comparison between welding defects caused by flux …

COMPARISON BETWEEN

WELDING DEFECTS CAUSED BY

FLUX CORED AND BARE

ELECTRODES

A PROJECT

BY

YOUNUS ALI

DEPARTMENT OF MECHANICAL ENGINEERING

DHAKA UNIVERSITY OF ENGINEERING & TECHNOLOGY, GAZIPUR

GAZIPUR-1700

COMPARISON BETWEEN


FLUX CORED AND BARE

ELECTRODES

YOUNUS ALI

DEPARTMENT OF MECHANICAL ENGINEERING

DHAKA UNIVERSITY OF ENGINEERING & TECHNOLOGY, GAZIPUR

GAZIPUR-1700

ii

COMPARISON BETWEEN


FLUX CORED AND BARE

ELECTRODES

A Project

By

YOUNUS ALI

Department of Mechanical Engineering

Dhaka University of Engineering & Technology, Gazipur

Gazipur-1700

March 2016

iii

COMPARISON BETWEEN


FLUX CORED AND BARE

ELECTRODES

A Project

By

YOUNUS ALI

Submitted to the Department of Mechanical Engineering, Dhaka University of

Engineering & Technology, Gazipur, in partial fulfillment of the requirements for the

degree of MASTER OF ENGINEERING IN MECHANICAL ENGINEERING.


Dhaka University of Engineering & Technology, Gazipur

Gazipur-1700

March 2016

iv

The project titled “Comparison Between Welding Defects Caused by Flux Cored

and Bare Electrodes”, submitted by Younus Ali, Student No. 112317 (P) session

2011-2012, has been accepted as satisfactory in partial fulfillment of the requirements

for the degree of Master of Mechanical Engineering on March 15, 2016.

BOARD OF EXAMINERS

1. Professor Dr. Md. Kamruzzaman Supervisor and Chairman


DUET, Gazipur.

2. Professor Dr. Mohammad Asaduzzaman Chowdhury

Head, Department of Mechanical Engineering

DUET, Gazipur.

Member

(Ex-officio)

3. Professor Dr. Mohammed Alauddin Member

Professor, Department of Mechanical Engineering

DUET, Gazipur.

4. Professor Dr. Md. Arefin Kowser Member

Professor, Department of Mechanical Engineering

DUET, Gazipur.

5. Professor Dr. Mohammad Mosharaff Hossain Member

Head, Department of Industrial and Production

Engineering

Rajshahi University of Engineering & Technology

(RUET), Rajshahi

(External)

v

Declaration

I do hereby declare that this work has been done by me and neither this project nor

any part of it has been submitted elsewhere for the award of any degree or diploma

except for publication.

Countersigned

Prof. Dr. Md. Kamruzzaman

Supervisor

&

Professor


DUET, Gazipur.

Younus Ali

vi

This Project work is dedicated to

My Beloved

Parents

vii

TABLE OF CONTENTS

TABLE OF CONTENTS ………………………………………………………. vii

LIST OF FIGURES …………………………………………………………….. x

LIST OF TABLES ……………………………………………………………... xi

LIST OF SYMBOLS ……………………………………………………….….. xii

ACKNOWLEDGEMENT …………………………………………….……….. xiv

ABSTRACT …………………………………………………………….……… xv

CHAPTER 1 INTRODUCTION …………………………………….…… 1

1.1 State of Welding …………………………………….……… 2

1.1.1 SAW ………………………………………………….…….. 2

1.1.2 Solid Wire use MIG power sources ………………………... 2

1.1.3 FCAW Process ………………………………………….….. 3

1.1.4 Flux Cored welding Wire Basics …………………….…….. 4

1.2 Description of Electrodes …………………………….…….. 4

1.2.1 Bared Electrodes ………………………….……. 4

1.2.2 Submerged Arc Electrode ………………..…….. 6

1.2.3 Flux core or Tubular Electrode ………………… 8

1.2.4 Classification of Flux-Cored Electrodes ……….. 11

CHAPTER 2 LITERATURE REVIEW ……………………………….…. 14

2.1 Welding Industry …………………………………….…….. 14

2.2 Welding Quality ……………………………………….…… 15

2.3 Welding Expenditure …………………………………….…. 17

2.4 Welding Quality Measures and Testing ……………….…… 18

2.5 Welding Processes Used …………………………………… 19

2.6 Welding Technique in welding operation ……………….…. 21

viii

2.7 Objectives of present works ………………………………... 22

2.8 Research Methodology ………………………………….….. 22

CHAPTER 3 Welding Defects & Non Destructive Testing ……………… 24

3.1 Description of defects ………………………………….…… 24

3.2 Solidification Cracking ………………………………….…. 27

3.3 Hydrogen induced cracking (HIC) …………………….…… 29

3.4 Non Destructive Testing ……………………………….…… 29

3.4.1 Visual Inspection …………………………….…… 31

3.4.2 Detection Visual Inspection …………………..….. 32

3.4.3 Liquid Penetrant Examination (LPE) ……….……. 32

3.4.4 Magnetic Particle Testing (MPT) ……………..….. 33

3.4.5 Acoustic Emission Testing (AET) …………….…. 35

3.4.6 Eddy Current Array (ECA) ………………….…… 36

3.4.7 X-Ray Inspection ………………………………..... 38

3.4.8 Radio graphic Testing ……………………………. 38

CHAPTER 4 CASE STUDY WITH DATA ANALYSIS ……………….. 41

4.1 Description of Phased Array Machine ……………………... 41

4.2 Principal of PAUT Operation …………………………….… 42

4.3 Basic Principal of DPT/LPU/DPI ……………………….…. 47

4.4 The Process of Testing ……………………………………... 48

4.5 Mild Steel Microstructure Analysis ………………………... 55

4.6 PAUT Report with Image ……………………………….…. 57

4.7 4.1 Testing Results…………………………………….. 61

ix

CHAPTER 5 RESULTS AND DISCUSSION ………………………….. 63

5.1 Results ……………………………………………………… 63

5.2 Discussion ………………………………………………….. 65

CHAPTER 6 CONCLUSIONS AND RECOMMENDATION …………. 67

6.1 Conclusions ………………………………………………… 67

6.2 Recommendations …………………………………………. 68

REFERENCES ………………………………………………………………… 70

APPENDICES ………………………………………………………………… 72

x

LIST OF FIGURES

No. Description Page

No.

Fig. 2.1 Non destructive Testing Methods 19

Fig. 2.2 Welding Processes used in companies 20

Fig. 2.3 Welding Technical in welding operation 21

Fig. 4.1 DPT solution 46

Fig. 4.2 PA Machine 51

Fig. 4.3 MIG Welding Process 51

Fig. 4.4 FCAW with CO2 gas after testing 52

Fig. 4.5 FCAW without CO2 gas after testing 52

Fig. 4.6 Solid Wire with CO2 gas after testing 52

Fig. 4.7 Solid Wire without CO2 gas after testing 53

Fig. 4.8 Butt weld by FCAW with CO2 gas before testing 53

Fig. 4.9 Butt weld by Solid wire with CO2 gas before testing 53

Fig. 4.10 Fillet Weld by FCAW with CO2 gas before testing 54

Fig. 4.11 Fillet Weld by Solid wire without CO2 Gas before testing 54

Fig. 4.12 FCAW with CO2 gas after testing 55

Fig. 4.13 FCAW without CO2 gas after testing 55

Fig. 4.14 Microstructure for Mild Steel (Magnification 200) 56

Fig. 4.15 Microstructure for Welded joint of FCAW (Magnification

200)

56

Fig. 4.16 Microstructure for Welded joint of Solid Wire (Magnification

200)

56

xi

LIST OF TABLES

No. Description Page

No.

Table 4.1 Used apparatus list 45

Table 4.2 Standard as per ASTM A572 Grade 50 45

Table 4.3 Testing Data for Mechanical Properties 46

Table 4.4 Report of butt weld FCAW with CO2 gas 57

Table 4.5 Report of butt weld FCAW without CO2 gas 58

Table 4.6 Report of butt weld Solid wire with CO2 gas 59

Table 4.7 Report of butt weld solid wire without CO2 gas 60

Table 4.8 Testing Results 61

xii

LIST OF SYMBOLS

ABS : American Bureau of Shipping

ASME : American Society of Mechanical Engineers

AWS : American Welding Society

AET : Acoustic Emission Testing

BS : British Standard

BV : Bureau Veritas

CNC : Computer Numeric Control

CO2 : Carbon dioxide

CT : Computed Tomography

DPT : Dye Penetrate Test

DR : Digital Radiography

ECA : Eddy Current Array

FCAW : Flux-Core Arc Welding

HIC : Hydrogen induced cracking

IIW : International Institute of Welding

ISO : International Organization of Standards

ISO / TC : International Organization of Standards Technical Committee

LPG : Liquefied Petroleum Gas

MPT : Magnetic Particle Testing

MIG / MAG : Metal Inert Gas / Metal Active Gas

OHSAS : Occupational Health and Safety Advisory Services

PAUT : Phased Array Ultrasonic Test

PAW : Plasma Arc Welding

PEBSAL : PEB Steel Alliance Limited

PPE : Personal Protective Equipment

SSL : Sarker Steel Limited.

RTR : Real Time Radiography

RGT : Radio Graphic Test

SAW : Submerged Arc Welding

xiii

SMAW : Shielded Metal Arc Welding

TIG : Tungsten Inert Gas

TWI : The Welding Institute

UTM : Universal Testing Machine.

VI : Visual Inspection

X – Ray : X – Radiation

xiv

ACKNOWLEDGEMENTS

I could never accomplish this task without the help of so many generous

people. I would like to thanks Professor Dr. Md. Kamruzzaman for giving privilege

the author to demonstrate his ability by researching in the field of welding and also

correcting his final script and making useful suggestions for creating the platform and

accepting him on this project. Also the author thanks the supervisor for his

constructive comments and directions during the course of the project and for his

suggestions, advice and constant motivation before and after this project work. He

listened to author’s interests and led him accordingly.

He also likes to thank especially to the Head of the Department of Mechanical

Engineering for the help rendered for allowing and providing shops facilities to carry

out the experiment whenever required. The help extended by the CASR for providing

research fund is highly acknowledged.

He would also likes to thank the staff members of the Department of

Mechanical Engineering of Dhaka University of Engineering and Technology for

their countless supports. Many thanks go to all the institutions which availed

themselves to participate in this project.

Finally, the author offers his sincere thanks to all those who either directly or

indirectly helped him in various ways to complete this project thesis.

xv

ABSTRACT

There are different welding techniques that are used to join materials

effectively and efficiently considering the fact that the foreign particles, darts, grease

and oil will be removed from the welded junction properly as a result the junction will

acquire the higher strength bonding in between the pure materials. Flux in the flux

cored electrode do this functions along with some tempering effects. A cover on the

welded junction made by molten slug reduces the heat dissipation rate due to its

insulating property. As a result residual stresses are eliminated. Sub-surface cracks or

micro-cracks are formed usually due to residual stress formed by trapped carbon

during welding. Carbon is usually trapped in the larger inter-atomic space of

martensitic or austenitic structure at high melting temperature. Welding junction

produced using bare electrode provide no slug layer on the junction as flux are not

used during welding. In absence of flux, darts do not separate from the base metal and

junctions made by using bare electrodes are not free from defects. Hardness of the

product become much more higher as a result product do not survive for a longer

period under dynamic loading condition.

