CWA_Welded Connections and the Versatility of Fillet Welds

An official publication of the Canadian Welding Association | Summer 2010Publication officielle de lAssociation canadienne de soudage | lt 2010

www.cwa-acs.org

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INSIDE:CWA CONFERENCE 2010SEPTEMBER 26-28, 2010BLUE MOUNTAIN, CO

LINTRIEUR :CONFRENCE LACS 2010 26-28 SEPTEMBRE 2010 BLUE MOUNTAIN, CO

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4 Canadian Welding Association Journal Summer 2010

Published for: / Publi pour : Canadian Welding Association / LAssociation canadienne de soudage 7250 West Credit Ave. Mississauga, ON L5N 5N1 Tel: 800-844-6790 ext. 256 Fax: 905-542-1318 Email: [email protected] Website: www.cwa-acs.org

Published by: / Publi par :

Naylor (Canada), Inc. 100 Sutherland Ave. Winnipeg, MB R2W 3C7 800-665-2456 www.naylor.com

Publisher: / diteur : Robert PhillipsProject Manager: / Gestionnaire de projet : Alana Place

CWA Editor: / diteur de lACS: Dan Tadic

CWA Journal Committee: / Comit du Journal de lACS : Robert Shaw, Chairman / prsident Shane Haskins Karsten Madsen Andy McCartney Mick J. Pates Kristy WaalderbosMarketing Associate: / Adjoint au marketing : Heather ZimmermanAccount Executives: / Chargs de compte : Mark Hawkins (bookleader), Robert Bartmanovich, Bill Biber, Brenda Ezinicki, Ralph Herzberg, Wayne Jury, Cheryll Oland, Darryl SawchukNaylor Editor: / diteur de Naylor : Michael SenecalLayout & Design: / Mise en page et illustration : ??

Advertising Art: / Art publicitaire : ??

Return undeliverable Canadian addresses to: Naylor (Canada), Inc., Distribution Dept., 100 Sutherland Ave., Winnipeg, MB R2W 3C7. Renvoyer toute correspondance ne pouvant tre livre au Canada : Naylor (Canada), Inc., Service de la distribution, 100 Sutherland Ave., Winnipeg, MB R2W 3C7.CANADIAN PUBLICATIONS MAIL AGREEMENT #40064978 CONVENTION DE LA POSTE PUBLICATIONS NUMRO 40064978PUBLISHED FEBRUARY 2010/CWA-Q0110/9708 PUBLI EN FVRIER 2010/CWA-Q0110/97082010 Naylor (Canada), Inc. All rights reserved. The contents of this publication may not be reproduced by any means, in whole or in part, without the prior written consent of the publisher. 2010 Naylor (Canada), Inc. Tous droits rservs. Le contenu de cette publication ne peut tre reproduit, en tout ou en partie, de quelque manire que ce soit, sans la permission crite de lditeur.

ContentsTable des matires

Messages / Messages

Chairmans Message/Directors Message Message du prsident/Message du directeur 9

Summer / Lt 2010

Buyers Guide Guide de lacheteur 60Close Up Gros plan 62www.cwa-acs.org

Welded Connections and the Versatility of Fillet Welds Assemblages souds et polyvalence des soudures dangle 11Influences on fatigue properties of welded structures and methods of assessment Influences sur les proprits de fatigue des constructions soudes et mthodes dvaluation 17Field Hardness Testing of Welds Essais de duret des soudures sur le terrain 24General Requirements for Built-Up Members Exigences gnrales relatives aux lments composs 31The Next Step in Plasma Beveling: When Straight Cutting Is Not Enough La prochaine tape du chanfreinage plasma : quand les coupes droites ne suffisent pas 34Design and Use of Cored Stainless Steel Electrodes Conception et utilisation des lectrodes fourres en acier inoxydable 42How to Make Economical 6 mm Semiautomatic Horizontal Fillet Welds Comment raliser semi-automatiquement des soudures dangle de 6 mm lhorizontale 54

Features / Articles

Published for: / Publi pour : Canadian Welding Association / LAssociation canadienne de soudage 8260 Parkhill Drive Milton, ON L9T 5V7 Tel: 800-844-6790 Fax: 905-542-1318 Email: [email protected] Website: www.cwa-acs.org

Published by: / Publi par :

Naylor (Canada), Inc. 100 Sutherland Ave. Winnipeg, MB R2W 3C7 800-665-2456 www.naylor.com

Publisher: / diteur : Robert PhillipsProject Manager: / Gestionnaire de projet : Alana Place

CWA Editor: / diteur de lACS: Dan Tadic

CWA Journal Committee: / Comit du Journal de lACS : Robert Shaw (Chairman / prsident), Shane Haskins Karsten Madsen Andy McCartney Mick J. Pates Kristy WaalderbosMarketing Associate: / Adjoint au marketing : Heather ZimmermanAccount Executives: / Chargs de compte : Ralph Herzberg (bookleader), Bill Biber, John Byrne, Anook Commandeur, Brenda Ezinicki, Wayne Jury, Cheryll Oland, Darryl SawchukNaylor Editor: / diteur de Naylor : Michael SenecalLayout & Design: / Mise en page et illustration : Bill Kitson

Advertising Art: / Art publicitaire : Elaine Connell

Return undeliverable Canadian addresses to: Naylor (Canada), Inc., Distribution Dept., 100 Sutherland Ave., Winnipeg, MB R2W 3C7. Renvoyer toute correspondance ne pouvant tre livre au Canada : Naylor (Canada), Inc., Service de la distribution, 100 Sutherland Ave., Winnipeg, MB R2W 3C7.CANADIAN PUBLICATIONS MAIL AGREEMENT #40064978 CONVENTION DE LA POSTE PUBLICATIONS NUMRO 40064978PUBLISHED AUGUST 2010/CWA-Q0310/4325 PUBLI EN AOUT 2010/CWA-Q0310/4325

2010 Naylor (Canada), Inc. All rights reserved. The contents of this publication may not be reproduced by any means, in whole or in part, without the prior written consent of the publisher. 2010 Naylor (Canada), Inc. Tous droits rservs. Le contenu de cette publication ne peut tre reproduit, en tout ou en partie, de quelque manire que ce soit, sans la permission crite de lditeur.

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The CWA organizing committee is planning a fun filled, information packed Annual Conference at the Blue Mountain Resort in Collingwood, ON. Come out and learn how your company can benefit from improved process technologies and production efficiencies while driving our welding industry toward global competitiveness. You have the opportunity to become familiar with new technological developments in: welding research, applied research, productivity improvement methodologies, robotic intelligence, recent laser advancements, welding gas applications, spatter free welding, maintenance and repair analysis, recent welding power source evolution, pipe automation implementation for the oil sands industry, process automation, lean manufacturing applications, and cost analysis, etc. Blue Mountain is the perfect setting for our first annual CWA Conference with the fresh water lakes, scenic caves, golf, hiking, and outstanding fall colours. There are also many small shops and boutiques where you can find art, pottery, gifts and the renowned, unique Scandinavian Spa. As always, there will be a great deal of networking and knowledge sharing within the welding industry. Please plan on attending this very exciting Conference and supporting the Canadian Welding Association.

