BY JOSEPH CAPRAROLA, JR., HARRY W. EBERT AND RICHARD A. LaFAVE
JOSEPH CAPRAROLA, JR., is a Welding Engineer, Consultant, a past A5 Committeee Chairman and AWS Director-at-Large. HARRY W. EBERT is an AWS Fellow and past AWS Director-at-Large and a Welding Engineer with Exxon Research and Engineering Co. RICHARD A. LaFAVE is the present A5 Chairman and a Welding Engineer with Elliott Turbomachinery Co.For years, suppliers and users of construction materials have recognized the need for documents that specify required mechanical properties, chemical compositions and usability. Organizations such as AWS, ASTM and SAE have performed this service and have issued filler metal and base metal specifications for commercial and military use. This article is written to explain some of the newer designations being used as optional supplemental designators in the more commonly used steel filler metal specifications.
In 1940, the welding industry issued its initial classification specification for arc welding electrodes (ASTM A233-40T, Tentative Specifications for Iron and Steel Arc-Welding Electrodes). This specification was novel since it introduced a classification system for shielded metal arc welding (SMAW) covered electrodes based upon minimum mechanical properties of the weld metal and the positional usability of the electrode. This resulted in the introduction of E6010, E6012 and E6013. More than a half century has passed and many of these original classifications continue to be used in today's specifications.
As new types of electrodes were developed and entered the welding market, new classifications such as E7018 and E7048 were included in revisions of the filler metal specifications. At the same time, the responsibility for these documents moved from the joint AWS-ASTM Committee to the AWS Filler Metal Committee. An AWS document was introduced in 1948 as AWS A5.1-48T, Tentative Specifications for Mild Steel Arc-Welding Electrodes. Eventually, in 1969, the American Welding Society took over entirely with the issuance of A5.1-69, Specification for Mild Steel Covered Arc-Welding Electrodes. Four years later this document was recognized as American National Standard ANSI W3.1-73.
To this day, the AWS classification concept meets most industrial needs, and receives extensive foreign support. Catalogs throughout the world tend to have nationally oriented electrode descriptions augmented with AWS filler metal classifications. Many countries have adopted national classification systems similar to the one used by AWS. Naturally, they made some modifications. For example, Japan and Canada converted the numbers identify the minimum tensile strengths to the metric and SI unit systems, respectively. The International Standards Organization (ISO) is considering the adoption of SI documents that follow many classification concepts developed by the AWS. Presently, the AWS is drafting metricated filler metal specifications for use in the next century.
The International Institute of Welding (IIW) has been preparing a generic numbering system for welding filler metals for use in future ISO specifications (Ref. 1). Much of the system makes use of AWS designations, especially in covered electrodes and in high-alloy steel filler metals. AWS is planning to publish an index of filler metals in national specifications using the proposed ISO designations to identify equivalent filler metals produced in different countries of the world. This index will be very useful to contractors seeking indigenous filler metals when working overseas projects.
Filler metal classifications are among the primary variables required in welding procedure specifications and qualifications. Other important documents, such as AWS D1.1, Structural Welding Code -- Steel, and ASME Boiler and Pressure Vessel Code, use AWS filler metal specifications and classifications for material selection, design, fabrication and testing.
Innovations in Filler Metals
Over the years, existing welding electrodes were improved and new electrodes were developed. Some of these innovations resulted from advances in technology while other changes were in response to the changing needs of industry. Most of these improvements can be placed into one of the following three general groups:
* Enhanced mechanical properties, such as toughness or ductility of the weld metal.
* Tighter controls of chemical composition, including residual elements.
* Lower hydrogen and moisture levels to reduce the risk of porosity and delayed cracking.
Some of these improvements resulted in the elimination of classifications. For example, the E4510 and E6030 covered electrodes became obsolete and were discontinued.
