials in a vertical or close to vertical position. (ESW) is similar to electro gas welding,
but the main difference is the arc starts in a different location. An electric arc is initially struck by wire that is
fed into the desired weld location and then flux is added. Additional flux is added until the molten slag,
reaching the tip of the electrode, extinguishes the arc.
The wire is then continually fed through a consumable guide tube (can oscillate if desired) into the surfaces of
the metal workpieces and the filler metal are then melted using the electrical resistance of the molten slag to
cause coalescence.
The wire and tube then move up along the workpiece while a copper retaining shoe that was put into place
before starting (can be water-cooled if desired) is used to keep the weld between the plates that are being
welded. Electroslag welding is used mainly to join low carbon steel plates and/or sections that are very thick. It
can also be used on structural steel if certain precautions are observed.
This process uses a direct current (DC) voltage usually ranging from about 600A and 40-50V; higher currents
are needed for thicker materials. Because the arc is extinguished, this is not an arc process
TYPES OF WELD TESTING
The majority of weld testing and inspection can be separated into two categories: destructive testing, and non-
destructive testing. We will be taking a look at some of the more commonly used methods.
One method that could fall into either category is load testing
NON-DESTRUCTIVE TESTING
There are numerous methods of NDT, some are reasonably simple, but others require specialist operators and
expensive equipment, such as
1. Radiographic inspection
2. Dye penetrants
3. Fluorescent test
4. Radiographic Inspection
SCHOOL OF MARITIME STUDIES Form no : 08/02
Date : 15/02/2012
VELS UNIVERSITY Issue no : 02/12
THALAMBUR Rev. no : 00
Radiographic inspection is one of the most thorough methods of NDT. It is quite expensive to carry out,
especially on items where the radiographic machinery needs to be bought to site to do an inspection. Common
uses of radiographic inspections are safety critical items such as pressure vessels, lifting equipment, and high
pressure pipe works. The two types that are used for weld inspections are X-ray and Gamma-ray.
DYE PENETRANT
Visible dye penetrant is a NDT (Non Destructive Testing) method. It is a simple test to perform, and a good
way to test welds before carrying out more expensive techniques like x-ray testing. It will show up bad cold
lap, cracks, holes... basically any defects where a very fine dye can penetrate, hence the name. It can be used for
various things, not just weld testing.
The surface is first cleaned using an volatile cleaner and degreaser. A fluorescent dye is then applied and a
certain time allowed for it to enter any flaws under capillary action. Using the cleaning spray, the surface is then
wiped clean. An ultra violet is shone on the surface, any flaws showing up as the dye fluoresce.
The more commonly used dye penetrant method is similar in application. The more commonly used dye
penetrant method is similar in application. The surface is cleaned and the viscosity penetrant sprayed on. After a
set time the surface is again cleaned. A developer is then used which coats the surface in a fine white chalky
dust he dye seeps out and stains the developer typically a red colour.
FLOURESCENT PENETRANTS
Fluorescent penetrants contain dyes that fluoresce when exposed to ultraviolet light. Theses fluorescent
penetrant systems are more sensitive than visible red penetrant systems. A disadvantage to this kind over visible
penetrants is a dark area and an ultraviolet light are required to see the indications, so a dedicated testing area is
required.
DESTRUCTIVE TESTING
Destructive testing is usually a cheaper method of inspection. It lends its self to mass produced parts, where
sacrificing one or two components for testing is acceptable. It is quite useful for setting up welding equipment.
It is also a good learning tool during training courses, as it allows the students to do lots of testing at minimal
cost, and is often easier to understand than some of the NDT methods.
The two most common tests used in training are
1. Macro Etch testing, an
2. Root and Face bend testing.
MACRO ETCH
SCHOOL OF MARITIME STUDIES Form no : 08/02
Date : 15/02/2012
VELS UNIVERSITY Issue no : 02/12
THALAMBUR Rev. no : 00
Macro etch testing allows the tester to see a cross section of the weld, and see the arrangement of the grains in
the parent metal and the weld material. This is known as its Macrostructure. Its can also show up defects such as
porosity, inclusions and poor fusion. You need minimal equipment to perform a macro etch test. Firstly, it
involves cutting a sample from the welded joint. Cold cutting methods are best for this, such as a bandsaw.
Then the surface needs to be polished. File away any burrs and rough marks, then use progressively finer grades
of emery until a smooth even polish is obtained.
ROOT AND FACE BEND TESTS
Root and face bend tests are another simple low cost method of testing. It gives very simple to understand
results and will show any signs of poor fusion or weaknesses such as porosity within the weld. There are
numerous variations on this method; we will look at one of the most simplest methods.
Whether the sample piece is bent root up or root down decides whether it is a root or face bend test, with the
root on the outside of the bend, in tension that would be a root bend test.
RESULT:
Thus Welding types, destructive and non-destructive test on welded materials is studied.