In this study, a comparison is done between the junction made by flux cored

electrode and that of bare electrode. Welding defects are tested under Dye Penetrant

Inspection and ultrasonic inspection. Mechanical properties are determined under

universal testing machine, microstructures are observed under Digital optical

microscope followed by etching with proper reagent. The study show that flux cored

electrode provide better result in comparison with bare electrode.

1

CHAPTER 1

INTRODUCTION

Welding has received a lot of attention worldwide since it is one of the methods

used for joining Materials in the most efficient and economical way [1, 2]. Recent

technologies behind welding have enormously created opportunities to add more value to

welded Steel structural products. Typical Examples are the automobiles, air-crafts, ships,

trains, Steel Structures, offshore platforms. As these Structures are predominated by

metals, the quest for the use of metals in manufacturing innovative Products by utilizing

welding as the main joining process is highly indispensable. In recent times, the interest

in MIG welding activities in up-and- coming economies in Bangladesh is on the increase.

This interest is as a result of the increasing need to outsource welding manufacturing Jobs

to rising economies since welding manufacturing jobs in developed economies are

becoming more expensive but cheaper in promising economies, and also the need to

boost welding purchasing Globally. Metal manufacturing jobs foreseen to originate in

Bangladesh shall be enormous and the use of welding technology shall increase

substantially. More so, huge volumes of metal production activities have been envisaged

in emerging economies as a result of metal deposit depletion in Europe and the USA.

This phenomenal change has resulted in technological shifts. Immense investments have

currently taking place and growth in investments in the next ten years in emerging

economies especially in Africa is highly feasible [3]. To make clear this claim, a survey

conducted by the American Welding Society (AWS) shows that the growth of welding

2

is forging into emerging economies / markets [4]. The significance of this thesis helps to

bridge this research gap in welding in Bangladesh province namely Savar, Gazipur,

Narayangonj, Comilla. This thesis therefore investigate into various aspects of welding

such as the type of products manufactured by means of welding, the industrial sectors

which employ welding in manufacturing, customers industry of operation, welding

quality issues (welding quality standards, certification and qualification of companies

and welders, welding processes, assessment of weld quality, and welding quality testing),

1.1 State of Welding

1.1.1 SAW

The submerged arc welding process, in which the weld and arc zone are

submerged by a layer of flux, is the most efficient fusion welding process in plate and

structural work such as shipbuilding, bridge building, and pressure vessel fabrication,

assuming the work pieces can be properly positioned and the equipment accurately

guided. However, when welds must be made out of position or when several short welds

are required on many pieces involving frequent moves of the welder or the work piece, a

flexible process such as shielded metal arc welding, gas metal arc welding, or flux cored

arc welding should be considered. The optimum process is selected based on a

compromise between welding speed (deposition rate), versatility, and portability.

1.1.2 Solid Wire use MIG power sources

MIG power sources use a continuous solid wire electrode for filler metal and

require a shielding gas delivered from a pressurized gas bottle. Mild steel solid wires are

usually plated with copper to prevent oxidation, aid in electrical conductivity and help

3

increase the life of the welding contact tip. The shielding gas protects the molten weld

pool from contaminants present in the surrounding atmosphere. The most common

shielding gas combination is 75 percent Argon and 25 percent CO2. While using solid

wire outdoors, the operator should use caution and prevent any wind from blowing the

shielding gas coverage away from the welding arc. Windshields may need to be used.

1.1.3 FCAW Process

FCAW is a process that uses an arc between a continuous filler metal electrode

and the weld pool. Shielding gas from a flux contained within the tubular is used in the

process. Utilization of the FCAW process started from a lower base and has been gaining

modestly. This trend will likely continue; however, lower filler metal utilization and

higher filler metal costs will keep it from growing as fast as gas metal arc welding. In

ship and bridge building, metal FCAW is habitually used for fillet welding of painted

steel plate and slag FCAW for all-position welding.

For bridges, where principal beams are few and these beam structural members

are large in size and thick, the sheet size and the length of the welding leg have also

grown; FCAW welding is used for the fillet. This welding has come into use not only for

490 N/mm2 grade steel and 590 N/mm2 grade steel but also for weather-resistant steel.

FCAW, with which upward welding is possible at high currents, is used when the gap is

large.

4

1.1.4 Flux Cored Welding Wire Basics.

There are two types of flux cored wires: gas shielded and self shielded. Gas

shielded flux cored wires require external shielding gas and the slag is easy to remove.

The operator may want to consider using gas shielded flux cored wires when welding on

thicker metals or in out-of-position applications. Gas shielded flux cored wires have a

flux coating that solidifies more quickly than the molten weld material. As a result, it

creates a "shelf" to hold the molten pool when welding overhead or vertically up. Self

shielding flux cored wire does not require external shielding gas; the weld pool is

protected by gas generated when flux from the wire is burned. As a result, self shielding

flux cored wire is more portable because it does not require an external gas tank.

1.2 Description of Electrodes

1.2.1 Bare Electrode

Bare or solid wire electrodes are made of wire compositions required for specific

applications, and have no coatings other than those required in wire drawing. These wire

drawing coatings have a slight stabilizing effect on the arc, but are otherwise of no

consequence. Bare electrodes are used for welding manganese steels and for other

purposes where a covered electrode is not required or is undesirable.

Solid steel electrode wires may not be bare. Many have a very thin copper coating on the

wire. The copper coating improves the current pickup between contact tip and the

electrode, aids drawing, and helps prevent rusting of the wire when it is exposed to the

atmosphere. Solid electrode wires are also made of various stainless steels, aluminum

alloys, nickel alloys, magnesium alloys, titanium alloys, copper alloys, and other metals.

5

When the wire is cut and straightened, it is called a welding rod, which is a form of filler

metal used for welding or brazing and does not conduct the electrical current. If the wire

is used in the electrical circuit, it is called a welding electrode, and is defined as a

component of the welding circuit through which current is conducted. A bare electrode is

normally a wire; however, it can take other forms.

Several different systems are used to identify the classification of a particular electrode or

welding rod. In all cases a prefix letter is used.

(1) Prefix R. Indicates a welding rod.

(2) Prefix E. Indicates a welding electrode.

(3) Prefix RB. Indicates use as either a welding rod or for brazing filler metal.

(4) Prefix ER. Indicates wither an electrode or welding rod.

The system for identifying bare carbon steel electrodes and rods for gas shielded arc

welding is as follows:

(1) ER indicates an electrode or welding rod.

(2) 70 indicate the required minimum as-welded tensile strength in thousands of pounds

per square inch (psi).

(3) S indicates solid electrode or rod.

(4) C indicates composite metal cored or stranded electrode or rod.

(5) 1 suffix number indicates a particular analysis and usability factor.

6

1.2.2 Submerged Arc Electrode

The system for identifying solid bare carbon steel for submerged arc is as follows [21]

(1) The prefix letter E is used to indicate an electrode. This is followed by a letter which

indicates the level of manganese, i.e., L for low, M for medium, and H for high

manganese. This is followed by a number which is the average amount of carbon in

points or hundredths of a percent. The composition of some of these wires is almost

identical with some of the wires in the gas metal arc welding specification.

(2) The electrode wires used for submerged arc welding are given in American Welding

Society specification, "Bare Mild Steel Electrodes and Fluxes for Submerged Arc

Welding." This specification provides both the wire composition and the weld deposit

chemistry based on the flux used. The specification does give composition of the

electrode wires. When these electrodes are used with specific submerged arc fluxes and

welded with proper procedures, the deposited weld metal will meet mechanical properties

required by the specification.

(3) In the case of the filler reds used for oxyfuel gas welding, the prefix letter is R,

followed by a G indicating that the rod is used expressly for gas welding. These letters

are followed by two digits which will be 45, 60, or 65. These designate the approximate

tensile strength in 1000 psi (6895 kPa).

(4) In the case of nonferrous filler metals, the prefix E, R, or RB is used, followed by the

chemical symbol of the principal metals in the wire. The initials for one or two elements

will follow. If there is more than one alloy containing the same elements, a suffix letter or

number may be added.

7

(5) The American Welding Society's specifications are most widely used for specifying

bare welding rod and electrode wires. There are also military specifications such as the

MIL-E or -R types and federal specifications, normally the QQ-R type and AMS

specifications. The particular specification involved should be used for specifying filler

metals. The most important aspect of solid electrode wires and rods in their composition,

which is given by the specification. The specifications provide the limits of composition

for the different wires and mechanical property requirements. Occasionally, on copper-

plated solid wires, the copper may flake off in the feed roll mechanism and create

problems. It may plug liners, or contact tips. A light copper coating is desirable. The

electrode wire surface should be reasonably free of dirt and drawing compounds. This

can be checked by using a white cleaning tissue and pulling a length of wire through it.

Too much dirt will clog the liners, reduce current pickup in the tip, and may create erratic

welding operation. Temper or strength of the wire can be checked in a testing machine.

Wire of a higher strength will feed through guns and cables better. The minimum tensile

strength recommended by the specification is 140,000 psi (965,300 kPa).

The continuous electrode wire is available in many different packages. They range from

extremely small spools that are used on spool guns, through medium-size spools for fine-

wire gas metal arc welding. Coils of electrode wire are available which can be placed on

reels that are a part of the welding equipment. There are also extremely large reels

weighing many hundreds of pounds. The electrode wire is also available in drums or

payoff packs where the wire is laid in the round container and pulled from the container

by an automatic wire feeder.

8

1.2.3 Flux-Cored or Tubular Electrode

a. The flux-cored arc welding process is made possible by the design of the

electrode. This inside-outside electrode consists of a metal sheath surrounding a core of

fluxing and alloying compounds. The compounds contained in the electrode perform

essentially the same functions as the coating on a covered electrode, i.e., deoxidizers, slag

formers, arc stabilizers, alloying elements, and may provide shielding gas. There are three

reasons why cored wires are developed to supplement solid electrode wires of the same

or similar analysis.

(1) There is an economic advantage. Solid wires are drawn from steel billets of the

specified analyses. These billets are not readily available and are expensive. A single

billet might also provide more solid electrode wire than needed. In the case of cored

wires, the special alloying elements are introduced in the core material to provide the

proper deposit analysis.

(2) Tubular wire production method provides versatility of composition and is not limited

to the analysis of available steel billets.

(3) Tubular electrode wires are easier for the welder to use than solid wires of the same

deposit analysis, especially for welding pipe in the fixed position.

b. Flux-Cored Electrode Design.

9

The sheath or steel portion of the flux-cored wire comprises 75 to 90 percent of

the weight of the electrode, and the core material represents 10 to 25 percent of the

weight of the electrode.

