New Joining Technology

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New Joining Technology for Metal Pipe in theConstruction Industry

Breakthrough Strategy Committee

BTSC Document 2003-01September 2003

BREAK THROUGH

Breakthrough Strategy CommitteeConstruction Industry Institute

BREAK THROUGH

Breakthrough Strategy CommitteeConstruction Industry Institute


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New Joining Technology for

Metal Pipe in the Construction Industry

Prepared by

Construction Industry Institute

Breakthrough Strategy Committee

BTSC Document 2003-1

September 2003


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Breakthrough Strategy Committee Members

Steve E. Brindza, The Procter & Gamble CompanyPaul D. Domich, National Institute of Standards & Technology

Edward S. Givens, Construction Industry InstitutePaul M. Goodrum, University of Kentucky* Carl T. Haas, The University of Texas at Austin

Robert C. Jacobs, 3M CompanyJohn B. Kapustay, Kier/CCC USA

* Changwan Kim, The University of Texas at AustinKenneth E. Olmsted, Smithsonian InstitutionJudith W. Passwaters, E. I. DuPont de Nemours & Co., Inc.C. Robert Seay, Tennessee Valley AuthoritySivaraj Shyam-Sunder, U.S. Department of Commerce/NISTC. Chatt Smith, JacobsGilbert M. Staudt, ExxonMobil Development Company

* Principal Author

Past Members

Raymond P. Baker, Rohm and Haas CompanyW. Kendall Burkhart, BIBB & AssociatesJohn T. Capener, Dillingham Construction N.A., Inc.Michael P. Childers, The Shaw Group Inc.John L. Cutts, POM Technology Americas

John F. Dunn, Chevron Project Resources CompanyBryson G. Edmonds, BE&K Construction CompanyPeter H. Emmons, Structural GroupDwight A. Fiveash, CelaneseLee R. Hale, ALCOA Inc.William B. Hardin, Technip USA CorporationJames F. Hilgers, Rust Constructors Inc.Emerson T. Johns, DuPont CompanyTimothy S. Killen, Bechtel CorporationBrigitte H. Laki, Exxon Chemical CompanyJohn S. Lambert, Eli Lilly and Company

Michael W. Lowder, Eastman Chemical CompanyDaniel J. Maas, National Center for ManufacturingGerhard Meinecke, SAP Labs, Inc.Kim Metcalf-Kupres, Johnson Controls, Inc.James W. Mortell, Cherne Contracting CorporationGet W. Moy, Naval Facilities Engineering CommandJeffrey Jay Osmond, U.S. Department of StateBoyd C. Paulson, Stanford University


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Kenneth F. Reinschmidt, Kenneth F. ReinschmidtK. Keith Roe, Burns and Roe Enterprises, Inc.Larry E. Ruhland, Bechtel CorporationRobert E. Sellers, Champion International CorporationMohan Singh, U.S. Army Corps of Engineers

Jack E. Snell, U.S. Department of Commerce/NISTZachary L. Zimmerman, Burns and Roe Enterprises, Inc.


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Table of Contents

List of Figures ................................................................................................... vi

List of Tables.................................................................................................... vii

Executive Summary .........................................................................................viii

Chapter 1: Introduction ...................................................................................... 1

Chapter 2: Current Joining Processes in the Construction Industry................. 3

Chapter 3: Need for Advanced Pipe-Joining Technology................................ 9

Chapter 4: Assessment of Advanced Joining Technologies........................... 12

Chapter 5: Evaluation Process for Advanced Joining Technologies ............. 30

Chapter 6: Evaluation of Advanced Joining Technologies ............................ 36Chapter 7: Business Analysis .......................................................................... 45

Chapter 8: Recommendations for Future Research ........................................ 48

Chapter 9: Conclusion and Recommendations ............................................... 55

References ........................................................................................................ 56


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List of Figures

Number Page

1. Technology Improvement Needs in the Construction Industry............. 4

2. Taxonomy of Joining Technology ........................................................ 12

3. Pressfit System .................................................................................... 13

4. Permalok System ................................................................................ 14

5. Metal Joining Using High Adhesive Bonding ...................................... 15

6. GasTungsten Arc Welding .................................................................. 17

7. Shielded-Metal Arc Welding ................................................................ 18

8. GasMetal Arc Welding ....................................................................... 199. Electron-Beam Welding ........................................................................ 20

10.Flash Butt Welding ............................................................................... 22

11.Explosion Welding ................................................................................ 23

12.Friction Welding ................................................................................... 24

13.Diffusion Weld Riveted ........................................................................ 25

14.Enclosed Orbital Weldhead .................................................................. 28

15.MIG Welding ........................................................................................ 29

16.Hierarchical Structure ............................................................................ 31

17.Ranking of Weighted Factors ................................................................ 34

18.Ranking of Applicability of Advanced Joining Technologies............... 44


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List of Tables

Number Page

1. Profile of Piping Surveyed ................................................................. 3

2. Percentage of Rework in Piping .........................................................4

3. Piping Steps ....................................................................................... 5

4. Pipe Materials .................................................................................... 5

5. Example of Step 2 in Factor-Weighting Process ............................. 32



8. Pipe Joining Score Sheet .................................................................. 339. Evaluation Model for Pipe Joining ...................................................35

10.Assessment of Mechanical Joining .................................................. 36

11.Assessment of Adhesive Bonding ................................................... 37

12.Assessment of Fusion Welding ........................................................ 39

13.Assessment of Non-Fusion Welding ............................................... 41

14.Assessment of Brazing and Soldering ............................................. 42

15.Assessment of Welding Automation ............................................... 43

16.Welding Expenditure in 2000 ............................................................46

17.Labor Cost for Welding, CII Model Plant ...................................... 47

18.Equipment Cost for Welding ........................................................... 47

19.Total Direct Cost of Welding ........................................................... 47


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Executive Summary

Pipe joining is one of the most critical but inefficient processes in the construction

industry. This report identifies several of the underlying causes for that inefficiency,including: (1) the shortage of skilled labor, (2) the low productivity of joining processes

currently in use, and (3) the reluctance on the part of welders to switch to newer

technology. Also discussed is the general agreement within the construction industry of

the need for identifying breakthrough methods that would improve the pipe-joining

process.

This paper covers mechanical joining, adhesive bonding, welding, and welding

automation. Successful adoption of these advanced joining technologies for metal pipe

could yield notable results, such as significant reductions in both processing time and the

need for skilled labor, a decrease in costs associated with the joining process; and

improvements in the strengths of joints. That is, advanced joining technologies may have

an impact not only on costs and scheduling, but on productivity and maintenance.

Which of these processes holds the most promise is open to question, however, for

two reasons: first, the uncertainty as to what types of joints produced with these methods

would be suitable for typical construction applications; and second, the fact that each of

them would have to be adapted for field application or prefabrication work and then

thoroughly tested before adoption by the industry.


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1

Introduction

Virtually every manufactured product contains joints that are used to assemble

similar materials into a more complex shape or product. In the U.S., the $50 billion-a-

year business of joining technologies is high tech and research efforts surrounding it are

intense.

In contrast to other industries, however, joining technology in construction has

not seen much advancement. In particular, metal-pipe joining is an extremely labor-

intensive and costly process. In 1982, The Business Roundtable released the summarypublication of its five-year study of the industry, the Construction Industry Cost

Effectiveness (CICE) Project. The Roundtable found that pipe joining is one of the most

expensive yet most inefficient elements of major industrial construction projects.

Furthermore, the Roundtable identified it as the task with the greatest potential for

technological advancement (Rickard and Tucker, 1982). Even today, some 20-plus years

after the CICE Project was completed, the inefficiency of processes used in metal-pipe

joining persists. In fact, according to 2002 benchmarking and metrics data published by

CII, the percentage of work that has to be redone in piping processes is much higher than

in other type of construction tasks.

Besides the need for improved processes, the shortage of skilled labor has also

become an issue of deep concern in the construction industry. Welders are offered lower

compensation in construction than in other industries, and therefore many competent

welders do not even consider taking on construction work.

Although considerable research has been conducted outside of the construction

industry in the area of welding, not all of the available technology is being used to its

potential (Tucker, 1982). Successful application of advanced joining technologies

requires a deep understanding of both current joining practice and advanced joining

technologies (Eager, 1990).


