The document discusses various welding defects classified into six groups: cracks, cavities, solid inclusions, incomplete fusion/penetration, imperfect shape/contour, and miscellaneous defects. It further categorizes defects into two types: visual/surface defects and hidden/subsurface defects. Various welding inspection and testing methods like tensile test, hardness test, toughness test, fatigue test, and non-destructive testing methods are described. The importance of a welding procedure specification for producing quality welds according to codes and standards is also highlighted.

1. ADVANCE WELDING
Mechanical Engineering Department, RKGIT Ghaziabad
Raj Kumar Goel Institute of Technology, Ghaziabad, U.P., India
Unit-5

2. WELDING DEFECTS
 The performance of welded structures or components in service
depends upon the quality of fabrication which in turn is based on
the presence or absence of defects in weld joints.

3. Classification of Weld Defects
 Classifies the weld defects into six groups as follows :
 Cracks-includes all types of cracks such as hot cracks, cold cracks, etc.
 Cavities-including blowholes, porosity, shrinkage, etc.
 Solid inclusions-including slag, flux, metal oxides, etc.
 Incomplete fusion or penetration-including lack of fusion, lack of penetration etc.
 Imperfect shape or Unacceptable contour-including dimensional deviations, undercut,
underfill, overlap, excessive reinforcement, excessive penetration, etc.
 Miscellaneous Defects-including arc strike, excessive spatter, rough surface, uneven ripples,
etc.
 However, all these defects are discussed under two categories, viz.,
(I) Visual/Surface defects,
(II) Hidden/Sub-surface defect

4. VISUAL SURFACE WELD DEFECTS
 Under this category are included the following defects:
 Surface cracks
 Distortion
 Incorrect or bad bead profile,
 Dimensional deviation/Incorrect weld size
 Undercuts
 Excess penetration/Excess reinforcement
 Start-Stop points
 Surface porosity
 Surface oxidation
 Excessive spatter
 Arc strike
 Bad surface appearance,

5. HIDDEN OR SUBSURFACE WELD DEFECTS
This category includes the following defects :
 Hidden or Subsurface cracks,
 Lack of fusion,
 Lack of penetration,
 Blowholes/Subsurface porosity,
 Slag inclusion,
 Coarse microstructure.

6.  The following are general sources of defects for most of the Conventional arc
welding processes.
 Improper selection of process
 Poor supervision
 Defects caused by the interaction of the weld metal with prior defects in the
base metal
 Incorrect joint edge preparations
 Undesirable shape and size of weld bead
 Apart from these general causes of weld defects there may also be some other
reasons for the occurrence of certain specific defects.

7. INSPECTION OF WELDED JOINTS
 To produce quality weld joints, it is necessary to keep an eye on what is being
done in three different stages of the welding
 Before welding such as cleaning, edge preparation, baking of electrode etc. to
ensure sound and defect free weld joints
 During welding various aspects such as selection of input parameters (pressure
of oxygen and fuel gas, welding current, arc voltage, welding speed, shielding
gases and electrode selection) affecting the heat input and so melting,
solidification and cooling rates besides protection of the weld pool from
atmospheric contamination
 After welding steps, if any, such as removal of the slag, peening, post welding
treatment.

8.  Selection of optimal method and parameters of each of above steps and their
execution in different stages of production of a weld joint determine the
quality of the weld joint.
 Inspection is mainly carried out to assess ground realties in respect of progress
of the work or how meticulously things are being implemented.
 Testing helps to: a) assess the suitability of the weld joint for a particular
application and b) to take decision on whether to go ahead (with further
processing or accept/reject the same) at any stage of welding and c) quantify
the performance parameters related with soundness and performance of weld
joints.

9.  Testing methods of the weld joint are broadly classified as destructive testing and
non-destructive testing.
 Destructive testing methods damage the test piece to more or less extent.
 The extent of damage on (destructive) tested specimens sometime can be up to
complete fracture (like in tensile or fatigue testing) thus making it un-useable for the
intended purpose
 While in case of non-destructive tested specimen the extent of damage on tested
specimen is either none or negligible which does not affect their usability for the
intended purpose in anyways.
 Weld joints are generally subjected to destructive tests such as hardness, toughness,
bend and tensile test for developing the welding procedure specification and
assessing the suitability of weld joint for a particular application.
 Visual inspection reflects the quality of external features of a weld joint such as weld

