Applied Welding Engineering. Processes, Codes, and Standards

334 Pages·2012·5.027 MB·English

by  Ramesh Singh (Auth.)

Applied Welding Engineering:
Processes, Codes and Standards
Applied Welding
Engineering: Processes,
Codes and Standards
By Ramesh Singh
AMSTERDAM • BOSTON • HEIDELBERG • LONDON
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First edition 2012
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Dedication
This book is dedicated to the memory of Sgt SA Siddique of the Indian Air
Force. I am eternally grateful to Sgt Siddique for instilling the seeds of met-
allurgy and welding engineering in my mind, and for his training in thought
processing and hard work. This book is just a small token of gratitude to the
great teacher.
Preface
There are several books on the market that address the needs of academia.
Some others address specific topics, and are aimed at that particular segment
of readers who are aware of the subject matter but are in search of new per-
spectives or new findings.
This book, Applied Welding Engineering, aims to bridge the gap left by
the two segments described above. It intends to support the under-supported,
by giving a practical perspective to the theoretical texts. Hopefully the stu-
dents trying to steer through the terminologies of the field, balancing theory
with the practical side of welding engineering, will find this book useful in
bridging that gap. The objective is to keep the budding engineers moored in
the theory taught in university and colleges while exploring the real world of
practical welding engineering. The book is also aimed at engineers, non-engi-
neers, managers and inspectors, to serve as a body of knowledge and source of
reference.
In writing this book I do not claim originality on all thoughts and
words; on a universal subject like welding engineering no single source can
claim the originality of thought. A lot of information contained in this book
comes from my personal experience, and also from several industry publica-
tions like the American Society of Mechanical Engineers (www.asme.org),
American Welding Society (www.aws.org), American Society of Metals
(www.asminternational.org), NACE International (www.nace.org), American
Petroleum Institute (www.api.org), etc. and several training manuals including
The Welding Institute, UK (www.twi.co.uk), Indian Air Force training manu-
als, ASNT (www.asnt.org), the Canadian Standard Association (www.cas.com)
and Canadian General Standard Board (CGSB) (www.tpsgc-pwgsc.gc.ca), just
to name a few. It is not possible for me to distinguish which part of my experi-
ence is gained from which specific source, but I cannot deny their combined
contribution in developing my knowledge base over the years. I acknowledg
them all, and I am proud of that. Where I have consciously borrowed matters
and ideas directly from theses sources, I have acknowledged them as best as
I can and appreciate the great service these bodies have rendered to welding
engineering.
Those individuals who need more detailed study on any specific topic cov-
ered in this book must reach out to these specialized associations and institu-
tions for further guidance. There are several published works available from
these bodies that can be of help in developing in-depth understanding of spe-
cific subjects.
xxi
Acknowledgment
Writing this book made me realize how dependent a person is on others in
accomplishing a task of this nature. The process started with retrieving several
years of notes, handouts and hand-written chits. Some were from as far back
as 1969, some of them had turned yellow and were torn, stained with sweat
and dirt, possibly from those physical punishments that were liberally given
to us as students in the Air Force Institute. Some of the papers were torn at the
folds, and tapes were used to save them until I had used the information con-
tained there. I needed help for all this.
I am extremely grateful to the management and team of Gulf Interstate
Engineering, Houston (www.gie.com) for creating an environment that encour-
aged me to write this book. I am especially grateful to James McLane Jr. III,
my friend and colleague at Gulf Interstate Engineering, who encouraged me
to take up this project. I am also indebted to the encouragement, support and
help from my friend Olga Ostrovsky. She helped me to negotiate the obstacles
of writing and editing the drafts. Without her expert help this book would not
have been possible.
Last, but not the least, I am also grateful to my loving wife Mithilesh, and
my son Sitanshu for their support in accomplishing this goal. Mithilesh toler-
ated my indulgence with the project. Without her support and understanding
this task would not have been possible.
Finally, a few words on the dedication of this book. I have dedicated this
book to Sergeant SA Siddique of the Indian Air Force. Sergeant Siddique
taught me the first lessons of metallurgy and welding engineering. Drawing
on my Indian ethos I know the protocol, “Teacher takes precedence even over
God”, hence the dedication.
xxiii
Chapter 1
Introduction
Chapter Outline
Pure Metals and Alloys 4
Smelting 4
Iron 4
Sponge Iron 4
When we talk of metallurgy as being a science of metals, the first question that
arises in the mind is what is a metal?
Metals are best described by their properties. They are crystalline in the solid
state. Except for mercury, metals are solid at room temperature; mercury is a
metal but in liquid form at room temperature. Metals are good conductors of
heat and electricity, and they usually have comparatively high density. Most
metals are ductile, a property that allows them to be shaped and changed per-
manently without breaking by the application of relatively high forces. Metals
can be either elements, or alloys created by man in pursuit of specific properties.
Aluminum, iron, copper, gold and silver are examples of metals which are ele-
ments, whereas brass, steel, bronze etc. are examples of manmade alloy metals.
Metallurgy is the science and technology of metals and alloys. The study of
metallurgy can be divided into three general sections.
1. Process metallurgy