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The primary objective here is to explore the applicability of advanced joining

technologies to the use of metal pipe in the construction industry. In support of this

objective, this paper investigates current practices in metal-pipe joining in construction as

well as utilization of advanced joining technologies in other industries. It is expected that

an enhanced understanding of both of these areas would result in a better determination

of the potential for application of alternative joining technologies in the construction

industry and more effective implementation of those technologies. In addition, a number

of advanced joining technologies are evaluated, from both technical and business

perspectives, and recommendations are made regarding the adoption of advanced joining

technologies that could serve as a replacement for current practices.

The scope of this paper is limited to metal-pipe used in industrial constructionprojects. It begins with a review of current practices with respect to metal-pipe joining in

construction. The current status of pipe joining is examined, and the materials from

which metal pipe is made, the methods used in metal-pipe joining, and piping codes and

specifications are discussed. Needs for, and benefits of, advanced joining technology are

identified, and a tool for evaluating the applicability of various methods to construction is

presented. New joining technologies, including mechanical joining, adhesive bonding,

welding, and welding automation, are then introduced, and their applicability to the

construction industry is assessed by means of this evaluation tool. A business analysis is

then carried out to identify the business impact of advanced joining technologies in the

industry. Finally, business cases are suggested.


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2

Current Joining Processes in the Construction Industry

This chapter provides background information on the joining of metal, beginning with

a review of processes currently in use for the joining of metal pipe. The current status of

pipe joining is addressed, and the materials and joining methods currently in use, as well

as piping codes and specifications, are discussed.

Status of Pipe Joining

Piping in the Construction Industry

Piping comprises a large portion of the work done in the construction industry, interms of both the amount of labor required and the cost of construction (see Table 1).

This is especially true of heavy construction and the power sector, where piping is the

largest single contributing factor of all the different categories of work involved (Tucker,

1982; CII, 2002).

Table 1. Profile of Piping Surveyed (Tucker, 1982)

BuildingLight

IndustryHeavy

Industry Power

Average Project Cost ($ millions) 25 120 190 470Average Peak Work Force 300 600 900 1600

Labor Percentage by Craft (%) 9 14 22 18

Construction Cost Distribution (%) 3.4 11.6 23.9 16.1

Piping Productivity

In spite of its importance, piping is the most inefficient of all major construction areas

(Tucker, 1982). According to 2002 CII benchmarking data, the amount of piping work

that has to be redone is about 13.3 percent of the total (Table 2), compared to only sixpercent of the total, on average, for all areas of construction combined (CII, 2002).


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Table 2 Percentage of Rework in Piping

TotalRework(hours/year) 288,480Total work(hours/year) 2,170,244

Percentage 13.29%

Technology Needs Assessment

Given its low productivity, piping is the area with the greatest need for technological

advancements that would yield improved processes. According to the technology needs

assessment for the CICE Project, piping ranked ahead of all other categories ofconstruction in terms of the need for technology improvements (Tucker, 1982). In Figure

1, the high numbers present significant opportunities for technological improvement.

0 50 100 150 200 250 300 350

Piping

Electrical

Structure

Mechanical

Equipment

Enclosure Skin

Interior Finishe sBuilding

Light Ind.

Hea vy Ind.

Power

Figure 1. Technology Improvement Needs in the Construction Industry (Tucker, 1982)


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Pipe Joining

Generally, piping encompasses six different tasks: lifting, joining, aligning,

inspecting, transporting of materials, and procurement. Of these, joining is the most

important, consuming 25 percent of the cycle time and requiring a greater degree of skill

than any of the other five tasks. Most of the problems associated with piping, however,

are related to the field of welding (Tucker, 1982) (Table 3).

Table 3 Piping Steps

Erection Step

Percentage ofTotal Cycle Time

(%)Ranking of Skill

Required

Lifting 25 3

Joining 25 1Aligning 20 2

Inspecting 15 4

Transporting of materials 10 6

Procurement 5 5

Materials from Which Metal Pipe Is Made

The selection of materials for pipe is a process that requires consideration of material

characteristics appropriate to the specific application at hand (Nayyar, 1992). Pipe is

available in many different materials. According to CII data, amassed by means of a

survey of 12 different projects in the construction industry, carbon steel and stainless

steel are heavily used for piping in the construction industry (CII, 2002) (Table 4). A

brief discussion of the characteristics of stainless steel and carbon steel commonly used

in the construction industry follows.

Table 4 Pipe Materials

Material TypePercentage

(%)

Carbon steel 57

Stainless steel 28

Chrome 3

Other alloys 12


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Stainless Steel

Stainless steel is commonly used in cryogenic and chemical pipelines, as well as in

stainless steel tubing for domestic water supplies, plumbing, and heating. Stainless steel

offers good corrosion resistance, toughness, ductility, and weld-ability, but is rather

expensive (Dickenson, 1999). Schedule 5S pipe and Schedule 10S light-wall stainless

pipe are commonly used to reduce costs (Nayyar, 1992).

Carbon Steel

Carbon steel, widely used for piping material, offers good strength and is relatively

inexpensive. It has low corrosion resistance, however, so its use is limited to non-

corrosive applications (Dickenson, 1999).

Current Methods of Metal-Pipe Joining

The choice of methods of pipe joining depends on a variety of factors, such as pipe

diameter, pipe material, pressure rating, and other service requirements (Dickenson,

1999). A brief discussion of current methods of metal-pipe joining follows.

Welding

Welding can be used to join pipes of any diameter and is a leak-proof method.

Because of the shortage of highly skilled welders, welding is somewhat limited

(Dickenson, 1999). Stick welding (shielded-metal arc welding) is the most popular

method in use in the construction industry. Even though MIG and TIG welding offer

better performance than stick welding, it is still dominant because there has been

considerable reluctance on the part of welders in the various construction trades to use

other methods (Kapustay, 2002).

Two of the major reasons for the welding processes being so inconvenient and costly

are the need to utilize heavy equipment and the high degree of skill required. It is not

uncommon for welders to have to take an hour or more of their time to break down the

heavy equipment before moving it to the place where the next set of welds is to be made.


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Some of the factors that contribute significantly to the high cost of welding stem from the

complexity of the welding processes themselves. There tends to be an unacceptably high

degree of variability in the welds that are produced, which results in a frequent need for

rework. In shielded-metal arc welding, for example, the need to shield the weld arc from

impurities in the atmosphere is a source of major concernand a source of extra expense

if rework is required (Tucker, 1982).

Mechanical Joining

The concept of joining pipes by mechanical methods originated during World War I,

when there was a need for rapid deployment of fuel and water, since traditional methods

such as welding were too slow (Dickenson, 1999). Mechanical joining is generallyeffective and uncomplicated, and little mechanical skill is needed. Its use is limited,

however, because it can be applied only to the joining of thick pipe (Dickenson, 1999).

The use of mechanical joining methods often results in time lost to rework because of

faulty assembly. This seems to stem from not having correct materials, and a tendency by

the crafts to use the incorrect materials in lieu of obtaining the proper ones. This has been

an ongoing problem in construction (Tucker, 1982).

Codes and Standards

Various codes and standards that are applicable to metal-pipe joining have been

prepared by committees of leading engineering societies, trade associations, and

standardization groups. These are generally written to cover requirements of design and

welding only, rather than to provide detailed regulations for piping (AWS, 1973). The

specifications of the American Society of Mechanical Engineers (ASME) Boiler and

Pressure Vessel Code, Section IX, are the requirements most widely recognized, not only

within the industry and by insurance companies, but by state and municipal regulatory

bodies (AWS, 1973).


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American National Standards Institute

The American National Standards Institute (ANSI) issued a joint code for pressure

piping nearly 30 years ago with the American Society of Mechanical Engineers (ASME)

Details follow:

ASME/ANSI Code for Pressure Piping B31, Pressure Piping Code Sections:

B31.1, Power Piping

B31.2, Industrial Gas and Air Piping

B31.3, Chemical Plant and Petroleum Refinery Piping

B31.4, Oil Transportation Piping

B31.5, Refrigeration PipingB31.6, Chemical Industry Process Piping

B31.7, Nuclear Power Piping

B31.8, Gas Transmission and Distribution Piping Systems

American Society of Mechanical Engineers

The ASME has issued code to cover piping connected to boilers. Of the 11 sections of

its Boiler and Pressure Vessel Code, ASME cites the following as related to industrialpiping:

Section I, Power Boilers

Section IV, Heating Boilers

Section VI, Recommended Rules for Care and Operation of Heating Boilers

Section IX, Qualification Standards for Welding and Brazing Procedures, Welders,

Brazers, and Welding and Brazing Operators

American Petroleum Institute

In 1973, the American Petroleum Institute (API) issued a standard for field welding

of pipeline, API Standard 1104, which includes weld-quality acceptability limits,

inspection requirements, and welding-procedure test requirements.


