Welding qualities

1. Quality Control
Quality: Degree of goodness.
Quality Control: It is the Engineering and management activities by which we can
measure the quality characteristics of the product, compare them with
standards/specifications and take appropriate remedial actions wherever there is deviation
of actual products w.r.t standard/specification.
Quality Assurance: Confidence given on the product of quality achieved is as
per standard/specification.

2. Project site- Quality procedure
Vs
Documentation
a) QAP (Quality Assurance Plan) : It is a document which reveals the
stage wise inspection process, by which a particular product is inspected. For
Ex; Starting from Incoming raw material inspection , fabrication, erection,
alignment,WQT, welding, until final painting.
QAP also suggests the Quantum & Class of checks, measuring instrument
required, reference document, format of record,
a) WPS(Welding Procedure Specification): This document defines the
process of welding procedure of a particular material, which includes all
welding parameters such as Joint design,Material
specification,filler/Electrode , Position of weld,pre heat,post heat, Shielding
and backing gas used,Electrical chracteristics,Weld cleaning methods etc.
c) EWS(Erection Welding Schedule): It gives detail of Welding, Quantum of
NDT and PWHT requirements.

3. WELDING
Welding is the process of bridging the gap
between two similar or dissimilar, metals or
nonmetals with or without applying pressure,
adding filler or without adding filler.

4. Types of Welding
Basically there are two different types of
Welding.
1) Pressure Welding
2) Fusion Welding

5. 1)Pressure Welding
The Welding takes places under pressure
and either with or without additional heating.
The material is brought into plastic state and
fillers are not used. Here are some methods.
1) Spot welding
2) Flash welding
3) Resistance welding

6. Fusion welding
The joint of the two components are formed
in the fluid state by external heating (gas,
electric) with adding filler metals. This
method is widely used in construction
industries. Some methods are
1) SMAW (MMAW)
2) MIG
3) TIG (GTAW)
4) SAW

7. SAW
In Submerged Arc welding (SAW), the arc is buried
under a granular flux bed. The noise, light and fumes
generated are submerged in the flux. SAW uses a
consumable electrode.
The tip of the electrode and weld zone are surrounded
and shielded by the molten flux which is used in the
granular state. It is an Automatic Welding process which is
widely used in production shops.

8. SMAW
Shield Metal Arc Welding:
In this method, the electric arc is drawn between the tip of
an electrode and the metal being welded. The electrode
has a metal core covered by a coat of flux. The electrode
is used up as the work piece is welded. The flux shields the
metal ions in the arc (Molten weld pool) from the
atmosphere and ensures arc stability. As the flux
decomposes, it produces airborne gases and a slag
blanket is formed to protect the hot weld metal from the
atmosphere as it cools.

9. GMAW
The Gas Metal Arc Welding (GMAW) is also known as
Metal Inert Gas Welding (MIG). In this type of welding, a
continuous solid wire is supplied through the welding gun
from the wire feeder. Shielding is provided by argon, helium
or a mix of these with Carbon dioxide. No slag is produced,
since no flux is used. It is a Semi automatic
process.
Its main advantage is its speed. More productivity can be
achieved.

10. GTAW
• Gas Tungsten Arc Welding (GTAW) is also known as
Tungsten Gas Inert Gas Welding (TIG). Here the electric
arc is established between the work piece and the
tungsten electrode. In contrast to SMAW, it is a non
consumable electrode process. The arc is protected by a
shielding gas commonly argon or helium, which
displaces atmospheric gases from the weld zone.
The arc can fuse two metals without adding of filler.
A hand held filler can be used to melt and fill any gaps.
The welding produces no slag, but produces small
amount of fumes which when inhaled are hazardous.

12. Joint weld detail
Root Opening
Groove Face
Bevel
Angle
Groove Angle
Root edge
Root face

13. NDT
Non Destructive Testing :
It is a testing technology based on applied physics. It is a method of identifying
material for any flaws or discontinuities without damaging their physical structure.
The complex products and new materials that are developed and available in
market need freedom from defects and assurance for trouble free performance.
On the contrary, NDT plays a vital part in judging the product service life.
There are basically five methods of NDT. These are the follows.
1.Visual Test (VT)
2. Radiography Test (RT)
3. Ultrasonic Testing (UT)
4. Liquid Penetrant Test(LPI)
5. Magnetic Particle Inspection(MPI)

14. Visual Inspection
This is the most preliminary stage of NDT.
Visual test is an important inspection, easy to perform as well as very effective.
For ex. In welding, visual examination is very much necessary before proceeding
with the next NDT stages.
We can check the surface defects such as un-uniform weld appearance, surface
undercuts, surface porosity, uncleaned surfaces including foreign particles such as slag
and spatters on the welds.
Similarly in equipments or pressure vessels such as boiler pressure parts, the visual
examination helps in finding any surface dents, corrosive areas, painting defects etc.