For a covered electrode, the steel represents 75 percent of the weight and the flux 25

percent. This is shown in more detail below:

Flux Cored Electrode Wire

(E70T-1)

Covered Electrode

(E7016)

By area Flux 25% By area Flux 55%

Steel 75% Steel 45%

By weight Flux 15% By weight Flux 24%

Steel 85% Steel 76%

More flux is used on covered electrodes than in a flux-cored wire to do the same job. This

is because the covered electrode coating contains binders to keep the coating intact and

also contains agents to allow the coating to be extruded.

c. Self-Shielding Flux-Cored Electrodes.

The self-shielding type flux-cored electrode wires include additional gas forming

elements in the core. These are necessary to prohibit the oxygen and nitrogen of the air

10

from contacting the metal transferring across the arc and the molten weld puddle. Self-

shielding electrodes also include extra deoxidizing and denigrating elements to

compensate for oxygen and nitrogen which may contact the molten metal. Self-shielding

electrodes are usually more voltage-sensitive and require electrical stick out for smooth

operation. The properties of the weld metal deposited by the self-shielding wires are

sometimes inferior to those produced by the externally shielded electrode wires because

of the extra amount of deoxidizers included. It is possible for these elements to build up

in multi pass welds, lower the ductility, and reduce the impact values of the deposit.

Some codes prohibit the use of self-shielding wires on steels with yield strength

exceeding 42,000 psi (289,590 kPa). Other codes prohibit the self-shielding wires from

being used on dynamically loaded structures.

d. Metal Transfer.

Metal transfer from consumable electrodes across an arc has been classified into

three general modes. These are spray transfer, globular transfer, and short circuiting

transfer. The metal transfer of flux-cored electrodes resembles a fine globular transfer.

On cored electrodes in a carbon dioxide shielding atmosphere, the molten droplets build

up around the outer sheath of the electrode. The core material appears to transfer

independently to the surface of the weld puddle. At low currents, the droplets tend to be

larger than when the current density is increased. Transfer is more frequent with smaller

drops when the current is increased. The larger droplets at the lower currents cause a

certain amount of splashing action when they enter the weld puddle. This action

decreases with the smaller droplet size. This explains why there is less visible spatter, the

11

arc appears smoother to the welder, and the deposition efficiency is higher when the

electrode is used at high current rather than at the low end of its current range.

e. Mild Steel Electrodes.

Carbon steel electrodes are classified by the American Welding Society

specification, "Carbon Steel Electrodes for Flux-cored-Arc Welding". This specification

includes electrodes having no appreciable alloy content for welding mild and low alloy

steels. The system for identifying flux-cored electrodes follows the same pattern as

electrodes for gas metal arc welding, but is specific for tubular electrodes. For example,

in E70T-1, the E indicates an electrode; 70 indicates the required minimum as-welded

tensile strength in thousands of pounds per square inch (psi); T indicates tubular,

fabricated, or flux-cored electrode; and 1 indicates the chemistry of the deposited weld

metal, gas type, and usability factor.

1.2.4 Classification of Flux-Cored Electrodes

• E60T-7 electrode classification

Electrodes of this classification are used without externally applied gas shielding

and may be used for single-and multiple-pass applications in the flat and horizontal

positions. Due to low penetration and to other properties, the weld deposits have a low

sensitivity to cracking.

• E60T-8 electrode classifications



12

positions. Due to low penetration and to other properties, the weld deposits have a low



Electrodes of this classification are designed to be used with carbon dioxide

shielding gas for single-and multiple-pass welding in the flat position and for horizontal

fillets. A quiet arc, high-deposition rate, low spatter loss, flat-to-slightly convex bead

configuration, and easily controlled and removed slag are characteristics of this class.


Electrodes of this classification are used with carbon dioxide shielding gas and are

designed primarily for single-pass welding in the flat position and for horizontal fillets.

However, multiple-pass welds can be made when the weld beads are heavy and an

appreciable amount of mixture of the base and filler metals occurs.



and are intended primarily for depositing single-pass, high-speed welds in the flat and

horizontal positions on light plate and gauge thickness base metals. They should not be

used on heavy sections or for multiple-pass applications.




positions. Due to low penetration, and to other properties, the weld deposits have a low


13


This classification covers electrodes primarily designed for flat fillet or groove

welds with or without externally applied shielding gas. Welds made using-carbon dioxide

shielding gas have better quality than those made with no shielding gas. These electrodes

have a globular transfer, low penetration, slightly convex bead configuration, and a thin,

easily removed slag.


Electrodes of this classification are similar to those of the E70T-5 classification,

but are designed for use without an externally applied shielding gas.

• E70T-G electrode classification

This classification includes those composite electrodes that are not included in the

preceding classes. They may be used with or without gas shielding and may be used for

multiple-pass work or may be limited to single-pass applications. The E70T-G electrodes

are not required to meet chemical, radiographic, bend test, or impact requirements;

however, they are required to meet tension test requirements. Welding current type is not

specified.

14

CHAPTER 2

LITERATURE REVIEW

This chapter presents current literature reviewed to underpin the experiential part

of this research work. The main contents include information about the metal industry,

the welding industry, and quality in welding, productivity in welding, and economy in

welding. Much emphasis is laid on welding quality requirements.

2.1 Welding Industry

The sector of welding industry comprises of micro enterprises. The level of

professionalism in this sector is low but welders in this sector are experienced as a result

of constant practice in the welding trade. Moreover, some of the welders from this sector

are actually working in companies even though they do not have academic qualifications

in welding or basic qualifications in welding. However, the main activities performed by

this group include fabrication of plate and sheet metals, manufacturing of metallic

products. With the issue of welding processes, most of the enterprises use shielded metal

arc (SMAW). And Metal inert gas welding (MIG). The welding machines for this

process are Chinese and Japanese the formal sector of the welding industry comprises of

companies operating as small and medium enterprises (SMEs) and medium and large

enterprises (MLEs) registered in Bangladeshi trade register with clear-cut business

objectives. The welding operations performed by companies in this sector are unveiled by

case studies from twelfth companies such as

15

1. SAKER STEEL LIMITED (SSL)

2. PEB STEEL ALLIANCE LIMITED (PEBSAL)

3. BUILDTRADE,

4. MCDONAND,

5. BANGLADESH BUILDING SYSTEM (BBS)

6. STEEL MARK

7. MARN STEEL

8. ANANDA SHIPYARD AND SLIPWAYS LIMITED

9. BANGLADESH RE-ROLLING MILL LIMITED (BSRM)

10. TK SHIPYARD

11. WESTERN MARRINE SHIPYARD

12. ABUL KHAIR

The case study encompasses company establishment information, customer

information, welding quality, productivity and economy related issues.

2.2 Welding Quality

The implementation of quality management systems such as ISO 9000, and ISO

9001 in industries have been beneficial at a greater extent despite its draw-backs

observed by some companies. Her as and his group presented in their empirical survey

paper a summary of the benefits and effects of implementing quality management

systems such as ISO 9000. It was observed that certified companies stand higher chances

16

of increasing their productivity, profitability, product quality and competitiveness,

increasing market share as well as increasing customer satisfaction. However, the effects

include long installation periods, and uncertain time to achieve return on investment [5].

In spite of these, in production and manufacturing networks where welding is a critical

enabling technology, the quality of welding is highly essential and cannot rely only on

quality management systems as mentioned. Even though ISO 9001 has been considered

as a stand-alone quality standard, in welding applications, there is the need for more

robust quality requirements. Moreover, due to increasing applications of welded products

in relation to customer demands as well as health, safety and environmental issues,

welded metallic products are therefore required to demonstrate quality attributes such as

reliability, efficiency and safety in a wide range of applications. This is evident in

applications such as offshore structures where welded metallic products are made to

withstand harsh environmental conditions [6]. Regardless of the product, quality must be

efficiently ensured, thus meeting sound quality requirements [7]. However, these

attributes of a welded metallic product cannot be built only in the final stages in welding

operation since the act and process of welding itself is characterized as a “special process

in that the final result may not be able to be verified by testing, thus the quality of the

weld is manufactured into the product, not inspected” [8]. For this reason, welded

metallic products require being quality assured through quality control and quality

management systems before, during and after welding operations. Most research papers

about welding quality tend to focus on ways of achieving welding quality with respect to

welding processes and parameters, welding techniques, material types, welding

consumables or a combination of either of them, and or monitoring of welding quality .

17

However, very few papers have made mention of the needed requirements to achieving

welding quality in metallic products. Ratnayake presented five “Ps” of welding quality in

his paper as suggested by Lincoln Electric Company. It was so that, in order to achieving

quality in welding, requirement such as: process selection, preparation, procedure,

pretesting and personnel must be considered [9]. Contributes made by other authors

suggest that welding quality could be obtained if the design of the joint, electrode,

technique, and the skill of the welder are acknowledged [11]. However, achieving the

required quality in a welded metallic product cannot be fully obtained by following

general hypothesis or emulating only quality management system guidelines or standards

such as ISO 9000:2005. As welded metallic products are bound to compete on both local

and international markets, quality must be built in them right from the onset. It is

therefore required that companies which operations chiefly depend on welding should

comply with welding quality standards in order to meet the expected quality in their

welded metallic products.

2.3 Welding Expenditures

The expenditures usually regarded in welding economy measurements include

labor cost, consumable cost, material cost, joint design and joint position, preparation of

the parts, cost of each weld, overhead cost, energy cost, and post weld treatment cost [1].

However, depending on the welding cost system, whether cost of specific weld, other

cost associated to research and development, process specification and certification,

welding personnel training, and welding consulting (including purchased inspection and

testing services) could be also considered [10].

18

2.4 Welding Quality Measures and Testing

Welding quality measurements and testing performed by the companies is

depicted vertically shows no of companies and horizontally shows the name of testing as

figure no 1. Analytical values in relation to responses obtained shows that 12 (100%)

companies perform visual test, 2 (34%) companies perform penetrant test , 3 (25%)

companies perform pressure test, 3 (25%) companies perform X-ray test (mostly done by

certification body), 6 (50%) of the companies perform magnetic particle test (mostly

done by certification body), 8 (67%) companies perform ultrasonic test (mostly done by

certification body), and 3 (25%) companies perform radiography test (mostly done by

certification body). Test such as pressure test, X- Ray test, ultrasonic test, radiography

test and magnetic particle test are done upon customer request.

19

Fig. 2.1 Non destructive Testing Methods

2.5 Welding Processes Used

The welding process used as indicated by the companies is depicted vertically

shows no of companies and horizontally shows the welding process used figure no 2.

Analytical values in relation to responses obtained shows that 12 (100%) companies use

SMAW, 3 (25%) companies use TIG, 8 (67%) companies use MIG/MAG, 2 (17%)

companies use oxyacetylene welding, 8 (67%) company uses SAW as well as FCAW.

The high level of usage of SMAW is associated to its low investment cost and the area of

application. Also it is as a result of it flexibility and familiarity, the type of dominant.