There was a need by industry for filler metals with requirements more stringent than the basic requirements of established classifications. As an example, all E7018 classified covered electrodes must be capable of meeting minimum impact test results at 20°F (29°C) when tested in accordance with the procedures and methods specified in ANSI/AWS A5.1. However, there is an industry need for some E7018 electrodes to meet the same minimum impact values at the lower temperature of 50°F (46°C). This need was met but the problem remained of how to designate and identify the filler metals that meet requirements in excess of the basic requirements of the AWS E7018 classification. More importantly, this designation and identification needed to be marked in such a way that the filler metal can be distinguished in the storeroom, in the shop and in the field.
Optional Supplemental Designators
To respond to the foregoing problem, the AWS Filler Metal Committee has followed a practice employed by the ASTM for base metals. The ASTM provides "supplementary requirements" for many of its base metal specifications. For example, ASTM A 516, Specification for Pressure Vessel Plates Carbon Steel, for Moderate- and Lower-Temperatures, does not have basic requirements for ultrasonic examination (UT). However, the purchaser may specify that the steel plates ordered must meet the "S8" supplementary requirement. This requires the plate supplied to be UT tested per ASTM A 435, Specification for Straight-Beam Ultrasonic Examination of Steel Plates. The plates must still conform to the basic requirements of A 516, but a specific additional nondestructive examination is required.
For filler metals, AWS has also adopted supplementary requirements and these are identified with "optional supplemental designators."
Therefore, as was shown earlier, an E7018, meeting all the basic requirements of the AWS A5.1 specification, will show satisfactory toughness values down to at least 20°F. Some trade designations of E7018 will show satisfactory toughness down to a lower 50°F. These also can be classified as E7018 because they meet all the basic requirements. However, they can also carry the optional supplemental designator of -1 and can be designated, labeled and marked as E7018-1.
Obviously, the E7018-1 can be used anywhere the E7018 is specified because it meets all the requirements of an E7018. However, in situations where toughness is required at lower temperatures than afforded in the basic requirements of E7018, then E7018-1 can be selected in order to give reasonable assurance that the toughness down to 50°F can be attained.
The -1 designator also has been employed in conjunction with E7024 electrodes. The basic classification requires a minimum elongation of 17% and no minimum notch toughness. However, when E7024 electrodes meet a minimum elongation of 22% and a minimum toughness of 20 ft-lb at 0°F (27J at 18°C), they can be provided with the -1 designator and thus be identified as E7024-1.
Optional supplemental designators containing letters have also been developed for other purposes and other classifications. These are usually appended to the classification without the use of a hyphen as shown below.
R -- Designates that a covered electrode is moisture resistant and has been tested in a humid environment of 80°F (26.7°C) and 80% R.H. for nine hours and still showed covering moisture less than 0.4% by weight. Example: E7018R, E8018-B2R, E7018-1R and E8018-W1R.
J -- Designates that a flux cored electrode will meet the minimum toughness values 20°F (11°C) below the standard temperature required for the basic classification requiring impact properties. Example: E71T-1J (20°F/29°C) and E71T-9J (40°F/40°C).
HZ -- Designates an electrode, an electrode/rod, or an electrode/flux combination that will meet an average diffusible hydrogen level Z when tested in accordance with ANSI/AWS A4.3, Standard Methods for Determination of the Diffusible Hydrogen Content of Martensitic, Bainitic and Ferritic Steel Weld Metal Produced by Arc Welding. The Z designator is usually limited to 16, 8 or 4 maximum average diffusible hydrogen in mL(H2) per 100 g of deposited weld metal. Other Z designators , such as 2, may be added for some classification systems, where appropriate. Examples: E7018H4, E7018H4R, E7018-1H4R, E71T-12H8, E8018-B2H8, F8A2-EW-WH8 and ER70S-3H4.
The R designated low-hydrogen classification gives the user reasonable assurance that the electrode can be exposed for up to nine hours to 80oF/80% R.H. without exceeding 0.4% moisture in the covering. This enabled ANSI/AWS D1.1, Structural Welding Code -- Steel, to permit electrodes designated as E7018R or E7018HZR to be used even if they are exposed to ambient conditions for up to nine hours. For high strength, low-alloy electrodes, the actual hours of exposure under atmospheric conditions may have to be limited to less than nine hours to control moisture to lower levels than the 0.4% threshold used to differentiate moisture-resistant covered electrodes from standard covered electrodes in the standard nine hour moisture exposure test.