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3

Need for Advanced Pipe-Joining Technology

This chapter describes the motivation for the development and adoption of advanced

pipe-joining technology in the construction industry, together with a discussion of the

requirements that would have to be metand the benefits that would accruein the

event of its use.

Motivation for Advanced Pipe-Joining Technology

Three major factors are forcing the construction industry to find alternatives for pipe

joining: (1) the shortage of skilled labor, (2) the low productivity of existing joining

methods, and (3) the reluctance of skilled laborers to adapt to new joining methods.

Shortage of Skilled Labor

The shortage of skilled welders is an issue of deep concern in the construction

industry. Welders are offered lower compensation in construction than in other industries,

so many competent welders do not even consider going into construction work.

Low Productivity of Existing Methods

Because of the low productivity of traditional joining methods in the construction

industry, piping is one of the most inefficient aspects of construction work. As mentioned

previously, some of the main causes of this low productivity are the variability of the

joints produced and the high incidence of a need for rework.

Reluctance of Skilled Laborers to Adapt to New Methods

The reluctance of skilled laborers to adapt to new joining methods is one of the major

factors that impede the construction industry to switch to improved joining processes. For

example, the reason why stick welding has remained the dominant welding process is the


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considerable degree of reluctance on the part of welders in the various construction trades

to give other methods a try (Kapustay, 2002).

Benefits/Requirements of Advanced Joining Technology

Successful adoption of advanced joining technology for metal pipe could yield

notable results, such as (1) significant reductions in both processing time and the need for

skilled labor, (2) a decrease in costs associated with the joining process, and (3)

improvements in the strengths of joints (Eager, 1990).

To reap the benefits of new technology, however, certain requirements must be

satisfied. The basic characteristics that any viable joining technique with a wide range of

applicability must offer include the following: (1) production of strong and reliable joints,

(2) suitability for small- and large-area bonding, (3) minimal need for surface preparation,

and (4) suitability for use in a production environment (Silverman, 1989). The study by

Thompson suggests six factors that are critical to the success of a pipe-joining operation:

(1) pressuretemperature ratings, (2) material compatibility, (3) external loading, (4)

operability, maintainability, and reliability, (5) long-term effects, and (6) cost.

The following discussion of the impact of using advanced joining technology is

broken down into four main categories: (1) structural integrity, (2) management concerns,

(3) productivity factors, and (4) maintenance issues.

Structural Integrity

The structural integrity of a joint is determined by its ability to function properly

within the overall system(s) of which it is a part. Structural integrity comprises three

elements: (1) joint strength, (2) material compatibility, and (3) durability.

Joint strength is a measure of the ability of a joint to sustain internal forces (such as

internal pressure) and external forces (including shear forces, torsion, and bending) that

are due to factors such as variations in temperature. Material compatibility is the degree

to which the individual elements of a joint are able to function as a unit and resist the


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tendency to corrode one another; this is important since corrosion can reduce the strength

of a pipe joint (Thompson, 1998). Durability is the ability of a joint to retain its strength

and serve its intended purpose over an extended period of time.

Management Concerns

Management concerns encompass all the factors that have an impact in terms of cost.

Any given type of joining technology that is adopted has the potential to affect not only

the direct costs of production, such as labor and equipment, but also indirect costs such as

training of the welders. The costs that must be considered by management in choosing a

joining technique can be classified as: (1) training, (2) materials, (3) equipment, and (4)

labor.

Productivity Factors

Productivity factors consist of everything that affects the efficiency of the joining

process. Productivity of any joining technique is dependent on the following properties:

(1) processing time, (2) degree of rework, (3) ease of installation, (4) field usability, and

(5) extent of surface preparation.

Maintenance Issues

The initial cost of producing a pipe joint is only part of its total cost. What needs to be

considered are all the costs that accrue over the expected life of the plant, as well as the

performance of the joints that are produced. Long-term effects due to erosion, fatigue,

and creep, all of which can affect the performance of a pipe joint, may be significant.

Maintenance issues can be grouped into two categories: (1) long-term performance

reliability and (2) life-cycle cost.


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Assessment of Advanced Joining Technologies

The three predominant reasons for joining materials are to achieve function, to

achieve structural efficiency, and to minimize costs (Messler, 1993). A number of

different joining technologies exist, each with its own set of advantages and

disadvantages.

Joining processes are usually divided into mechanical joining, welding, and adhesive

bonding (fig. 2). A discussion of the characteristics of existing processes in these three

categories, replete with examples of systems currently on the market, follows.

Mechanical Joining

In mechanical joining, materials are joined by the use of fasteners (mechanical

fasteners) or through an integral design feature (mechanical interlocking; Messler, 1993).

Figure 2.Taxonomy of Joining Technology


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The mechanical joining process relies on residual stresses, which ensure the integrity of

the joints (Brandon and Kaplan, 1997). These stresses may occur either in the fastening

(mechanical fastener) or in the components themselves (mechanical interlocking;

Brandon and Kaplan, 1997). Mechanical joining has several advantages, such as ease of

installation and stability of the chemical composition of the materials. Because of

significantly concentrated stresses resulting from this approach, however, mechanical

joining has limited applicability (Messler, 1993).

Mechanical Fastening

Mechanical fastening, which applies interference forces to the elements, is divided

into two categories: threaded fasteners and non-threaded fasteners. Threaded fasteners

apply force using threads such as those in bolts, screws, or nuts, while non-threaded

fasteners apply force using pin action such as that which takes place in rivets, pins, or

keys (Messler, 1993).

An example of a mechanical fastening process is the Pressfit

System, developed by

Victaulic , which has been widely used; this technology is used in piping installations

and employs a system of Pressfit

couplings, elbows, tees, reducers, and adapters

(Victaulic, 2002). It incorporates Schedule 5 stainless product and carbon steel productfrom inch to 2 inches in length (Victaulic 2002). Currently, the Victaulic

Pressfit

System is available only on Schedule 5 pipe, and its use is limited to the conveyance of

water because it cannot withstand pressures above300 psi (Victaulic, 2002).

Figure 3. Pressfit System (Victaulic, 2002)


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Mechanical Interlocking

While mechanical fastening uses fasteners to apply force, mechanical interlocking

exploits the interaction between the elements themselves (Messler, 1993).

An example of a mechanical interlocking system is one developed by Permalok for

joining steel pipes. As with the Victaulic

Pressfit

System, the Permalok

Steel Pipe

Joining System is easy to install and requires no field welding (Argent, Pecknold, and

HajAli, 1999). Since the interference forces in a mechanical interlocking process act

between the elements themselves, this system provides a simpler way to join pipes than

does the Victaulic

Pressfit

System.

Adhesive Bonding

In adhesive bonding, materials are joined with adhesives that hold them together by

means of surface-attachment attraction forces (Messler 1993). The adhesives are applied

at room temperature to the surfaces to be bonded; they harden after curing and treatment

such as heating or irradiation (Brandon and Kaplan, 1997). Adhesive bonding is divided

into two categories: structural adhesives and non-structural adhesives. In structural

adhesive bonding, the adhesives have the capacity to endure strengths close to the point

at which the member collapses. Currently, structural adhesive bonding extends the limits

of applicability of metal-to-metal bonding all the way up to those of structural bonding.

Non-structural adhesive bonding is widely used in automobiles (Messler 1993).

Figure 4. Permalok

System (Argent et al., 1999)


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The major benefits of adhesive bonding are convenience and relatively low cost.

Adhesive bonding is difficult to use in the joining of pipe, however,because of the lack

of a chemical bond between the composite and the adhesive (Lea, Stubblefield, and Pang,

1998). The low resistance of adhesive bonding techniques as a function of bending load

is regarded as the most significant obstacle to its use (Lea, Stubblefield, and Pang, 1998).

The magnitude of the resistance is just 30 percent of that which is obtained using butt-

weld methods, so failure is common at the composite-adhesive interface (Lea,

Stubblefield, and Pang, 1998).

The limitations of adhesive bonding have been lessened as a result of technology

advances. In fact, 3M has developed a high-strength adhesive bonding technique that

offers a normal tensile strength of 160 psi and dynamic shear strength of 100 psi. High-strength adhesive bonding, developed by 3M, demonstrate the potential of this technique

for use in a wide range of applications. They have been used in interior and exterior

applications for the past 20 years. In many applications, these adhesives can replace

mechanical fasteners while creating virtually invincible bonds. Unlike the stress points

common to mechanical fasteners, high-strength bonding distributes the stress. They

provide a clean, direct, and durable bonding of 24-oz. and 48-oz. copper panels, as well

as 3/16-inch-thick cast-bronze medallions, to brass without the use of mechanical

fasteners. The bond resists weathering and compensates for thermal expansion and

contraction of the metals due to seasonal changes in temperature (3M, 2002).

