ANSI AWS C5.7-2000 Recommended Practices for Electrogas Welding《气电焊的推荐规程》.pdf

1、RecommendedPractices forElectrogas WeldingAWS C5.7:2000 (R2006)An American National Standard550 N.W. LeJeune Road, Miami, FL 33126AWS C5.7:2000 (R2006)An American National StandardApproved by theAmerican National Standards InstituteMay 5, 2000Recommended Practicesfor Electrogas WeldingSupersedes ANS

2、I/AWS C5.7-89Prepared by theAmerican Welding Society (AWS) C5 Committee on Arc Welding and CuttingUnder the Direction of theAWS Technical Activities CommitteeApproved by theAWS Board of DirectorsAbstractElectrogas Welding (EGW) is a specialized welding process having similarities to the gas metal ar

3、c welding(GMAW) or the flux cored arc welding (FCAW) processes for vertical position welding. The electrode deposits fillermetal in the cavity formed by backing plates or shoes that bridge the groove between the plates being welded. The elec-trode may be solid, metal cored, or flux cored, and additi

4、onal shielding may or may not be obtained from an externallysupplied gas or gas mixture. The weld is usually completed in a single pass.Fundamentals of the process, including the various methods of welding, are presented. A discussion of equipment,consumables, applications, and metallurgical advanta

5、ges and limitations is provided. The selection of process variablesand operating conditions and typical EGW procedures is then presented. Inspection of welds, and training and qualifica-tion of welding procedures and operators are described. Finally, a troubleshooting guide, safety considerations, a

6、nd asupplementary reading list are presented.iiAWS C5.7:2000 (R2006)International Standard Book Number: 0-87171-575-9American Welding Society550 N.W. LeJeune Road, Miami, FL 33126 2000 by American Welding SocietyAll rights reservedPrinted in the United States of AmericaReaffirmed: October 16, 2006Ph

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9、iiiAWS C5.7:2000 (R2006)Statement on the Use of American Welding Society StandardsAll standards (codes, specifications, recommended practices, methods, classifications, and guides) of the AmericanWelding Society (AWS) are voluntary consensus standards that have been developed in accordance with the

10、rules of theAmerican National Standards Institute (ANSI). When AWS American National Standards are either incorporated in, ormade part of, documents that are included in federal or state laws and regulations, or the regulations of other govern-mental bodies, their provisions carry the full legal aut

11、hority of the statute. In such cases, any changes in those AWSstandards must be approved by the governmental body having statutory jurisdiction before they can become a part ofthose laws and regulations. In all cases, these standards carry the full legal authority of the contract or other documentth

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19、rata, when discovered, are postedon the AWS web page (www.aws.org).Official interpretations of any of the technical requirements of this standard may only be obtained by sending a request,in writing, to the Managing Director, Technical Services Division, American Welding Society, 550 N.W. LeJeune Ro

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21、r do these oral opinions constitute officialor unofficial opinions or interpretations of AWS. In addition, oral opinions are informal and should not be used as asubstitute for an official interpretation.This standard is subject to revision at any time by the AWS C5 Committee on Arc Welding and Cutti

22、ng. It must bereviewed every five years, and if not revised, it must be either reaffirmed or withdrawn. Comments (recommendations,additions, or deletions) and any pertinent data that may be of use in improving this standard are required and should beaddressed to AWS Headquarters. Such comments will

23、receive careful consideration by the AWS C5 Committee on ArcWelding and Cutting and the author of the comments will be informed of the Committees response to the comments.Guests are invited to attend all meetings of the AWS C5 Committee on Arc Welding and Cutting to express theircomments verbally. P

24、rocedures for appeal of an adverse decision concerning all such comments are provided in theRules of Operation of the Technical Activities Committee. A copy of these Rules can be obtained from the AmericanWelding Society, 550 N.W. LeJeune Road, Miami, FL 33126.This page is intentionally blank.ivAWS

25、C5.7:2000 (R2006)vAWS C5.7:2000 (R2006)Personnel (Reaffirmation)*AdvisorAWS C5 Committee on Arc Welding and CuttingN. A. Sanders, Chair Hypertherm, IncorporatedD. B. Holliday, Vice Chair Northrop Grumman CorporationR. M. Dull, 2nd Vice Chair Edison Welding InstituteB. C. McGrath, Secretary American

26、Welding Society*E. R. Bohnart Welding Education moving shoes must be watercooled. The shoes are usually grooved to develop the de-sired weld reinforcement. The shoes may or may notcontain gas ports for impinging shielding gas directlyAWS C5.7:2000 (R2006)10onto the molten weld pool. When gas ports a

27、re not usedin the shoes, a “gas box” arrangement may be mountedon the shoes so as to surround the electrode and the weld-ing arc. Gas ports in the shoes and gas boxes are not re-quired when using self-shielded flux cored electrodes.5.6 Controls. With the exception of the vertical travelcontrol, EGW

28、controls are primarily adaptations of thedevices used with gas metal arc and flux cored arc weld-ing. Vertical travel controls, either electrical, optical, ormanual, maintain a given electrode extension with thetop of the movable shoe a specific distance above themolten weld pool.On equipment using

29、a self-shielded flux cored elec-trode, starting procedures must be carefully controlled tominimize porosity in the starting weld tab area. Weldsare usually started at lower wire feed speeds and volt-ages. These lower settings must be maintained while thearc stabilizes and the starting area is heated

30、. After a pre-set time, the equipment should automatically adjust thefeed speed and voltage to the desired welding speed andvoltage. Automatic rather than manual adjustment helpsto minimize starting porosity. Small amounts of sub-merged arc flux may also be added at the start to elimi-nate porosity.