Conference Fees (Registration includes all meals, business meetings and social programs.) Early Bird Registration (Before August 31st, 2010) Members $375 + taxNon-Members $500 + taxStudents $300 + tax

Spousal Fee* $125 + tax

Standard Registration (After August 31st, 2010)Members $500 + taxNon-Members $625 + taxStudents $350 + taxSpousal Fee* $125 + tax

Spousal ProgramScandinave Spa $65 + taxCanoeing or Kayaking $138 + taxArtisan Tour $120 + tax

* spousal fee includes reception and awards dinner

CWA Annual Conference: Agenda

Productivity Lean Welding Methodology (Max-Weld Diagnostic) Jean Claude, Brisson National Research Council Automating Robotic Welding - Nick McDonald, ABB Robotics Power factor Dominique Dodd, Thermonic Electric Company Energy Efficiency and Costs in Arc Welding Jim Galloway, Conestoga College Pipe Welding in the Wild West James Gilbank, AECON Lockerbie The Benefits of Real Time Data Acquisition to Manufacturers Chris Brodnick, Lincoln Electric Energy Applications for Advanced Joining Processes Ed Hansen, ESAB

Process CMT Technology- Martin Willinger, Fronius Canada Fiber Laser Processing at Extreme Speed Extreme Power - Charles Caristan, Air Liquide Industrial US LP Diffusion Brazing of Nickel Based Super Alloys - Jesse Brenneman, University of Waterloo Wire Welding of Pt-10% Ir to 316-LVM Stainless Steel Y.D. Huang, G.S. Zou & Y. Zhou, University of Waterloo Weldability of AA-5182 Sheets Seam Welded N. Joshi and D.C. Weckman, University of Waterloo The Effects of Aluminum Coating Layer on Steel During Laser Brazing of Steel-AZ31B Mg Alloy Ali Nasiri, Y. Zhou, & D.

Weckman, University of Waterloo The Effect of Variable Changes in Alternating Current Output in Submerged Arc Welding Dale Malcolm, Lincoln Electric Is Spatterless Welding Possible with GMAW Process? Brian Doyle Panasonic Factory Solutions The Magnetic Pulse Impact Welding of Magnesium Sheets Alex Berlin University of Waterloo

Applications Welding Productivity: Challenges and Opportunities for Canadas Fabrication and Construction Industry - Matthew Yarmuch,

Alberta Research Council Effect of Welding Parameters on Tungsten Carbide: Metal Matrix Composites (WC-MMC) Produces by GMAW - Matt Yar-

much, Alberta Research Council/University of Alberta The Canadian Centre for Welding and Joining Patricio Mendez, University of Alberta Theoretical Analysis of Penetration Depth of Keyhole Laser Welding Process Ali Nasiri, Y. Zhou, & D. Weckman, University of Waterloo Fabrication Challenges in the Construction of Four 630M3 Autoclave Vessels Victor Taylor Hatch, Auto Clave Technology Group Hybrid Automated Welding System (HAWS) A New Way to Robotically Weld Pipe Fabrications Carl Heinrich Roboweld

Inc & Mathew Yarmuch, Alberta Innovates Technology Futures 20/20 Vision (Back to the future with intelligent robotic welding sensors) Jeffrey Noruk, Servo-Robot Corp. Consumables and Safety Improvements in Tubular Welding Wire Consumables Joseph C. Bundy, Hobart Brothers Automation Trends Support Continued Growth of Metal Cored Wire Garth Stapon, National Standard Reducing the Hazard Jay Smith, Nederman Canada Shielding Gases for Challenging Joining Applications Kevin A Lyttle, Praxair Technical Center Improved economics in MIG-welding of automotive Al-structures by using O2 doped argon-helium welding gas mixtures -

Christoph Matz Linde Canada.

CONTACT US NOW TO REGISTERPhone: 1-800-844-6790 | Fax: 905-542-1318 | Web: www.cwa-acs.org | Email: [email protected]

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Journal de lAssociation canadienne de soudage Lt 2010 9

Directors Message/Message du directeur

CWA National Advisory Council Chairmans MessageMessage du prsident du conseil consultatif national de lACS

Don GemmellCWA National Advisory Council ChairmanPrsident du conseil consultatif national de lACS

Dan TadicDirector, Canadian Welding AssociationDirecteur, Association canadienne de soudage

We have exp er ienc ed a ver y strong membership growth and are over 10,000 at this moment. Our plan is to be at 50,000 members by early 2014. Our chapter expansion program is well under way with most recent additions in Kelowna, Saskatoon, Montreal, Moncton, Fort McMurray,

St. Johns and student chapter at Universities of Alberta and Waterloo. By the end of this year, we will have new chapters added in Windsor, Scarborough, Sudbury and Barrie. Starting with this Journal issue we will be profil-ing various chapter activities, events and individuals. We hope that you will get involved with a chapter activity in your community.

Im sure everyone is reflecting on the past year both personally and profes-sionally and planning or looking for-ward to some summer vacation to enjoy some special times with family and/or friends. While the summer season is upon us, along with the great weather that is usually associated with it as well,

we are all too familiar with how quickly Labour Day will arrive. Now is the time to review the first annual fall agenda and conference information which is scheduled for September 26-28, 2010, in Collingwood, ON. Visit the CWA website at www.cwa-acs.org and take advantage of the early registration discount to be part of the seminars, social activities and awards presentations amongst some of the most highly respected experts in the welding com-munity. When you consider that there are twenty eight various topics to choose from, the seminars alone are a tremendous value. Wishing you all a safe and relaxing summer and hoping to see you at the conference.

Don Gemmell

Dan Tadic

Je suis sr que tout le monde pense lanne qui vient de se terminer, tant du point de vue personnel que professionnel, et que vous planifiez tous vos vacances dt afin de profiter pleinement de moments spciaux en famille et avec les amis. Bien que la saison estivale soit dj arrive, avec le beau temps qui y est normalement associ, nous savons tous que la fte du Travail arrivera bien assez vite. Cest le moment de passer en revue le premier calendrier annuel dautomne et linformation sur la confrence qui aura lieu du 26 au 28 septembre 2010 Collingwood, en Ontario. Visitez le site Web de lACS au www.cwa-acs.org et profitez des rabais offerts ceux qui sinscrivent lavance et qui veulent participer aux colloques, aux activits sociales et la remise des prix et se joindre quelques-uns des spcialistes les plus respects de la communaut du soudage. En pensant que vous pouvez choisir parmi vingt-huit sujets diffrents, vous constaterez que les colloques offrent une grande valeur eux seuls. Nous vous souhaitons tous un t relaxant en toute scu-rit et nous esprons vous voir la confrence.

Nous avons connu une croissance trs forte au niveau des ins-criptions, de sorte que nous comptons actuellement plus de 10 000 membres. Notre plan est daugmenter ce chiffre 50 000 membres dici le dbut de lanne 2014. Le programme dexpansion de notre section locale est en cours et nous avons ajout tout rcemment des sections Kelowna, Saskatoon, Montral, Moncton, Fort McMurray et St. Johns ainsi quune section tudiante aux Universits dAlberta et de Waterloo. Dici la fin de lanne, nous aurons ajout des nouvelles sec-tions Windsor, Scarborough, Sudbury et Barrie. Avec le prsent numro du Journal, nous commencerons tablir le profil de plusieurs activits et vnements organiss par les diffrentes sections ainsi que de certains de leurs membres. Nous esprons que vous participerez aux activits de la section dans votre communaut.SA

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Welded Connections and the Versatility of Fillet WeldsAssemblages souds et polyvalence des soudures dangleNeil A. Paolini

The five basic joint types (Butt, Tee, Corner, Lap, Edge) can be welded with fillet welds, groove welds, plug/slot welds or bead welds. The latter is used for weld overlay, sealing welds and edge welds; these are not generally considered as being calculated strength welds. Partial penetration groove welds (PJP), full penetration groove welds (CJP), and fillet welds are designed to transfer calculated stresses across (or along) a joint. When the full strength of a joint is needed, structural designers will often specify CJP welds. They should, in reality, specify full-strength welds since full strength on Tee joints, in particular, can be achieved using fillet welds. Fillet welds are more eco-nomical than PJP or CJP groove welds, since edge preparation

