AWS PWE-2000 The Practical Welding Engineer《实践焊接工程师》.pdf

1、 The Practical Welding Engineer BY J. Crawford Lochhead and Ken Rodgers Brown and Root McDermott Fabricators, Ltd., Inverness, Scotland. American Welding Society 550 N.W. LeJeune Rd. Miami, FL 331 26 International Standard Book Number: 0-87171-620-8 American Welding Society, 550 N.W. LeJeune Road, M

2、iami, FL 33126 O 2000 by American Welding Society. All rights reserved. Text edited by Tim Heston. Printed in the United States of America The American Welding Society is not responsible for any statement made or opinion expressed herein. Data and information developed by the authors are for informa

3、tional purposes only and are not intended for use with- out independent, substantiating investigation on the part of potential users. Table of Contents Preface v Chapter 1 : Contracts and Role of the Welding Engineer . .i Commercial Awareness . 1 Dealing with Specifications . 7 Chapter 2: Selection

4、of Welding Processes, Equipment. and Consumables 13 Welding Process Selection . 13 Equipment and Consumable Evaluation . 18 Chapter 3: Weld Procedure Qualification 25 Assessing Weld Procedure Requirements . 25 Routine Mechanical Tesis . 30 SimpleChecks 36 Fracture Mechanics Test 37 Test Failures 39

5、Chapter 4: Production Welding Control . 43 Defect Analysis 43 Welder Training and Qualification . 47 Supervision 50 Useful Aids 51 Consumable Control 58 Production Weld Test Pieces . 60 Chapter 5: Estimating and Reducing Welding Costs 67 Estimating Welding Costs . 67 Reducing Welding Costs . 72 Chap

6、ter 6: Practical Problem Solving . 83 WhatisaProblern? 83 Chevron Cracking in Submerged Arc Welds . 84 Low Toughness in Selt-Shielded Flux Cored Arc Welds 89 Cast-to-Cast Variability . 90 MagneticArcBlow . 92 Elimination of Postweld Heat Treatment . 94 Fitness for Purpose . 99 Chapter 7: Common Defe

7、cts and Remedial Actions 101 Cracks 102 Profile Defects . 106 Volumetric 114 Incomplete Fusion . 120 Some Additional Information on Solidification Cracking 122 Chapter 8: Oxyfuel Cutting, Arc Air, and Electrode Gouging . 125 OxyiuelCuiiing . 125 Air Arc GouginglCuting . 129 Electrode GougingKutting

8、. 130 Appendix I: Recommended Reading . 133 Appendix II: Useful Tables, Formulas, and Diagrams . 135 Index 149 iii When we, the authors, decided to write this book, we had a definite aim in mind - to present a “practical” approach to the application of welding theories. Over recent years universitie

9、s and colleges have recognized the previous lack of attention paid to the welding fraternity and subsequently greatly improved teaching capabilities and lecture contents. As a result, the modem engineer is well versed in basic metallurgical behavior; he is aware of the application of electronic wiza

10、rdry to modem equipment; fracture mechanics is not just an obscure theory but a practical everyday tool; and, modem materials and consumables have apparently eliminated many of the problems of the past. What the modem welding engineer lacks is the knowledge of how to apply this knowledge in a practi

11、cal sense. What we have attempted to write is basically a distillation of almost 60 years (between the two of us) of hard-gained realism in heavy engineering fabrication. The basis of the book is therefore an assumption that the reader is already knowl- edgeable of basic welding and metallurgical th

12、eory. He is most likely a metallurgist, materials science or mechanical engineering graduate who, during his or her univer- sity career has stumbled, or been fortuitously directed, into the welding field. It is obviously a biased view, but in the opinion of the authors, welding is one of the most ex

13、citing fields available to a young graduate. It is both vibrant and dynamic with new avenues to be explored becoming available on a regular basis. Synergic gas metal arc welding and inverter power sources, electron and laser welding, magnetic-impelled arc butt-joint welding (MIAB), robotic welding,

14、and diffusion bonding are careers in themselves. It is difficult to identify another discipline where the range of possibili- ties are as diverse, broad, and exciting, and where the potentials for exploration and discovery stretch enticingly into the future. However, enough of such esoteric digressi