Figure 5. Metal Joining Using High Adhesive Bonding (3M, 2002)


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Welding

According to Messler, welding is defined as a process in which materials of the same

type or class are joined together through the formation of primary bonds under the action

of heat, pressure, or the combined action of heat and pressure (Messler, 1993). The

primary reason for welding being used so extensively as a joining process is that it offers

high integrity of joints, a wide variety of processes and approaches, and considerable

opportunities for automation. In spite of its many benefits, however, welding has serious

disadvantages, such as high operating costs, a shortage of skilled labor, and lack of

controllability of the process itself (Messler, 1993).

Even though there are several classification systems for welding processes, welding is

typically classified as either fusion welding or non-fusion welding, depending on whether

or not significant melting is involved (Messler, 1993).

Fusion Welding

In fusion welding, the materials to be joined are heated to a temperature that lies

above the melting points of both of them. Fusion welding processes include all those in

which the melting or fusion of portions of substrates play a significant role in the

formation of joining (Messler 1993). Fusion welding includes gas, arc, resistance, and

high-energy beam welding; it requires significant melting, and usually produces a joint

via the application of heat rather than pressure (Ageorges, Ye, and Hou, 2001)

Arc Welding

Arc welding uses an electric arc as a source of heat. The arc employed is created

between an electrode and a workpiece. Arc welding is further subdivided into

nonconsumable-electrode processes and consumable-electrode processes, depending on

whether the electrode is intended to be permanent or not (Messler, 1993). One important

feature of arc welding is the shielding that is done to prevent oxidation of the highly

reactive molten weld metal, thereby helping to stabilize the arc (Messler, 1993).


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Gastungsten arc welding and plasma arc welding are the predominant forms of

nonconsumable-electrode arc welding. Gasmetal arc welding, shielded-metal arc

welding, flux-cored arc welding, submerged-arc welding, electrogas welding, and

electroslag welding are common forms of consumable-electrode arc welding (Messler,

1993). The processes reviewed here are (a) gastungsten arc welding, (b) shielded-metal

arc welding and (c) gas-metal arc welding. Because of their strong potential for

automation, these types of arc welding are the most heavily developed and most widely

used in the industry.

Gastungsten arc welding:Gastungsten arc welding, also referred to as tungsten

inert-gas (TIG) welding, enables a wide range of ferrous alloys to be welded without the

use of a flux, which is a chemical agent that is used to clean and activate the surface of amaterial in order to promote bonding. Gastungsten arc welding uses a permanent,

nonconsumable tungsten electrode to create an arc (Messler, 1993). With this method, the

arc burns between the tungsten electrode and the workpiece, both of which are shielded

by the inert gas argon, thereby keeping out air and preventing contamination of the

electrodes and the molten metal (Davies, 1993). The gastungsten arc welding process

is good for welding thin sections and, because of its inherently low heat input, offers

excellent bonding and better control of weld filler dilution by the substrate than many

other processes. Its greatest limitation is its slow deposition rate (Messler, 1993).

Figure 6. GasTungsten Arc Welding (Messler, 1993)


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Shielded-metal arc welding (stick welding): In shielded-metal arc welding, also

referred to as stick welding, metal joining is brought about by the heat from an electric

arc that is maintained between the tip of a consumable electrode and the surface of the

base metal being welded. A core wire conducts the electric current from a constant-

current power supply to the arc and delivers most of the filler metal to the joint (Messler,

1993). Advantages of shielded-metal arc welding are that it is simple and portable, and

does not require expensive equipment. Like all manual processes, however, and to an

even greater degree than most, shielded-metal arc welding requires considerable welding

skill for best results. In addition, the operating cost of shielded-metal arc welding is

higher than MIG welding because of the lower deposition rate achieved with the former

(Messler, 1993).

Gas-metal arc welding:The gas-metal arc welding process, referred to as metal-inert-

gas (MIG) welding, utilizes an externally supplied inert shielding gas and a continuous

solid-wire electrode. The consumable solid-wire electrode provides all of the filler to the

weld joint. The externally supplied shielding gas guards the arc and the molten weld

metal from penetration by air and offers desired arc uniqueness throughout its effect on

Figure 7. Shielded-Metal Arc Welding (Messler, 1993)


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ionization (Messler, 1993). Gas-metal arc welding offers flexibility, versatility, and the

potential for automation. In addition, it requires less welding skill and has a higher

deposition rate than shielded-metal arc welding, thus making available a much faster

process. Its greatest limitation is its high cost (Messler, 1993).

Gas Welding.

Typically, gas welding includes any welding process in which the source of heat is a

combustible fuel such as natural gas, propane, or butane. Oxyacetylene welding, which

uses acetylene gas as fuel, is the most commonly applied gas welding technique (Messler,

1993). In this method, the oxygen is supplied from steel cylinders, and the acetylene from

cylinders or an acetylene generator. Acetylene is passed to the blowtorch, where it is

mixed with oxygen in approximately equal proportions and then passed into the tip to be

burned (Davies, 1993).

The oxyacetylene-gas welding process is simple and highly portable, and the

equipment needed for its use is inexpensive. It is rather limited in its applicability,

Figure 8. GasMetal Arc welding (Messler, 1993)


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however, on account of the small amount of energy provided by the source and the very

nature of the process, which provides relatively little in the way of protective shielding

and require high skill to weld (Messler, 1993).

High-Energy Beam Welding

High-energy beam welding, which uses a high-intensity beam as the heat source, is

subdivided into two categories: electron-beam welding and laser-beam welding. In these

two processes, heat is generated from collisions of electrons and photons, respectively,

with the workpieces. High-energy beam welding is quite expensive, yet the joint fit is

excellent, on account of the fact that the process takes place autogenously (Messler,

1993).

Electron-beam welding of pipe was first developed in the late 1970s, but it was

reported that welds exhibited poor mechanical properties on account of the high-vacuum

requirement. Advances in other industrial sectors have since led to the ability to form an

electron beam in the atmosphere (Blackman and Borling, 2000). Kawasaki Heavy

Industries has developed an internal electron-beam welding process in which 30 in.

0.76 in. pipe can be welded in the 5G position in only one pass (Hara et al., 2000).

Figure 9. Electron-Beam Welding (Messler, 1993)


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Resistance Welding

Resistance welding is a process that takes advantage of a workpieces inherent

resistance to the flow of electric current. As current is passed through the parts to be

welded, the parts resist the passage of the current, thus generating the welding heat. A

force is simultaneously applied, and the parts are joined together. Unlike other forms of

welding, resistance welding does not utilize additional materials such as fluxes and filler

rods. The weld nugget is formed directly from the base materials (Messler, 1993).

Usually, resistance welding is used for joining overlapping sheets or plates. However,

the rapid rate of heating, extremely short welding time, and rapid rate of cooling allow

resistance welding to be used wherever heat input must be minimized, such as in joining

refractory metals and alloys. The major types of resistance welding are resistance spot

welding, resistance seam welding, projection welding, flash welding, upset welding, and

percussion welding (Messler, 1993).

Flash butt welding: In flash butt welding, heating at the faying surfaces (that is, the

surfaces of the mating parts) is generated by a combination of resistance and arcing. Once

the faying surfaces are heated to the welding temperature under the action of an applied

current, force is applied immediately and a weld is produced. Molten metal is expelled,the hot metal is plastically upset, and a flash of frozen expelled metal is formed (Davies,

1993).

Flash butt welding was successfully developed for pipelines, and the process was

accepted for inclusion in the API standard. However, it has not been commercialized,

because of the unsatisfactory mechanical properties of the available materials (Blackman

and Dorling, 2000).


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Non-Fusion Welding

Non-fusion welding is defined as a welding process that occurs through plastic

deformation by the application of pressure, or a combination of heat and pressure, at a

temperature that lies below the melting point of the base material and without the

addition of a filler that melts (Messler, 1993). In non-fusion welding, the base metals are

heated but not significantly melted, and melting is not directly responsible for the joining

process (Messler, 1993). In this regard, non-fusion welding has an advantage over fusion

welding, in that the heat-affected zone is kept to a minimum, resulting in negligible

alterations in the characteristics of the materials involved. Non-fusion welding is divided

into four categories with respect to the source of energy: cold pressure, hot pressure,

friction, and diffusion welding (Messler, 1993).