The HZ designated classifications give the user reasonable assurance that when the welding product is stored, handled and used as recommended by the manufacturer, the diffusible hydrogen in the weld metal will not exceed the stated Z level when tested under the reference welding and atmospheric conditions. This can then be used to determine the minimum preheat levels required to avoid delayed or underbead cracking. In certain critical applications, such as fabrication of fracture critical nonredundant members in the ANSI/AASHTO/AWS D1.5-95, Bridge Welding Code, HZ designated classifications may be required.
Electrode Labeling and Marking
When electrodes were first classified, packaging was labeled with the AWS specification and classification, but individual covered electrodes were not labeled. A series of color codes were used to mark the grip end of the electrode and these colors corresponded to the AWS classification. About 30 years ago, the U.S. Navy insisted that the alphanumeric electrode classification be marked on the covering within two inches of the grip end on each electrode. This has since become the AWS and ASME code requirement and has thereby replaced color coding in most areas.
Labels of electrode packaging are required to include the following minimum information:
* AWS specification A5.XX (Year need not be included).
* AWS classification including any optional supplemental designators.
* Supplier's name and trade designation.
* Size and net weight.
* Heat, lot or control number (this must be traceable to the manufacturer and must be unique -- not repeating).
It is important that the user understand that the optional supplemental designators appended to the classification only show enhancements to the classification. Therefore, a product designated on the package label as E7018-1H4R also meets the requirements of the following classification and designations without their having to be marked: E7018, E7018R, E7018-1, E7018-1R, E7018H4, E7018H4R, E7018-1H4,E7018-1H4R, E7018H8, E7018H8R, E7018-1H8, E7018-1H8R, E7018H16, E7018H16R, E7018-1H16, E7018-1H16R.
The supplier may indicate these as "also meets the requirements of" on the label. This is not considered dual classification since the classification is still only E7018. However, in most cases the supplier is going to assume that the user understands that meeting all the enhancements in the most restrictive levels includes meeting the less restrictive or singular enhancements as well.
Imprinting of the covered electrode with the AWS classification and any applicable optional supplemental designators, as shown in Fig. 1, is the supplier's certification that the product will meet the requirements of the classification when tested in accordance with the AWS specification. This imprint should duplicate the designation marking on the label with the exception that the prefix E may be omitted from the electrode imprint. Table 1 shows the various imprints for E7018 classification with one, two or up to three optional supplemental designators. The order of these designators is clearly defined in the ANSI/AWS A5.1 specification. The words "also meets the requirements of" listed on the label do not need to be imprinted on the electrode since they are placed on the label for information only.
As with any change that occurs, these new optional supplemental designators will take some getting used to. Electrodes and welding consumables continue to be improved as the technology changes. There is no easy way to upgrade the classifications without the use of optional supplemental designators. Throwing out the existing classifications and developing new classifications would result in a loss of continuity with what has been qualified or prequalified with existing classifications. Adding optional supplemental designators allows enhancements to be made known to the user without losing what has been prequalified or procedure qualified with the basic classifications. If you have any questions concerning optional supplemental designators, please contact the secretary of the AWS Filler Metal Committee at 1(800) 443-9353 or 1(305) 443-9353, Extension 301. *
The authors wish to acknowledge the voluntary assistance of other members of the AWS Filler Metal Committee and its subcommittees in providing their expertise in reviewing this article and making sure it is technically correct.
1. Welding in the World. 1996. Vol. 37, No. 3, pp. 155-160.
Table 1 -- Varous Imprints for E7018 Classification
Low Hydrogen "Extra" Low Hydrogen
Standard Improved Standard Improved
Toughness Toughness Toughness Toughness
& Ductility & Ductility & Ductility & Ductility
Standard E7018 E7-18-1 E7018H4 E7018-1H4
Moisture E7018R E7018-1R E7018H4R E7018-1H4R
Fig. 1 -- Photo showing AWS Classification and optional supplemental designator imprinted on a covered electrode.