15、ons. This book was not written from that approach. It is intended to present the inexperienced welding engineer with some “sage” advice on some of the pitfalls awaiting in the hard commercial world that awaits. Be under no illusions; it is not sufficient to be the best theoretical welding engineer i

16、n your company. You must know how to apply that knowledge in an almost “street-wise manner. Welding is regarded by many employers as a “black art.” Some of this reputation has been due to welding engineers camouflaging their inadequacies, or uncertainties, with professional jargon. Telling ones empl

17、oyer that the problem is one of “cracking initiated in a highly tensile stressed region of hard martensite or body centered cubic microstructure of poor crack resistance surrounded by material of similar sensitivity to crack propagation into which atomic hydrogen has diffused, and that until the dif

18、- fusion rate is beneficially altered the problem will persist,” is not clear. Telling him that you have identified the problem to be “one of delayed hydrogen cracking and that increasing the preheat temperature by 25C will resolve it” will undoubtedly raise your standing in the company - unless you

19、 have an enlightened employer who asks you why you didnt recognize that a higher preheat was necessary in the first place. The book is entitled “The Practical Welding Engineer.” We hope you find it to be practical. We also hope that, although you may not totally or even partially agree with its cont

20、ents, you find it readable and interesting. Good Reading J. C. Lochhead and K. J. Rodgers Acknowledgments The authors would like to thank the following personnel for their assistance in the execution of this work. T. Clement and M. Dorricott, Managing Directors, Brown but it also must be profitable.

21、 Commercial awareness usually is presented as an unessential part of the welding engineers discipline. This thinking is misguided because in most fabrications weld- ing plays a primary role of cost containment. If it is not right, either technically or commercially, the companys profitability will s

22、uffer. This is an aspect that still is not sufficiently recognized by many companies and engineers. This chapter will deal with two aspects in some detail - commercial awareness, and dealing with specifications. 1.1 Commercial Awareness This section is not intended to be a detailed study of the comm

23、ercial management of a project. It is intended simply to make you, the welding engineer, aware and appre- ciative of the key links and actions in the chain of events that will ensure your com- pany is fully compensated for everything it does for a client - or, conversely, receives everything it is p

24、aying for as a client. The following subjects will be discussed: 1. What is commercial awareness? 2. Making a profit. 3. The key elements of a contract. 4. Ensuring the company is fully compensated (or receives a full ser- 5. Variations and claims. vice). In all of these elements there are fundament

25、al points applicable to the welding engineer, regardless of the size of the company in which he operates. They may not be instantly recognizable under the descriptions given. However, they will exist in some form, and the welding engineer should play a leading role in all these aspects. 2 The Practi

26、cal Welding Engineer 1.1.1 What is Commercial Awareness? In simple terms, commercial awareness is the need for everyone to carry out their This means that work in such a way that the company makes a profit. estimates for welding should be constructed on the basis of sound everything should be done r

27、ight the first time and completed in the everything possible should be done to maximize revenue and judgments and well-defined logic, most cost-effective and economic manner, and reduce expenditure. These objectives can be achieved only if the welding engineer is fully aware of his role and of the c

28、ost and planning parameters that control his functions. 1.1.2 Making a Profit Profit is the lifeblood of any company. The essential ingredients that will ensure a company makes a profit are a good cost and price estimate, a good plan, an ability to manage both people and work efficiently, quality (g

29、et it right the first time), safety (bad practices cost money), cost-effective execution of all work, and maximizing revenue (i.e., ensuring that the company is paid in full for everything it does). 1.1.3 Key Elements of a Contract The seven key elements of a contract are 1. the tender (i.e., the bi

30、d), 2. the plan, 3. the scope of work, 4. purchasing, 5. subcontracting, 6. measurement and evaluation of the work, and 7. contractual obligations. Contracts and the Role of the Weldno Engineer 3 On first impression, the welding engineer may perceive that few of these aspects are applicable to him.