10. TENSILE TEST
 Tensile properties of the weld joints namely yield and ultimate strength and
ductility (%age elongation, %age reduction in area) can be obtained either in
ambient condition or in special environment (low temperature, high temperature,
corrosion etc.) depending upon the requirement of the application using tensile
test.
 Tensile properties of the weld joint are obtained in two ways a) taking specimen
from transverse direction of weld joint consisting base metal heat affected zone-
weld metal-heat affected zone-base metal and b) all weld metal specimen

11. Schematic of tensile specimens from a) transverse section of weld
joints and b) all weld specimen

12.  Tensile test results must be supported by respective engineering stress and strain
diagram indicating modulus of elasticity, elongation at fracture, yield and
ultimate strength .
 Tests results must includes information on following point about test conditions
 Type of sample (transverse weld, all weld specimen)
 Strain rate (mm/min)
 Temperature or any other environment in which test was conducted if any
 Topography, morphology, texture of the fracture surface indicating the mode of
fracture and respective stress state

13. HARDNESS TEST
 Hardness is defined as resistance to indentation and is commonly used as a
measure of resistance to abrasion or scratching.
 Indentation is the penetration of a pointed object (harder) into other object (softer)
under the external load.
 Resistance to the penetration of pointed object (indenter) into the softer one
depends on the hardness of the sample on which load is applied through the
indenter.
 All methods of hardness testing are based on the principle of applying the
standard load through the indenter and measuring the penetration in terms of
diameter/diagonal/depth of indentation.
 High penetration of an indenter at a given standard load suggests low hardness.
 Various methods of hardness testing can be compared on the basis of three criteria
1) type of indenter, 2) magnitude of load 3) measurement of indentation.

14.  Penetration due to applied normal load is affected by unevenness on the surface
and presence of hard surface films such as oxides, lubricants, dust and dirt etc. if
any. Therefore, surface should be cleaned and polished before hardness test.
 In case of Brinell hardness test, full load is applied directly for causing
indentation for measuring hardness .
 While in case of Rockwell hardness test, minor load (10 kN) is applied first
before applying major load. Minor load is applied to ensure the firm metallic
contact between the indenter and sample surface by breaking surface films and
impurities if any present on the surface.
 Minor load does not cause indentation. Indentation is caused by major load only.
Therefore, cleaning and polishing of the surface films becomes mandatory for
accuracy in hardness test results in case of Brinell test method as major load is
applied directly.

15.  In case of Rockwell hardness test first minor load of 10 kg is applied and then
major load of 50-150kg is applied on the surface of the work-piece through
the indenter and the same is decided by scale (A, B, C and D) to be used as
per type of material to be tested.
 Minor load is not changed. Out of mainly scales, B and C scales are
commonly used. Different indenter and major load are required for each
scale.
 Steel ball and diamond cone are two types of indenters used in Rockwell
testing.
 B scale uses hardened steel ball and major load of 90kg whereas C scale uses
diamond cone and major load of 140kg accordingly hardness is written in
terms of HRB and HRC respectively.

16. Schematic diagram showing indentation using different indenters
corresponding to different hardness test methods

17. Toughness testing
 The toughness test simulates service conditions often encountered by
components of the system used in transportation, agricultural, and
construction equipment.
 A material high impact resistance is said to be a tough material.
Toughness is the ability of a material to resist both fracture and
deformation.
 Toughness is the combination of strength and ductility.
 To be tough, a material must exhibit both fairly good strength and
ductility to resist cracking and deformation under impact loading.
 Notches are made intentionally in impact test specimens to increase
the stress concentration so as to increase tendency to fracture as
most of the mechanical components have stress raisers.
 To withstand an impact force, a notched material must be tough.

18.  To study the behaviour of material under dynamic load conditions (at high
rate of loading) toughness test is frequently conducted.
 There are two methods used for toughness testing namely Izod and Charpy
test, based on the common principle of applying the load at high rate and
measuring the amount of energy absorbed (kg m or Joule) in breaking the
sample due to impact.
 However, there are some differences also in these two methods in terms of
sample size and shape, method of holding of the sample and maximum
energy content of pendulum that hits the sample during the test.
 Standard sample for both testing methods having a notch and is mounted on
the machine in specific ways i.e. notch faces to pendulum in case Izod test
while pendulum hits the sample from back of the notch in Charpy test

