Applied welding engineering : Processes, codes and standards

Applied Welding Engineering:

Processes, Codes and Standards

Applied Welding

Engineering: Processes,

Codes and Standards

By Ramesh Singh

AMSTERDAM • BOSTON • HEIDELBERG • LONDON

NEW YORK • OXFORD • PARIS • SAN DIEGO

SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO

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11 12 13 14 15 16 10 9 8 7 6 5 4 3 2 1

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.

Dedication

xxi

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.

Preface

xxiii

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.

Acknowledgment

Applied Welding Engineering: Processes, Codes and Standards.

Copyright © 2012 Elsevier Inc. All rights reserved. 3

Introduction

Pure Metals and Alloys 4

Smelting 4

Iron 4

Sponge Iron 4

Chapter Outline

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.

Chapter 1

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 (Fe3O4), hematite (Fe2O3), goethite (αFeO(OH)), limonite (generic

formula: FeO(OH).nH2O) and siderite (FeCO3) are iron ores, and Cu5FeSO4

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.

Applied Welding Engineering: Processes, Codes and Standards.

Copyright © 2012 Elsevier Inc. All rights reserved. 7

Alloys

Alloys 7

Effects of Alloying Elements 8

Carbon Steels 8

Sulfur 8

Manganese 8

Phosphorus 9

Silicon 9

Alloy Steels 9

The Effect of Alloying

Elements on Ferrite 9

Effects of Alloying

Elements on Carbide 10

Nickel Steels (2xx Series) 10

Nickel-Chromium

Steels (3xx Series) 10

Manganese Steels

(31x Series) 10

Molybdenum Steels

(4xx Series) 11

Chromium Steels

(5xx Series) 11

Chapter Outline

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; Mg2Sn and Cu2Se are examples of these.

Chapter 2

8 SECTION | 1 Introduction to Basic Metallurgy

Interstitial compounds are formed between transition metals such as tita￾nium and iron with hydrogen, oxygen, carbon, boron, and nitrogen. They are

usually metallic, with high melting points and are extremely hard; TiC and

Fe3C are examples of interstitial compounds.

Electron compounds are formed from materials with similar lattice systems

and have a definite ratio of valence electrons to atoms; Cu3Si and FeZn are

examples of electron compounds.

Solid solutions are solutions in the solid state and consist of two kinds of

atoms combined in one kind of space lattice. The solute atoms can be present

in either a substitutional or an interstitial position in the crystal lattice.

There are three possible conditions for solid solutions:

l Unsaturated

l Saturated and

l Supersaturated.

The solute is usually more soluble in the liquid state than in the solid state.

Solid solutions show a wide range of chemistry so they are not expressed as

a chemical formula. Most solid solutions solidify over a temperature range,

rather than having a defined freezing point.

Having gained this basic understanding of alloy formation and type of

alloy, we move forward to learn about a specific alloy – steel – and the effects

of various alloying elements on its properties.

EFFECTS OF ALLOYING ELEMENTS

Carbon Steels

Metals are alloyed for a specific purpose, generally with the aim of improving a

property or a specific set of properties. In order to take full advantages of such

alloying, it is important that the resulting property of alloying elements is known.

In the following discussions we shall learn, with the help of steel metallurgy,

about some of the most common alloying practices and the resulting alloy metals.

Sulfur

Sulfur in steel is generally kept below 0.05% as it combines with iron to form

FeS, which melts at low temperatures and tends to concentrate at grain bounda￾ries. At elevated temperatures, high sulfur steel becomes hot-short due to melting

of the FeS eutectic. In free-machining steels, the sulfur content is increased to

0.08% or 0.35%. The sulfide inclusions act as chip breakers, reducing tool wear.

Manganese

Manganese is present in all commercial carbon steels in the range of 0.03%

to 1.00%. Manganese functions to counteract the effect of sulfur by forming

Chapter | 2 Alloys 9

MnS. Any excess manganese combines with carbon to form Mn3C; the com￾pound associated with cementite. Manganese also acts as a deoxidizer in the

steel melt.

Phosphorus

Phosphorus in steel is kept below 0.04%. The presence of phosphorus at lev￾els over 0.04% reduces the steel’s ductility, resulting in cold-shortness. Higher

levels (from 0.07% to 0.12%) are included in steels that are specifically devel￾oped for machining, to improve cutting properties.