Materials are applicable for its use and availability of workforce. As already noticed,

most of the welding operations are carried out in the construction industrial sector, thus

favoring the usage of SMAW. However the usage of TIG and MIG/MAG welding

0

2

4

6

8

10

12

14

Visual Test Dye

Penetrant

Test(DPT)

Presure

Test

X-Ray Test Magnetic

Partical

Test(MPI)

Ultrasonic

Test

Radio

Graphy

Test

processes is comparatively higher than the usage of oxyacetylene welding, SAW and

FCAW even though investment cost and usage cost (equipment cost, shielding gas and

other consumable cost) in the former processes is a bit high than the investment cost in

the latter processes. The main reason to this is due to the area of application of the

processes and the suitable material availability. The trend in the usage of welding

processes can be attributed to investment cost, area of application, types of dominant

materials and the availability of workforce.

Fig. 2.2 Welding Processes used in companie

0

2

4

6

8

10

12

14

SMAW

20


hough investment cost and usage cost (equipment cost, shielding gas and



ses and the suitable material availability. The trend in the usage of welding


materials and the availability of workforce.

Welding Processes used in companies

TIG MI/MAG Oxy Acetylene SAW


hough investment cost and usage cost (equipment cost, shielding gas and



ses and the suitable material availability. The trend in the usage of welding


FCAW

2.6 Welding Techniques in Welding Operation

Welding techniques used in welding operations as indicated by the companies are

illustrated as figure no 03. Analytical values in relation to responses obtained shows that

12 (100%) companies employ manual welding technique, 8 (75%) companies employ

semi-automatic welding technique and none employs automatic welding and robotic

welding techniques. It is therefore evident that manual welding technique is the

commonly used welding technique by

investment cost in equipment, machines and infrastructure as compared to the other

welding techniques. Although the initial investment costs and other considerable factors

pertaining to the use of automatic welding and robotic welding techniques are high,

integrating them with manual welding technique would increase productivity

substantially.

Fig. 2.3 Welding Technical in welding operation

However, there is a general mindset that, introducing such sophisticated welding

techniques will affect welder employmen

0

2

4

6

8

10

12

Manual

Welding

21

Welding Techniques in Welding Operation




utomatic welding technique and none employs automatic welding and robotic


commonly used welding technique by the companies. The obvious reason is low initial

n equipment, machines and infrastructure as compared to the other



with manual welding technique would increase productivity

Welding Technical in welding operation


techniques will affect welder employment rate as well as lowering the

Manual

Welding

Semi

Automatic

Automatic Robotic




utomatic welding technique and none employs automatic welding and robotic


. The obvious reason is low initial

n equipment, machines and infrastructure as compared to the other



with manual welding technique would increase productivity


t rate as well as lowering the skill of welders.

Robotic

22

Nevertheless, manual welding technique is a cheap means to utilize the full potentials of

welders.

2.7 Objectives:

The main objectives of this project work are as followings:

i. To find out the various defects on coated and non coated electrodes at the stage

of CO2 gas and absent of CO2 Gas.

ii. To identify the defect detecting techniques used in the metal

manufacturing/structures industries where welding is extensively used in

Bangladesh.

iii. To determine the welding quality, productivity and economy measurement in

companies operating in the metal manufacturing/Structures industries in

Bangladesh.

iv. Among the destructive tests microstructure, composition and tensile test will be

done.

v. Among the non destructive tests dye penetrant test and ultrasonic test will be

done to detect the defect along with its size and/or location.

2.8 Research Methodology:

i. Chamfering the edges of the base metals to produce a Vee.

ii. Employing of a MIG (GMAW) welding machine to weld the base metals for 1 G

and 2 F positions accordingly.

23

iii.

iv. Use flux cored electrode and bare electrode to make the weldments.

v. Destructive tests, microstructure, composition and tensile test will be done. A

sample will be prepared by grinding, using emery of different grade, polishing

and finally etching the produced surface by a special reagent produced as per the

requirement of composition. Composition of the elements will be measured under

SEM or XRD and using UTM (Universal testing machine) tensile tests will be

completed.

vi. Testing of the prepared weldments under dye penetration test and ultrasonic test.

vii. Compare the test results with AWS or ASME code.

viii. Review of literature on current trends in metal production of steel structures and

manufacturing as well as issues in welding quality, welding productivity and

international welding quality standard handbooks and journal were used as

sources of data.

24

Chapter 3

Welding Defects & Non destructive testing

The main and common weld defects include are as following.

i. Lack of fusion

ii. Lack of penetration or excess penetration

iii. Porosity

iv. Inclusions

v. Cracking

vi. Undercut

vii. Lamellar tearing

viii. Blow hole/pin hole

Any of these defects are potentially disastrous as they can all give rise to high stress

intensities which may result in sudden unexpected failure below the design load or in the

case of cyclic loading, failure after fewer load cycles than predicted.

3.1 Description of defects

i and ii. - To achieve a good quality join it is essential that the fusion zone

extends the full thickness of the sheets being joined. Thin sheet material can be joined

with a single pass and a clean square edge will be a satisfactory basis for a join. However

thicker material will normally need edges cut at a V angle and may need several passes to

fill the V with weld metal. Where both sides are accessible one or more passes may be

25

made along the reverse side to ensure the joint extends the full thickness of the metal.

Lack of fusion results from too little heat input and / or too rapid traverse of the welding

torch (gas or electric). Excess penetration arises from to high a heat input and / or too

slows transverse of the welding torch (gas or electric). Excess penetration - burning

through - is more of a problem with thin sheet as a higher level of skill is needed to

balance heat input and torch traverse when welding thin metal.

ii. Porosity - This occurs when gases are trapped in the solidifying weld metal.

These may arise from damp consumables or metal or, from dirt, particularly oil or grease,

on the metal in the vicinity of the weld. This can be avoided by ensuring all consumables

are stored in dry conditions and work is carefully cleaned and degreased prior to welding.

iv. Inclusions - These can occur when several runs are made along a V join when

joining thick plate using flux cored or flux coated rods and the slag covering a run is not

totally removed after every run before the following run.

v. Cracking - This can occur due just to thermal shrinkage or due to a

combination of strain accompanying phase change and thermal shrinkage.

In the case of welded stiff frames, a combination of poor design and inappropriate

procedure may result in high residual stresses and cracking.

Where alloy steels or steels with carbon content greater than about 0.2% are being

welded, self cooling may be rapid enough to cause some (brittle) marten site to form.

This will easily develop cracks. To prevent these problems a process of pre-heating in

stages may be needed and after welding a slow controlled post cooling in stages will be

required. This can greatly increase the cost of welded joins, but for high strength steels,

such as those used in petrochemical plant and piping, there may well be no alternative.

26

vi Undercutting - In this case the thickness of one (or both) of the sheets is

reduced at the toe of the weld. This is due to incorrect settings / procedure. There is

already a stress concentration at the toe of the weld and any undercut will reduce the

strength of the join.

vii Lamellar tearing - This is mainly a problem with low quality steels. It occurs

in plate that has a low ductility in the through thickness direction, which is caused by non

metallic inclusions, such as sup hides and oxides that have been elongated during the

rolling process. These inclusions mean that the plate cannot tolerate the contraction

stresses in the short transverse direction.

Lamellar tearing can occur in both fillet and butt welds, but the most vulnerable

joints are 'T' and corner joints, where the fusion boundary is parallel to the rolling plane.

These problems can be overcome by using better quality steel, 'buttering' the weld area

with a ductile material and possibly by redesigning the joint.

27

3.2 Solidification Cracking

This is also called centerline or hot cracking. They are called hot cracks because

they occur immediately after welds are completed and sometimes while the welds are

being made. These defects, which are often caused by sulphur and phosphorus, are more

likely to occur in higher carbon steels.

Solidification cracks are normally distinguishable from other types of cracks by

the following features:

• they occur only in the weld metal - although the parent metal is almost always the

source of the low melting point contaminants associated with the cracking

• they normally appear in straight lines along the centre line of the weld bead, but

may occasionally appear as transverse cracking

• solidification cracks in the final crater may have a branching appearance as the

cracks are 'open' they are visible to the naked eye

A schematic diagram of a centerline crack is shown below:

On breaking open the weld the crack surface may have a blue appearance, showing the

cracks formed while the metal was still hot. The cracks form at the solidification

boundaries and are characteristically inter dendritic. There may be evidence of

28

segregation associated with the solidification boundary.

The main cause of solidification cracking is that the weld bead in the final stage of

solidification has insufficient strength to withstand the contraction stresses generated as

the weld pool solidifies. Factors which increase the risk include:

• insufficient weld bead size or inappropriate shape

• welding under excessive restraint

• material properties - such as a high impurity content or a relatively large

shrinkage on solidification

Joint design can have an influence on the level of residual stresses. Large gaps between

components will increase the strain on the solidifying weld metal, especially if the depth

of penetration is small. Hence weld beads with a small depth to width ratio, such as is

formed when bridging a large wide gap with a thin bead, will be more susceptible to

solidification cracking.

In steels, cracking is associated with impurities, particularly sulphur and phosphorus and

is promoted by carbon, whereas manganese and sulphur can help to reduce the risk. To

minimize the risk of cracking, fillers with low carbon and impurity levels and relatively

high manganese content are preferred. As a general rule, for carbon manganese steels, the

total sulphur and phosphorus content should be no greater than 0.06%. However when

welding a highly restrained joint using high strength steels, a combined level below

0.03% might be needed.

Weld metal composition is dominated by the filler and as this is usually cleaner than the

metal being welded, cracking is less likely with low dilution processes such as MMA and

29

MIG. Parent metal composition becomes more important with autogenously welding

techniques, such as TIG with no filler.

3.3 Hydrogen induced cracking (HIC)

Hydrogen induced cracking also referred to as hydrogen cracking or hydrogen

assisted cracking, can occur in steels during manufacture, during fabrication or during

service. When HIC occurs as a result of welding, the cracks are in the heat affected zone

(HAZ) or in the weld metal itself.

Four requirements for HIC to occur are:

a) Hydrogen be present, this may come from moisture in any flux or from other sources.

It is absorbed by the weld pool and diffuses into the HAZ.

b) A HAZ microstructure susceptible to hydrogen cracking.

c) Tensile stresses act on the weld

d) The assembly has cooled to close to ambient - less than 150o

C

HIC in the HAZ is often at the toe, but can be under the weld bead or at the weld root .in

fillet welds cracks are normally parallel to the weld run in but welds cracks can be

transverse to the welding direction.

3.4 Non Destructive Testing

Nondestructive Examination (NDE), also referred to as nondestructive testing

(NDT), consists of a wide variety of related technical inspection techniques that are able

to examine and obtain information on materials, components, or welds and compare them

against specific criteria for acceptance or rejection without damaging or destroying them.

30

This is opposed to destructive testing where the part being tested is damaged or destroyed

during the testing process.NDE methods are an integral part of the oil & gas industries

along with several other industries such as aerospace, automotive, chemicals, and

defense. It is important for all refinery and pipeline owners to have a thorough

understanding of NDE and the capability to carry out NDE on components when

necessary. This is because most codes and standards require periodic examination of

machinery and components and thus being able to carry out these inspections as they

come up is an integral part of ensuring safety and continued service.