Cold Pressure Welding

Cold pressure welding is a method of joining sections of metal together by the

application of pressure but using no heat or flux (Davies, 1993). Cold welding uses

substantial pressure at room temperature to produce joining of materials through plastic

deformation at the weld. It is of limited applicability, however, because it requires

extremely clean surfaces and high pressures and it is difficult to accomplish consistently.

Figure 10. Flash Butt Welding (Davies, 1993)


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However, cold welding provides a valuable option for joining materials in the

environment of outer space (Messler, 1993).

Hot Pressure Welding

Hot pressure welding uses heat and pressure as an energy source to accomplish the

joining of materials through plastic deformation. Hot pressure welding includes forge

welding, hot roll welding, and explosion welding (Messler, 1993). A discussion of

explosion welding, which is the dominant form of hot pressure welding, follows.

Explosion welding: In explosion welding, the cores of the workpieces remain cold, but at

the surfaces they undergo local heating that is both significant and rapid. Air between the

workpieces is squeezed out at supersonic speeds in order to achieve high temperatures

and yield a metallurgical bond (Messler, 1993). Explosion welding is very successfully

applied to the welding of tubes, either for joining one tube to another or for joining a tube

to a tube plate, as well as for welding plugs into leaking tubes in order to seal the leaks

(Davies, 1993). The applicability of explosion welding is limited, because the weld

bondline is very distorted locally (Messler, 1993).

Figure 11. Explosion Welding (Messler, 1993)


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Friction Welding

Friction welding relies on friction to cause the heating that is needed to produce a

weld. The friction is created by the use of machines that are designed to convert

mechanical energy into heat at the joint that is to be welded. In friction welding, materials

are joined under the compressive-force contact of workpieces moving relative to one

another, either linearly or in rotation (Messler, 1993). A description of ultrasonic

weldingone type of friction welding, albeit an exceptional form of itfollows.

TWI developed radial friction welding (RFW) for the specific purpose of welding

pipe. This method, in which a radial compression ring is rotated between two stationary

pipes, overcomes some of the handling problems that tend to crop up with other types of

friction welding. The ring is rotated under compression; as a result, heat is generated, and

a weld is created between the ring and the two pipes (Gainand et al., 2000).

Although this technology has been available for some twenty years, the RFW process

has not been commercially exploited, in part due to the high cost of the equipment.

However, its potential for use in the joining of titanium alloy risers for the offshore oil

industry looks rather promising. Affordable RFW equipment will have to be developed,

however, before the advantages of this process can be used to a significant extent in

commercial applications (TWI, 2002).

Figure 12. Friction Welding (Messler, 1993)


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Diffusion Welding

Diffusion welding is a process that relies on heat and pressure to accelerate diffusion

and produce joining through mass transport in the solid state (Messler, 1993). Usually,

the solid-state bonding process based on the combined application of pressure and heat isalso termed diffusion welding (Brandon and Kaplan, 1997).

In diffusion welding, two surfaces are brought together under load. Under conditions

of both high temperature and high pressure, there is considerable plastic flow in the

region of greatest surface asperity, which continues until the interfaces have achieved a

high degree of conformity with each other. At this point, the joint will have achieved

considerable strength as a result of metallic bonding (Schwartz, 1979). Diffusion welding

offers precise joining, with no fusion zone and no heat-affected zone. However, its use is

limited, because of the expense of the materials involved and the small dimensional

tolerance with which the pieces/components must comply (Messler, 1993).

Brazing and Soldering

A major characteristic of brazing and soldering is that metals are joined without

changing the composition of the workpieces, because the base metal is not melted

(Bowditch, 1997).

Figure 13. Diffusion Weld Riveted (Messler, 1993)


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Brazing is a type of welding in which the joint is heated to a suitable temperature in

the presence of a filler material having a liquidus that is above 840F and yet below the

solidus of the base metal. (The liquidus of a pure metal is the lowest temperature at which

it is completely liquid, while its solidus is the highest temperature at which it is

completely solid.) Bonding is accomplished without melting the substrate (Messler 1993).

Brazing offers advantages such as the negligible effect it has on the composition of the

base materials, the ability to join large structures under relatively low-stress conditions,

and its high potential for automation. However, brazing is of limited applicability, on

account of the low melting point of the filler (Messler, 1993).

Soldering is another type of welding that requires a filler that melts and a substrate

that does not. It is distinguished from brazing by the fact that the fillers liquidus is below840F. Soldering offers almost the same advantages as brazing, but because of the

weakness of the soldered joint, it is of limited applicability (Messler, 1993).

Welding Automation

The advantage of using welding automation to improve productivity has long been

realized in the manufacturing industry. Besides improved productivity, welding

automation offers reliability and lower labor costs, and it eliminates variability. One ofthe main reasons for the automation of welding is productivity, which is much higher in

automated welding processes than in manual systems. In many cases, welding with a

robot is two to five times faster than other methods (Woodnam, 2001).

The shortage of skilled welders has become a matter of deep concern in the

construction industry. Because welders are offered lower compensation in construction

than in other industries, many competent welders do not consider going into construction

work. In light of this skilled-welder shortage, welding automation is one of the best

alternatives to current welding practice (Eager, 1990).

Welding automation is divided into two categories: semi-automatic and fully

automatic. In semi-automatic welding, a weld controller is involved in the welding

process, to control the motion of the torch and the parts and to adjust the welding


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parameter. Fully automatic welding uses machines to index the part or torch into position

and to monitor the quality of the welds. A discussion of the characteristics of orbital TIG

welding and MIG welding, which are the dominant automatic welding methods, follows.

Orbital TIG Welding

Orbital TIG welding has been applied in many industries, such as aerospace, boiler

tubes, nuclear piping, offshore applications, semiconductors, and tube/pipefitting. This is

because of its advantages over other joining technologies in the way of productivity,

quality, consistency, and versatility (Mannion and Heinzman, 1999).

Orbital TIG welding uses the gastungsten arc welding process as the source of the

electric arc that melts the base material and forms the weld. Orbital TIG welding systems

include a power supply and an orbital weldhead. The power supply/control system sets

the welding parameter according to the specific program in use, which is stored in the

control system.

In orbital TIG welding systems, welding parameters are stored in a controlling

computer for a variety of applications; the computer sets specific welding parameters for

specific applications (Mannion and Heinzman, 1999). An orbital weldhead rotates an

electrode and an electric arc around the joint to be welded, with the angle of rotation as

welding parameter. The power supply/control system also supplies the arc welding

current, switches the shielding gas, and sets the power that drives the motor in the

weldhead (Mannion and Heinzman, 1999). Standard enclosed orbital weldheads are used

in welding tubes with a diameter of 1/16 inch to 6 inches, with a wall thickness of up

to .154 inch. Open orbital heads are used in tubes of larger diameter and wall thickness

(Mannion and Heinzman, 1999).


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Mechanized Gas-Metal Arc (MIG) Welding

Mechanized gas-metal arc (MIG) welding is an important process in welding

fabrication practice because of advantages such as the consistently high quality of the

joints and the great degree of compliance with radiographic standards for welds that areto be performed at high welding speeds (Thompson, 1998).

The MIG torchesusually air cooled, even for currents up to 450 Aare carried on

welding heads connected to the control system (Thompson, 1998). For repair work on

thin sheets, as in the motor trade, semi-automatic MIG welding has replaced the

traditional oxyacetylene methods because of the lower heat input required for the former.

For larger fabrication work, use of mechanical handling equipment with automatic MIG

welding heads enables a reduction in the amount of skilled labor employed in the joining

process (Davies, 1993).

Mechanized gas-metal arc welding is the most widely used welding process for large-

diameter transmission pipelines in the U.S (Blackman and Dorling, 2000).

Figure 14. Enclosed Orbital Weldhead (Mannion and Heinzman, 1999)


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Figure 15. MIG Welding (Davies, 1993).


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5

Evaluation Process for Advanced Joining Technologies

This chapter provides a discussion of an evaluation process that can be used todetermine the applicability of each of the various joining technologies. In earlier chapters,

the major categories of joining methods were described, and factors that have a

significant impact on the applicability of those techniques to the joining of pipe were

highlighted. Here, the Analytic Hierarchy Process (AHP) is used in order to weight the

various factors according to their degree of impact.

Factor-Weighting Methodology

In Chapter 3, various factors that should be considered in selecting joining technology

for piping in the construction industry were identified. Not all of these factors are equally

important, however, in terms of their potential impact on the joining of pipe. Certain

factors are higher in the hierarchical order than others with respect to their relative

importance. Therefore, it is necessary to weight all of the factors relative to one other.

