Low Hydrogen Electrodes

In this article, we will be discussing about low hydrogen electrodes and their advantages, and why are used widely.

low hydrogen electrodes

The following hydrogen electrodes are very popular in industries for the following reasons;

* Ability to produce X-ray quality welds

* Good weld bead appearance

* Ability to weld thick material with the high deposition rate

* Less susceptible to failures and cracks especially hydrogen-induced cracks

* Sound weld metal properties with good toughness

* A smooth, steady, and quiet arc with less splatter

* Good penetration and deposition rate

* Good arc initiation and good arc control for welders

* Fast post-weld cleaning

* Ability to join steels with poor weldability such as high carbon steels, low alloy steels, etc.

The above benefits have made low hydrogen electrodes the first choice for welding critical components that suffer from failures during service or that involve many hazards and hazards.

Advantages of low hydrogen electrodes than others

The reason behind the above-mentioned properties lies in the casing or flux material. The flux of a low hydrogen electrode has two unique characteristics;

1. Low hydrogen content:

The amount of hydrogen content of hydrogen in the cover of such hydrogen is very less. High levels of hydrogen in the weld metal are near the risk of brittle failures and delayed breakage or hydrogen-induced breakdown. Therefore, covering the lower levels of hydrogen in the electrode will ensure that only a limited amount of hydrogen enters the weld metal, which may prevent the above failures.

2. Contains basic minerals:

Basic minerals in electrode coverings mean that the chemicals present in the casing reduce the amount of oxygen in the weld and the harmful oxide inclusions at the grain boundaries of the microstructure, resulting in higher hardness A cleaner is deep.

Which electrodes is known as a low hydrogen electrode?

The lower electrode is known as the low hydrogen electrode;

* Exx15 (E7015)

* XX16 (E7016)

* Exx18 (E6018, E7018)

* Exx28 (E7028)

* XX48 (E7048)

The following table (Table - 1) gives a list of all inferior hydrogen electrodes, types of coverings, applicable welding conditions, and types of current and polarity required;

Electrode classification (AWS 5.1)	Type of covering	Applicable welding positions	Current and polarity
E6018	Low-hydrogen potassium, iron powder	F, V, OH, H	AC or DCEP
E7015	Low-hydrogen sodium	F, V, OH, H	DCEP
E7016	Low-hydrogen potassium	F, V, OH, H	AC or DCEP
E7018	Low-hydrogen potassium, iron powder	F, V, OH, H	AC or DCEP
E7028	Low-hydrogen potassium, iron powder	H-fillet, F	AC or DCEP
E7048	Low-hydrogen potassium, iron powder	F, OH, H, V-down	AC or DCEP
Where, F – Flat, V – Vertical, OH – Overhead, H – Horizontal, H-fillet – Horizontal Fillet AC – Alternating Current DCEP – Direct Current Electrode Positive (Reverse Polarity)

 

What happens if hydrogen weld is present in the metal?

From the above discussion, it is clear that a low hydrogen electrode is used to prevent failures or cracks by preventing hydrogen from entering the weld metal. Nevertheless, what if a significant amount of hydrogen enters the weld metal? Or how does a lower level of hydrogen ensure good welding?

If a significant amount of hydrogen atoms is dissolved in the weld metal and there is no chance of escape then delayed cracks arise. Delayed cracks can occur several hours or days after the weld metal freezes.

Such cracks may occur within the fusion boundary and parallel to the heat-affected zone or may also arise in weld deposits. It is also known as underbed cracking.

If the molten weld puddle cools rapidly, two things can happen;

1. The resulting crystal structure will be a mixture of ferrite and carbide: hydrogen is almost insoluble in ferrite, so the hydrogen atom will escape or diffuse from the weld metal and the weld metal will be more ductile and crack resistant.

2. The structure of the crystal will be changed to martensite: hydrogen atoms do not separate from a martial crystal structure and are trapped in the weld metal. Therefore, it will be more likely to crack. It can be preheated to prevent this. Preheating base metals essentially slows down the cooling rate and helps in the diffusion (escape) of hydrogen atoms from the weld metal.

Baking of Low Hydrogen Electrodes:

Low-hydrogen electrodes should be kept free of moisture and other contaminants. Because moisture/water is a powerful source of hydrogen.

To prevent electrodes from contamination of moisture, they are often packaged and supplied in vermis sealed containers.

According to the manufacturer's recommendation, the electrode must be baked before use. However, initial guidance for baking is available in ASME Section II Part C; A summary of this is available in

 

Electrodes (As per AWS 5.1)	Holding Ovens	Drying Conditions
E6018 E7015 E7016 E7018 E7028 E7048	30°C to 140°C	260°C to 425°C 1 to 2 hours at temperature

 

The E7018 electrode is one of the most preferred low hydrogen electrodes in the industry. It contains a sufficient amount of iron powder in the coverings and works best if used with direct current reverse polarity (DCEP).

Due to the presence of iron powder, a high deposition rate is obtained and it cools the metal transfer. And due to this weld quality and the bead appearances are very good.

The coverings of the E7018 and E7015 electrodes are the same, except for a slightly higher percentage of iron powder in the E7018 cover. The casing on these electrodes is relatively thicker than the E7016 electrode.

The E7016 is designed for direct current AC; The E7015 is similar to the E7016 but works with DC.

The casing of the E7028 electrode is quite thick and has a high iron powder content. All low-hydrogen electrode types have the highest deposition rates. However, they can be used in horizontal and flat positions.

The E7048 class is similar to the E7018 type but is designed for downhill applications only

Compulsory and optional complimentary designator on the electrode:

An electrode is identified by the following;

* Mandatory Classification Designers

* Optional complement designer

For example EXXXX-1 HZR

The first four letters after the 'E' are known as the mandatory classification designer and the digits and numbers after the hyphen (-) is known as optional complementary designers and are optional so depending on the requirements may be used.

Now, we will understand the meaning of compulsory classification constructors;

In E7018:

* The letter 'E' is for an electrode

* The first two digits i.e. two 70 'denote the minimum tensile strength i.e. 70 Ksi (or 70000 psi).

* The second last digit i.e. '1' indicates the position of welding in which the electrode can be used. In particular, the letter '1' depicts all the terms

* The last two digits together reflect the polarity and the flow structure of the electrode.

To read more about electrode symbols and their meaning please click here

As we have understood about compulsory electrode designers, we will now understand about alternative complementary designers;

EXXXX-1 in HZ R

‘1’ indicates that the electrodes (E7016, E7018, or E7024) meet the requirements for rectification;

*  The difficulty for electrodes E7016 and E7018

* Flexibility for electrode E7024

'HZ' states that the electrode meets the requirements of diffusive hydrogen testing, with no more than "Z" mL of hydrogen per 100 grams of deposited metal, where "Z" is 4, 8, or 16.

For example, E7018-H4R indicates that a 4g (AVG) deposit is a differentiated hydrogen content in 100 g of hydrogen metal.

Finally, the final optional designation, Design R, designates that the electrode meets the requirements of the absorbent moisture test. The electrode is exposed to an atmosphere of 80 ° F [27 ° C] / 80% relative humidity (RH) for no less than nine hours by any suitable method for moisture testing.