How to do Filler Electrode Selection for Welding? Where to Begin?

Let’s have a brief insight into the basics of filler electrode selection, and filler wires, generally referred as “welding rods“.

So you are here, by now you know that choosing the right electrodes are very important to the success of weld process. They are chosen based on a variety of factors, including ease of cleanup, weld strength, bead quality, and minimizing any spatter.

On the other hand, appropriate filler metal used you also minimize the cost of welding and time. Also, avoiding the risk of cracking, corrosion, and/or weld defects.

Therefore, I’ve outlined some basic the factors that affect the selection of the welding rods for your perfect “welding outcome“.

Material to Weld

Firstly, Base materials or Parent Metals. That is to say, the filler metal chemistry, and of the welds, to be exact. If the filler chemistry matches, the mechanical properties like the tensile and yield strength, will also match. So, choosing an electrode with a minimum tensile strength equivalent to the parent metal being welded.

If filler electrodes have different strength, match the filler metal to the lower strength of both base materials. Moreover, the higher strength base material is sufficient to strengthen the weld metal deposit.. As the welding process continues, the weld metal deposit from the higher strength welding rod will be sufficient for a proper fusion.

Plan and prepare a properly drafted PQR and lab testing analysis. Alternatively, a much faster approach, EGT probe (electro-galvanic testing), checks the material for certain elements that indicate the presence of a particular base metal.

Position of the Weld

At some site locations, there may be limitations in accessing the workpiece and the weld position of material, hence may required to be welded in multiple positions.

Out-of-position welds, like using a 3/32″ Dia. wire for vertical welds, are difficult and more erratic metal flow. Rather opting a 1/16″ D wire with an alternate setting as required for the job.

Filler electrode selection with the wrong welding position is one of the main factors contributing to slow process, including lesser efficiency of the weld. To know more on welding position please visit link here

Codes and Specifications

No matter wherever you are and whatever weld specific jobs you are in, the job specifications – Regulatory or Code applicable to the job scope, is recommended to be followed.

Quite simply, if you tend to use a mild steel filler for services related to harsh environments, the welds deteriorate, rust and corrode, becomes more susceptible to failure at the weld.

It could lead to undesirable situations like high temperature piping failure or a structural weld failure supporting a hydrocarbon vessel.

Following Codes and Regulations mandate the welding rods meet the service condition of the product so as to last more than the base material of concern. Visit this link to know more on Codes and Standards

Whether it is a critical or non-critical job, following the relevant job codes is recommended.

Joint Preparation

Different Filler metals have different penetration characteristics. Welding on a thinner material requires that arc characteristics are appropriate so that it doesn’t burn through the material.

Ensure that the welding rods meets or exceeds job specification.  For instance, the arc characteristics should be appropriate when welding on thin material. The welding operator may get a burn through if a wire is deep penetration..

Most of the basic repairs or failures in welds can be avoided by a proper joint design or groove configuration, and the penetration characteristics laid out for weld requirements to the job.

Sheilding Gas

While choosing a welding rod, the available gas, desired weld characteristics and compatibility with the shielding gas need to be verified before hand.

A good shielding gas mixture gives consistent weld quality, good weld pool control and lower spatters during welds. Addition of CO2 (oxidizing gas) directly, may burn off the weld metal elements in thinner materials, compared to thicker ones. Likewise adding a CO2+Argon mixture is desirable, allowing more filler metal chemistry to the weld deposit and less spatter. Note that here, the risk of potential cracking is high.

PWHT

Based on the certain factors like criticality of service or to the code requirements, certain steels and material thicknesses requires pre-heating to a certain temperature before welding, and Post weld heat treatment, after welding. Welding rod selection should be appropriate to the application of heating.

Pre-heat avoids the weld-shrinking issues and cracking, while the Post weld heat treatment reduces the stresses in the weldment and allows the weld and base metals to return to their desired properties for a strong weldment.

Welding Equipment

The capacity of welding machines, size and type have an impact on what filler electrode is right for the job. Generally, have machines with proper amperage variations. Lower amperage will require that wire diameters to change from recommended ones. This in-turn increases time and reduces the weld production. Wrong current gives spatters, and a poor weld quality.

Welding rods have designs that work well with alternating current (AC) supply, others work with direct current (DC) and yet others work with both types of power.

My Opinion

Various elements in the filler metals require proper in-depth technical review, and should be decided based on their properties to determine which filler metal is ideal for the job.

Filler electrode selection is an important aspect as Filler metals vary on their properties on hardness, tensile strength, wear resistance, ductility, impact, and machine ability.

Likewise, their alloying elements have different properties to deoxidize, refine grain structures, or improve ductility. There are also various types like Fast Freeze, Fill-Freeze, Fast-Fill, Low Hydrogen and more.

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