AHP (Analytic Hierarchy Process)

The Analytic Hierarchy Process (AHP) is a powerful and flexible decision-making

process for establishing priorities among quantitative and qualitative sets of criteria by

using data and the users knowledge or experience as input (Satty, 1990). The process has

been formalized by Satty and used in a wide variety of problem areas. The AHP process

involves the structuring of a problem according to a primary objective and then

proceeding to secondary levels of objectives. Once the hierarchies have been established,

comparison matrices are constructed (Satty, 1983).

Factor-Weighting Process

By the use of AHP, a weighting of the major factors that contribute to decisions

regarding the use of various advanced joining technologies is derived. The steps of the

AHP weighting process are given below (Tucker, 2001):


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Step 1: Establish the hierarchical structure in the following way: First, list the major

categories across the page from left to right. Then, for each of the major categories, list

its subcategories below it (fig. 16).

Step 2: Compare the four major categories in pairwise fashion, ranking each pair on a

scale of 1 to 5 according to the criteria indicated below, and then fill in the upper half of a

matrix with the results. Then, for each of the major categories, use the same procedure to

compare its subcategories in pairwise fashion. An example of one possible outcome of

step 2 for a comparison of the subcategories within the management category is given in

Table 5.

1: The two factors contribute equally

2: One factor is slightly favored over the other

Figure 16. Hierarchical Structure


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3: One factor is moderate favored over the other

4: One factor is strongly favored over the other

5: One factor dominates

Table 5 Example of Step 2 in Factor Weighting Process

Training Cost Labor Cost Equipment Cost Material Cost

Training Cost 1 0.20 0.25 0.33

Labor Cost 1.00 3.00 4.00

Equipment Cost 1.00 3.00

Material Cost 1.00

Step 3: Now complete each of the matrices constructed in Step 2 as follows: First,

compute the reciprocals of the entries in the cells in the upper half of the matrix, and

place the resulting numbers into the appropriate cells in the lower half of the matrix.

Once that has been done, add a new row at the bottom of the matrix, sum up the entries in

each column, and fill in the cells of the new bottom row of the matrix with those sums.

Now, add a new column to the matrix, to the right of the existing rightmost column. For

each row of the matrix, compute the sum of the quantities ai/bi where ai is the entry in the

ith column of the row and bi is the ith column sum. As the computation for each row is

completed, place the resulting row sum in the appropriate cell of the new column of the

matrix. The example from step 2 is worked out in Table 6.


Training Cost Labor Cost Equipment Cost Material Cost Row Sum

Training Cost 1.00 0.20 0.25 0.33 0.28

Labor Cost 5.00 1.00 3.00 4.00 2.08

Equipment Cost 4.00 0.33 1.00 4.00 1.07

Material Cost 3.00 0.25 0.33 1.00 0.56

Column Sum 13.00 1.78 4.58 8.33 4.00

Step 4: Compute a priority vector from the column of row sums by normalizing the

entries in the far-right column to the number in the bottom row. The example from step 3

is worked out in Table 7.


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Row Sum Normalization

0.28 0.07

2.08 0.52

1.07 0.27

0.56 0.244.00 1.00

Step 5: Perform a consistency check on the comparison scales. The consistency ratio

should be smaller than 10%.

CR = 0.04 (CI) / 0.9 (Random Consistency Index) = 4.7% The CR is 4.7%, indicating a

good consistency is reached.

Finalizing the Weighting Process

Once the factor-weighting process is completed, the weight for each factor is

finalized by multiplying its weight by the weight for its category. For instance, if the

weight for the structure category is 0.18 and the initial weight for joint strength is 0.61,

then the final weight for joint strength is (0.18)(0.61) = 0.110. The completed score sheet

for pipe joining overall is given in Table 8.

Table 8 Pipe Joining Score Sheet

Category Weight Subcategory WeightRelativeWeight

Structure 0.18 Joint Strength 0.61 0.110

Material Compatibility 0.27 0.049

Durability 0.12 0.022

Management 0.4 Training Cost 0.07 0.028

Labor Cost 0.52 0.208

Equipment Cost 0.27 0.108

Material Cost 0.14 0.056

Productivity 0.32 Processing Time 0.14 0.072

Rework Reduction 0.24 0.102Field Usability 0.40 0.102

Ease of Installation 0.13 0.022

Surface Preparation 0.08 0.035

Maintenance 0.1PerformanceReliability 0.67 0.067

Life-Cycle Cost 0.33 0.033


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Analyzing the Weighted Factors

The weighted factors are displayed in descending order of their absolute weights, as

shown in Figure 17. The factors with the highest weights may be regarded as the most

important factors in making decisions about the use of advanced joining technology. The

figure shows that the most important factors turn out to be labor cost, field usability, joint

strength, and equipment cost.

Evaluation Model

Now an evaluation model is established and is based on the weights of the various

factors in the table just constructed. First, each factor is divided into three categories

high, medium, and lowand then the various joining technologies are classified on the

basis of their impacts on that factor. Once the different joining technologies are assessed

relative to each factor, a weighted score is computed for each, and the joining technology

with the highest total score is the one of greatest applicability.

Figure17. Ranking of Weighted Factors

0.000 0.050 0.100 0.150 0.200 0.250

Durability

Surface Preparation

Training Cost

Life-Cycle Cost

Ease of Installation

Material Compatiblity

Processing Time

Material Cost

Performance Reliability

Rework Reduction

Equipment Cost

Joint Strength

Field Usability

Labor Cost


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Table 9 Evaluation Model for Pipe Joining

Category Weight Subcategory WeightRelativeWeight

Level ofImpact

WeightWeightedScore

Structure 0.18 Joint Strength 0.61 0.110 High 1 0.110

Integrity Medium 0.7 0.077

Low 0.3 0.033

Material Compatibility 0.27 0.049 High 1 0.049

Medium 0.7 0.034

Low 0.3 0.015

Durability 0.12 0.022 High 1 0.022

Medium 0.7 0.015

Low 0.3 0.006

Management 0.4 Training Cost 0.07 0.028 High 1 0.028

Concern Medium 0.7 0.020

Low 0.3 0.008

Labor Cost 0.52 0.208 High 1 0.208Medium 0.7 0.146

Low 0.3 0.062

Equipment Cost 0.27 0.108 High 1 0.108

Medium 0.7 0.076

Low 0.3 0.032

Material Cost 0.14 0.056 High 1 0.056

Medium 0.7 0.039

Low 0.3 0.017

Productivity 0.32 Processing Time 0.14 0.056 High 1 0.056

Factor Medium 0.7 0.039

Low 0.3 0.017

Rework Reduction 0.24 0.077 High 1 0.077Medium 0.7 0.054

Low 0.3 0.023

Field Usability 0.4 0.128 High 1 0.128

Medium 0.7 0.090

Low 0.3 0.038

Ease of Installation 0.13 0.042 High 1 0.042

Medium 0.7 0.029

Low 0.3 0.012

Surface Preparation 0.08 0.026 High 1 0.026

Medium 0.7 0.018

Low 0.3 0.008Maintenance 0.1 Performance 0.67 0.067 High 1 0.067

Issue Reliability Medium 0.7 0.047

Low 0.3 0.020

Life-Cycle Cost 0.33 0.033 High 1 0.033

Medium 0.7 0.023

Low 0.3 0.010


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6

Evaluation of Advanced Joining Technologies

This chapter provides a brief discussion and assessment of the applicability of each ofthe various joining technologies to the joining of pipe. Each joining technology is

assessed by use of the evaluation model, and then the final results are presented.

Mechanical Joining

In general, mechanical joining is uncomplicated and effective, requiring little

mechanical skill to install. Because of the requirement of using thick pipe in this process

and the high cost of the materials involved, however, its applicability to pipe joining islimited. In addition, many situations do not readily lend themselves to mechanical joining.

An assessment of the applicability of this method to pipe joining is given in Table 10.