19. Sr.
No.
Toughness
test
Sample Holding
1
Izod Held vertically on anvil as
cantilever
Cantilever type and notch faces the
pendulum
2 Charpy
Held horizontally on anvil as
simply supported beam
Simply supported type and notch is
opposite side of pendulum impact
(not facing to pendulum)

20.  Results of impact tests are expressed in terms of either amount of energy
absorbed (Nm) or amount of energy absorbed per unit cross sectional area
(Nm/cm2) by standard sample.
 It may be noted that values directly used for design purpose but these only
indicate the ability of the material to withstand against shock/impact load i.e.
load applied at very high rate.
 These tests are useful for comparing the resistance to impact loading of
different materials or the same material in different processing conditions
such as heat treatment, procedure and mechanical working etc.

21. Fatigue behaviour of weld joint
 The fatigue performance of the metallic components in general is
determined in two ways
 a) endurance limit i.e. indicating the maximum stress, stress amplitude or
stress range for infinite life (typically more than 20 million of load cycles)
and
 b) number of load cycle a joint can be withstand for a set of loading
conditions as desired.

22.  The fatigue performance is appreciably influenced by the various variable
related with fatigue test namely
 stress ratio, type of stress (tension- tension, reverse bending, tension-compression, zero-
tension), maximum stress, stress range, loading frequency and surrounding
environmental conditions such as temperature, corrosion, vacuum, tribological
conditions.
 The fatigue test results should include following.
 Test conducted according to ASTM E466 standard
 Type of loading: axial pulsating/reverse bending/tension-compression
 Maximum stress:
 Stress ratio (ratio of minimum stress to maximum stress)
 Temperature: ambient/vacuum/corrosion
 Frequency of pulsating load: load cycles per min
 Type of sample

23.  To conducting fatigue test,
 first step is conduct the tensile test on the weld joint for establishing the
yielding strength of metal as maximum stress becomes 0.9 times of yield
strength of material.
 For plotting the stress-number of cycle (S-N) curve, fatigue test is first
conducted with maximum applied tensile load corresponding to 0.9 times
of yield strength of weld joint under study to determine the number of load
cycle required for fracture and then in the same way test is repeated at 0.85,
0.8, 0.75, 0.7 …. times of yield strength of weld joint until endurance limits
or desired fatigue life is not achieved .

24. Typical data on fatigue test showing peak stress/ultimate stress vs. number of
cycle relationship for structure steel

25. NON-DESTRUCTIVE TESTING (NDT)
 To determine the presence of surface and surface imperfections, non-destructive
testing of weld joints can be carried out using variety of techniques as per needs.
 Apart from the visual inspection, many non-destructive testing methods
including dye penetrant test (DPT), magnetic particle test (MPT), eddy current
test (ECT), ultrasonic test (UT), radiographic test (RT) etc. are used in
manufacturing industry for assessing the soundness of weld joints.

26. DYE PENETRANT TEST
 This is one of the simplest non-destructive testing methods primarily used for
detecting the presence of surface defects only.
 In this method surface to be tested a thin low viscosity and low surface tension
liquid containing suitable dye is applied.
 The thin liquid penetrates (by capillary action) into fine cavities, pores and cracks,
if any, present on the surface. Excess liquid present at surface is wiped out.
 Then suitable developer like talc or chalk powder is sprinkled over the surface.
Developer sucks out thin liquid with dye wherever it is present inside the surface
discontinuities present on the weld joints.
 Dye with liquid changes colour of developer and indicates location, and size of
surface defects.

32. MAGNETIC PARTICLE TESTING
 Magnetic particle testing is a nondestructive inspection method used
to detect surface or near-surface defects or discontinuities in
magnetic materials.
 The method is based on the principle that magnetic lines of force,
when present in a ferromagnetic material, will be distorted by an
interruption in material continuity, such as a discontinuity or a
considerable change in chemical composition.

33.  If a magnet is bent and the two poles are joined so as to form a closed ring, no
external poles exist and hence it will have no attraction for magnetic material.
 Thus, as long as the part to be inspected is free of cracks or other
discontinuities, magnetic particles will not be attracted.
 When a crack or other discontinuity is present, north and south magnetic poles
are set up at the edges of the discontinuity (or crack). The magnetic particles
will be attracted to the poles which are the edges of the crack or discontinuity.
 Magnetic particle testing is obviously limited to ferrous metals, nickel, and
cobalt alloys; and that also when these materials are magnetic.
 It will not work on aluminium, copper, zinc, austenitic stainless steels, or
austenitic high-manganese steels because all these materials are non-magnetic.