Some examples of NDE include

• Visual Inspection (VI)

• Dye Penetrant Inspection (DPI)

• Magnetic Particle Testing (MPT)

• Acoustic Emission Testing (AET)

• Eddy Current Array (ECA)

• Ultrasonic Testing (UT).

• Radio Graphic Inspection(RGI)

• X-Ray

31

3.4.1 Visual Inspection

Visual Inspection is the oldest and most basic method of inspection. It is the

process of looking over a piece of equipment using the naked eye to look for flaws. It

requires no equipment except the naked eye of a trained inspector. One can use visual

inspection for the inspection of a variety of equipment. These include storage tanks,

pressure vessels, and piping along with other equipment cover storage tanks [12], covers

pressure vessels [13], covers piping [14]. Visual inspection is simple and less

technologically advanced compared to other methods. Despite this, it still has several

advantages over more high-tech methods. Compared to other methods, it is far more cost

effective. This is because there is no equipment that is required to perform it. For similar

reasons it is also one of the easiest inspection techniques to perform. It is also one of the

most reliable techniques. A well-trained inspector can detect most signs of damage. The

method does come with its fair share of disadvantages as well though. Not every defect or

flaw can be seen with the naked eye. Those that can’t are often just as dangerous, if not

more so, than those that can. This means that in most all cases a visual inspection alone

won’t be enough to ensure total safety. It will need to be supplemented with other, more

advanced, techniques. Also, some flaws, such as subsurface flaws, may be in areas that

are difficult or impossible to examine safely. Flaws in these areas often require other

methods to detect. Although in most of these cases one could use remote visual

inspection instead. Most testing methods rely on sound or electromagnetic waves, or the

inherent properties of the material to work. For example, MPT involves magnetizing

ferrous materials and spreading colored magnetic particles onto it; because of the way

32

magnetic waves work the particles will collect around flaws of defects making them more

visible.

3.4.2 Detection Visual Inspection

Prior to any welding, the materials should be visually inspected to see that they

are clean, aligned correctly, machine settings, filler selection checked, etc.

As a first stage of inspection of all completed welds, visual inspected under good lighting

should be carried out. A magnifying glass and straight edge may be used as a part of this

process. Undercutting can be detected with the naked eye and (provided there is access to

the reverse side) excess penetration can often be visually detected.

3.4.3 Liquid Penetrant Examination (LPE)

Liquid Penetrant Examination (LPE), also referred to as penetrant testing (PT),

liquid penetrant testing (LP), and dye penetrant testing (DP), is a nondestructive

examination (NDE) method that utilizes fluorescent dye to reveal surface flaws on parts

and equipment which might not otherwise be visible. The technique works via the

principle of “capillary action,” a process where a liquid flows into a narrow space without

help from gravity. Because it is one of the easiest and least expensive NDE techniques to

perform, LPE is one of the most commonly used inspection techniques in many

industries, including oil and gas.

Serious cases of surface cracking can be detected by the naked eye but for most cases

some type of aid is needed and the use of dye penetrant methods are quite efficient when

used by a trained operator.

33

This procedure is as follows:

• Clean the surface of the weld and the weld vicinity

• Spray the surface with a liquid dye that has good penetrating properties

• Carefully wipe all the die off the surface

• Spray the surface with a white powder

• Any cracks will have trapped some die which will weep out and discolor the white

coating and be clearly visible

3.4.4 Magnetic Particle Testing (MPT)

Magnetic Particle Testing (MPT) is a nondestructive examination (NDE)

technique used to detect surface and slightly subsurface flaws in most ferromagnetic

materials such as iron, nickel, and cobalt, and some of their alloys. Because it does not

necessitate the degree of surface preparation required by other NDE methods, conducting

MPT is relatively fast and easy. This has made it one of the more commonly utilized

NDE techniques out there today.

MPT is a fairly simple process with two variations: Wet Magnetic Particle Testing

(WMPT) and Dry Magnetic Particle Testing (DMPT). In either one, the process begins

by running a magnetic current through the component. Any cracks or defects in the

material will interrupt the flow of current and will cause magnetism to spread out from

them. This will create a “flux leakage field” at the site of the damage.

The second step involves spreading metal particles over the component. If there

are any flaws on or near the surface, the flux leakage field will draw the particles to the

34

damage site. This provides a visible indication of the approximate size and shape of the

flaw.

There are several benefits of MPT compared to other NDE methods. It is highly

portable, generally inexpensive, and does not need a stringent pre-cleaning operation.

MPT is also one of the best options for detecting fine, shallow surface cracks. It is fast,

easy, and will work through thin coatings. Finally, there are few limitations regarding the

size/shape of test specimens. Despite its strengths, the method is not without its limits.

The material must be ferromagnetic. Likewise, the orientation and strength of the

magnetic field is critical. The method only detects surface and near-to-surface defects.

Those further down require alternative methods. Large currents are sometimes required to

perform this method, thus “burning” of test parts is sometimes possible. In addition, once

MPT has been completed, the component must be demagnetized, which can sometimes

be difficult.

This process can be used to detect surface and slightly sub-surface cracks in Ferro-

magnetic materials (it cannot therefore be used with austenitic stainless steels).

The process involves placing a probe on each side of the area to be inspected and passing a high

current between them. This produces a magnetic flux at right angles to the flow of the current.

When these lines of force meet a discontinuity, such as a longitudinal crack, they are diverted and

leak through the surface, creating magnetic poles or points of attraction. A magnetic powder

dusted onto the surface will cling to the leakage area more than elsewhere, indicating the location

of any discontinuities.

This process may be carried out wet or dry, the wet process is more sensitive as finer

particles may be used which can detect very small defects. Fluorescent powders can also be used

to enhance sensitivity when used in conjunction with ultra violet illumination.

35

3.4.5 Acoustic Emission Testing (AET)

Acoustic Emission Testing (AET) is a nondestructive testing method that is based

on the generation of waves produced by a sudden redistribution of stress in a material.

When a piece of equipment is subjected to an external stimulus, such as a change in

pressure, load, or temperature, this triggers the release of energy in the form of stress

waves, which propagate to the surface and are recorded by sensors. Acoustic emissions

can come from natural sources, such as earthquakes or rock bursts, or from the equipment

itself such as melting, twinning, and phase transformations in metals. Detection and

analysis of AE signals can provide information on the origin and importance of

discontinuities in a material.

AET is different than other NDT techniques in two major ways:

• Instead of supplying energy to the object under examination, AET listens for the energy

released by the object naturally. AE tests can be, and often are, performed on structures

while they are in operation, since this provides adequate loading for propagating defects

and triggering acoustic emissions.

• AET deals with dynamic processes in a material. This is particularly useful because only

active features are highlighted during the examination. Thus, it is possible to discern

between developing and stagnant defects. However, one should be aware that it is

possible for flaws to go undetected if the loading isn’t high enough to cause an acoustic

event that can be detected by the system.

AET is most often used in a dynamic test environment, meaning that it is used to

monitor for crack detection in pressure equipment when the equipment is experiencing an

36

increase in stress. AET systems generally contain a sensor, preamplifier, filter, and

amplifier, along with measurement, display, and storage equipment. Acoustic emission

sensors respond to any dynamic motion caused by an AE event. This is achieved through

transducers which convert mechanical movement into an electrical voltage signal. The

majority of AE equipment responds to movement in a range of 30 kHz to 1 MHz For

materials with high attenuation, such as plastic composites, lower frequencies may be

used to better distinguish AE signals. The inverse is true as well.

Because of its versatility, AET has many applications within the industry, such as

assessing structural integrity, detecting flaws, testing for leaks, or monitoring weld

quality. Because of the diverse number of situations it can be applied to, it sees extensive

use in several areas including: the detection of active corrosion in the bottom of

aboveground storage tanks, detecting creep damage in high energy piping (HEP) systems,

pressure vessel inspection, and leak detection.

3.4.6 Eddy Current Array (ECA)

Eddy Current Array (ECA) is a form of nondestructive eddy current testing that

involves electronically driving eddy current coils placed next to each other in a probe

assembly. Each coil in the probe produces a signal, the strength of which depends on the

phase and amplitude of the object the probe is placed over. This signal can be measured

and the data recorded. This data can then be referenced to an encoded position and time

and represented visually as a C-scan image.

37

In general, eddy current inspections are a method of non-destructive testing that

use the principle of electromagnetic induction. When alternating current is applied to a

conductor, in the case of an eddy current probe, a magnetic field develops around it

which changes in intensity as the current alternates. If another conductor, in this case the

material being tested, is brought close to the first field, a current will be induced in it as

well. If there are any flaws in this material then the eddy current emanating from it will

be distorted.

ECA is capable of reproducing the flaw detection techniques of most other eddy

current methods. This method though had several distinct advantages such as:

• Being able to scan a larger area at one time while maintaining a high resolution,

• A lesser need for complex robotics to actually move the probe,

• Improved flaw detection due to the C-scan imaging, and

• Complex shapes can be inspected using this method because the probes can be

customized to the profile of the part being inspected.

This method is widely used for a number of industry applications. It can be used both

measuring the thickness of steels and detecting corrosion. ECA can be used on materials

as diverse as vessels, columns, storage tanks & spheres, piping systems, and even

structural applications.

38

3.4.7 X-Ray Inspection

Sub-surface cracks and inclusion can be detected X ray examination .this is

expensive but for safety critical joint in submarines and nuclear power points 100% X ray

examination of weld joints will normally be carried out.

3.4.8 Radio graphic Testing

This method of weld testing makes use of X-rays, produced by an X-ray tube, or

gamma rays, produced by a radioactive isotope. The basic principle of radiographic

inspection of welds is the same as that for medical radiography. Penetrating radiation is

passed through a solid object, in this case a weld rather that part of the human body, onto

a photographic film, resulting in an image of the object's internal structure being

deposited on the film. The amount of energy absorbed by the object depends on its

thickness and density. Energy not absorbed by the object will cause exposure of the

radiographic film. These areas will be dark when the film is developed. Areas of the film

exposed to less energy remain lighter. Therefore, areas of the object where the thickness

has been changed by discontinuities, such as porosity or cracks, will appear as dark

outlines on the film. Inclusions of low density, such as slag, will appear as dark areas on

the film while inclusions of high density, such as tungsten, will appear as light areas. All

discontinuities are detected by viewing shape and variation in density of the processed fill

Radiographic testing can provide a permanent film record of weld quality that is

relatively easy to interpret by trained personnel. This testing method is usually suited to

having access to both sides of the welded joint (with the exception of double wall signal

39

image techniques used on some pipe work). Although this is a slow and expensive

method of nondestructive testing, it is a positive method for detecting porosity,

inclusions, cracks, and voids in the interior of welds. It is essential that qualified

personnel conduct radiographic interpretation since false interpretation of radiographs

can be expensive and interfere seriously with productivity. There are obvious safety

considerations when conducting radiographic testing. X-ray and gamma radiation is

invisible to the naked eye and can have serious health and safety implications. Only

suitably trained and qualified personnel should practice this type of testing. In

Radiography Testing the test-part is placed between the radiation source and film (or

detector). The material density and thickness differences of the test-part will

attenuate (i.e. reduce) the penetrating radiation through interaction processes involving

scattering and/or absorption. The differences in absorption are then recorded on film(s) or

through an electronic means. In industrial radiography there are several imaging methods

available, techniques to display the final image, i.e. Film Radiography, Real Time

Radiography (RTR), Computed Tomography (CT), Digital Radiography (DR), and

Computed Radiography (CR) [19]. There are two different radioactive sources available

for industrial use X-ray and Gamma-ray. These radiation sources use higher energy level,

i.e. shorter wavelength, versions of the electromagnetic waves. Because of the

radioactivity involved in radiography testing, it is of paramount importance to ensure that

the Local Rules is strictly adhered during operation. Computed Tomography (CT) is one

of the lab based advanced NDT methods that TWI offers to industry. CT is a radiographic

based technique that provides both cross-sectional and 3D volume images of the object

under inspection. These images allow the internal structure of the test object to be

40

inspected without the inherent superimposition associated with 2D radiography. This

feature allows detailed analysis of the internal structure of a wide range of components

[14].