Les cinq types dassemblages fondamentaux (bout bout, en T, en L, recouvrement et sur chant) peuvent tre souds au moyen de soudures dangle, de soudures sur prparation, de soudures en bouchon ou en entaille ou de cordons de soudure. Les cordons sont utiliss pour raliser des sou-dures de rechargement, dtanchit et sur chant, qui ne sont gnralement pas considrs comme des soudures de rsistance calcule. Les soudures sur prparation pntration partielle et complte ainsi que les soudures dan-gle sont conues pour transfrer les contraintes calcules travers un joint ou le long de celui-ci. Lorsque la soudure doit tre compltement saine, les concepteurs de structures prescriront souvent les soudures pntration complte. En fait, ils devraient plutt prconiser les soudures complte-ment saines puisquil est possible dobtenir une rsistance maximale sur

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Fillet Weld Design Resistances

Weld resistance Vrw cannot exceed Base Metal resistance Vrm

NOTE: S16.1-2001 has increased the Xu values from 480 MPa to 490 MPa

Am = Aw when AW = fillet leg area

Vrw = .67 x x Aw x XU (1 + .5sin 0 )

Angledegrees01520253035404549505055606570758090

SIN0

0

0.259

0.342

0.423

0.5

0.574

0.643

0.707

0.755

0.766

0.819

0.866

0.906

0.940

0.966

0.935

1

SIN0

0

0.132

0.200

0.275

0.354

0.434

0.515

0.595

0.656

0.670

0.741

0.806

0.863

0.911

0.949

0.977

1

Vrw (leg)

kN/mm/mm

0.156

0.166

0.172

0.177

0.184

0.190

0.196

0.202

0.207

0.208

0.214

0.219

(Vrw=0.18 max for A36)

300W/300WT/350W max350WT only350WT only350 WT max.Vrw Cannot exceed0.214

0 = angle between line of action offorce and axis of the weld

For 300W, 2350WT & 350W material, Vr = .202 kN/mm/mm for angles greater than 49 degrees

For 350WT material, use Vr = .214 kN/mm/mm for angles 60 degrees and greater

Total resistance Vr = Vrw x Fillet Leg Size (mm) x Weld Length (mm)

Fu = 450 MPa(300W/350W300WT)Fu = 480 MPa (350WT)

ow1.5

Vrw = .67 x x Aw x XU (1 + .5sin 0 )ow 1.5 /2 .^5

Vrw = .67 x x Aw x Fu = 0.202 Aw kN/mm/mm max for

Vrw = .67 x x Aw x Fu = 0.215 Aw kN/mm/mm max for

ow

ow

Xu = 490 MPa= 0.220 (1 + .5 sin 0 ) Aw (E.T area)

= 0.156 (1 + .5 sin 0 ) Aw (fillet leg area)

1.5

1.5

Percent Waste When Size #1 Fillets are Specifiedand Size #2 Fillets are made

Size #2 1/4 5/16 3/8 7/16 1/2 9/16 5/8 11/16 3/4

0.25 0.313 0.4 0.438 0.5 0.5625 0.63 0.688 0.75Size #1 PERCENT WASTE1/45/163/8

Figure 2

For example, if a 5/16 fillet is sepcified and the welder makes a 7/16 fillet,96% of the weld is wasted. Even going from a 1/4 fillet to 5/16 willwaste 56%

0 56 125 206 300 406 525 656 800 0 44 96 156 224 300 384 476 0 36 78 125 178 236 300

is not required and joint geometry is simpler (because there is no root gap to maintain). In addition, fillet welds require less welder skill than required for making groove welds.

The use of fillet welds is far greater than all other types of welds. More care should be taken by draftsmen and design-ers to take advantage of available economies at the design or detailing stage.

Weld Design CriteriaAllowable stresses and Imperial units were prevalent in the 1950s, 60s and 70s. Electrodes were classified in accordance with their minimum tensile strength. E60XX electrodes had a UTS of 60 kips/sq. in.; E70XX UTS had 70 ksi, etc. Fillet welds were designed using 1% of the UTS in lbs/in of length/sixteenth inch of leg size. For example, using E70XX electrodes, the design value of a fillet was 700lbs/in of weld / 1/16 of leg length. A 1/4 fillet had a resistance of 4 x 700 = 2,800 lbs/in of weld. Testing soon proved these values were unacceptably low.

The CSA W59.1-70 code increased the allowable shear on a welds effective throat to 3% of the UTS. This resulted in an allowable throat shear stress of 21,000 psi for E70XX welds. The 450 component shear on the leg of a fillet became 14,850 psi or 925 #/in/sixteenth, a 32% increase from the 700 # value.

un assemblage en T, en particulier, en utilisant des soudures dangle. Ces dernires sont plus conomiques que les soudures sur prparation pntration partielle ou complte puisque la prparation du bord nest pas requise et que la gomtrie du joint est plus simple (parce quil ny a aucun cartement la racine maintenir). De plus, le soudeur nest pas tenu dtre aussi qualifi pour excuter une soudure dangle que pour une soudure sur prparation.

Les soudures dangle sont celles qui sont les plus couram-ment utilises par rapport aux autres types de soudures. Les dessinateurs et les concepteurs doivent sassurer de tirer profit des conomies qui soffrent eux lors de la phase de conception ou de finition.

Critres de conception des souduresLes contraintes admissibles et les units impriales taient courantes lors des annes 50, 60 et 70. Les lectrodes taient classes selon leur rsistance la traction minimale et celle des lectrodes E60XX et E70XX, par exemple, tait de 60 kips/po2 et de 70 ksi respectivement. Les soudures dangle taient conues en utilisant 1 % de la rsistance la traction en lb/po par longueur/seizime de pouce de dimension des cts. Par exemple, dans le cas de llec-trode E70XX, la valeur de calcul dune soudure dangle tait de 700 lb/po de soudure par 1/16 po de longueur de ct. Donc, une soudure dangle de po avait une rsistance de 4 x 700 = 2 800 lb/po de soudure. Les essais ont vite dmontr que ces valeurs taient trop basses et donc inadmissibles.

Selon la norme CSA W59.1-70, le cisaillement admissible sur la gorge eff icace dune soudure devait tre augment 3 % de la rsistance la traction, permettant ainsi une contrainte de cisaillement de 21 000 lb/po2 pour les soudures ralises au moyen dune lectrode E70XX. Le cisaille-ment dun composant 450 sur le ct dune soudure dangle devenait donc 14 850 lb/po2 ou 925 no/po/un seizime, soit une augmentation de 32 % par rapport la valeur du numro 700.

Avec la venue de la conversion mtrique et de la mthode de calcul aux tats limites, la rsistance est devenue encore plus leve. Les charges taient prises en considration et les coefficients de rsistance ont t labo-rs de manire tenir compte des charges pondres. Les soudures taient soumises un coefficient de rsistance rduit de 0,67. La rsistance au

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With the advent of metric conversion and Limit States Design, the bar was raised even higher. Loads were fac-tored and resistance factors developed to accommodate the factored loads. Welds were subject to a reducing weld resistance factor of 0.67. The shear resistance of a weld for a factored load became Vrw = 0.67 x w x effective throat area x weld UTS. The metric UTS (Xu) was set at 480MPa (i.e., Vrw = 0.67wAwXu). The weld resistance factor vw is also set at 0.67.

Further research indicated that the UTS (Xu) should be increased from 480MPa to 490MPa. Fillet weld resistances also increased when the angle between the line of force and weld axis increased from zero to 900. The increase was also dependent on the base material strength. The formula now becomes Vrw = 0.67wAwXu (1 + 0.5sin

1.5).Figure 1 simplifies these equations for all angles of force

and Xuu = 490MPa applied to 300W and 350W base materi-als. The note at the bottom of figure 1 illustrates how easily fillet welds can be designed. A conservative approach, if the angle is not known, is to assume it is zero and use the factor Vrw = 0.156.

Points to Consider Groove weld strength is limited to the plate thickness.

Groove welds cannot be overwelded. Filletweldstrength(size)isnotlimitedtoplatethickness.

Fillet welds sizes are not limited. Overweldingafilletincreasestheamountofweldmetalby

the square of the increase (figure 2). (Doubling the size of a fillet results in four times the amount of weld metala 300% increase).