Silicon

Silicon is present in most steels in the 0.05% to 0.3% range. Silicon dissolves

in ferrite, increasing its strength while maintaining ductility. Silicon promotes

deoxidation in the molten steel through the formation of SiO2, hence it is an

especially important addition in castings.

ALLOY STEELS

Plain carbon steel is satisfactory where strength and other property requirements

are not severe, and when high temperatures and corrosive environments are not a

major factor in the selection of a material. Alloy steels have characteristic prop￾erties, due to some element other than carbon being added to them. Alloying ele￾ments are added to obtain several properties including the following:

l Increased hardenability

l Improved strength at ambient temperatures

l Improved mechanical properties at low and high temperatures

l Improved toughness

l Improved wear resistance

l Increased corrosion resistance

l Improved magnetic permeability or magnetic retentivity.

There are two ways in which alloyed elements are distributed in the main

constituents of steel:

l Dissolved in ferrite

l Combined with carbon to form simple or complex carbides.

THE EFFECT OF ALLOYING ELEMENTS ON FERRITE

Nickel, aluminum, silicon, copper, and cobalt are all elements which largely

dissolve in ferrite. They tend to increase the ferrite’s strength by solid solution

hardening.

10 SECTION | 1 Introduction to Basic Metallurgy

Alloying elements change the critical temperature range, eutectoid point

position, and location of the alpha (α) and gamma (γ) fields on the iron-iron

carbide phase diagram. These changes affect the heat-treating requirements

and final properties of alloys.

EFFECTS OF ALLOYING ELEMENTS ON CARBIDE

Carbide-forming elements, including manganese, chromium, tungsten, molyb￾denum, vanadium, and titanium, increase room temperature tensile properties

since all carbides are hard and brittle. The order of increasing effectiveness

is chromium, tungsten, vanadium, molybdenum, manganese, nickel, and sili￾con. Of these, nickel and silicon do not form carbides. Complex carbides are

sluggish and hard to dissolve. They act as inhibitors to grain growth and often

improve high temperature properties. Chromium and vanadium carbides are

exceptionally hard and wear resistant.

Tempering temperatures are raised significantly and in some cases sec￾ondary hardening may occur with higher tempering temperatures due to the

delayed precipitation of fine alloy carbides.

Some of the alloys in general use are discussed briefly here.

Nickel Steels (2xx Series)

Nickel has unlimited solubility in γ-iron and is highly soluble in ferrite. It

widens the range for successful heat treatment, retards the decomposition of

austenite, and does not form carbides.

Nickel promotes the formation of very fine and tough pearlite at lower car￾bon contents, thus, toughness, plasticity, and fatigue resistance are improved.

Nickel alloys are used for high-strength structural steels in the as-rolled condi￾tion and for large forgings that cannot be hardened by heat treatment.

Nickel-Chromium Steels (3xx Series)

The effect of nickel on increasing toughness and ductility is combined with

the effect of chromium on improving hardenability and wear resistance. The

combined effect of these two alloying elements is often greater than the sum of

their individual effects.

Manganese Steels (31x Series)

Manganese is one of the least expensive of the alloying elements and is always

present as a deoxidizer and to reduce hot-shortness. When the manganese

content exceeds 0.8%, it acts as an alloying element to increase strength and

hardness in high carbon steels. Fine-grained manganese steels have excellent

toughness and strength.

Steels with greater than 10% manganese remain austenitic after cooling

and are known as Hadfield manganese steel. After heat treatment, this steel has

Chapter | 2 Alloys 11

excellent toughness and wear resistance as well as high strength and ductility.

Work hardening occurs as the austenite is strain hardened to martensite.

Molybdenum Steels (4xx Series)

Molybdenum has limited solubility in α and γ-iron and is a strong carbide

former. It has a strong effect on hardenability and increases high-temperature

strength and hardness. Molybdenum alloys are less susceptible to temper brit￾tleness. Chromium-molybdenum alloys (AISI 41xx) are relatively cheap and

ductile, have good hardenability, and are weldable.

Chromium Steels (5xx Series)

Chromium forms both simple (Cr7C3 and Cr4C) and complex carbides

[(FeCr)3C]. These carbides have high hardness and resist wear. Chromium is

soluble up to about 13% in γ-iron and has unlimited solubility in ferrite. It

increases the strength and toughness of the ferrite and improves high-tempera￾ture properties and corrosion resistance.