31、6. Electrodes and Shielding Gas6.1 Electrodes. Either flux cored or solid electrodes maybe used with the electrogas welding process. The spooledwelding electrode supply must be adequate to completethe entire weldment in a single pass.Flux cored EGW electrodes contain a lower percent-age of slag form

32、ing compounds than typical electrodesused in the flux cored arc welding process (FCAW).These electrodes allow a thin slag layer to form betweenthe shoes and the weld to provide a smooth weld surface.Flux cored electrodes are supplied in sizes from 1/16 to1/8 in. (l.6 to 3.2 mm). Only flux cored elec

33、trodes specif-ically designed for EGW should be used (see 6.3).Solid electrodes are generally identical to those usedfor gas metal arc welding. They are supplied in sizesfrom 1/16 to 1/8 in. (1.6 to 3.2 mm).Both flux cored and solid electrodes are available invarious chemical compositions designed t

34、o introduce thenecessary alloying elements to achieve strength, impactproperties, or appropriate combinations of these in theweld metal, depending upon the particular requirement.To obtain desired strength and impact properties in theweld metal comparable to those of the base metal, addi-tional allo

35、ying elements such as manganese, silicon, andnickel are incorporated in the electrodes. These proper-ties are normally obtained in the as-welded condition.6.2 Shielding. Self-shielded flux cored electrodes forEGW contain core materials that shield the molten weldmetal from oxygen and nitrogen. Other

36、 flux cored elec-trodes require a shielding gas normally carbon dioxide(AWS A5.32/A5.32M, Specification for Welding Shield-ing Gases, class SG-C). Recommended gas flow ratesrange from 30 to 140 CFH (14 to 66 L/min). A mixtureof argon and carbon dioxide (AWS class SG-AC-X) isnormally used for welding

37、 steel with solid electrodes andmay be used with flux cored electrodes. Recommendedgas flow rates range from 40 to 140 CFH (19 to 66 L/min).Gas flow rates are dependent upon the equipment de-sign and the manufacturers recommendations should befollowed.6.3 AWS Specification for Electrogas Filler Meta

38、l.Composite flux cored and metal cored electrodes areclassified in AWS A5.26/A5.26M, Specification for Car-bon and Low Alloy Steel Electrodes for Electrogas Weld-ing, on the basis of whether a shielding gas is required,and on the chemical composition and as-welded mechan-ical properties of the weld

39、metal (see Tables 1 through 3).The solid electrodes are classified on the basis of theirchemical composition and on the as-welded mechanicalproperties of the weld metal (see Tables 2 and 3). Note inTable 3 that three levels of strength have been estab-lished. For each level of strength, electrode cl

40、assifica-tions are provided that define three levels of minimumtoughness as determined by the Charpy V-notch impacttest. Mechanical properties shown in Table 3 are ob-tained with a standard welding procedure using typicalelectrogas welding conditions, with specified types ofsteel base metal.7. Appli

41、cations7.1 Base Metals. Among the many alloys that have beenelectrogas welded on a production basis in the UnitedStates, the most common from a weight standpoint havebeen in the low carbon, structural, and pressure vesselquality steels as follows:(1) Low carbon steels: AISI 1018, 1020(2) Structural

42、steels: ASTM A 36, A 131, A 242,A 283, A 441, A 572, A 573, A 588(3) Pressure vessel steels: ASTM A 285, A 515,A 516, A 537.In addition to the above steels, EGW has been used tojoin aluminum and some grades of stainless steels, al-though they are not presently covered in this standard.Electrogas wel

43、ding of steels that are quenched andtempered or normalized may not be permitted by somestandards (e.g., AWS D1.1, Structural Welding CodeSteel).AWS C5.7:2000 (R2006)117.2 Joint Design. The most commonly used joint is abutt joint with a square-groove joint geometry and ap-proximately 7/8 in. (22 mm)

44、root opening. This joint isnormally used with two moving shoes see Figure 7(A).The next most commonly used design is a butt joint witha V-groove joint geometry, which is commonly used withone moving and one stationary shoe see Figure 7(B).This joint usually has a root opening of 5/32 in. (4 mm)and a

45、 face opening of 7/8 in. (22 mm). A moving shoe isused to contain the weld metal at the weld face, and a sta-tionary shoe is used to contain the weld metal at the root.The joint designs illustrated in Figure 7 should not betaken as restrictions, but only as a reflection of currentlyused types.Any jo

46、int design that gives complete fusion may beconsidered and tested by the fabricator (see Figure 8).Many successful welds have been made in T-joints, double-V-grooves with welded backing bars, and some in multi-pass joints. The welding engineer, once familiar with theelectrogas process, should experi

47、ment with any joint thathe or she believes will work and qualify the procedureaccordingly.7.3 Assembly and Alignment7.3.1 Misalignment. Workpiece surface misalignmentshould be limited to 1/8 in. (3 mm) on both front and backsurfaces. On heavier plate greater misalignment may beencountered and succes

48、sfully welded. Grinding may be re-quired to stay within this tolerance. Greater misalignmentcreates a variety of problems, including leakage of weldmetal, irregular bead shape, incomplete fusion, undercut,and loss of shielding with attendant porosity. In addition,when using a steel backing bar, exce

49、ssive misalignmentcan result in excessive fusion through a backing bar.7.3.2 Strongbacks. Suitable clamps or brackets, orboth, are required to hold the workpieces in alignmentduring welding. U-shaped brackets, designed to allowclearance for the outboard moving shoe or outboard sta-tionary backing, as shown in Figure 9, are commonlyused. The brackets must hold the workpieces in align-ment, but not be rigid enough to cause weld metal solidi-fication cracking. Generally, smaller brackets can beused for stationary shoe applications than are needed forclearance of a moving shoe.Table 1Chemic