Table 10 Assessment of Mechanical Joining

Major Category Subcategory Joining Methods

MechanicalFastening

MechanicalInterlocking

Structure Joint Strength 0.077 (High) 0.077 (High)Integrity Material Compatibility 0.034 (Med) 0.034 (Med)

Durability 0.015 (Med) 0.015 (Med)

Management Training Cost 0.028 (High) 0.028 (High)

Concern Labor Cost 0.208 (High) 0.208 (High)

Equipment Cost 0.108 (High) 0.108 (High)

Material Cost 0.017 (Low) 0.017 (Low)

Productivity Processing Time 0.056 (High) 0.056 (High)

Factor Rework 0.054 (Med) 0.054 (Med)

Field Usability 0.128 (High) 0.128 (High)

Ease of Installation 0.029 (Med) 0.029 (Med)

Surface Preparation 0.026 (High) 0.026 (High)

MaintenancePerformanceReliability 0.047 (Med) 0.047 (Med)

Issue Life-Cycle Cost 0.023 (Med) 0.023 (Med)

Total Score 0.85 0.85


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Adhesive Bonding

Currently, adhesive bonding is used for many applications because of its low cost and

convenience of use. In addition, it is of sufficiently high strength that it can be used in the

assembly of airplane parts. The low resistance of adhesive-bonding techniques as a

function of bending load, however, has been regarded as the most significant obstacle to

the use of adhesive bonding (Lea, Stubblefield, and Pang, 1998). This limitation has been

lessened with technology advances in adhesive bonding. In fact, 3M has developed a

high-strength adhesive bonding technique that offers a normal tensile strength of 160 psi

and dynamic shear strength of 100 psi.

Adhesive bonding has great potential and soon may become one of the best

alternatives to current pipe-joining methods. Table 11 contains an evaluation of the

applicability of adhesive bonding to pipe joining.

Table 11 Assessment of Adhesive Bonding

Joining Method

Major Category Subcategory Adhesive BondingStructure Joint Strength 0.077 (Med)Integrity Material Compatibility 0.049 (High)

Durability 0.015 (Med)Management Training Cost 0.028 (High)Concern Labor Cost 0.208 (High)

Equipment Cost 0.108 (High)

Material Cost 0.039 (Med)Productivity Processing time 0.056 (High)Factor Rework 0.077 (High)

Field Usability 0.128 (High)

Ease of Installation 0.042 (High)

Surface Preparation 0.008 (Low)Maintenance Performance Reliability 0.047 (Med)

Issue Life-Cycle Cost 0.033 (High)Total Score 0.915


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Welding

Fusion Welding

Arc Welding: In general, arc welding techniques have been widely used for pipe joiningfor decades, and still dominate this area because of their good track record for durability

and performance. However, various industries are reluctant to use these methods, because

of the requirements for highly skilled labor and the inconsistent quality of the welds, so

they are forced to find alternative technologies. Among arc welding methods, stick

welding is the most popular joining method in the construction industry, even though it

offers low productivity compared to gastungsten arc welding (TIG) and gasmetal arc

welding (MIG) (Kapustay, 2002). In spite of the advantage that they have to offer in

terms of performance, however, MIG and TIG welding suffer from some of the same

problems as stick welding, such as a shortage of highly skilled labor. Another factor that

contributes to the relatively low degree of adoption of MIG and TIG welding in the

construction industry is the reluctance of welders to switch to new techniques (Kapustay,

2002).

Gas Welding:The oxyacetylene-gas welding process is simple and highly portable, and

the equipment needed for its use is inexpensive. The main drawbacks to its use in pipejoining in the construction industry may be its low productivity and the need for highly

skilled labor.

High-Energy Beam Welding: High-energy beam welding offers excellent performance,

so it is extensively used in joint-fabrication applications that require high accuracy in

terms of placement of the weld. Advances made in electron-beam welding, one of the

high-energy beam welding techniques, have eliminated the need to work in vacuum, so

this method can now be used in the atmosphere. Research on high-energy beam welding

is ongoing.

Resistance Welding:Resistance welding is a very useful joining technology because of

benefits such as short processing time, mechanizability of the process, and high


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performance. It is widely used in the manufacturing industry for the joining of

overlapping sheets or plates.

Flash butt welding, one form of resistance welding, is recognized as a very

satisfactory method for fabrication of pipe (Thompson, 1998). It offers good quality and

productivity because of its automated, remote-control system. However, it requires large

equipment, so its applicability is limited to shop fabrication.

Table 12 provides an assessment of the applicability of various types of fusion

welding to pipe joining.

Table 12 Assessment of Fusion Welding

MajorCategory Subcategory Joining Methods

TIGStick

Welding MIG

Oxy-Gas

Welding

Electron-

BeamWelding

FlashButt

Welding

Structure Joint Strength0.11

(High)0.11

(High)0.11

(High)0.11

(High)0.11

(High)0.11

(High)Integrity Material

Compatibility0.049(High)

0.049(High)

0.049(High)

0.049(High)

0.049(High)

0.049(High)

Durability0.022(High)

0.022(High)

0.022(High)

0.022(High)

0.022(High)

0.022(High)

Management Training Cost

0.008

(Low)

0.008

(Low)

0.008

(Low)

0.008

(Low)

0.028

(High)

0.028

(High)

Concern Labor Cost0.062(Low)

0.062(Low)

0.062(Low)

0.062(Low)

0.208(High)

0.208(High)

EquipmentCost

0.032(Low)

0.032(Low)

0.032(Low)

0.032(Low)

0.032(Low)

0.032(Low)

Material Cost0.039(Med)

0.039(Med)

0.039(Med)

0.039(Med)

0.039(Med)

0.039(Med)

ProductivityProcessingTime

0.039(Med)

0.017(Low)

0.039(Med)

0.017(Low)

0.056(High)

0.056(High)

Factor Rework0.054(Med)

0.023(Low)

0.054(Med)

0.031(Low)

0.077(High)

0.077(High)

Field Usability0.128(High)

0.128(High)

0.128(High)

0.128(High)

0.038(Low)

0.038(Low)

Ease ofInstallation 0.012(Low) 0.012(Low) 0.012(Low) 0.012(Low) 0.029(Med) 0.029(Med)SurfacePreparation

0.026(High)

0.026(High)

0.026(High)

0.026(High)

0.026(High)

0.026(High)

MaintenancePerformanceReliability

0.047(Med)

0.047(Med)

0.047(Med)

0.047(Med)

0.067(High)

0.067(High)

Issue Life-Cycle Cost0.01

(Low)0.01(Low)

0.01(Low)

0.01(Low)

0.023(Med)

0.023(Med)

Total Score 0.638 0.593 0.638 0.593 0.804 0.804


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Non-Fusion Welding

Explosion Welding:Explosion welding, one of the hot pressure welding techniques, has

been successfully applied to the welding of tubes, either for joining one tube to another or

for joining a tube to a tube plate. It has also been used for welding plugs into leaking

tubes in order to seal the leaks (Davies, 1993).

Friction welding:Friction welding has several advantages, such as ease of use, low cost,

and speed of processing. In addition, it can be operated in the field, on account of the

simplicity of the process. TWI developed radial friction welding for the specific purpose

of welding pipe; this technique overcomes some of the handling problems associated with

other types of friction welding. In view of its high cost and the need to use very heavy

machinery that has large hydraulic and power requirements, however, radial friction

welding has seen relatively little use, as it is best suited to the shop environment

(Kapustay, 2002).

Diffusion welding: Diffusion welding is a very precise joining process, with no fusion

zone and no heat zone, so it is an ideal joining technology. However, the high cost of the

materials used with this method militates against its applicability (Messler, 1993).

The suitability of various types of non-fusion welding for pipe joining is summarized

in Table 13.


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Table 13. Assessment of Non-Fusion Welding


ExplosionWelding

FrictionWelding

DiffusionWelding


(High)0.11

(High)0.11

(High)

Integrity Material Compatibility0.049(High)

0.049(High)

0.049(High)


0.022(High)

0.022(High)

Management Training Cost0.02

(Med)0.02

(Med)0.02

(Med)

Concern Labor Cost0.146(Med)

0.146(Med)

0.146(Med)

Equipment Cost0.032(Low)

0.032(Low)

0.032(Low)


0.039(Med)

0.039(Med)

Productivity Processing Time0.056(High)

0.056(High)

0.056(High)

Factor Rework0.077(High)

0.077(High)

0.077(High)

Field Usability0.038(Low)

0.090(Med)

0.038(Low)

Ease of Installation0.012(Low)

0.029(Med)

0.012(Low)

Surface Preparation0.008(Low)

0.018(Med)

0.008(Low)


0.067(High)

0.067(High)

0.067(High)

Issue Life-Cycle Cost0.023(Med)

0.023(Med)

0.023(Med)

Total Score 0.679 0.805 0.679


Brazing and soldering are widely used in the manufacturing industry because of their

utility in joining large structures under relatively low-stress conditions and their high

potential for automation (Messler, 1993). Because of the low melting point of the filler

metal used in these processes and the weakness of the joints produced, brazing and

soldering are generally used in low-pressure pipe work. An assessment of the

applicability of brazing and soldering to pipe joining is presented in Table 14.