Fillet sizes shouldbekept to aminimum (inaccordancewith code and heat input criteria).

A5mmfillet100mmlonghasthesamestrengthasa10mm fillet 50 mm long with half the weld metal.

A smaller, longer fillet ismore economical than a largershorter fillet of equal resistance.

Sizethefilletweldtosuit the load.Continuousfilletsarenot always required.

Standardize,ifpractical,oneithera6mmor8mmsingle-pass fillet for any given assembly.

Iffeasible,replacePJPandCJPTeejointgrooveweldswithequal strength fillet welds.

Converting a Large Tee Joint Fillet to a More Economical Equal Strength Combination Bevel/Fillet Weld (Figure 3)When the calculated fillet size equals, or exceeds, 16 mm, a combination of fillet and single bevel groove welds should be considered. A fillet half the size of the large calculated fillet size combined with a partial penetration 450 single bevel chamfer equal to the half fillet leg plus 3 mm will result in resistance equal to the large calculated fillet size. This combination uses half the weld of the calculated large fillet, thereby reducing heat input, distortion, weld metal and welding time. The only additional cost would be the bevel preparation on the Tee stem. For example, a 20 mm fillet would be replaced by a 13 mm (10 + 3) single 45 bevel chamfer weld overlaid with a 10

cisaillement dune soudure pour une charge pondre devenait donc Vrw = 0,67 x w x la section de la gorge efficace x la rsistance la traction de la soudure. Celle-ci en units mtriques (Xu) a t rgle 480 MPa (c.--d., Vrw = 0,67wAxXu). Le coefficient de rsistance de la soudure w est aussi rgl 0,67.

Des recherches plus avances ont indiqu que la rsistance la traction (Xu) devrait tre augmente de 480 MPa 490 MPa. La rsistance des soudures dangle a aussi augment lorsque langle entre la ligne de force et laxe de la soudure est mont de zro 900. Cette augmentation dpendait aussi de la rsistance du matriau de base. La formule devient donc Vrw = 0,67wAxXu (1 + 0,5sin

1.5).La figure 1 simplifie ces quations pour tous les angles de force et Xuu

= 490 MPa est appliqu aux matriaux de base 300 W et 350 W. La note la fin de la figure 1 illustre quel point il est facile de concevoir des soudu-res dangle. Une approche conservatrice, lorsque langle nest pas connu, est dassumer que celui-ci est zro et dutiliser le coefficient Vrw = 0,156.

Points considrer La rsistance des soudures sur prparation se limite lpaisseur de la

plaque. Ces soudures ne peuvent pas faire lobjet dun soudage excessif. Larsistancedessouduresdangle(dimension)neselimitepaslpais-

seur de la plaque. Il ny a aucune limite quant aux dimensions des soudures dangle.

Une quantit excessive demtal dpos dans une soudure dangle aug-mente la quantit de mtal fondu par le carr de laugmentation (figure 2). (Doubler la dimension dune soudure dangle rsulte en quatre fois la quantit de mtal dpossoit une augmentation de 300 %).

Les dimensions des soudures dangle devraient demeurer minimales(conformment aux codes et aux critres dapport thermique).

Unesouduredanglede5mmayantunelongueurde100mmalammersistance quune soudure dangle de 10 mm ayant une longueur de 50 mm, avec la moiti de la quantit de mtal dpos.

Unesouduredanglemoinslargeetpluslongueestplusconomiquequunesoudure dangle plus courte et plus large ayant la mme rsistance.

Ladimensiondelasouduredangledoitconvenirlacharge.Lessoudu-res dangle continues ne sont pas toujours requises.

Ilfautstandardiser,lorsquecelaestpratique,surunesouduredanglede6 mm ou de 8 mm ralise en une seule passe pour un assemblage donn.

Dans la mesure du possible, remplacer les soudures sur prparation pntration partielle ou complte ralises sur les assemblages en T par des soudures dangle ayant la mme rsistance.

Conversion dune large soudure dangle ralise sur un assemblage en T une soudure sur prparation en demi-V/soudure dangle combine plus conomique ayant la mme rsistance (figure 3)Lorsque la dimension dune soudure dangle calcule est gale ou suprieure 16 mm, la combinaison dune soudure dangle et dune soudure sur prpara-tion en demi-V devrait tre considre. Une soudure dangle dont la dimension est la moiti de celle dune soudure dangle calcule plus large combine un chanfrein simple de type 450 pntration partielle gal la moiti du ct de la soudure dangle plus 3 mm donnera une rsistance gale la dimension de la large soudure dangle calcule. Cette combinaison utilise la moiti de la large soudure dangle calcule, rduisant ainsi lnergie linaire, la distor-sion, la quantit de mtal fondu et la dure du soudage. Le seul cot addition-nel serait la prparation du chanfrein sur lassemblage en T. Par exemple, une soudure dangle de 20 mm serait remplace par un chanfrein simple de 45 et

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mm fillet. The 3 mm is required to compensate for an effective throat code reduction for a 45 bevel (figure 3b).

This combination is applicable for a Tee joint where the Tee stem is in longitudinal shear (i.e., the line of force is along the axis of the weld). Conservatively, this could be applied to lines of force at angles to 900 with the weld axis. However, when the stem is in tension (i.e., the angle = 900), applying CSA S16-01, Clause 13.13.3.3, the tensile resistance of a par-tial joint penetration groove weld combined with a fillet weld would be more economical (figure 3a).

The evolution of structural joint design has progressed from forging to riveting, to bolting, to high-tensile bolting, to combinations of bolting/welding, and to welding only. Today, welding is a mature science that has resulted in stronger, lighter more economical structures, and has also expanded the imagination, scope and creativity of engineers and archi-tects. Elegant structures are now routinely designed that are only possible through the use of welded joints. The artistic canopy shown at the beginning of this article is an example of artistic imagination that relies on welded joints.

Neil A. Paolini, P. Eng., works at ProWeld Engineering.

de 13 mm (10 + 3) chevauche par une soudure dangle de 10 mm. Le 3 mm est requis pour compenser la rduction de la gorge efficace pour une prparation de 45 exige par le code (figure 3b).

Cette combinaison sapplique aux assemblages en T lorsque celui-ci subit un cisaillement longitudinal (c.--d., la ligne de force se trouve le long de laxe de la soudure). En demeurant conservateur, cela pourrait sappliquer aux lignes de force des angles allant jusqu 900 par rapport laxe de la soudure. Cependant, lorsque lassemblage en T est sous tension (c.--d., que langle = 900), selon larticle 13.13.3.3 de la norme CSA S16-01, la rsistance la traction dune soudure sur prparation pntration partielle combine une soudure dangle serait plus conomique (figure 3a).

La conception des joints de structure a volu du forage au rivetage, au boulonnage, au boulonnage haute traction, au boulonnage et soudage combin et finalement, au soudage seulement. Aujourdhui, le soudage est une science avance qui a produit des structures plus fortes, plus lgres et plus conomiques et largi limagination, le champ dapplication et la crativit des ingnieurs et des architectes. Les structures lgantes mainte-nant conues de faon rgulire ne sont possibles que grce aux assemblages souds. La structure illustre au dbut de cet article est un exemple dimagi-nation artistique qui repose sur des assemblages souds.

Neil A. Paolini, ing., travaille chez ProWeld Engineering.

