Comparison of The Use of Rutile And Cellulosic Electrodes

Types of electrodes and their compositions

Many types of manual metal arc (MMA) electrodes are available on the market. Depending on the main constituent of their flux, they are grouped into three categories: cellulosic, rutile, and basic. All electrodes consist of a core wire (typically 2.5–6mm diameter) coated by a flux. The core wire is generally made of low-quality riming steel and the fluxes contain many elements allowing refinement of the weld microstructure.

The composition of the flux impacts the electrodes’behaviour. The main constituents of the different types of electrodes and the shielding gas created for each are described in Table 1.

Table 1 Main constituent of the three possible types of electrodes and shielding gas created by its combustion

MMA electrodes’ main characteristics have been extensively described. The following paragraphs are a summary of general-purpose electrode (rutile and cellulosic) characteristics of interest.

Mild steel welding electrode E6013 rutile grade

The rutile electrode

The difference between the E6012 and E6013 electrodes is that the E6012 covering contains sodium, while the covering of E6013 contains potassium. They can both run under direct current (DC+) but only the latter is suitable for running under alternative current (AC). Working with a constant current is recommended to counterbalance the unsteadiness of the welder’s hand.

With a high proportion of titanium dioxide (also called titania) the rutile electrode gives a smooth bead surface, easily removal slag and a smooth arc. During the combustion, the flux coating will mainly create carbon dioxide.

This flux also contains cellulose. Even though the cellulose content is far lower than for a cellulosic electrode, its presence, along with that of moisture, means that these electrodes produce relatively high levels of hydrogen: up to 25ml/100gm weld metal. This restricts their use to mild steels with a thickness lower than 25mm and thin-section low-alloy steels of the C/Mo and 1Cr1/2Mo type.

Rutile electrodes can be used to weld in all positions apart from vertical down position. Deposition can be improved through the addition of iron powder, which leads to more metal being deposited at the same current. However, electrodes with added iron powder can only be used in a flat position.

Rutile electrodes have a medium penetration, quiet arc and create little spatter. They create a large amount of self-releasing slag which requires little cleaning after welding.

They are probably the most widely used general purpose electrodes. However, these electrodes should not be used on structures where high toughness is required. Table 2 summarises their mechanical properties.

Table 2 Typical mechanical properties obtained with E6012 and E6013 AWS A5.1/A5.1M, 2012

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The cellulosic electrode

Similarly to rutile electrodes, the differences between E6010 and E6011 cellulosic electrodes are the electrical parameters used during welding and their type of covering. The covering of E6010 contains sodium; E6011 contains potassium. They can both run under direct current (DC+) but only the latter is suitable for running under alternative current (AC). The MMA process can be used in DCEN, DCEP or AC but again a constant current is recommended to counterbalance the unsteadiness of the welder’s hand.

The gas shield generated by cellulosic combustion contains hydrogen, carbon monoxide and carbon dioxide. Between 30 and 45ml hydrogen/100gm can be found in the weld. This has two consequences: good protection of the weld pool and a high level of diffusible hydrogen in the weld metal and heat-affected zone (HAZ). The high percentage of hydrogen is the cause of the high deposition rate and deeper penetration by the creation of the punchy arc for which this kind of electrode is well known.

Another consequence of the hydrogen content of the gas shield is the requirement for a higher voltage (around 70V).

However, the high hydrogen content in the shielding gas is also this electrode’s main drawback. It causes a high level of diffusible hydrogen in the weld, which is one of the parameters influencing hydrogen cracking (also called cold cracking) if good practices are not followed and preventive actions are not taken.

The high hydrogen level means that any steel welded with these electrodes should have a very high resistance to hydrogen-induced cold cracking. These electrodes are mainly used on low-carbon, non-alloyed steel. They should be used only with due consideration of the steel composition, restraint and need for preheat.

One other advantage of cellulosic electrodes is their ability to weld in the stove piping (or vertical down) position. E6010 electrodes are sometimes called ‘stove pipe electrodes’. This position can enhance the weld and helps to improve efficiency and productivity, thanks to quick cooling of the slag.

This method of welding should be performed by an experienced welder who can put down welds in quick succession, to maintain a hot welding condition and enable hydrogen to escape. On thick-wall pipe, the welder can experience difficulty controlling the weld pool because of its increase in size and the risk for it to over-run the arc and flood the joint. It should be noted that any type of cellulosic electrode requires a highly skilled welder, so stove pipe welding especially should not been carried out without care and proof of competence of the welder.

The amount of spatter created will limit the use of very high current. A large amount of fume is also produced by cellulosic electrodes but the amount of slag to remove after each weld is small.

The mechanical properties of the cellulosic electrodes are presented in Table 3. Impact values are available up to -30°C in the as-welded condition.

Table 3 Typical mechanical properties obtained with E6010 and E6011, AWS A5.1/A5.1M, 2012

Its characteristics of deep penetration, high deposition rates and ability to be used in vertical down position means that the main use for these electrodes is for cross-country pipelining, although they are used to a more limited extent for welding storage tanks.

In a more industrial environment the use of this type of electrode is usually restricted to the root pass of the welding procedure. After root pass, a hot pass should be deposited within the next ten minutes to limit the cooling of the welding pass and allow hydrogen to escape. This limitation should be specified in the welding procedure specification.

Again, these electrodes require a skilled welder. This is particularly relevant when working with a pipe of outside diameter below eight inches, because the vertical down welding position can be difficult.

Conclusion of the comparison

The following table summarises the comparison and the previous conclusions.

Short Description of Landyoung Rutile Grade E6013

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