31、This is erroneous. In fact, the welding engineer should have a fun- damental role in every phase of the contract from the preparation of a tender to the fulfillment of the last contractual obligation; and greater emphasis on this role should be undertaken by the conscientious engineer. The seven key

32、 elements presented above will now be described briefly. The Tender job will be measured are specifications, drawings, scope of work, procedures, resources, methods, and price. The key elements of a tender (i.e., the bid) that form the criteria against which the The tender describes the criteria and

33、 assumptions upon which the work is priced and planned, and it establishes the base from which all changes will be measured. Therefore, it is of paramount importance to define clearly the data and assumptions used in compiling the price and plan. In addition, it must be made clear that if the assump

34、tions are wrong, or if they are not acceptable to the client, then there will be an effect on the price, or the delivery date, or both. All factors and calculations used in compiling the price and plan must be clearly recorded and retained throughout the life of the contract. Remember, they will for

35、m the basis for any cost adjustments resulting from changes. The Plan The plan describes how, when, and where the work will be carried out, as well as the resources to be used. There are many instances when the time allowed by a client for the tender period is very short, and the information relatin

36、g to the scope of work and deliverables is incomplete. This combination of factors complicates the develop- ment of a comprehensive plan. Nevertheless, the aim should be to develop an accu- rate plan that represents the way the work is intended to be carried out. The plan is the base from which the

37、effect of all changes will be measured, and this includes self- induced changes. The Scope of Work In an ideal situation, the work would be executed strictly in accordance with the original plan and cost estimate. In the real world, however, this rarely happens - usu- 4 The Practical Welding Enginee

38、r ally because the work is insufficiently defined at the time of the tender. It is important that the people who are responsible for executing the work are fully aware of how the work was planned and costed, so they can operate within their parameters or can iden- tify and notify change to the same.

39、 The identification and notification of changes is the most important link in the chain of events that leads to payment for the effects of changes. Purchasing Cost-effective purchasing is a key factor in successfully executing a contract. At the tender stage, delivery dates and prices for all requir

40、ed materials should be obtained. After the contract is awarded, it is important that materials are procured in accordance with the needs of the production department - that is, in accordance with the plan and within the quoted prices. Additionally, if items such as new welding machines or consumable

41、s are necessary for the job, sufficient notice should be given by the weld- ing engineer to the relevant departments to obtain adequate quotations. Any relevant purchase lead-times also must be included in the plan. Subcontracting Regardless of the size of the subcontract. the rules are the same. Th

42、e subcontract must o o o o clearly define the scope of work, specify the dates for deliverables to the subcontractor, agree to a schedule for completion, and specify the services to be provided (if any) to the subcontractor. Subsequent changes in specifications given to the subcontractor should be m

43、ini- mized. If this is unavoidable, any effects must be properly monitored. It is the respon- sibility of the welding engineer to ensure that all necessary approvals of the subcon- tractors welding procedures, etc., are made on time; otherwise, claims for conse- quential delays are likely to appear

44、on his desk. Measurement and Evaluation of the Work There are a number of ways of measuring the work, but the two most common are lump-sum pricing with a schedule of rates, in which only variations lump-sum pricing based on a bill of quantities, and a schedule of are measured; and rates, in which al

45、l of the work is measured. The work is measured from the drawings, and all changes that flow through draw- ings should be picked up in that measurement. Of course, the increased work result- ing from a change to drawings would be picked up in a subsequent re-measure and valued at the schedule rates,

46、 and the effect of the increase on the schedule would war- rant a claim for extending the duration of the contract. Contracts and the Role of the Welding Engineer 5 Changes initiated by means other than drawings are the subject of variation orders, for example, changes in specification, changes in t

47、iming, and changes in design after work has been completed. Generally, such changes would be measured as an effect on the cost of labor, equip- ment, and facilities and would be priced accordingly - not on the basis of the sched- ule of unit rates. Contractual Obligations The major contractual oblig

48、ations that affect the performance of the work are: execution of the work in accordance with drawings and specifica- tions; execution of the work in accordance with the schedule, unless it can be proven that this has been prevented by factors beyond the com- pany?s control; provision that work is fr

49、ee from defects (noting that, even where work has been inspected and/or certified, the manufacturer is liable for any defects that may be found subsequently; and, while a con- tractual obligation extends through to the end of the maintenance period, a common-law and/or moral obligation extends far beyond that date); appreciation that approval of drawings, method statements, weld procedures, etc., do not relieve the company from contractual oblig- ations; appreciation that inspectors and certifications by certifying authori- ties do not relieve the