41

CHAPTER 4

CASE STUDY WITH DATA ANALYSIS

4.1 Description of Phased Array Machine

The EPOCH 1000 is an advanced conventional ultrasonic flaw detector that can

be upgraded with phased array imaging at an authorized Olympus service center. Key

features include: EN12668-1 compliant, 37 digital receiver filter selections, and 6 kHz

pulse repetition rate for high speed scanning. Welding has received a lot of attention

worldwide since it is one of the methods used for joining Materials in the most efficient

and economical way [1, 2]. Recent technologies behind welding have enormously created

opportunities to add more value to welded Steel structural products. Typical Examples

are the automobiles, air-crafts, ships, trains, Steel Structures, offshore platforms. As these

Structures are predominated by metals, the quest for the use of metals in manufacturing

innovative Products by utilizing welding as the main joining process is highly

indispensable. In recent times, the interest in MIG welding activities in up-and- coming

economies in Bangladesh is on the increase. This interest is as a result of the increasing

need to outsource welding manufacturing Jobs to rising economies since welding

manufacturing jobs in developed economies are becoming more expensive but cheaper in

promising economies, and also the need to boost welding purchasing Globally.

42

4.2 Principal of PA Ultrasonic Operation

This method of testing makes use of mechanical vibrations similar to sound waves

but of higher frequency. A beam of ultrasonic energy is directed into the object to be

tested. This beam travels through the object with insignificant loss, except when it is

intercepted and reflected by a discontinuity. The ultrasonic contact pulse reflection

technique is used. This system uses a transducer that changes electrical energy into

mechanical energy. The transducer is excited by a high-frequency voltage, which causes

a crystal to vibrate mechanically. The crystal probe becomes the source of ultrasonic

mechanical vibration. These vibrations are transmitted into the test piece through a

coupling fluid, usually a film of oil, called a coolant. When the pulse of ultrasonic waves

strikes a discontinuity in the test piece, it is reflected back to its point of origin. Thus the

energy returns to the transducer. The transducer now serves as a receiver for the reflected

energy. The initial signal or main bang, the returned echoes from the discontinuities, and

the echo of the rear surface of the test piece are all displayed by a trace on the screen of a

cathode-ray oscilloscope. The detection, location, and evaluation of discontinuities

become possible because the velocity of sound through a given material is nearly

constant, making distance measurement possible, and the relative amplitude of a reflected

pulse is more or less proportional to the size of the reflector.

One of the most useful characteristics of ultrasonic testing is its ability to determine the

exact position of a discontinuity in a weld. This testing method requires a high level of

operator training and competence and is dependent on the establishment and application

of suitable testing procedures. This testing method can be used on ferrous and nonferrous

43

materials, is often suited for testing thicker sections accessible from one side only, and

can often detect finer lines or plainer defects which may not be as readily detected by

radiographic testing [16].

Ultrasonic Testing (UT) is a group of nondestructive examination (NDE)

techniques that use short, high-frequency ultrasonic waves to identify flaws in a material.

They generally work by emitting waves into a material. By measuring these waves, the

properties of the material and internal flaws can be identified. Most UT devices consist of

many separate units. These can include pulsers and receivers, transducers, and display

monitors. The components included depend on the type of UT that the inspector is

performing [16, 17].

There are several different types of ultrasonic testing. These include methods such

as Automated Ultrasonic Backscatter Technique (AUBT), Phased Array Ultrasonic

Testing (PAUT), Long Range Ultrasonic Testing (LRUT), Internal Rotating Inspection

Systems (IRIS), and Time of Flight Diffraction (TOFD).

Automated Ultrasonic Backscatter Technique (AUBT) is a UT technique developed for

detecting damage from High-Temperature Hydrogen Attack (HTHA). The technique is

for use in pressure vessels and piping. The technique makes use of high frequency,

broadband UT probes and a digital oscilloscope. These allow it to provide both an A-

Scan display and frequency analysis.

Phased Array Ultrasonic Testing (PAUT) is a UT technique that utilizes a set of

UT probes made up of numerous (anywhere from 16 to over 250) small elements. Each

of the elements in a PAUT system is able to pulse individually. This is done with

44

computer calculated timing, through a process known as phasing. This allows the system

to steer focused beam through various angles and focal distances.

Long Range Ultrasonic Testing (LRUT) is a UT method developed to allow for

testing large volumes of material from a single test point. This method works by fixing

transducer rings uniformly around a pipe. These rings then generate a series of low

frequency guided waves. The waves can then propagate symmetrically along the pipe

axis. This provides complete coverage of the pipe wall.

An Internal Rotating Inspection System (IRIS) is an ultrasonic technique used to

detect corrosion in piping and tubing. using an internally inserted probe that generates

sound waves. The system works by inserting a probe into a flooded pipe. The probe them

move through the pipe, scanning as it goes.

Time of Flight Diffraction (TOFD) is a method used to look for flaws in welds. It

uses the time of flight of an ultrasonic pulse to find the location of a reflector. To find the

TOF, the method uses a pair of ultrasonic transducers. The transmitter emits low

frequency waves that propagate at an angle. They only diffract back to the receiver if they

hit a defect [13]. In general, UT has several advantages and disadvantages. It’s useful

because it can scan for flaws both on and underneath the surface. It is also useful for it's

incredible accuracy. On the other hand, not all materials are receptive to ultrasonic

testing. It also has the disadvantage that it requires a good deal of skill and training to

perform [19] Surface and sub-surface defects can also be detected by ultrasonic

inspection. This involves directing a high frequency sound beam through the base metal

and weld on a predictable path. When the beam strikes a discontinuity some of it is

45

reflected beck. This reflected beam is received and amplified and processed and from the

time delay, the location of a flaw estimated.

Porosity, however, in the form of numerous gas bubbles causes a lot of low

amplitude reflections which are difficult to separate from the background noise.

Results from any ultrasonic inspection require skilled interpretation.

Table 4.1 Used Apparatus List

Apparatus Name/Testing

Name Description Remark.

UT tools EPOCH 1000I,Phased Array Good condition

Base Material ASTM A572Grade 50 Good condition

DPT Spotcheck Good condition

Reagent Solution of HNO3 and H2SO4 Good condition

Tensile Test Universal Testing Machine Good condition

Microscope Digital optical Microscope Good condition

Table 4.2 Standard as per ASTM A572 Grade 50

Item No Major five elements

(Chemical Composition)% Mechanical Properties

MS Plate C Si Mn P S

Yield

Strength(Mpa)

Tensile Strength

(Mpa) Elongation (%)

0.23 0.4max

1.5D 0 0.1 345 450 21

46

D = For each reduction of 0.01 percentage point below the specified carbon maximum, an

increase of 0.06 percentage point manganese above the specified maximum is permitted,

up to a maximum of 1.60 % [22].

Table 4.3 Testing data for Mechanical Properties

Ty

pe

of

Wel

din

g

Spec

imen

Th

ickn

ess

(mm

)

W

idth

(mm

)

Len

gth

(mm

)

C

ross

sec

tio

nal

Are

a(m

m2)

Ult

imat

e T

ensi

le

Lo

ad

Ult

imat

e T

ensi

le

Str

ength

Yie

ld S

tren

gth

(kN

)

Yie

ld S

tren

gth

(MP

a)

% E

long

atio

n

FCAW

Sample-1 10

45.5 600 455 258 567 190 418 11.5

Sample-2

10 45.5 600 455 255 560 190 418 11.5

Solid

Sample-1 10

45.5 600 455 330 725 232 510 13

Sample-2

10 45.5 600 455 342 751 238 523 13

Fig. 4.1 DPT Solution

47

4.3 Basic Principal of DPT/LPI/DPI

More options have developed in the way liquid penetrant inspection is performed

now a day. Liquid penetrant inspection (LPI), also known as dye penetrant inspection

(DPI) or penetrant testing (PT), was first developed in the early 1940s to detect flaws on

the surface of materials. Although there are more options in the way the test is performed,

the basic principles have not changed over the years. Liquid penetrant inspection is a

nondestructive test method which does not harm the samples or parts being inspected.

The test is very effective in detecting porosity, cracks, fractures, laps, seams and other

flaws that are open to the surface of the test piece and may be caused by fatigue, impact,

quenching, machining, grinding, forging, bursts, shrinkage or overload. As a result, it is

often used on lots of machined parts, as well as weldments, manufactured products,

castings, forgings and other items that will be placed into service. Liquid penetrant

inspection can be used successfully on nonporous and fairly smooth materials such as

metals, glass, plastics and fired ceramics.

This test is named for the liquid, called penetrant, that is applied to the sample

during testing in order to make any surface flaws more visible. A variety of penetrant

materials are available and selection is often based on the required sensitivity level of the

test, equipment available at the test site to conduct the test and other factors

• The penetrant comes in two types of liquids-visible dye (colored red) and fluorescent

dye (colored green-yellow).

48

• Fluorescent penetrants are also classified by sensitivity levels ranging from one through

four, with four being the most sensitive for detecting the finest flaws.

• Penetrants can be washable with water, removable with a solvent or require treatment

with an emulsifier that is lipophilic (oil-based) or hydrophilic (water-based).

4.4 The Process of Testing

The testing process can be broken down into the following distinct steps:

1. Pre-cleaning

2. Penetrant application

3. Penetrant dwell time

4. Penetrant removal

5. Developer application

6. Developer dwell time

7. Inspection

8. Post-cleaning

• Pre-cleaning. The very first step is a thorough surface cleaning to be sure the test

piece is free of oil, grease, water, heat-treat scale, paint, plating and other contaminants

that may prevent liquid penetrant from entering flaws. A solvent is often used for this

step, but the test sample may require steam, vapor, chemical or ultrasonic cleaning. Parts

49

that have been machined, sanded or grit-blasted may require etching to remove material

that could be block the opening of the flaw and prevent the penetrant from entering.

• Penetrant application. Both the visible and fluorescent dye penetrants can be applied

to the test sample by spraying, brushing or immersing the part in a penetrant bath. The

choice of application is usually a matter of preference, but can be influenced by the size

and shape of the test piece, the equipment available for conducting the test or the

requirements of the test specification(s) applicable to the samples.