Partial Joint Penetration Groove Weld combined with Fillet Weld (Matching Electrodes)EXAMPLEClause 13.13.3.3

L = 100mmD = 10mmC = 10mm

An = nominal area of fusion face normal to Tr = C x L =Aw = Area of effective throat = D/2^.5 x L =

Tr

3mm

Fusion FaceC

D

D/2^0.5

Figure 3b

1000 mm^2707 mm^2

S16.1Tr = o x ((An x Fu)^2 + (Aw x Xu) ^2)^.5Depth of chamfer = C + 3 Length = L mm

Fu = 450 MPaXu = 490 MPa

0.450.49

300W; 350W; 300WT

Tr = 381 kN

NOTE: Depth of chamfer is C + 3 due to 3mm LOP on 45 degree bevel

Replacing Large Fillet with Equal Resistance Combination Fillet and ChamferChamfer = 50% large fillet leg size (+ 3 mm for LOP in root)Combination Fillet = 50% large fillet size

Tr = 0.67 x Aw x Xu

Single Large FilletEffective Throat ET1 = 2D/2^.5=1.414 DCombination Chamfer + FilletChamfer =2D/2 +3 = Effective DEffective Throat ET2 = Chamfer face = D X 2^.5 = 1.414D

ET1 = ET2

Combination weld has same resistance as large fillet, with 50% of the weld metal.

Figure 3a

Tr

D+-3

D

45o

ET

D+3

D

2D

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Influences on fatigue properties of welded structures and methods of assessmentInfluences sur les proprits de fatigue des constructions soudes et mthodes dvaluationAdolf F. Hobbacher

Welded structures can terminate their usage life by various reasons, including wear, corrosion, brittle fracture, overload, buckling, creep ormost importantfatigue. Besides wear and corrosion, about 80% of all failures of welded struc-tures subjected to repeated loads are due to fatigue. The fatigue properties and life of a welded component or joint are dependent on several parameters. First, on the loading side, there is the effect of load f luctuations, which can be described according to the magnitude of stress, the stress

La dure de vie des constructions soudes peut tre rduite pour diverses raisons, y compris lusure, la corrosion, la rupture fragile, les surcharges, le f lambage, le f luage oule plus importantla fatigue. Outre lusure et la corrosion, environ 80 % de toutes les dfaillances de constructions soudes soumises des charges rptes sont causes par la fatigue. Les proprits de fatigue et la dure de vie dun assemblage soud ou dun joint dpendent de plusieurs paramtres. Premirement, du ct charge, il y a leffet des f luctuations de charge, qui peuvent tre dcrites selon lampleur et la gamme des contraintes et le nombre de cycles. Du ct

Terr

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f Wat

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range, and the number of cycles. On the fatigue resistance side, there are the effects of material type, the surface of the welded joint, the temperature that may modify the material properties, and the shape as the main governing parameter. This implies that, in most failure cases, design and fabrica-tion (i.e., weld quality and severity of notch) are primary, and material selection and properties are secondary.

When designing welded components of structures that are subjected to repeated loads, fatigue considerations are essential. Methods for calculating fatigue (1) the nominal stress method (e.g., ASME, CSA S16, S6 and W59); (2) the structural hot spot stress method and its variations (e.g., Eurocodes and offshore structures); (3) the effective notch stress method; and (4) fracture mechanics. The best but most expensive method is (5) direct component testing. It is applied in areas with a high commercial or human risk, such as automotive and aircraft engineering. Another point is that there is considerable variation as to the effects of fatigue, and a design standard must cover worst-case conditions. In test-ing, the real fatigue property of the specific component can be used (see figure 1).

Many areas of technology refer to officially introduced or agreed design code or standard. Here, the problem is that a code or standard is always a reduction of a complex set of possibilities, and is valid only for the limited set of circum-stances for which it was established. An application in a slightly different area might cause problems. It is important for the designer to have adequate knowledge of the basics of fatigue in addition to the background of an applied code

Figure 1. Example of data collection of a structural detail and code. Figure 1. Exemple de collecte de donnes dun dtail de conception et dun code.

de rsistance la fatigue, il y a les effets du type de matriau, de la surface de lassemblage soud, de la temprature qui peut modifier les proprits du matriau et de la forme, qui constitue le principal paramtre. Cela signif ie que dans la plupart des cas de dfaillance, la conception et la fabrication (c.--d., la qualit de la soudure et la gravit de lentaille) sont dune importance primordiale, alors que la slection des matriaux et les proprits sont des facteurs secondaires.

Lors de la conception des assemblages souds sur des structures sou-mises des charges rptes, il est essentiel de tenir compte de la fatigue. Il existe cinq mthodes pour calculer la fatigue, soit (1) la mthode de contraintes nominales (p. ex., ASME, CSA S16, S6 et W59); (2) la mthode de contraintes dans la zone chaude structurale et ses variations (p. ex., les Eurocodes et les constructions en mer); (3) la mthode de contraintes den-taille efficace; et (4) la mcanique de la rupture. La meilleure mthode et la plus dispendieuse est la mthode (5), soit la mthode dessais directs des composants. Cette mthode sapplique dans des endroits o un risque com-mercial et humain lev est prsent, comme dans les industries de lauto-mobile et du gnie technique des aronefs. Un autre point est la variation considrable quant aux effets de la fatigue et une norme de conception doit couvrir les pires ventualits. Lors des essais, la proprit de fatigue relle du composant prcis peut tre utilise (voir la figure 1).

Dans plusieurs domaines technologiques, des rfrences sont faites au code ou la norme de conception officielle ou adopte. Le problme ici est quun code ou une norme est toujours une rduction dun ensemble complexe de possibilits et nest valide que dans le cadre de circonstances limites pour lesquelles il ou elle a t tabli(e). Une utilisation dans un endroit lgrement diffrent pourrait causer des problmes. Il est impor-tant que le concepteur connaisse suffisamment les notions lmentaires de la fatigue en plus de lhistorique dun code ou dune norme appliqu(e).

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or standard. This enables him or her to offer a true critical engineering assessment for the designed structure.

Parameters of FatigueFatigue failures are as old as the use of technology by humans. It was once thought that fatigue was induced by simple over-load, and the way to eliminate fatigue was to eliminate overload. Around the year 1790, however, experiments showed that over-load was not the cause of fatigue; rather, it is caused by the fre-quency of load repetitionsor the number of load cycles, to use modern terms.

Today, the determination of load history is the most crucial factor in fatigue assessment. In many cases it is not possible to make long-term measurements, and in those situations, assump-tions based on applicable codes or standards may fill the gap. The problem is reflected by the partial safety factors in various building codes. On the loads it is about a factor of 1.5, whereas on the resistance side it is only 1.1 in Eurocodes and 0.9 in CSA standards.

Stresses are usually not evenly distributed over the sectional area of a weld. With fillet welds, there are stress concentrations at the weld toe and at the root. These notch effects are an import-ant parameter and dominate the design. Weld imperfections (e.g., inclusions, porosity, cracks, lack of fusion and penetration, and others) are also sources of fatigue. It is not the metallurgy, it is the stress rising effect that reduces the fatigue properties.

The process of fatigue is orderly. Crack initiation is fol-lowed by crack propagation and then the final rupture of

Cela lui permet doffrir une vritable valuation technique essentielle pour la structure quil a conue.

Paramtres de fatigueLes ruptures par fatigue sont aussi anciennes que lutilisation de la tech-nologie par les humains. On pensait autrefois que la fatigue tait induite par une simple surcharge et que la faon de lliminer tait dliminer la surcharge. Autour de lanne 1790, cependant, des essais ont dmontr que la surcharge ne causait pas la fatigue, mais quelle tait plutt occasionne par la frquence des rptitions de charge ou par le nombre de mises en charge cycliques, pour utiliser des termes modernes.

Aujourdhui, la dtermination des antcdents de charge est le facteur le plus essentiel de lvaluation de la fatigue. Dans bien des cas, il est impossible deffectuer des mesures long terme et, dans de telles situa-tions, des hypothses fondes sur les codes ou sur les normes pertinent(e)s peuvent combler le vide. Le problme est ref lt par les facteurs de scurit partiels prciss dans les divers codes du btiment. Sur les charges, il sagit dun facteur denviron 1,5, alors que du ct rsistance, il nest que de 1,1 dans les Eurocodes et de 0,9 dans les normes CSA.

