Welding Electrodes & Filler Metals

Welding consumables are an important part of welding. Having a quality electrode in hand is vital to the quality of joint to be made. In this article, we shall see some aspects of electrodes and filler rods used for welding.

The most authoritative classification of welding consumables has been done by American Welding Society (AWS). The system adopted by ASME in the Boiler and Pressure Vessel Code (BPVC) is identical to the system adopted by AWS. In the BPVC, the Part C of Section II has been dedicated to the subject of welding consumables.

The Section II Part C (or commonly called as Section II C) is divided about 39 parts, titled SFA 5.1, SFA 5.2, SFA 5.3, and so on. Each article deals with a particular process and a particular grade of consumables. For example, SFA 5.1 deals with carbon steel electrodes used with SMAW process, SFA 5.23 deals with low alloy steel bare wires used with SAW process, and so on.

Stick Electrodes

The term stick electrode refers to the electrodes used for shielded metal arc welding. These electrodes come in a wide variety. Stick electrodes today are available in the market for welding almost every commercially used metal.

The classification system for shielded metal arc welding electrodes  is different for different grades. For example, stainless steel electrodes for SMAW – which are classified under SFA 5.4, are generally designated as E309, or E304, etc. The E indicates electrode, while the next three digits indicate the chemical composition.

The classification system for carbon steel and low alloy steel electrodes (found under SFA 5.1 and SFA 5.5) is quite different. For example, E7018 is a very commonly used electrode. Here, 70 indicates the tensile strength of the weld metal deposited with this electrode will be 70 ksi minimum. 18 indicates the type of covering, type of current, and welding positions with which the electrode can be used. The classification system for carbon steel electrodes and low alloy steel electrodes is somewhat similar.

Nickel alloy electrodes for SMAW welding are classified under SFA 5.11. The digits appearing after the E indicate the main alloying elements present in the electrode.

The type of coating on the electrodes plays a very important role in not just providing shielding to the arc from atmospheric gases, but also as a means to add important alloying elements to the weld metal through the flux.

The coating also performs the function of stabilizing the arc. It reduces sulphur and phosphorous from the weld metal which are harmful to the weld.

The coatings come in a wide variety; each of which serves a specific purpose.

Non-Consumable Electrodes

The term non-consumable electrodes indicates that the electrode does not get consumed during the welding process like the stick electrodes do. There are mainly two types of non-consumable electrodes: one is tungsten electrodes; another is carbon electrodes that are used with carbon arc welding process.

The  Tungsten Electrodes are non-consumable electrodes used to carry current in the gas tungsten arc welding process. These electrodes generally come color coded, and can be easily identified by the color present at one end.

For example, pure tungsten electrodes are marked green, 2% thoriated electrodes are marked red, etc. Grinding of electrodes to the right taper angle is necessary to get the right size of weld puddle. Selection of the right size of tungsten electrode is also essential. The right amount of stick-out of tungsten electrode from the nozzle also plays an important role in obtaining the desired weld quality.

Flux Cored Arc Welding Electrodes

The flux-cored arc welding electrodes come wound in spools of suitable sizes. The wire is cored with the flux that provides the shielding action.

The flux cored arc welding electrodes for carbon steel welding are classified under SFA 5.20 of ASME Section II C. The stainless steel FCAW electrodes are classified under SFA 5.22, while low alloy steel FCAW electrodes are classified under SFA 5.29. The nickel alloy electrodes for flux cored arc welding are classified under SFA 5.34.

Solid Wires

As opposed to flux-cored wires, solid wires are solid. That is, they are not cored with flux. These wires generally come in the bare form. They can be used with GTAW process or GMAW process or SAW process.

Welding wires for gas metal arc welding are generally smaller in diameter than those used with other processes. This is because of the high current and speed with which the wire is introduced into the weld puddle. The MIG Welding Wires generally come in the form of spools. The spool is mounted on the wire-feeder reel present on the MIG welding equipment.

The wires for submerged arc welding also come wound in the form of spools. The carbon steel wires are classified under SFA 5.17, while low alloy steel wires are classified under SFA 5.23. These two specifications SFA 5.17 and SFA 5.23 also classify matching suitable fluxes for these wires.

The stainless steel wires for submerged arc welding are not classified under a separate specification; in fact all bare stainless steel electrodes and rods have been clubbed together under SFA 5.9. Ditto for bare nickel alloy electrodes and rods, which are classified under SFA 5.14.

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