• Penetrant dwell time. The liquid penetrant is left on the surface for a sufficient time

to allow the liquid to seep into any surface openings or defects. The total time that this

liquid is in contact with the surface of the sample is called the penetrant dwell time.

Dwell time varies for different types of penetrants and is generally dictated by the test

specifications called out for the testing. The surface finish, temperature and type of the

material also will affect dwell requirements.

• Penetrant removal. After the dwell time has elapsed, the excess liquid penetrant is

carefully removed from the surface to avoid removing any of the captured penetrant from

the flaw or defect. When working with a visible dye, excess penetrant is usually removed

with a solvent (solvent-removable). Excess fluorescent dye may be water-washable and

rinsed with water or emulsifiable-post and first treated with an emulsifier before rinsing.

When using the water-washable or post-emulsifiable methods, the part is placed in a low-

temperature oven and allowed time to dry before applying the developer.

• Developer application. A thin layer of developer is applied to the part to assist in

drawing penetrant trapped in flaws back to the surface where it will be visible as

50

indications. Developers may be applied by dusting with a dry powder or spraying a wet

developer. The resulting indications are larger than the actual flaw and have a high level

of contrast between the penetrant and developer, making them more visible to aid in

inspection.

• Developer dwell time. The developer remains on the sample piece for the required

amount of time stated in the test specification to allow indications to develop prior to

inspection.

• Inspection. The inspection process is performed by trained and certified inspectors

using a visual examination. When working with fluorescent penetrants, indications must

be viewed under darkened conditions with a high-intensity UV lamp or black light.

Testing with a visible dye requires sufficient white light. The sample will be accepted or

rejected based on the specification or acceptance criteria followed for the order. The

inspector also will attempt to determine the origin of the discontinuity.

• Post-cleaning. The final step in the process is to thoroughly clean the surface of the

sample to remove any penetrant testing residues.

51

Fig. 4.2 PA Machine

Fig. 4.3 Welding Process

52

Fig. 4.4 Size (T-12,L-600,W-45.5mm) FCAW with CO2 gas after testing

Fig. 4.5 Size (T-12,L-600,W-45.5mm) FCAW without CO2 gas after testing

Fig. 4.6 Size (T-12,L-600,W-45.5mm) Solid Wire with CO2 gas after testing

53

Fig. 4.7 Size (T-12,L-600,W-45.5mm) Solid Wire without CO2 gas after testing

Fig. 4.8 Size (T-12,L-600,W-45.5mm) Butt weld by FCAW with CO2 gas before

testing

Fig. 4.9 Size (T-12,L-600,W-45.5mm) Butt weld by Solid wire with CO2 gas before

testing

54

Fig. 4.10 Section (T-12,L-600,W-200mm) Fillet Weld by FCAW with CO2 gas before

testing

Fig. 4.11 Section (T-12,L-600,W-200mm) Fillet Weld by Solid wire without CO2 Gas

before testing

55

Fig. 4.12 Section (T-12,L-600,W-200mm) FCAW with CO2 gas after testing

Fig. 4.13 Section (T-12,L-600,W-200mm) FCAW without CO2 gas after testing .

4.5 Mild Steel Microstructure Analysis

The Aim of the course is to examine how microstructures are formed in metals

during solidification and heat treatment. To motivate the course, the mechanical

properties of structural materials are introduced through the course. A major focus is the

thermodynamics of the formation of phases and the construction of phase diagrams. The

steels phase diagram is introduced

56

Fig. 4.14 Microstructure for Mild Steel (Magnification 200)

Fig. 4.15 Microstructure for Welded joint of FCAW (Magnification 200)

Fig. 4.16 Microstructure for Welded joint of Solid Wire (Magnification 200)

57

4.6 PAUT Report with Image[21]

Table 4.4 Report of butt weld FCAW with CO2 gas

File:1 Id:AB06 16/11/2015 3:20 PM

Inspector ID:01 Location Note: At SAJ

Engineering

Description: Butt Weld Use

Flux Cored Wire With CO2

7 31.03 2.25 48.20

1L3

Unit:MM - PA

Delay:0.00

Range:100.00

Gain:24.4+0.0dB PRF:920Hz Mode:P/E

Velocity:3221m/s Freq:5.00MHz Filter:1.5-8.5

Zero : NA Energy:100V Rect:Full

Angle:57.0° Damp:50Ω Thick:12.00

Reject:0 Pulser:Square Video Filter:Off

Start:23.80 Width:30.14 Level:80% Alarm:Off

Probe ID:5L16-

A10P

Wedge

ID:SA10P-

N55S

Start

Angle:40

End

Angle:70

Angle

Step:1 Aperture:16

First

Element:1

Calibration:CAL

GAIN Point:1

Calibration:CAL Zero

Overlay

Name:T-12

Weld

Rotation:0

Results: Ok and Satisfactory Result

58

Table 4.5

Report of butt weld FCAW without CO2 gas

File:2 Id:AB14 16/11/2015 3:20 PM


Engineering

Description: Butt Weld Use

Flux Cored Wire Without

CO2

110 24.71 6.21 37.90 3.00 2.00

1L2

Unit:MM - PA

Delay:0.00 Range:100.00







Probe ID:5L16-

A10P

Wedge

ID:SA10P-

N55S

Start

Angle:40

End

Angle:70

Angle

Step:1 Aperture:16

First

Element:1

Calibration:CAL

GAIN Point:1

Calibration:CAL

Zero

Overlay

Name:T-10

Weld

Rotation:0

Result: Found Blow Hole And Lack Of Fusion.

59

Table 4.6 Report of butt weld used Solid wire with CO2 gas

File: 3 Id:AB11 16/11/2015 3:20 PM


Engineering

Description: BUTT WELD

USE SOLID WIRE WITH

CO2

60 19.53 4.59 34.49 2.00 3.00

1L2

Unit:MM –

PA








Probe ID:5L16-A10P

Wedge

ID:SA10P-

N55S

Start Angle:40

End Angle:70

Angle Step:1

Aperture:16 First Element:1

Calibration:CAL

GAIN Point:1

Calibration:CAL

Zero

Overlay Name:T-

10

Weld

Rotation:0

Result: Ok but not get satisfactory result

60

Table 4.7 Report of butt weld solid wire without CO2 gas

File:4 Id:AB07 16/11/2015 3:20 PM


Engineering

Description: Butt Weld Used

Solid Wire Without CO2

59 34.64 8.28 54.92

1L3

Unit:MM – PA








Probe ID:5L16-

A10P

Wedge

ID:SA10P-

N55S

Start

Angle:40

End

Angle:70

Angle

Step:1 Aperture:16

First

Element:1

Calibration:CAL

GAIN Point:1

Calibration:CAL

Zero

Overlay

Name:T-12

Weld

Rotation:0

Result: Not ok and not get satisfactory result.

61

4.8 Testing Result

Table 4.8 Testing Results UT Testing, DPT/LPI, Tensile Testing and Micro Structure

Testing

Testing Name Machine

Name

Category Result Comments

UT Testing

PA

EPOCH

1000I

By Flux core wire with

CO2 gas

Ok as per

AWS code

Satisfactory AWS

D.1.1code

By Solid wire with CO2

gas

Ok but not

satisfactory

as per AWS

D.1.1 code

Found some

dissimilarities

By Flux core wire without CO2 gas

Not Ok as per AWS

D.1.1 code

Found Blow holes, Pin holes, Lack of

fusion.

By Solid wire without

CO2 gas

Not Ok as

per AWS

D.1.1 code

Found Blow hole,

Pin hole, Lack of

fusion AWS

D.1.1code

DPT/LPI

Spotcheck

(SKL-

SP1,SKC-

S,SKD-S2)

Welding by Flux cored with CO2 gas

Ok as per AWS D.1.1

code

Satisfactory AWS D.1.1code

Welding by Flux Core

Wire without CO2

Not Ok as

per ASME

code

Found Blow Holes

Welding by Solid Wire

with CO2

Not

satisfactory

as per AWS

D.1.1code

Found Blow Hole,

Pin Holes AWS

D.1.1code

Welding by Solid Wire without CO2

Not Ok as

per ASME

code

Found Blow Hole, Pin Holes

62

Testing Name Machine Name

Category Result Comments

Tensile

Testing

Universal

Testing

Machine

Welding by FCAW Not Ok as

per ASME

Standard

More Harder

Welding by Solid wire Ok as per

ASTM

Standard

Micro

Structure

Testing

Microscope

Welding by Flux core

wire

Less

percentage of

carbons

Welding by Solid wire More

percentage of

carbons

Mild Steel Ok Ok

63

CHAPTER 5

RESULTS AND DISCUSSION

5.1 Results

The general parameters companies encounter in welding operations in the

Bangladesh as below.

Microstructures:

(a) Found high carbon of solid wire welding than Flux cored arc welding

(b) Found change the Structural Level compared with original Picture.

Strength:

Flux cored arc welding is less stronger than solid wire welding junction.

Quality:

Flux cored arc welding is more quality than solid wire welding

Welding feasibility:

Flux cored arc welding is more prefer than Solid wire

Welding health, safety and environmental issues:

(a) Lack of access to personal protective equipment (PPE), especially right

welding shields or helmet. There is high risk of ocular eye problems among

welders.

64

(b) Welders are over-stressed as a result of the welding technique employed and

long hours of working

(c) The disposal of waste from welding workshops have received less attention,

thus causing environmental problems

Poor welding management practices:

(a) Welders are regarded as low level professionals and are always at the bottom

of the organizational chart

(b) The welding department has been fused together with other departments, thus

leading to improper management as well as records and documentation handling.

Lack of government support:

(a) Very low motivation from the government to create awareness in welding

technology development

(b) No governmental supports such as a government funding agency to promote

research, development and innovation in welding technology.

Poor welding quality practices:

( a) Reluctance in the use of welding quality standards since companies rely on

customer request.

(b) Quality is less attended to since it is compromised with cost.

(c) Types of machines, equipment, materials and electrodes on the market account

for the quality level of manufactured products.

65

5.2 Discussions

Weldments normally contain defects. However we need to keep weld defects at a

minimum level to maintain reliable products. Structural discontinuities that occurs in the

welding process are called welding defects. A weld defect is any physical characteristic

in the completed weld that reduces the strength and/or affects the appearance of the weld.

In the weld, there is change in metallographic structure at certain points which is not

homogenous. The defects normally occurs in weldments are crack, porosity, lack of

fusion, lack of penetration, tungsten inclusion, slag inclusions, oxide inclusions and

undercutting.

Inherent flaws in the work piece of a machine such as cracks, pores and micro cavities

may result is a fatal failure of the machine, thus affecting the production. Hence it is very

important to detect the flaws in the part. Destructive method of testing may not help for

machine parts due to structural damage occurring with it. Thus, Non Destructive Testing

is a method used to test a part for the flaws without affecting the physical properties and

causing no structural damage to it.