Normalement, les contraintes ne sont pas distribues uniformment sur la section transversale de la soudure. Dans les cas des soudures dangle, des concentrations de contraintes sont prsentes au raccordement len-droit et la racine. Ces effets dentaille constituent un paramtre impor-tant et dominent la conception. Les imperfections des soudures (p. ex., les inclusions, la porosit, les fissures, le manque de fusion et le manque de pntration) sont aussi des sources de fatigue. Ce nest pas la mtallurgie, mais plutt leffet de la concentration des contraintes qui rduit les pro-prits de fatigue.

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the remaining sectional area. In welded joints, the period of crack initiation is brief in comparison to the period of crack propagation. The relevant parameter for crack propagation is the modulus of elasticity, which makes the fatigue proper-ties independent within a type of material. The reduction of fatigue properties at higher temperature is primarily due to the reduction of the modulus of elasticity.

Methods of AnalysisTo assess the fatigue properties of welded joints, anticipated load history is compared with fatigue resistance and is repre-sented by a log-log plot of stress range versus life cyclesthe so-called Woehler SN curve. There are different possibilities for the selection of the reference stress range. The nominal stress method specifies the fatigue life of a welded joint accord-ing to the characteristic global geometry of the joint and the history of nominal stresses at specified locations. In design codes, this simple method requires a catalogue of all struc-tural details, each of them associated with a special Woehler SN curve. Modern codes and standards may have more than 80 structural details associated with six to ten SN curves.

The structural hot-spot stress method is measured by sum-marizing all stress rising effects except the notch effects of the weld. In codes, only one or two Woehler SN curves are needed.

In mechanical engineering it is usual to take the stress within a notch as a reference stress. This procedure is not directly applicable to the irregular notches of weld toes.

Le processus de fatigue est ordonn. Lamorce de fissures est suivie par la propagation de celles-ci, puis par la rupture finale de la section restante. Dans les joints souds, la priode damorage des fissures est brve compa-re celle de la propagation des fissures. Le paramtre pertinent pour la propagation des fissures est le module dlasticit, qui rend les proprits de fatigue indpendantes lintrieur dun type de matriau. La rduction des proprits de fatigue des tempratures plus leves est principalement cause par la rduction du module dlasticit.

Mthodes danalysePour valuer les proprits de fatigue des joints souds, lhistorique des charges anticipes est compar la rsistance la fatigue et reprsent dans un graphe bilogarithmique de la gamme de contraintes par rapport aux cycles de viela soi-disant courbe SN de Woehler. Il existe diffrentes possibilits quant la slection de la gamme de contraintes de rfrence. La mthode de contraintes nominales prcise la dure de vie en fatigue dun joint soud selon la gomtrie globale caractristique du joint et lhistorique des contraintes nominales des endroits stipuls. Dans les codes de conception, cette simple mthode exige un catalogue de tous les dtails de conception, chacun tant associ une courbe SN de Woehler spciale. Les codes et les normes modernes peuvent stipuler plus de 80 dtails de conception associs entre six et dix courbes SN.

La mthode de contraintes dans la zone chaude structurale est mesure en rsumant tous les effets de la concentration des contraintes, lexception des effets des entailles de la soudure. Dans les codes, seulement un ou deux cour-bes SN de Woehler sont requises.

En gnie mcanique, la contrainte dans lentaille est normalement utilise titre de contrainte de rfrence. Cette procdure ne sapplique pas directement aux entailles irrgulires des raccordements lendroit. On a

478927_Pearl.indd 1 5/18/10 12:00:19 PM

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The problem was overcome by the replacement of the actual notch by a fictitious effective notch, which gives consistent results. It requires a fine finite element meshing. In codes only, one SN curve is needed.

An entirely different approach is the use of fracture mech-anics. Here it is assumed that there was an initial crack or crack-like imperfection on the surface, followed by the onset of crack propagation on the fluctuating service loads until a final rupture occurs. This method can be applied universally and will become more important in the near future. The drawback is that is requires a highly skilled and experienced analyst and some computational power. The advantage is in the ability to rationally make a determination of remaining fatigue life.

Fabrication QualityIn fabrication, irregularities and imperfections can never be completely avoided. Many quality assurance systems were based on ISO 5817. This code was established as a means of understanding the difference between fabricators and inspect-ors. Fatigue properties were not a point of consideration. As a consequence, the quality levels B, C and D are not consistent in terms of fatigue. Different industry standards try to over-come that problem. Currently, a joint working group between ISO and IIW has been established with the task of bringing the different approaches in line.

There are post-weld treatments available that improve the fatigue properties of welded joints. Two basic effects are

rgl le problme en remplaant lentaille relle par une entaille efficace fic-tive, ce qui donne des rsultats consistants. Cela exige le maillage dlments finis. Dans les codes seulement, une seule courbe SN est requise.

Une approche entirement diffrente est lutilisation de la mcanique de rupture. Ici, en thorie, la surface comporte une fissure initiale ou une imperfection qui ressemble une fissure, suivie par le dbut de la propa-gation de fissures sur les charges de service f luctuantes jusqu ce quune rupture finale se produise. Cette mthode peut tre mise en uvre universel-lement et deviendra plus importante dans un proche avenir. Linconvnient est quelle exige un analyste hautement comptent et expriment et une certaine puissance de calcul. Lavantage est dans la capacit de dterminer rationnellement la dure de vie en fatigue restante.

Qualit de la fabricationLors de la fabrication, il est impossible dviter compltement les irrgulari-ts et les imperfections. Plusieurs systmes dassurance de la qualit taient fonds sur le code ISO 5817. Ce dernier a t adopt en vue dtablir la diff-rence entre un fabricant et un inspecteur. Les proprits de fatigue ntaient pas un point analyser. Par consquent, les niveaux de qualit B, C et D ne sont pas conformes en matire de fatigue. Diffrentes normes de lindustrie essaient de contrer ce problme. Actuellement, un groupe de travail mixte form de lISO et lIIS a t mis sur pied avec la tche dharmoniser les diff-rentes approches.

Deux traitements aprs soudage sont disponibles en vue damliorer les proprits de fatigue des assemblages souds, avec deux effets fondamentaux. Dans le premier cas, la forme de lassemblage est amliore en meulant ou en fraisant le raccordement au moyen dune broyeuse ou en le refondant avec un enrobage TIG. Dans le deuxime cas, des contraintes de compression

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available. The first improves the shape by grinding, milling the toe with a burr grinder, or re-melting with TIG dressing. The second involves the introduction of benign residual com-pressive stresses with a hammer, a needle, shot or ultrasonic peening.

Human ResourcesFatigue properties are first of all dependent on design. But a design is always accomplished by a designer. It has been shown that most failure cases are due to poor design and not to poor fabrication in shop. What was wrong was not scientific question per se, but rather a lack of knowledge of the state of the art. So designer education is crucial and has a huge influ-ence on the fatigue properties of welded joints. In a normal university engineering education, fatigue is not taught at an adequate level, and so dedicated company-based or other pro-fessional-level training is needed.

ConclusionKnowledge of appropriate fatigue design for welded compon-ents is not a mere academic exercise, it is essential for economic and safety reasons. Most failures could have been avoided just by applying the existing state of the art.

Adolf F. Hobbacher is a research consultant and former director of the Institute for Materials and Production Technology at the University of Applied Sciences in Mannheim, Germany.

rsiduelles bnignes sont introduites dans lassemblage au moyen dun mar-teau, dune aiguille, dun grenaillage de prcontrainte ou dun martelage par ultrasons.

Ressources humainesLes proprits de fatigue dpendent dabord de la conception, mais une conception est toujours accomplie par un concepteur. Il a t dmontr que dans la plupart des cas, les dfaillances sont causes par une mauvaise concep-tion et non pas par une mauvaise fabrication latelier. Ce qui nallait pas ntait pas une question scientifique pour ainsi dire, mais plutt un manque de connaissance de la technique davant-garde. Il est donc essentiel de bien former le concepteur puisquil a une norme influence sur les proprits de fatigue des assemblages souds. Dans un programme dingnierie offert nor-malement au niveau universitaire, la notion de fatigue nest pas aborde ad-quatement, de sorte quune formation spcialise offerte linterne par les entreprises ou une formation professionnelle est requise.