15. Radiography Test
Radiography is a non-destructive testing tool widely used in industry. Its capability to
penetrate into opaque materials especially, steel is remarkable. As the need for
engineering materials of high quality increased with the dawn of Nuclear age,
radiography attained very great importance.
Radiography employs the penetrating capacity of ionizing radiation like X-rays or
Gamma rays to produce a shadow of the internal condition of jobs on a recording
medium. The record in a film is known as Radiography.
Its unique advantage over other NDT method is that it presents a permanent record,
simple to read out. Its greatest handy cap is its hazardous nature of harmful radiation
and the recurring cost involved.
Basic requirements for radiography are
a) An enclosure or a cordoned area to operate the equipment.
b) X-Ray source (X-Ray Machine) or Gama Ray source (Radio Isotopes)
c) Recording medium like X-ray film and accessories to handle and process them.
d) Evaluating equipments like illuminator and the knowledge of RT standards.

16. Radiography
X-Ray
Object
Cassette or film holder
Film
d
t

17. Radiography Isotopes
Some frequently used radio isotopes are
1) Radium 226.
2) Cobalt 60.
1) Cesium 137.
2) Iridium 192.
3) Thulium 170.
Though Iridium192 is the isotope used widely in India.

18. Radiography Techniques
There are four techniques of radiography.
1) Single Wall, Single Image.
2) Double Wall, Double Image.
3) Double Wall, Single Image.
4) Panoramic Radiography.

19. Single wall technique
A B
A
B
C
C
D
D
FILMS : A-B, B-C, C-D, D-A

20. Double Wall Technique
Source
Weld joint

21. Panoramic Exposure
Source

22. Radiography Isotopes
Iridium192 is the isotope used widely in industry.
Source Half Life
Iridium 192 74.4 days
Cobalt 60 5.27 years
Thulium 170 127 days
Cesium 137 33 years

23. Latent Image & Film processing
• Latent Image
The silver bromide grains in the emulsion layer when exposed to
radiation (X rays or Gama rays) are ionized by these radiations and a latent image
is formed on the film. The latent image in film is noticeable only after developing
the film.
. Film processing:
The purpose of film processing is to transform the invisible latent image to permanent
visible image. There are four main stages involved.
1) Developing: The creation of the visible image.
2) Fixation: The removal of unexposed silver halide.
3) Washing: The removal of fixation products.
4) Drying: The removal of unwanted water.

24. RADIATION DETECTION AND
MEASUREMENT
DOSIMETER : To measure the dose or
dose rate (Roentgen)
SURVEY METER : To measure the Intensity
Of Radiation
DENSITOMETER : To judge the density of
Film.

25. Ultrasonic Test
• Mechanical vibrations which have frequency higher than the audible
range of human ear viz.20 to 20KHz are called Ultrasonic waves.
When the waves are passed on to any object, it reflects back from its
another end, if there is discontinuity in between the waves reflect back
without moving further, thereby indicating the defect.
Most common modes of propagation of ultrasonic waves are;
• 1. Longitudinal waves: The waves generated are parallel to the
direction of propagation. These waves are readily used in liquids and
gases as well as in elastic solids.
• 2.Transverse waves: The waves generated are perpendicular to the
direction of propagation.
• 3. Surface/Rayleigh waves: The waves travel along with the flat or
curved surfaces . It is used for checking the soundness of surfaces.

26. Major variables in UT
• Probes: It works on the theory of Piezo electric effect. The piezo electric crystal in
the probe develops electric charges when pressure is applied. This vibration in turn
develops sound waves of high frequency which penetrates into the material.
• Reference blocks: Ultrasonic inspection is basically comparison process and
requires the use of ref blocks for calibration of the equipment and probe set up before
put to use on actual job.
The calibration is done with standard reference blocks. The calibration of set up is
done to check the following:
a) Time base
b) Linearity
c) Resolution
d) Sensitivity
e) Beam path
f) Probe Index

27. Normal
Probe
Angular
Probe

28. Distance Amplitude curve
DISTANCE
Initial echo
Defect Indication
Backwall echo
A
M
P
L
I
T
U
D
E
20%
50%
80%

29. Inspection methods
UT can be performed by
a)Pulse echo method
b)Through transmission method
c)Resonance method
Pulse echo is widely used in industries. Pulse echo method
can be accomplished by longitudinal, shear, surface waves. In this
method short bursts of ultrasonic energy(pulse or wave brackets) are
introduced into the test piece at a regular interval of time.If the pulses
encounter the reflecting surfaces/ Discontinuities, some or all of the
energy is reflected.

