Knowledge Corner : December 2009





ELECTRODE AND FILLER METAL SPECIFICATION GUIDE: (SFA, F, A Numbers)

Introduction

Filler metals are defined as the metal to be added in making a welded, brazed or soldered joint. The filler metals are used or consumed and become a part of the finished weld. The definition includes electrodes considered non consumable such as: tungsten, fluxes for brazing, submerged arc and electroslag welding.

The importance of selecting the proper filler metal for each welding application cannot be over emphasized. In weldment fabrication, it is important that the weld metal is compatible with the base material.
AWS and ASME:

The American Welding Society publishes numerous documents covering the use and quality control of welding. These documents include filler metals. The AWS filler metal specifications cover most types of consumables used with the various welding processes.

These specifications are periodically updated.

Example: AWS A5. 1 to AWS A5. 31

AWS A5. 1 – Carbon Steel covered arc welding electrodes.

Most AWS filler metal specifications have been approved by ANSI as American National Standards and most code making organizations such as the American Society of Mechanical Engineers (ASME) and the American Petroleum Institute (API) recognize and use the AWS specifications.

The welding consumables for welding of carbon, low alloy and stainless steel are selected based on guidelines provided in ASME Section – II, Part.C

When ASME adopts an AWS filler metal specification, either in its entirety or with revisions, it adds the letter “SF” to the AWS alphanumeric designation. Thus, ASME SFA 5.4 specification would be similar, if not identical, to the AWS A5.4 specification.

The relevant specifications are indicated here:

AWS A 5.1 – ASME SFA 5.1 – C.S. electrodes

AWS A 5.4 – ASME SFA 5.4 – S.S. electrodes
‘F’ Numbers:

As we know, there are a large number of electrodes that can be selected. All the electrodes and filler rods are grouped under different ‘F’ numbers. The object of the ‘F’ number grouping is to reduce the number of welding procedure and performance qualifications.

The ‘F’ number grouping is based essentially on their usability characteristics, with respect to coating which fundamentally determine the ability of the welders to make satisfactory welds with a given filler metal.

According to Section IX of the ASME Boiler and Pressure Vessel code the electrodes and filler rods are placed into the following categories:

F.No:1– Heavy rutile coated iron powder electrodes-E7024 (high deposition group)
2– Most rutile consumables such as E 6013 (mild penetration group)
3- Cellulosic electrodes such as E 6010, E 6011(deep penetration group)
4- Basic coated electrodes such as E 7016, E 7018 (low hydrogen group)
5- High alloy austenitic stainless steel and duplex E 316L -16
6- Any steel solid or cored wire (with flux or metal)
2X- Aluminium and its alloys
3x- Copper and its alloys
4x- Nickel alloys
5x- Titanium
6x- Zirconium
7x- Hard facing and overlay
x- Represents any number 0 to 9

If any of the electrodes in the more difficult F4 grouping is based on the welder qualification test, a welder who passes the test will be qualified on all the electrodes in this group, as well as on all lesser group numbers and the electrodes they represent.

However, many companies use this grouping system to eliminate the need for their welders to qualify for WPS’s unless absolutely necessary.

For example, the low H2 electrodes have been grouped under ‘F’ number 4 and the rutile electrodes under ‘F’ number 2. Obviously a welder who is able to produce a sound weld with a E 6013 (rutile) electrode (F.no.2) may not be able to produce a sound weld with a E 7018 ( low H2) electrode ( F.no.4)

The skills required to use both these electrodes is definitely not the same. ‘F’ number 2 is thus the easier than F.No. 4.

The ASME Code section II, Part - C further specifies metals with a series of F- numbers based on usability, and A – numbers based on the chemical composition of weld metal analysis.
‘A’ Numbers:

 ‘A’ numbers do not apply to welder approval tests or welder performance qualification.
‘A’ number refer to the chemical analysis of the deposited weld and not the parent material.
They only apply to welding procedures in steel materials.
A1 – Plain unalloyed C – Mn steels.
A2 to A4 – Low alloy steel containing Moly and Chrome Moly.
A8 – Austenitic stainless steel such as type 316.
Bibliography

  • HIWT welding guide EW – 385 – 1995, Page 68

  • HIWT SMAW EW 472 – 1998, Technical guide pages 16, 18, 19.

  • Welding Technology for Engineers – Page 344.

  • Modern Arc Welding Technology – Page 662, 663.

  • AWS handbook vol.1 Welding Technology 8th edition Page– 420,422.

  • Modern Welding Technology – 6th edition 2005, Page 573.

  • Welding Principles and Practices – 3rd edition 2005 Page 353.

  • Indian Institute of Welding – Welding Inspector Manual.





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