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Table 14 Assessment of Brazing and Soldering

MajorCategory Subcategory Joining Method


Structure Joint Strength 0.033 (Low)Integrity Material Compatibility 0.034 (Med)

Durability 0.022 (High)

Management Training Cost 0.02 (Med)

Concern Labor Cost 0.146 (Med)

Equipment Cost 0.076 (Med)

Material Cost 0.039 (Med)

Productivity Processing Time 0.039 (Med)

Factor Rework 0.054 (Med)

Field Usability 0.09 (Med)

Ease of Installation 0.029 (Med)

Surface Preparation 0.026 (High)

MaintenancePerformanceReliability 0.067 (High)

Issue Life-Cycle Cost 0.023 (Med)

Total Score 0.698

Welding Automation

Welding automation is an emerging technology that has already been successfully

employed in the manufacturing industry. Benefits such as improvements in productivity

and reliability, reductions in labor costs, and elimination of variability in weld quality

have been realized through welding automation. In addition, the shortage of skilled

welders in the construction industry may force companies to use welding automation in

the near future. Despite its high initial cost and its lack of availability under certain

circumstances and environments, the advantages of using welding automation in pipe

joining will eventually become evident to those in the construction industry.

Orbital TIG welding is one of best alternatives to current practice in the construction

industry because it offers highly productivity and the process is simple and portable.

Mechanized MIG welding is more suitable for the shop environment than the field

environment because of the heavy equipment that is required for its use.


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An assessment of the applicability of welding automation to pipe joining is presented

in Table 15.

Table 15 Assessment of Welding Automation


OrbitalArc Welding

MechanizedMIG Welding


(High)0.11

(High)

Integrity Material Compatibility0.049(High)

0.049(High)


0.022(High)

Management Training Cost0.02

(Med)0.02

(Med)

Concern Labor Cost0.208(High)

0.208(High)

Equipment Cost0.032(Low)

0.032(Low)


0.039(Med)

Productivity Processing Time0.056(High)

0.056(High)

Factor Rework0.077(High)

0.077(High)

Field Usability0.09

(Med)0.038(Med)

Ease of Installation0.042(High)

0.042(High)

Surface Preparation0.026(High)

0.026(High)


0.067(High)

0.067(High)

Issue Life-Cycle Cost0.033(High)

0.033(High)

Total Score 0.915 0.819

Conclusion of Evaluation

The applicability of each of the various joining technologies to the joining of pipe has

been determined on the basis of the evaluation described in this chapter. According to the

results of this evaluation, the processes that are of greatest applicability to pipe joining

are orbital arc welding and adhesive bonding.


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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Stick welding

Oxyacetylen gas weldingGas-tungsten arc welding

Gas-metal arc welding

Explosion welding

Diffusion welding


Electron beam welding

Flash butt welding

Friction welding

Mechanized MIG welding

Mechanical Fastening

Mechanical Interlocking

Adhesive Bonding

Orbital Arc welding

Figure 18. Ranking of Applicability of Advanced Joining Technologies to Pipe Joining


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7

Business Analysis

Market Analysis for Pipe Welding in the Construction Industry

In 2002, the American Welding Society (AWS) released its Welding-Related

Expenditures, Investments, and Productivity Measurement Report, which states that

welding expenditures represent a substantial contribution to the U.S. economy. This

report also states that the construction sector alone spent over $10 billion on welding in

2000 (Table 16) and that this constituted over 30 percent of the total expenditure on

welding in the U.S. that year. Though this report does not provide figures for pipe

welding per se, it does indicate that the total cost of industrial construction (includingfactors other than pipe welding) amounted to about $30 billion in 2000. This figure

would be even higher if costs associated with welding of pipe for purposes other than

industrial buildings, such as in the construction of pipe to be used in pipeline construction

and commercial buildings, were taken into account.

Table 16 Welding Expenditures in 2000

Labor($1 M)

Materials &

Consumables($1 M)

OtherWelding-

Related Costs($1 M) Total($1 M)Industrial Buildings 2,526 201 300 3,027

Commercial Buildings 831 40 48 919Bridge & Tunnel Construction 17 12 4 32

Pipeline Construction 191 75 115 381Structural Steel Erection 210 66 11 287Fabricated Structural MetalProducts 2,191 360 69 2,620Miscellaneous Construction 2,394 509 446 3,349

Totals 8,358 1,264 993 10,615

Source: AWS (2002)

Estimation of the Cost of Welding in the Construction of the CII Model Plant

In the previous section, the total market cost of pipe joining was identified. In this

section, the direct cost of pipe welding for the CII Model Plant is estimated.


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One factor that figures heavily in the analysis of the impact of applying new

technology to the joining of pipe in the construction industry is the ratio of pipe welding

costs to the total cost of a construction project. An estimate of that ratio, based on the

scope of the CII Model Plant project and data from R.S. Means, is given here.

CII Model Plant. The Model Plant is a hypothetical installation valued at about $85

million that is to be constructed in 78 weeks. The scale and schedule are typical of

industrial projects. Nine major components of a typical plant (refraction unit, tank farm,

compressor unit, two turbine generators, underground piping, pipe bridge, and complete

civil site package) were assembled to form the model plant.

Basic Assumptions about Welding Costs. The estimates of welding costs presented in this

paper are based on the following data, which combine the scope of the CII Model Plant

project with basic data on labor and equipment costs taken from R.S. Means (2002):

Number of joints: 12,514 (CII Model Plant Project)

Bare wage of skilled welder: $173 per joint (R.S. Means, 2002)

Equipment cost: $20.50 per joint (R.S. Means, 2002)

Labor Cost for Welding. The bare wage of a skilled welder is $173 per joint (R.S. Means,

2002), based on use of 12 and schedule 40 steel pipe. Once overhead is calculated, the

cost of labor rises to about $251 per joint (R.S. Means, 2002). Thus the total labor cost of

welding in the construction of the CII Model Plant is about $3.14 million (table 17).


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Table 17 Labor Cost for Welding, CII Model Plant

Bare Wage of Skilled Welder: $173 per joint $173.00

Workers Compensation Insurance

Average for U.S.: 18.7% $32.35

Incremented Employee Cost per Joint $205.35

Average Fixed OverheadFederal and State Unemployment Insurance Costs: 7.0% $12.11

Social Security Taxes (FICA): 7.65% $13.23

Builders Risk Insurance Costs: 0.3% $0.52

Public Liability Costs: 1.55% $2.68


Other Overhead Costs

Average for U.S.: 10% (depends on factors such as the contractorsannual volume and staff requirements) $17.30


Number of Joints 12,514

Total Labor Cost $3.14 M

Sources: R.S. Means (2002) and CII Model Plant project

Equipment Cost for Welding.The equipment cost for welding is about $26.50 per joint,

based on use of 12 and schedule 40 steel pipe (R.S. Means, 2001). Therefore, if welding

were the only technique used for all the welding work done on the CII Model Plant, the

total equipment cost of welding in the construction of the CII Model Plant would come to

about $330,000 (Table 18).

Table 18 Equipment Cost for Welding

Cost per Joint $26.50

Number of Joints 12,514

Total Equipment Cost $330 k

Sources: R.S. Means (2002) and CII Model Plant project

Total Direct Cost of Welding.The total direct cost of pipe joining for the CII Model Plant

project is about $3.47 million (Table 19). Since the total construction cost of the project

is $85 million, the cost of pipe joining makes up more than 4 percent of the total.

Table 19 Total Direct Cost of Stick Welding

Wages $3.14 M

Equipment Cost $330 k

Total Cost $3.47 M


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8

Recommendations for Future Research

Several advanced technologies that could be applied to the joining of metal pipe in

the construction industry and that are particularly likely to be of interest to CII members

are recommended below. A brief discussion is given of each of the recommended

techniques, including an identification of potentially interested parties; a classification of

the payoff period, the level of risk, and the potential for success; and a suggested path for

future research.

New MechanicalAdhesive Bonding Technology

Description

The Welding Institute in the U.K. has done research on a hybrid joining system,

known as AdhFASTTM, in which adhesives and fasteners are combined. The point of

developing such a hybrid system is to exploit the desirable properties of each of the two

components separately, such as the rapidity and ease of use of fasteners and the

significant sealing ability and high fatigue resistance of adhesives.

According to Kellar and Jones (2000), t

New Joining Technology

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