36. ULTRASONIC TESTING
 Vibrational waves of high frequency that is frequency above the hearing
range of normal human ear are called ultrasonic waves.
 This term generally includes all waves having a frequency greater than
about 20,000 hertz or CPS (cycles per second).
 Ultrasonic testing is a NDT method in which ultrasonic waves are introduced
into a test object to detect and locate surface and internal defects or
discontinuities.
 This is because when a sound beam is directed into the test object it is
reflected at interfaces and discontinuities or defects. The reflected beam is
detected

37. WELDING SYMBOL

71. WELDING PROCEDURE SPECIFICATION
(WPS)
 A Welding Procedure Specification, or WPS, is a formal written document
describing standard welding procedures.
 The Welding Procedure Specification is a required document for all code
welding. Your customer either directly or indirectly specifies to what code your
company must qualify. The WPS outlines all of the parameters required to
perform your welding operation.
 In short the WPS is the recipe for your welding operation. It describes the
welding process or processes used, the base materials used, the joint design and
geometry, gases and flow rates, welding position and includes all of the process
conditions and variables. Each code has a recommended format.
 These procedures provide clear direction for your welders to make quality
products that are up to code and industry standards. They will include any details
and information that are required to make a desired weld.

72.  These are proven and tested procedures that include but are not limited to,
information such as the materials needed, the tools required, the processes to
follow, the techniques to employ and finally confirmation of the desired
outcome.
 A WPS can go beyond just a great weld. Although a WPS will ensure the
welded component meets design requirements, a WPS can also help you make
hiring decisions.
 You can employ welders and welding operators whose skills are in line with the
WPS and a WPS can also help you complete a fast inspection with quick testing
times. Since your employees will follow strict safety standards, you can also
reduce the risk of company liability.

73. WHY YOU NEED A WPS
 A Welding Procedure Specification is essential for every welding company to have because it
maintains quality standards across every weld. It isn’t just a nice guide to follow.
 Under various Australian and international standards (eg.ISO 15612, ISO 15609), a WPS is
required to ensure a stable weld.
 Under the Work Health and Safety Act of 2011, business owners have an obligation and duty
of care to construct and operate a safe plant. For compliance to the Act, welders need to ensure
they are following correctly designed WPS.
 In Australia, Standards Australia is the in-charge of the approval of welding standards. Their
73 member group has created basic WPS for some of the most common welding types,
including welding of carbon steels, stud welding, and welding stainless steels for structural
purposes.
 Because every company has different welds to complete, Standards Australia has not created
WPS for every type of weld. If your company uses a weld that does not have a WPS, it is your
obligation to create one.

74. RECORD
 The Welding Procedure Qualification Record is the document that qualifies the
Welding Procedure Specification.
 In order to qualify your WPS, a procedure qualification plate is welded the code
requirements. The actual test parameters are recorded at the time of welding to
ensure the WPS was being followed.
 Generally any supporting documentation, such as material specifications,
electrode specifications and shielding gas specifications, are included as part of
the WPQR.
 All required testing, both non-destructive and destructive, is recorded as well.
These tests typically include X-Ray examinations, ultrasonic examinations,
tensile testing, bend testing and when required impact testing.

75.  The WPQR combines all of the information of the WPS and adds the test results
to provide a complete document that certifies the welding specification.
 This document is also required by all codes unless you are qualifying under
American Welding Society (AWS) specifications. Under certain conditions the
WPS may be considered prequalified in which the WPQR is not required.

76. INTRODUCTION TO WELDING CODES
 Almost all design, welding, fabrication, material, repair, testing, and
inspection requirements are covered under three main organizations.
 These main organizations are the, the American Society of Mechanical
Engineers (ASME), INDIAN STANDARDS (BIS) and International
Standards Organization (ISO).
 All of these organizations have multiple specific codes for various types of
construction, processes, and/or materials.
 Design specifications and approved materials are included in these codes.

79. WELDING OF PIPE‐LINES AND PRESSURE
VESSELS
 The tank and pressure vessel market is worth USD$ 11 billion in the US alone.
 From food processing and fermentation, through to nuclear waste storage and
pharmaceutical processing, vessels are used in a no. of industries to both store
and transfer liquids and gases under high pressure.
 Given the critical nature of pressure vessels, the welds used in their fabrication
undergo a rigorous quality control and assurance process, including x-ray
inspections, ultrasonic testing and a variety of other forms of non-destructive
testing (NDT).

