Understanding Heat Treatment Welding of Pipe and Tube Preparations for Welding New Nuclear

PUBLISHED BY THE AMERICAN WELDING SOCIETY TO ADVANCE THE SCIENCE, TECHNOLOGY, AND APPLICATION OF WELDINGAND ALLIED JOINING AND CUTTING PROCESSES, INCLUDING BRAZING, SOLDERING, AND THERMAL SPRAYING

June 2010

Understanding Heat Treatment

Welding of Pipe and Tube

Preparations for Welding New Nuclear Power Plants

Understanding Heat Treatment

Welding of Pipe and Tube

Preparations for Welding New Nuclear Power Plants

Bonus: The American

Welder

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Welding waveforms are used to limit dis-tortion, weld open roots, and to control HAZproperties. Waveform control is essential forcommon processes like uphill GMA pulsewelding. Power sources that support pulsing(GMAW-P, GTAW-P, etc.) are the most com-mon waveform- controlled power sources.Those marketed as synergic, programmable,or microprocessor-controlled are also likelyto support waveform-controlled welding.

The correlation between heat input andmechanical properties is blurred when heatinput is calculated using current and voltagereadings from conventional meters. This in-cludes external meters and even those lo-cated on the welding power source. It’s notthat the meters are incorrect — in fact, mostare calibrated and tested to NIST standards.Rather, the inaccuracy involves the meansof capturing and displaying the data.

Conventional DC meters display aver-age voltage and average current. Conven-tional AC meters display RMS values. Toaccurately indicate the energy input to aweld, the voltage and current readingsmust be multiplied together at very rapidintervals that will capture brief changes inthe welding waveforms. This frequency isin the order of magnitude of 10,000 timesper second. Specialized meters are re-quired to accomplish this.

Revisions to ASME Section IX providea new method of calculating heat inputthat allows comparison of the heat inputfrom various welding power sources andvarious welding waveforms. This will allowproduction welding to take place with awelding procedure specification (WPS)that specifies either conventional or wave-form-controlled welding, which is sup-ported by a procedure qualification record(PQR) using either conventional or wave-form-controlled welding.

Calculating Heat Input

Many welding codes use the equationshown in Equation 1 to calculate heatinput. Because the welding process(GMAW, SAW, etc.) is an essential vari-able, a process or efficiency factor is notincluded in the heat input calculation. Thenew equations that will be in the 2010 edi-tion of ASME Section IX are shown inEquations 2 and 3, either of which givesequivalent results. Both equations areshown because some welding powersources and meters display energy values,and others display power values.

Voltage × Amperage × 60 Travel Speed (in./min or mm/min)

Equation 1: Traditional heat input equa-tion, ASME Section IX QW-409.1 (a).

Energy (Joules) Weld Bead Length (in. or mm)

Equation 2: New heat input equation formeters displaying energy measurement(Joules), ASME Section IX QW-409.1(c)(1).

Power (Joules/s) × Arc Time (s) Weld Bead Length (in. or mm)

Equation 3: New heat input equation formeters displaying power measurement(Joules/s or W), ASME Section IX QW-409.1 (c)(2).

Three examples from GMA weldingare shown in Fig. 1. The axial spray wave-forms are essentially constant, and the dif-ference between the measurement meth-ods is minimal. For the two waveform-con-

trolled procedures, there is an error be-tween the measurement methods that canbe in a positive or negative direction. It isclear from the significant differences whya new measurement method is needed.

Changes in ASME Section IX

ASME codes and standards have along history, now in their 125th year. Therules for welding were removed from theconstruction codes when ASME SectionIX was published in 1941. ASME SectionIX has become a global standard, refer-enced by the ASME construction codes,owners, engineering firms, and other fab-rication and construction codes.

The ASME IX Standards Committeehas subcommittees that address procedureand performance qualifications, materials,general requirements, and brazing. Morethan three years ago, a task group wasformed to work on issues surrounding weld-ing with complex waveforms from micro-processor-controlled power sources. Thefirst result of this group’s work will be achange to the measurement and calcula-tion method for heat input.

QW409.1 is the main Section IX vari-able that deals with heat input. Currently,there are two ways to calculate heat input.Method (a) is the traditional heat inputequation shown in Equation 1. Method(b) is a measurement of the volume ofweld metal deposited. A new method (c)is added in the 2010 edition, which in-cludes Equations 2 and 3.

Any of the methods can be used whenwelding following procedures that arenot waveform controlled. When weldingfollowing waveform-controlled proce-

New CodeRequirements for

Calculating Heat Input Welders, inspectors, and engineers should be aware of the changes

to QW-409.1 of ASME IX regarding waveform-controlled welding

BY TERESA MELFI

TERESA MELFI is with The Lincoln Electric Co., Cleveland, Ohio. She is chair of the AWS A5B Committee on submerged arc welding, a member of the AWS A5 Committee on filler metal specifications, a member of ASME Section IX, including the materials subgroup and aworking group on advanced waveform welding, and is the U.S. delegate to the International Institute of Welding commission that covers pres-sure vessels, boilers, and pipelines.