ConclusionLa connaissance dune conception de fatigue approprie pour les assembla-ges souds nest tout simplement pas un exercice acadmique, mais est plu-tt essentielle pour des raisons conomiques et de scurit. La plupart des dfaillances auraient pu tre vites en utilisant tout simplement les techni-ques avant-gardistes actuelles.

Adolf F. Hobbacher est conseiller en recherche et ancien directeur de lInstitute for Materials and Production Technology lUniversity of Applied Sciences Mannheim, en Allemagne.

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Non-destructive examination is essential in verifying weld soundness, but it tells us little about the metallurgical properties of a weldment. Hardness testing is unique among mechanical test methods in that it can be performed in a manner that is essentially nondestructive. While in situ hardness testing has been employed for a long time, its prominence is growing due to several factors: The increasing use ofmetallurgicallymore complex struc-

tural steels and other alloys. Theextremedemandsplacedonmaterialsbyever-increasing

operating pressures and temperatures (e.g., in the many new steam and power generation plants).

Thegrowthoffitness-for-purposeandrisk-basedinspectionprograms, concurrent with aging plant infrastructure.

AvailabilityofimprovedportabletestingequipmentThis apparently simple test method is frequently called for in

technical specifications and some construction codes. Hardness limits are given not just as a general precaution, but also to avoid specific failure modes that may affect welds in their oper-ating environments. This article provides a brief overview of the applications and methods of field hardness testing of welds and describes basic elements of a successful technique.

Why Is Weld Hardness Testing Important?Welders, supervisors and engineers are familiar with the possible consequences of welding carbon and low alloy steels: hydrogen-assisted cracking, high hardness in the heat-affected zone (HAZ),

Lexamen non destructif est essentiel pour vrifier la qualit dune soudure. Par contre, cet examen ne nous dit pas grand chose sur les proprits mtallurgiques dun assemblage soud. Lessai de duret est uni-que parmi les mthodes dessai mcaniques parce quil peut tre effectu dune manire essentiellement non destructive. Alors que des essais de duret in situ ont t longtemps utiliss, ceux-ci deviennent plus importants en raison de plusieurs facteurs : Lutilisationcroissantedaciersdeconstructionetdalliagespluscomple-

xes du point vue de la mtallurgie. Lesexigencesextrmesplacessur lesmatriauxpar lespressionset les

tempratures dutilisation qui augmentent constamment (p. ex., dans les nombreuses nouvelles usines de gnration de vapeur ou dnergie lectrique).

Laugmentation des programmes dinspection fonds sur les risques etdaptitude lusage, en mme temps que le vieillissement des infrastructu-res dusines.

Ladisponibilitdappareilsdessaiportatifsamliors.Cette mthode dessai manifestement simple est souvent exige dans

les spcifications techniques et dans certains codes de la construction. Les limites de duret sont fournies non seulement titre de prcaution gnrale, mais aussi pour viter les modes de dfaillance spcifiques qui peuvent avoir une incidence sur les soudures dans leurs environnements oprationnels. Cet article donne un bref aperu des applications et des mthodes dessais de duret sur le terrain des soudures et dcrit les lments fondamentaux dune technique russie.

Field Hardness Testing of WeldsEssais de duret des soudures sur le terrainGordon Snieder

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and reduced low-temperature fracture toughness. But hardness is also restricted for other reasons, including resistance to cor-rosion. For example, NACE MR0175 (Materials for Use in H2S-containing Environments in Oil and Gas Production) and CSA Z662 (Oil and Gas Pipeline Systems) both address high hard-ness as a risk factor in sulphide stress corrosion cracking (SSC). Another example is the Cr-Mo steels (in particular, grade P-91, which has been growing in popularity), where hardness testing is crucial in checking the effectiveness of stress relief after forming or welding. Of the zones in a steel weldment, the HAZ is of most concern, and is also the most difficult to test. This narrow region bordering the weld metal is where the base metal is heated above the transformation temperature before cooling. The resulting structure and hardness of the HAZ is dependent on a variety of factors, primarily composition, but also thickness, preheat temperature, and heat input. Hardness testing is the only way to evaluate the HAZ condition.

A welding procedure specifications (WPS) developed for critical applications such as high-energy piping will include supplementary testing such as Charpy impact and hardness testing. The applicable code and/or construction specification should provide guidance as to the test methods and locations.

Pourquoi les essais de duret des soudures sont-ils si importants?

Les soudeurs, les superviseurs et les ingnieurs connaissent bien les consquences ventuelles du soudage des aciers au carbone et faiblement allis : la fissuration par lhydrogne, une duret leve dans la zone ther-miquement affecte (ZTA) et une tnacit rduite base temprature. Mais la duret est aussi limite pour dautres raisons, y compris la rsistance la corrosion. Par exemple, la norme MR0175 de NACE et la norme CSA Z662 traitent toutes les deux de la duret leve titre de facteur de risque dans la fissuration par corrosion sous contrainte du sulfure. Un autre exemple porte sur les aciers Cr-Mo (en particulier de classe P-91, qui devient de plus en plus populaire) o les essais de duret sont essentiels afin de vrifier lefficacit de la relaxation des contraintes aprs le formage ou le soudage. Parmi les zones dans un assemblage soud en acier, la ZTA est la plus proccupante et la plus difficile tester. Cette rgion troite en bordure du mtal dpos est lendroit o le mtal de base est chauff au-dessus de la temprature de transformation avant le refroidissement. La structure rsultante et la duret de la ZTA dpendent de plusieurs facteurs diffrents, surtout la composition, mais aussi lpaisseur, la temprature de prchauffage et lapport de chaleur. Lessai de duret est le seul moyen dvaluer ltat de la ZTA.

Une spcif ication de mode opratoire de soudage (SMOS) mise au point pour des applications critiques telles que la tuyauterie haute nergie

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These requirements can usually be met comfortably under the controlled con-ditions of qualification welding by the constructors top welder, but what about the construction site, where conditions are often less than ideal?

Guidelines for TestingThe first step is choosing the appropri-ate test method. It must suit the shape and size of the work piece, and take into account possible access restrictions. The applicable ASTM standard describes not only the method and technique, but

also the requirements for a valid test that must be taken into account by the techni-cian. These include minimum thickness, corrections for convexity and concavity of the work surface, and surface finish. Unfortunately in practice much of the portable hardness testing is ineffective or even misleading, a situation that can be dangerous. An effective field hardness testing procedure will include the follow-ing steps:1. Remove the weld reinforcement by

coarse grinding, flush with the sur-rounding base metal profile.

2. Improve the surface finish using pro-gressively finer abrasive grits320 grit is usually sufficient.

3. Etch the surface to locate the various weld zonesbase metal (BM), heat-affected zone (HAZ), and weld metal (WM).

4. Calibrate on an appropriate test block.5. After each test, subsequent exam-

ination with a low power eyepiece is helpful to visually confirm correct indentation location within the coarse-grained HAZ, which can be less than 1 mm wide.

6. Recognize the scatter inherent with each method, and report an average of several readings within each zone.Where possible, test the HAZ on both

sides of the jointthe base metals may be different, and the bead sequence may result in quite different results.

Types of Portable Hardness TestersHardness may be defined as the resist-ance to indentation by an indenter under an applied load. In the metallurgical lab-oratory, this is performed on finished sec-tions using heavy, fixed instruments such as a Rockwell tester. The test piece is pre-pared and brought to the testing equip-ment: the conditions are controlled and the results reproducible.

