Designing Weldments

Ramesh Singh

• Publisher: Wiley-Scrivener
• Year: 2022
• Print ISBN: 9781119865155
• eBook ISBN: 9781119865827
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Designing Weldments

An important tool for professionals wishing to enhance their understanding or those who are new to the subject, Designing Weldments bridges that gap between structural engineers and a deeper understanding of the welding engineering within the structures.

In modern-day construction, welding is the primary method to join various members of any structure. Welds are required to meet various types of load in tension, compression, torsion, and perform in static or cyclic loading conditions. The weld has to be at least as strong as the parent metal to meet the demands of various stress working on the structure. It should meet the structural requirement, add value to the integrity of the structure, and prevent failures.

However, many design engineers lack even a fundamental insight or a basic understanding of essential welding processes and design requirements. Simply copying a few joint configurations in a drawing will not suffice. All-embracing and readable, Designing Weldments delivers a deeper understanding of many design factors that play a critical role in the design. The book clarifies welding design principles and applications. With this reference in hand, designers will have expert knowledge to consider very early on in the project, the implications of the choice of what type of weld to use for joining structural members, and how the component is made. The author explains the many welding techniques developed over the years, as well as some of which are still evolving.

The reader will also find in this book:

• Rules of thumb for saving time and money in the design phase of a project.
• An insider's view for choosing the proper welding approach to ensure the overall strength of a structure.
• Offers structural engineers a deeper understanding of the weld within their structures.
• Clarifies welding design principles and applications, limiting the necessity to redesign the structure.

Audience

The intended market for this book is professionals working on the infrastructural projects in shipbuilding, construction of buildings, bridges, offshore platforms, wind towers for renewable energy, and other structures that join plates, pipes, and pipelines in power plants, manufacturing, and repair.

1
Properties and Strength of Material

Synopsis

This chapter defines what is meant by the term weldment. How it is distinguished from other structures. What are the factors that should be considered in deciding the conversion of a Cast structure to a welded structure? This introduction chapter gives essential basic knowledge quired for design of weldments.

Keywords

Weldment, static, dynamic, structure, cast, forged, NDE, distortion

1.1 Introduction

A weldment is an assembly of various members of a structure that are joined by welding. The word structure may include from a simple joint of two members, for a trailer hitch, motor vehicle chassis, building frame, or a more complex joint of say a bridge-spurs of road over pass, construction of a ship, of an offshore platform, where multiple members are joined by welding in complex configurations to address varying static or dynamic stresses. The joining of different members by welding to create a complex structure is a preplanned activity with following basic objectives.

1. (i) to provide the intended purpose of the structure and
2. (ii) to be a reliable and safe structure.

Of course, the technical feasibility, ease of fabrication, availability of the material, and the cost are the other important factors that are associated and woven with the basic objectives, and all those are considered at the design stage.

Often to reduce the weight and/or the cost of a cast structures it may be selected for conversion to a welded structure. It may be noted with caution that a machines or a component constructed (Cast) out of a cast-steel or cast iron is not an automatic fit-design for welded design of the same component. This is a very common error among the designers of machine parts. Same caution also applies for any forged part, considered for the conversion to a welded design.

Figure 1.1 A typical strain and stress diagram, describing various elements of tensile test.

When welded design is used to convert Cast and Forged components, it can significantly reduce the cost of the component, the weight of the component, and also improve its aesthetics. But it needs very careful, and in depth study of both the designs, for usability, and the end objective of the component.

As a minimum the weldment designer should have good knowledge and experience of the following manufacturing processes.

1. 1. Casting and Forging process by which the original component is made of,
2. 2. Welding and other joining processes,
3. 3. Cutting and machining process,
4. 4. Inspection and testing methods,
5. 5. Fabrication activities and tools available for the task,
6. 6. Properties of various materials,
7. 7. Weldability of materials,
8. 8. Effects of restrains on welds,
9. 9. Distortion control,
10. 10. Design for appropriate stiffness and or flexibility as desired of the structure,
11. 11. Designing to address, required tension, compression and torsional load on the structure,
12. 12. Weld and NDE symbols,
13. 13. Knowledge of nondestructive inspection (NDE) methods, with their specific advantages and limitations.
14. 14. Applicable codes, regulations and practices,
15. 15. Selection of suitable weld design for welding.

The strength of steel is an important aspect of design, typically the tensile strength is used for the design purpose. A typical stress and strain diagram of steel shown the Figure 1.1 above with various strength related elements of the steel that can be determined by testing a specimen of the steel.

2
Properties of Metals

Synopsis

This chapter discusses the properties of material, structure sensitive and structure insensitive properties are defined. How properties are determined for engineering applications. Behavior of metal in extreme environ conditions like heat and cold are introduced.

Keywords

Mechanical, physical, corrosion, modulus of elasticity, tensile strength, fatigue strength, cyclic loading, HAZ

2.1 Material Properties

Knowledge of the properties of the metal is an essential aspect of welding engineer’s ability to be a good welding engineer. This knowledge allows the engineer to choose the most suitable material to improve upon the cost and functioning of the component being designed.

Various metals and non-metals are used in fabrication and construction, they all possess certain specific properties that differentiates them from others to be more desirable for the specific demands of the design to be an engineering material. All these metal properties are assessed and classed in three specific metal properties that are relevant to the engineering evaluations, for the suitability for the project.

Metal properties can be classified as,

1. 1. Mechanical properties
2. 2. Physical properties and
3. 3. Corrosion properties.

These are the primary properties however they can also be classified on the basis of their nuclear and optic properties. Further they can be classified on the basis of, if these properties are structure sensitive, or structure insensitive etc. Some details of these properties given the Table 2.1 below.

Table 2.1 Properties of materials.

General group	Structure-insensitive properties	Structure–sensitive properties
Mechanical	Elastic moduli	• Ultimate strength, • Yield strength, • Fatigue strength, • Impact strength, • Hardness, • Ductility, • Elastic limit, • Damping capacity, • Creep strength, • Rupture strength.
Physical	Thermal Expansion, Thermal conductivity, Melting point, Specific heat, Emissivity, Thermal evaporation rate, Density, Vapor pressure, Electrical conductivity, Magnetic properties, Thermionic emission.	Ferromagnetic properties
Corrosion	• Electrochemical potential, • Oxidation resistance	Corrosion of metals does affect some of the mechanical properties leading to metals failures.
Optical	• Color, • Reflectivity.
Nuclear	• Radiation obsorbtivity, • Nuclear cross section, • Wavelength of characteristic X-rays

The following is the discussion on these material properties.

2.1.1 Structure Insensitive Properties

These are well stablished and defined properties of a metal. These properties are standard from one piece of metal to another, from the engineering aspect they do not change. These properties are verifiable and can be tested for verification. These can be calculated, rationalized by consideration of the chemical compositions and crystallographic structure of metal.

2.1.2 Structure Sensitive Prop...

Table of contents

• Cover
• Table of Contents
• Title Page
• Copyright
• List of Figures
• List of Tables
• Foreword
• Preface
• 1 Properties and Strength of Material
• 2 Properties of Metals
• 3 Design: Load Conditions
• 4 Design of Welds and Weldments
• 5 Introduction to Welding Processes
• 6 Welding Symbols
• 7 Structural Design and Welding Specifications, and Other Useful Information
• Index
• Also of Interest
• End User License Agreement