Process metallurgy is concerned with the extraction of metals from their
ores and the refining of metals. A brief discussion on the production of
steel, castings and aluminum is included in this section.
2. Physical metallurgy
Physical metallurgy is concerned with the physical and mechanical properties
of metals as affected by their composition, processing and environmental con-
ditions. A number of chapters in this section specifically address this topic.
3. Mechanical metallurgy
Mechanical metallurgy is concerned with the response of metals to applied
forces. This is addressed in subsequent chapters of this section.
Applied Welding Engineering: Processes, Codes and Standards.
Copyright © 22001122 Elsevier Inc. All rights reserved. 3
4 SECTION | 1 Introduction to Basic Metallurgy
PURE METALS AND ALLOYS
Pure metals are soft and weak and are used only for specialty purposes such as
laboratory research work, or electroplating. Foreign elements (metallic or non-
metallic) that are always present in any metal may be beneficial, detrimental or
have no influence on a particular property. Disadvantageous foreign elements
are called impurities, while advantageous foreign elements are called alloying
elements. When these are added deliberately, the resulting metal is called an
alloy. Alloys are grouped and identified by their primary metal element, e.g.
aluminum alloy, iron alloy, copper alloy, nickel alloy etc.
Most of the metallic elements are not found in a usable form in nature.
They are generally found in their various oxide forms, called ores. Metals are
recovered from these ores by thermal and chemical reactions. We shall briefly
discuss some of these processes. Those for the most common and most abun-
dantly used metal – iron – are discussed in the following paragraphs.
SMELTING
Smelting is an energy-intensive process used to refine an ore into a usable
metal. Most ore deposits contain metals in the reacted or combined form.
Magnetite (Fe O ), hematite (Fe O ), goethite (αFeO(OH)), limonite (generic
3 4 2 3
formula: FeO(OH).nH O) and siderite (FeCO ) are iron ores, and Cu FeSO
2 3 5 4
is a copper ore. The smelting process melts the ore, usually for a chemical
change to separate the metal, thereby reducing the one to metal or refining it
to metal. The smelting process requires lots of energy to extract the metal from
the other elements.
There are other methods of extraction of pure metals from their ores: appli-
cation of heat, leaching in a strong acidic or alkaline solution, and electrolytic
processes are all used.
IRON
The modern production process for recovery of iron from ore includes the use
of blast furnaces to produce pig iron, which contains carbon, silicon, man-
ganese, sulfur, phosphorus, and many other elements and impurities. Unlike
wrought iron, pig iron is hard and brittle and cannot be hammered into a
desired shape. Pig iron is the basis of the majority of steel production.
Sponge Iron
Removing the oxygen from the ore by a natural process produces a relatively
small percentage of the world’s steel. This natural process uses less energy and
is a natural chemical reaction method. The process involves heating naturally
occurring iron oxide in the presence of carbon, which produces ‘sponge iron’.
In this process the oxygen is removed without melting the ore.
Chapter | 1 Introduction 5
Iron oxide ores, as extracted from the earth, are allowed to absorb carbon
by a reduction process. In this natural reduction reaction, as the iron ore is
heated with carbon it gives the iron a pock-marked surface, hence the name
sponge iron. The commercial process is a solid solution reduction; also called
direct-reduced iron (DRI). In this process the iron ore lumps, pellets, or fines
are heated in a furnace at 800–1,500°C (1,470– 2,730°F) in a carburizing envi-
ronment. A reducing gas produced by natural gas or coal, and a mixture of
hydrogen and carbon monoxide gas provides the carburizing environment.
The resulting sponge iron is hammered into shapes to produce wrought
iron. The conventional integrated steel plants of less than one million tons
annual capacity are generally not economically viable, but some of the smaller
capacity steel plants use sponge iron as charge to convert iron into steel. Since
the reduction process is not energy intensive, the steel mills find it a more
environmentally acceptable process. The process also tends to reduce the cost
of steel making. The negative aspect of the process is that it is slow and does
not support large-scale steel production.
Iron alloys that contain 0.1% to 2% carbon are designated as steels. Iron
alloys with greater than 2% carbon are called cast irons.
Chapter 2
Alloys
Chapter Outline
Alloys 7 Effects of Alloying
Effects of Alloying Elements 8 Elements on Carbide 10
Carbon Steels 8 Nickel Steels (2xx Series) 10
Sulfur 8 Nickel-Chromium
Manganese 8 Steels (3xx Series) 10
Phosphorus 9 Manganese Steels
Silicon 9 (31x Series) 10
Alloy Steels 9 Molybdenum Steels
The Effect of Alloying (4xx Series) 11
Elements on Ferrite 9 Chromium Steels
(5xx Series) 11
ALLOYS
An alloy is a substance that has metallic properties and is composed of two or
more chemical elements, of which at least one, the primary one, is a metal. A
binary alloy system is a group of alloys that can be formed by two elements
combined in all possible proportions.
Homogeneous alloys consist of a single phase and mixtures consist of sev-
eral phases. A phase is anything that is homogeneous and physically distinct if
viewed under a microscope. When an allotropic metal undergoes a change in
crystal structure, it undergoes a phase change.
There are three possible phases in the solid state:
l Pure metal
l Intermediate alloy phase or compound
l Solid solution.
Compounds have their own characteristic physical, mechanical, and chemi-
cal properties and exhibit definite melting and freezing points. Intermetallic
compounds are formed between dissimilar metals by chemical valence rules, and
generally have non-metallic properties; Mg Sn and Cu Se are examples of these.
2 2
Applied Welding Engineering: Processes, Codes and Standards.
Copyright © 22001122 Elsevier Inc. All rights reserved. 7