Microstructures: From figure 4.14, Fig. 4.15 and Fig. 4.16, it is clear that the micro-

structure of pure base metal before welding is feritic in nature. Welded junction made by

FCAW is to some extent deviated from feritic and pearlitic structure is not fully

developed because of slower heat dissipation due to slag shield. Slag shield slow down

the dissipation rate due to its heat insulating properties being a insulating cover on and

over the junction. Welded junction made by bare electrode is fully developed pearlitic

structure because of comparative quicker heat dissipation due to absence of slag shield.

66

Strength: From Table 4.3 it is clear that ultimate tensile strength of welded junction

using bare electrode is more than that of obtained using flux cored electrode. Cause

behind it is the content of carbon in the junction made by using bare electrode is more

than the junction made by using flux cored electrode. Slower heat dissipation rate allow

the trapped carbon to release easily in case of FCAW. For this reason, junction made by

using flux cored electrode becomes tougher than that of obtained by using bare electrode

due to increase in ductility and malleability.

Quality: The overall quality of FCAW product is defect free which is clear from Table

4.4.

67

CHAPTER 6

CONCLUSIONS AND RECOMMENDATIONS

6.1 Conclusions

From the above experimentation the following conclusions can be drawn:

i. As compared to base metal percent of carbon content in weldment

microstructure is higher in case of solid wire than that of FCAW.

ii. Less strong joints are produced in case of FCAW because this type of

junctions composes with lesser carbon. As a result tougher junctions along

with good quality are produced under FCAW.

iii. In Bangladesh, Welding is extensively used in construction industrial sector,

capitalized repair and maintenance industrial sector and the heavy industrial

manufacturing sector.

iv. Weld quality is assessed through destructive test and also non-destructive test

according to standards such as the ASME, ABS, BS, API, AWS and also ISO

3834.

v. With reference to welding processes, the SMAW, TIG and MIG/MAG are

used in welding operations. As a result of low investment cost, the SMAW is

the commonly used welding process. Moreover, the use of MIG/MAG has

been considered as better competitive option to SMAW despites the cost

involved in its usage.

vi. Welding health, safety and environmental issues were the main challenges

companies encounter in their day-to-day operations. Poor welding

68

management practices, lack of government support, poor welding productivity

practices and lack of welding education, training, qualification and

certification are the problems hindering the progress and competitiveness of

companies.

6.2 Recommendations:

Based on the findings and conclusions of this research work, the author have

proposed a number of recommendations in tabular format considering challenges and its

remedial recommendations which could be useful and wealth exploiting for companies in

the Bangladesh also for Finnish companies and higher education institutions as well as

the entire international community if treated with urgency.

Challenges Remedial Recommendations

1. The use of

MIG/MAG Process

Considering the fast production rate, uninterrupted

electrode supply, smoothness in operation, surface

finish, minimum number of defects and post

operation cleaning industry should use MIG / MAG

Process.

2. Welding health,

safety and

environmental

issues

a. Welding personnel should be educated on the use

of protective equipment and should be entrusted to

use them.

b. Waste from welding workshops must be disposed

appropriately through waste management agencies.

c. Welders must be covered with insurance schemes

to safeguard their profession.

d. Management should focus on welders and also

device strong management methods to develop

welders quality and productivity levels.

3. Poor Welding

management

practices

a. The welding workshop must be managed separately

from other departments so that proper records and

documentation could be tracked.

69

b. Total welding management principle or lean

management principles should be practiced to improve issues in quality and productivity in welding.

4. Poor Welding

quality practices

a. Companies must be encouraged to use welding

standards and follow the requirement so as to be

competitive on the domestic and international markets.

b. Companies must be enforced to carry out routine

maintenance on their equipment and machines.

70

REFERENCES

[1] H. B. Cary and S. C. Helzer, Modern Welding Technology, Pearson Education,

Inc.: New Jersey, USA, 2005.

[2] H. B. Cary and S. C. Helzer, Modern Welding Technology, Pearson Education,

Inc.: New Jersey, USA, 2005.

[3] M. Ericsson, "Trends in the Mining and Metal Industry," International Council on

Mining and Metals, London, UK, 2012.

[4] A. Cullision and M. Johnson, "Welding Forges into the Future," American

Welding Society, 1999.

]5] I. Heras, M. Casadesus and C. Ochao, "Effect of ISO 9000 Certification on

Companies Profitability: An Empirical Study," in Integrated Management:

Proceedings of the 6th International Conference on ISO 9000 and TQM, Spain,

2001.

[6] Royal Dutch Shell Plc., "Technology in the Artic," Shell Exploration and

Production International B.V, The Netherlands, 2011.

[7] J. Martikainen, "Total Welding Quality Management for Customer-Oriented

Mechanical Workshop," in International Conference on Total Welding

Management in Industrial Applications, Lappeenranta, Finland, 2007.

[8] Finnish Standard Association - SFS, "Quality Requirement for Fusion Welding of

Metallic Materials - Part 2: Comprehensive Quality Requirement (ISO 3834-

2:2005)," European Standard, 2005.

71

[9] R. Ratnayake, "An Algorithm to Prioritize Welding Quality Deterioration Factors:

A case study from a piping component fabrication process," Emerald Group

Publishing Limited, vol. 30, no. 6, pp. 616-638, 2013.

[10] G. Mathers, "Welding Cost," Job Knowledge 96, 30 July 2013.

[11] David J Grieve, Welding quality and acknowledge of welding18th September

2003.

[12] Anonymous, API 510, Pressure Vessel Inspection Code.

[13] Anonymous, API 570, Piping Inspection Code.

[14] Anonymous, API 653, Tank Inspection, Repair, Alteration, and Reconstruction

[15] Anonymous, ESAB Knowledge center.

[16] Mailloux R., ‘Phased Array Antennas Handbook’, Vol.1 pp.313-356

[17] Brookner, E. ‘Practical Phased Array Antenna Systems.

[18] Paul A. Meyer, Ultrasonic Testers To Detect Surface, Sub-surface And

Dimensional Flaws Detector, USA

[19] Kraut Kramer Branson, Ultrasonic Testing equipment and accessories for

industrial NDT,USA

[21] Anonymous, American Welding Society, Welding defect and visual inspection

table 6.1, PP-199 to 220

[22] Anonymous, ASTM A572, “Chemical Requirement Heat Analysis.

Designation”A 572/A 572M – 06, Page-1 to 3

72

APPENDICES

A. Review of

Requirements

The manufacturer must review product standards to be used in

conjunction with statutory and regulatory requirements as well

as any additional requirement, etc

B. Technical review

The manufacturer must review technical requirements right

from the start of the welding operation to the end. These

technical requirements to be reviewed include elements number

from ‘‘C to O’’ in the column of the welding quality

requirements element in this table.

C. Welding Personnel

Welders and welding operators – The qualification of such

personnel shall be approved by an appropriate test as specified

in ISO 3834-5:2005 quality requirement for arc welding,

electron beam welding, laser beam welding, gas welding and other welding processes.

Welding coordination personnel – The quality activities

performed by such personnel shall be vividly defined as

specified in ISO 3834-5:2005 quality requirement for arc

welding, electron beam welding, laser beam welding, gas

welding and other welding processes.

D. Inspection and

testing personnel

Non-destructive testing personnel – A qualified personnel shall

be responsible for the planning, performing, and supervision of

the inspection and testing of welding operations as specified in

ISO 3834-5:2005 quality requirement for arc welding, electron

beam welding, laser beam welding, gas welding and other

welding processes.

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E. Equipment

Production and testing equipment-

The availability of equipment is required when necessary. These include: power sources, joint and surface preparation equipment,

thermal cutting equipment, jigs and fixtures, cranes and

handling equipment, personal protective and safety equipment,

ovens, quivers for treatment of welding consumables, surface

cleaning facilities, destructive and non-destructive facilities, etc.

Description of equipment – A list of important equipment for

production must be maintained in order to evaluate the

capability and capacity of a workshop. These include:

maximum capacity of cranes, handling capacity of the

workshop, capacity of mechanized or automatic welding

equipment and forming equipment, post-weld heat treatment

dimension and maximum temperature.

Suitability of equipment – The equipment must be suitable for the intended job.

New equipment - Testing and documentation conforming to

appropriate standards shall be performed for newly installed

equipment.

Equipment maintenance – The manufacturer must have a plan to

maintain its equipment and document the outcomes. Items such

as cables, hoses, connectors, flow meters, measuring

instruments must be checked and defective once should not be

used.

F. Welding and

related activities

Production planning – The manufacturer is to ensure adequate

production planning including sequence and identification of

individual processes for construction; specification for inspection and testing; environmental conditions; and allocating

qualified personnel, etc. Welding-procedure specifications – The

manufacturer must prepare and ensure the use of the welding-

procedure specification correctly in production as specified in



welding processes.

Qualification of the welding procedures – Relevant product

standards must be used to qualify welding procedures before

production as specified in ISO 3834-5:2005 quality requirement

for arc welding, electron beam welding, laser beam welding, gas

welding and other welding processes.

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Work instructions – The manufacturer must decide to use

instructions in the welding-procedure specification or a work instruction prepared from a qualified welding-procedure

specification.

Procedures for preparation and control of documents – The

manufacturer establishes and maintains procedures for the

preparation and control of important quality documents

including welding-procedure specification, welding-procedure

qualification record, welders and welding-operations

qualification certificates.

G. Welding

consumables

Batch testing – Welding consumables shall be batch tested if

specified.

Storage and handling – With reference to the supplier’s

recommendation, the storage, handling, identification and use of welding consumables which eschew moisture pick-up,

oxidation, and damage shall be produced and implemented by

the manufacturer.

H. Storage of parent

materials

Identification shall be maintained during storage in order not to

destroy materials.

I. Inspection and

testing

Inspection and testing before welding – The suitability; validity

of welding personnel qualification certificates; welding-

procedure specification; identity of parent material and welding

consumables; joint preparation; fit-up, jigging and tacking; and

working conditions for welding such as environment should be

checked.

Inspection and testing during welding – Welding parameters such as welding current, arc voltage and travel speed; and

preheating/inter pass temperature; cleaning and of runs and

layers of weld metal; back gouging; welding sequence; correct

use and handling of welding consumables; control of distortion;

intermediate examination should be checked at suitable intervals

or by continuous monitoring as specified in ISO 3834-5:2005

quality requirement for arc welding, electron beam welding,

laser beam welding, gas welding and other welding processes.

Inspection and testing after welding – Visual inspection; non-

destructive inspection; destructive inspection; form, shape and

dimension of the construction; and results and records of post-

weld operations should be checked after welding as specified in


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welding processes.

Inspection and test status – Measurements shall be taking to

indicate test of the welded construction.

J. Non-conformance

and corrective

actions

Measurements should be implemented to control items and

activities in order to prevent re-occurrences of non-

conformances. Repair works should be re-inspected,

K. Inspector’s

qualifications,

acceptance criteria

The requirements for the Inspector’s qualifications and

responsibilities, acceptance criteria for discontinuities, and

procedures for NDT according to AWS D1.1/D1.1M:2004 “An

American National Standard”. Chapter 6

comparison between welding defects caused by flux …

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