30. No Defect

32. SMALL DEFECT

34. Liquid penetrate testing
This is a method to detect surface as well as sub surface defects. In
industrial components surface defects can be visually checked upto an
extent with assistance of magnifying glasses. But in case of surface cracks
it is difficult to detect by VT, so here DPT comes in picture.
Principle: The surface defects like crack , porosity are bleeded with penetrant,
which has the property to penetrate any voids. Developer exposes the
discontinuities by its reverse capillary action.
Following steps are involved:
a) Surface preparation
b) Application of the penetrant
c) Controlling time for penetration
d) Removal of excess penetrant
e) Application of developer
f) Observation of developing process
g) Interpretation and evaluation
h) Post cleaning.

35. Magnetic Particle Inspection
It is used to detect the surface/sub surface defects. MPI is a technique used
for inspecting ferromagnetic material. The technique is simple and can be
applied for raw material, billets, plates,castings, finished components, hot rolled
bars etc.
The technique enables detection of cracks, seams,inclusions,lack of
fusion, lamination and similar flaws. The detection is possible to max depth of
6mm.
Principle: The job is magnetized and magnetic lines of forces(Flux) is
made available. Discontinuities in the path of magnetic flux create disturbance
in the uniform magnetic field, causing flux leakage, which attracts iron powder
when it is sprayed on the testing zone and forms a pattern of discontinuity.

36. Steps in testing
• Magnetize the job suitably
• Apply the examination medium(i.e. Iron powder) over the test surface.
• Interpret and evaluate the indications.
Kinds of Magnetizations:
• Longitudinal magnetization:Magnetisation is parallel to the long axis of
component, Eg:Yoke method,Coil method.
• Circular magnetization:magnetic field is transverse to the length of the
component and flux path is contained within the article. Eg:Prod method,
Head shot method.

37. Welding Discontinuities
• If welding is done, defects are bound to occur. The intensity of defects may be more or
less which may vary in different welds. The tolerance limit of particular defect varies
from that of the other. Following are some Welding defects which are likely to occur :
a) Lack of Fusion
b) Lack of Penetration
c) Cracks
d) Slag Inclusion
e) Porosities/Blow hole
f) Tungsten Inclusion
g) Overlap/Mismatch
h) Excess Penetration
i) Undercuts
j) Surface Depression/Excess capping
k) Burn through

38. Comparison of Defects in different welding
Weldin
g
Proces
s
Welding Defects
SMAW LOP/LF - Slag
Inclusion Crack Porosity Burn
through
TIG LOP/LF Tungsten
Inclusion
Crack Porosity _
MIG LOP/LF - Crack Blow
holes _

39. Preheating & Post Heating
Preheating: It is the process of Heating the parent metal around the
welding area to a specified temperature before welding and maintaining the
same during welding. The purpose of preheating are as follows:
1) To minimise the risk of cracking in the weld and heat affected zone of steels
this is achieved by
a) Reducing the rate of cooling experienced by the weld and HAZ which
retards the formation of hard martensite.
b) allowing the Hydrogen/moisture to diffuse away from the weld at a faster
rate.
c) Reducing the Residual stresses induced in the weld region.
2) Uniform preheating reduces the distortion due to welding.
Post Heating: It is the heat applied to the joint immediately after completion
of welding before the joint cools down to ambient temperature.

40. PWHT
• Post Weld heat Treatment: It is a type of heating Process applied in
High thickness materials ranging from carbon steel to high alloy steels. It is
done after welding completion. It consist of heating the weldment at a
controlled rate to temp range below the transformation temperature and
Holding(Soaking) it for certain time and cooling it down at a controlled rate.
• Purpose of PWHT:
• a) To Relieve the Residual stresses produced during welding. & this stress
are heavily restrained & susceptible for cracking.
• b)To obtain machinability & also to increase the material resistance against
stress corrosion cracking.
• c) To obtain Hard surfaces
• d) To obtain the required Hardness and improve the toughness & ductility.

41. THANK YOU
By
N.Jayakumar
SGS India Pvt ltd