80. TIG WELDING
 This is a versatile, all-position welding process, which typically utilize a non-
consumable tungsten electrode to make the weld.
 It provides the highest quality weld and hence has become highly attractive
replacement for gas and manual metal arc welding in pressure vessel fabrication.
 TIG welding is mostly used where precise, small welds are needed on stainless
steel and non-ferrous metals such as aluminum, magnesium, and copper alloys.
 Conventional TIG tends to be restricted to currents below 250 amps because
higher amperage (resulting high arc pressure) depresses the weld pool surface
and creates an unstable, turbulent weld pool.
 The practical upper limit for single pass GTAW welding is generally considered
to be 2mm.

81.  Beyond this thickness, a V-groove root pass is normally applied, followed by
filler passes. Machined groove preparation is preferred for the sake of process
consistency, which adds cost, and the removed joint metal must be replaced
with filler metal.
 The low energy density arc has limited penetration capability, and the root and
fill passes are performed at a slow travel speed, typically resulting in many weld
passes and lengthy welding times.

82. PLASMA ARC WELDING
 Plasma arc welding is a widely utilized welding process in pressure vessel
fabrication wherein plasma, which is heated to an extremely high temperature
and ionized, is used to transfer an electric arc to a work piece.
 The plasma welding process brings the highest quality standards to pressure
vessel fabrication and it helps make strong and precision welds on both thick and
thin metal.
 The method provides advanced level of control and accuracy to produce high
quality welds at extremely high speed compared to other welding processes.
 The practical upper limit for single pass PAW welding is generally considered to
be 8mm to 10mm.

83. K-TIG WELDING
 A high energy density variant of GTAW, K-TIG (Keyhole TIG) is a high speed,
single pass, full penetration welding technology that welds up to 100 times faster
than TIG welding in materials up to 5/8in (16mm) in thickness, and typically
operates at twice the speed of plasma welding.
 K-TIG works across a wide range of applications, and is particularly well suited
to lower conductivity materials such as stainless steels, nickel alloys, titanium
alloys and most corrosion resistant and exotic materials.
 It performs longitudinal and circumferential welds on pipe, plate, spooling,
vessel, tank and other applications in a single pass.

84.  Titanium up to 5/8-inch (16mm) thickness
 Stainless steel up to ½ inch (13mm) thickness
 Nickel Alloys and Super Alloys up to ½ inch (13mm) thickness
 High Quality Carbon Steel up to ¼ inch (6mm) thickness

85.  K-TIG’s extremely fast welding times result in dramatic reductions in labor
costs, welding cycle times, rework and repair costs, gas and power usage.
 K-TIG’s single pass, full penetration welds significantly reduce or eliminate
grinding and reworking.
 The K-TIG process dramatically reduces or eliminates the need for wire,
eliminates edge bevelling,. No root gap is required.
 K-TIG (Keyhole TIG) is a highly refined version of TIG/GTAW developed by
the Australian Government’s Commonwealth Science & Industrial Research
Organization (CSIRO).
 This welding process has been quietly adopted by some of the world’s most
productive fabricators and largest vessel fabricators.

86.  K-TIG has 8x the penetration of GTAW, allowing it to perform x-ray quality
welds in materials up to 5/8 inch (16mm) thick in a single pass, without the need
for edge bevelling.
 Gas consumption is reduced by more than 90%, and wire consumption is reduced
by in excess of 90% or eliminated entirely.
 The physics of the K-TIG process create high energy density in the welding arc,
allowing it to open up a ‘keyhole’ and fully penetrate the material being welded
and weld at high speed.
 In contrast to plasma welding, K-TIG is simple to operate. The arc structure
and keyhole develop spontaneously and are maintained automatically by the
controller throughout the weld.
 There is no plasma nozzle or orifice, no precise electrode alignment is required,
only one welding gas is used, flow rate is not critical, and the torches are very

88. INSPECTION OF PRESSURE PIPING
 All pipe welds, unless otherwise approved by an inspector shall be
hydrostatically tested to one and one half times the working pressure in
accordance with the A.S.M.E. codes.
 All pipe welds shall be subject to examination by x-ray.
 Testing methods shall be in accordance with the American
National Standards Institute (A.N.S.I.) Pressure Piping Code and the A.S.M.E.
Code.