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dures, only methods (b) or (c) are per-mitted. With these methods, it is possi-ble to determine the compliance of aproduction weld made using a wave-form-controlled welding procedure to anexisting qualified procedure, even whenthe procedure qualification was per-formed using nonwaveform controlledwelding. An appendix to ASME SectionIX has been provided to guide usersthrough these code changes. The ap-pendix provides guidance with new pro-cedure qualifications, existing qualifiedprocedures, and comparing heat inputsbetween waveform-controlled and non-waveform-controlled welding. ASMESection IX does not mandate separateperformance qualifications for wave-form-controlled welding.

How to Comply with ASME Code Changes

To use method (c) of the code, a read-ing of energy (Joules) or power (Joules/s)must be obtained using a meter that cap-tures the brief changes in a welding wave-form and filters out extraneous noise. Thesimplest place to obtain this is from thewelding power source. Many powersources that output pulsing waveforms willdisplay these readings, although somemight require software upgrades to en-able this. Details and software upgradesfor Lincoln Electric’s Powerwave “M” se-ries and several other models are avail-able free of charge at www.powerwavesoftware.com. For a power source that

doesn’t support the display of energy orpower, external meters are available. Ameter with demonstrated accuracy in thisapplication is the Fluke® 345 Power Qual-ity Clamp Meter.

With the proper software installed, it issimple to access the energy reading — Fig.2. In the setup menu, enable the option to“Display Energy.” When an arc is started,the energy value will begin to increment.The value will continue to increase, show-ing the real-time energy put into that weld— Fig. 3. When the welding stops, the finalenergy value will be displayed until weld-ing resumes again. This value represents

Fig. 1 — Heat input differences calculated using Equation 1 vs. Equation 2.

Fig. 2 — With the proper software installed,access to the energy reading entails pressingthe menu option “Display Energy.”

Fig. 3 — The real-time energy is continuouslyincremented while welding, and the final en-ergy is displayed until the next arc start.

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the amount of energy that went into thatweld, from arc start to arc stop.

To calculate the heat input, the finalvalue is simply divided by the length of theweld — Fig. 4. In this case, the heat inputwould be 22.3 kJ/3.6 in., or 6.2 kJ/in.

A detailed matrix has been developedshowing how a PQR qualified with eitherwaveform or nonwaveform-controlledwelding may be used to support weldingwith waveform or nonwaveform-con-trolled procedures and QW-409.1(a) or

QW-409.1(c). This can be downloadedfrom www.lincolnelectric.com.

Summary

The ASME Section IX welding andbrazing standard is widely used by publicagencies and private companies con-cerned about the safety and integrity ofwelds. Just as specifications change whennew materials are developed, ASME Sec-

tion IX has changed to recognize modernwelding waveforms. The changes involvethe measurement of energy or powermade at very rapid intervals, and the useof these to calculate heat input. Thesecode changes establish the relationshipbetween heat input across a range ofpower sources and welding waveforms.

Welders, inspectors, and engineersshould be aware of the new ways to calcu-late heat input. While no code can guaran-tee good workmanship, these changesmake it easier for welders to use waveformsthat help improve their welds. The newmethod will allow flexibility in the way onecompares the heat input used in procedurequalification and in production welding.♦

Fig. 4 — The heat input is calculated by taking the final energy value and dividing it by thelength of the weld.

PQR qualified with: Qualifies for welds produced with:

Non-waveform

controlled welding using conventional

volt and ammeters

and QW-409.1(a)

• Non-waveform controlled power supply using conventional volt meters and ammeters and QW-409.1(a).

• Non-waveform controlled power supply displaying instantaneous energy or power measurement and QW-409.1(c).

• Waveform controlled power supply displaying instantaneous energy or power measurement and QW-409.1(c).

• Waveform controlled power supply which does not display instantaneous energy or power measurement using external meters that display instantaneous power or energy measurements and QW-409.1(c).

Non-waveform controlled welding

using instantaneous

energy or power and

QW-409.1(c)




• Waveform controlled power supply which does not display instantaneous energy or power measurement using

external meters that display instantaneous power or energy measurements and QW-409.1(c).

Waveform controlled

welding using

instantaneous energy

or power and QW-409.1(c)





Waveform controlled

welding using

conventional volt and ammeters and QW-

409.1(a) (qualified

prior to 2010 code change)





Note: In some cases, it might benefit the user to amend a PQR to show the heat input calculated using instantaneous power or energy. This can be done by welding a simple bead on plate using the same parameters (mode or program,

voltage, current, etc) as were used in the procedure qualification. Utilizing either a welding power source or external

meter that displays instantaneous energy or power, the heat input may be calculated per QW-409.1(c) based on those

readings.

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Assist Chart for ASME IX QW-409.

The Lincoln Electric Company22801 Saint Clair Avenue

Cleveland, OH 44117-1199 U.S.A.1.216.481.8100

www.lincolnelectric.com

Reprinted with permission from WELDING JOURNAL, June 2010. On the Web at www.aws.org.© American Welding Society. All Rights Reserved. Foster Printing Service: 866-879-9144, www.marketingreprints.com.

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Understanding Heat Treatment Welding of Pipe and Tube Preparations for Welding New Nuclear

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