Applied Welding Engineering: Processes, Codes, and Standards

Applied Welding Engineering: Processes, Codes, and Standards

by Ramesh Singh

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Product Details

ISBN-13: 9780128041765
Publisher: Elsevier Science
Publication date: 11/10/2015
Pages: 444
Product dimensions: 6.00(w) x 9.00(h) x 0.90(d)

About the Author

Ramesh Singh, MS, IEng, MWeldI, is registered as Incorporated Engineer with British Engineering Council UK and a Member of The Welding Institute, UK. He worked as engineer for various operating and EPC organizations in Middle East, Canada and US. Most recently, he worked for 10 years with Gulf Interstate Engineering, Houston, TX. He is now consulting in the fields of pipeline integrity and related materials and corrosion topics. Ramesh is a graduate from Indian Air Force Technical Academy, with diplomas in Structural Fabrication Engineering and Welding Technology. He has been member and officer of the Canadian Standard Association and NACE and serves on several technical committees. He has worked in industries spanning over aeronautical, alloy steel castings, fabrication, machining, welding engineering, petrochemical, and oil and gas. He has written several technical papers and published articles in leading industry magazines, addressing the practical aspects of welding, construction and corrosion issues relating to structures, equipment and pipelines.

Read an Excerpt

Applied Welding Engineering: Processes, Codes and Standards


By Ramesh Singh

Butterworth-Heinemann

Copyright © 2012 Elsevier Inc.
All right reserved.

ISBN: 978-0-12-391917-5


Chapter One

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 permanently 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 elements, 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 conditions. 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.

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 nonmetallic) 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 abundantly 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: application 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, manganese, 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.

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 environment. 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 Two

Alloys

Chapter Outline

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

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 several 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:

• Pure metal

• Intermediate alloy phase or compound

• Solid solution.

Compounds have their own characteristic physical, mechanical, and chemical 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.

Interstitial compounds are formed between transition metals such as titanium 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:

• Unsaturated

• Saturated and

• 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 boundaries. 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 MnS. Any excess manganese combines with carbon to form Mn3C; the compound 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 levels 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 developed for machining, to improve cutting properties.

(Continues...)



Excerpted from Applied Welding Engineering: Processes, Codes and Standards by Ramesh Singh Copyright © 2012 by Elsevier Inc.. Excerpted by permission of Butterworth-Heinemann. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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Table of Contents

Section 1: Introduction to Basic Metallurgy 1: Introduction 2: Alloys 3: Physical Metallurgy 4: Structure of Materials 5: Production of Steels 6: Classification of Steels 7: Cast Iron 8: Stainless Steels 9: Non-Ferrous Materials 10: Working with Metals 11: Mechanical Properties and Testing of Metals 12: Heat Treatment of Steels

Section 2: Welding Metallurgy & Welding Processes 1: Introduction 2: Physics of Welding 3: Welding and Joining Processes 4: Effect of Heat on Material During Welding 5: Stresses, Shrinkage and Distortion in Weldments 6: Welding, Corrosion Resistant Alloys-Stainless Steel 7: Welding Non-Ferrous Metals and Alloys 8: Welding Defects and Inspection

Section 3: Nondestructive Testing 1: Introduction 2: Visual Inspection (VT) 3: Radiography 4: Magnetic particle Testing 5: Penetrant Testing 6: Ultrasonic Testing 7: Eddy Current Testing 8: Acoustic Emission Testing (AET) 9: Ferrite Testing 10: Pressure Testing

Section 4: Codes and Standards 1: Introduction 2: Codes, Specifications and Standards

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