Conversely, in construction the test equipment must be brought to the work piece, on which we can only test the sur-face. Apart from the massive nature of laboratory testers, there are difficulties in reproducing laboratory methods in the field, the most significant of which are measuring the applied load and measur-ing the indentation dimensions.

Portable Brinell and Rockwell testers. The Brinell method has been used in the field for many years in the form of the pin Brinell and Telebrineller testers. While portable and easy to use, Brinell is completely unsuited for HAZ testing due to the large indentation diameter. (Beware of contractors reporting HAZ hardness in Brinellamazingly this still happens.) Positional capability may be limited, and a second person may be required to achieve an effective strike with the hammer.

Several adaptations of the Rockwell method have been devised for f ield work, but they are not all that portable.

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comprendra des essais supplmentaires tels que lessai de rsilience Charpy et lessai de duret. Le code ou le devis de construction devrait fournir des lignes directrices quant aux mthodes dessai et aux emplacements. Ces exigences peuvent nor-malement tre satisfaites sans aucun problme dans les conditions contrles associes au sou-dage de qualification ralis par le soudeur le plus qualifi du constructeur. Mais quadvient-il du site de construction o les conditions laissent souvent dsirer?

Lignes directrices sur la mise lessaiLa premire tape est de choisir la mthode des-

sai approprie. Celle-ci doit convenir la forme et la dimension de la pice souder et tenir compte des restrictions daccs ventuelles. La norme ASTM pertinente dcrit non seulement la mthode et la technique, mais aussi les exigences pour un essai valide dont le technicien doit tenir compte. Celles-ci incluent lpaisseur minimale, les corrections pour la convexit et la concavit de la surface de travail et le fini de surface. Malheureusement, en pratique, la majorit des appareils dessai de duret portatifs sont inefficaces et les rsultats sont mme fausss, une situation qui pourrait se rvler dangereuse. Une mthode dessai de duret sur le terrain efficace comprendra les tapes suivantes :1. Enlever la surpaisseur par broyage gros-

sier, de niveau avec le profil de mtal de base environnant.

2. Amliorer le fini de surface en utilisant des par-ticules abrasives progressivement plus finesles particules 320 sont gnralement suffisantes.

3. Graver la surface afin de localiser les diverses zones de soudagele mtal de base, la zone thermiquement affecte et le mtal dpos.

4. talonner sur un bloc dessai appropri.5. Aprs chaque essai, il est utile de procder

dautres examens avec un oculaire faible puissance afin de confirmer lil nu que les empreintes sont correctes dans la ZTA grains grossiers, qui peuvent tre de moins de 1 mm de largeur.

6. Reconnatre la diffusion inhrente chaque mthode et consigner une moyenne de plusieurs lectures lintrieur de chaque zone.Dans la mesure du possible, tester la ZTA des

deux cts de lassemblageles mtaux de base pourraient tre diffrents et la squence des cordons pourrait donner des rsultats trs diffrents.

Types dappareils dessai de duret portatifs

La duret pourrait tre dfinie comme la rsis-tance aux empreintes ralises par un pntrateur sous une charge applique. Dans le laboratoire

mtallurgique, ces empreintes sont ralises sur des sections finies au moyen dinstruments fixes lourds tels que la machine Rockwell. Lprouvette est prpare et emporte jusqu lappareil des-sai : les conditions sont contrles et les rsultats sont reproductibles. Rciproquement, dans la construction, lappareil dessai doit tre apport jusqu la pice souder, sur laquelle seule la sur-face peut tre teste. Non seulement les appareils dessai utiliss en laboratoire sont-ils massifs, mais il est aussi difficile de reproduire les mthodes de laboratoire sur le terrain, la plus importante tant la mesure de la charge applique et des dimensions des empreintes.

Machines Brinell et Rockwell portatives

La mthode Brinell a t utilise sur le terrain pendant plusieurs annes sous forme des machines Brinell goupille et Telebrineller. Bien que la machine Brinell soit portative et facile utili-ser, celle-ci ne convient absolument pas pour les essais de la ZTA en raison du diamtre des larges empreintes. (Prenez garde aux entrepreneurs qui indiquent une duret de la ZTA avec une machine Brinelltonnamment, cela arrive encore.) La capacit positionnelle pourrait tre limite et une deuxime personne pourrait tre requise pour assurer une frappe efficace avec le marteau.

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Furthermore, the indenter size is still fairly large and is less than ideal for HAZ testing.

One advantage of these methods is that they are more tolerant of surface roughness.

Portable hardness testers. Over the past several decades, two basic types of portable hardness testers have been developed that offer better position capability and ease of use.

Dynamic hardness testers (rebound type) are based on the principle that the loss of velocity of a hardened ball

projected at a metal surface is an indi-cation of the materials hardness. The results are then converted to recognized hardness scales.

Dynamic testers are fast, lightweight, easy to use in all positions, and leave a very small indentation. It is best suited to relatively thick, massive sections such as castings and forgings.

Disadvantages for weld testing: dif-ficulty in isolating the HAZ, operator variability, minimum work piece mass (to avoid an inertia effect), scatter in results, and surface effects.

The ultrasonic contact impedance (UCI) method uses a Vickers dia-mond indenter at the end of a metal rod. Piezoelectric transducers excite the rod to a longitudinal oscillation fre-quency of 70 kHz. When the diamond penetrates the work piece, there is a frequency shift that is proportional to the depth of indentation. Softer materi-als have deeper indentations and yield greater frequency shifts, and vice versa. The instrument converts the result into one of the conventional hardness scales.

The UCI method is very portable, easy to use in all positions, and leaves a small indentation. It has the advan-tage of being able to isolate the HAZ. Testing can be done on a variety of alloys, although calibration must be done on a test block having a similar modulus of elasticity as that of the work piece.

Disadvantages for weld testing: operator variability, minimum work piece mass and thickness, scatter in results; and surface effects.

New developments. The through-diamond technique (TDT) is a recent innovation that overcomes the limita-tions of other methods. It observes and measures the indentation made by a Vickers diamond indenter while under load. While the two portable methods described above measure hardness indirectly, TDT solves both problems of measurement while under a known load and of indentation measurement. Moreover, it overcomes work piece thickness and mass issues, opening up possibilities for mobile testing of a wide variety of products and shapes.

SummarySupported by a testing procedure pre-pared specifically for the task, hard-ness testing is a cost-effective and useful method for evaluating the condition of welds in the field. The demand for hard-ness testing will only grow in future. New technologies can overcome the drawbacks of previous testers and offer greater flexibility in application and reliability of results.

Gordon Snieder, P.Eng., is a consultant based in Sarnia, ON.

WELDING PRODUCTS

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Plusieurs adaptations de la mthode Rockwell ont t conues pour le travail sur le terrain, mais elles ne sont pas trs portables. De plus, la dimension du pntrateur est toujours assez large et pas trs recommande pour les essais de la ZTA.

Un avantage de ces mthodes est quelles sont plus tolrantes en matire de rugosit de la surface.

Appareils dessai de duret portatifs. Au cours des dernires dcennies, deux types fonda-mentaux dappareils dessai de duret portatifs ont t mis au point, offrant une meilleure capa-cit positionnelle et une meilleure convivialit.

Les appareils de duret dynamiques (de type rebond) sont fonds sur le principe que la perte de vitesse dune balle durcie projete sur une surface en mtal est une indication de la duret du matriau. Les rsultats sont ensuite convertis des chelles de duret reconnues.

Les appareils dessai dynamiques sont rapides, lgers, faciles utiliser dans toutes les positions et ne laissent quune trs petite empreinte. Ils sont mieux adapts aux sections paisses massives telles que les pices coules et forges. Parmi les inconvnients des essais de soudures, on retrouve la diff icult isoler la ZTA, la variabilit de loprateur, une masse minimale de la pice souder (afin dviter un effet dinertie), des rsultats diffuss et des effets de surface.

La mthode dimpdance par contact ultra-sonique utilise un pntrateur au diamant Vickers

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