The Case for Using Low-Hydrogen Covered Electrodes

With its versatility, ease of use, and ability to reduce harmful hydrogen diffusion in weld deposits, a low hydrogen cover electrode is a wise choice.

Although mechanized welding is seen as the future for many applications, shielded metal arc welding (SMAW) in combination with low hydrogen electrodes can often prove to be the best option. Low-hydrogen electrodes are the logical choice for a wide variety of welding applications. Here's a look at what the following hydrogen electrodes are and why they work so well.

Fig. 1 - Low-hydrogen electrodes are made to move towards a wooly woolen (100 ° to 300 ° F) to bend downward and to keep the pipette in the downward moving area.

Low Moisture Coating = Hydrogen Control

During welding, the arc and its resulting heat release the moisture in the coating, the surrounding atmosphere, and hydrogen from substances on the base material, among other sources. Of course, timely moisture is a good thing without it, formation and extruding are not possible. But, sometimes you can have a very good thing. The low moisture in the electrode coating reduces the chance of diffuser hydrogen being deposited into the weld metal, which can result in weld failure from hydrogen-induced cracking, also known as hydrogen emission of cold cracking.

Low-hydrogen electrodes, most simply defined, are SMAV consumables that have less than 0.6% coating moisture - compared to 4 to 6% moisture in conventional cellulosic electrode coatings.

AWS A5.1 / A5.1M: 2020, Specification of carbon steel electrodes for shielded metal arc welding, states that a low-hydrogen electrode must have a humidity level of less than 0.6% when tested at 1800 ° F, but Very few hydrogen electrodes carry very low humidity levels. The low moisture level corresponds to the relatively low diffractive hydrogen levels in the deposited weld metal.

Typical American welding society (AWS) classifications for the shielded metal arc welding (SMAW) electrodes include EXX15-x, EXX16-x, EXXX18-x, and Exx28-x. Deviated hydrogen levels, measured in maximum milliliters of hydrogen per 100 grams of weld deposit, are often listed as alternative complementary designers at the end of the AWS classification for electrodes. For example, according to the A5.1 specification, a low-hydrogen electrode can be tested, as measured no more than 8 mL / 100 g. Therefore, the electrode will carry the designation of H8. Low-hydrogen electrodes typically measure 16 mL / 100 g or less, with H8 and H4 as common designers. An example of the complete AWS classification is the E7018 H4.

Some low-hydrogen electrodes are manufactured with special moisture-resistant coatings. This type of electrode can be identified by the addition of an "R" to their classification number. American welding society (AWS) defines guidelines for testing electrodes to carry this designation. Designers of 'R' in low-hydrogen electrodes typically exhibit extended shelf life and room-air exposure time, and better resistance to weld defects such as porosity and hydrogen-induced cracking.

Typically, for low-hydrogen electrodes, the exposure time of room air is limited to about four hours, while with the designer of can R ', the electrode can be exposed to nine hours, possibly for the entire work shift.

There is a limit to how low-hydrogen electrodes can be exposed to room air before taking hydrogen from condensation and can no longer be considered "low hydrogen". Consequently, it is a recommended practice to store electrodes in an air-tight container at an elevated temperature to prevent condensation. For low hydrogen electrodes properly need to be store in a rod oven. If the stock was exposed to the environment for a long period of time, the electrode may also require rebinding under strict guidelines.

Low-hydrogen electrodes should be stored in rod ovens (temperature between 100 ° to 300 ° F) to take them out and prevent moisture pickup in the coatings.

Fig. 1 - Low-hydrogen electrodes are made to move towards a wooly woolen (100 ° to 300 ° F) to bend downward and to keep the pipette in the downward moving area.

 A variety of applications

The low-hydrogen class of electrodes is most widely used for SMAW. Common applications include welding thick metal sections, restrained joints, and building welds critical for bridge and building construction, offshore, and power generation. The use of low-hydrogen electrodes for nontraditional applications is increasing to provide an additional protection measure against weld defects.

There are several reasons contributing to this widespread use. Most notably, the shielded metal arc is considered to be the easiest welding method to learn and employ. In comparison, semi-automatic wire electrode welding demands more extensive training and higher initial capital investment. Low hydrogen-covered electrodes also provide a smooth low splatter arc that simplifies welder training.

These types of versatile electrodes can be used to weld virtually anything. Consider process pipeline construction. An alternative option may be mechanized wire electrode welding. However, given the inconsistent fitup and compressed space capability, mechanized welding is generally not a good option. Manual shield metal arc welding, on the other hand, allows for flexibility in handling highs and lows on pipe weld welds and other poor-fit-up issues. Covered electrodes can be "bent" to allow welding pipes in confined spaces. Often, in these applications, a manual welder can maintain a level of productivity that matches mechanized processes.

Another advantage of SMAW is its portability. The cover electrode eliminates the need for external shielding gases. When welding is done outdoors or in hard-to-reach locations, there is no need to transport, footprint, and care for shielding gas bottles.

The AWS E7018 electrode is the most popular low-hydrogen cover electrode type in use today. It has certain characteristics that distinguish it from other classes. This class of covered electrodes is an ideal choice for all-position welding, with the exception of downhill welds. They offer smooth, quiet arc characteristics with low spatter levels and easy slag removal, making the E7018 a desirable electrode to be used by welders of all skill levels. They provide weld deposits with moderate penetration levels, ensuring good fusion to the base metal. Another advantage, possible with the addition of iron powder to the coating, is the relatively high deposition rate. Strong deposition rates can make cover electrode welding cost-effective for a wide range of applications. Finally, in most circumstances, these low-hydrogen electrodes provide good arc starting and restriction capability. These reduce the onset and restriction characteristics and initiate striking porosity.

Protect against cracking

But why should you specifically choose a low-hydrogen electrode? The answer is simple: to avoid cracking. Low hydrogen-covered electrodes are ideal for use in crack-sensitive applications because they reduce the risk of hydrogen-induced crack.

This phenomenon occurs when elevated levels of hydrogen, which naturally differ from insoluble or liquid metals, are trapped in a rigid, highly stressed weld material or heat-affected zone (HAZ). Trapped hydrogen finds an escape route and eventually produces voids and cracks in the substrate, ultimately leading to failures of the welded material. This is particularly true for high-strength steels, which are susceptible to cracking due to their high carbon content.

Today, engineers specify high-strength steels for a greater number of applications. If the strength of the material is high, often, a part can be made of lightweight, thin metal. These thinner materials typically have lower transport costs and lower weld metal volumes with fewer weld passes - and a reduction in all labor expenses. In addition, high-strength steel, which is used correctly, can hold environmental and force stresses well.

Most importantly, in high strength weld or HAZ cracking, high-carbon-material steels arising from trapped hydrogen are an unacceptable defect requiring the weld to be ejected and add significant cost. By specifying low-hydrogen electrodes, eliminating a variable that may contribute to cracking may provide a safety margin in some applications. The use of low-hydrogen electrodes has increased significantly in high-strength steels by grappling with varying hydrogen levels.

Welding codes recognize low-hydrogen benefits

Various welding codes specify the use of low-hydrogen-covered electrodes. Codes and specifications can refer to hydrogen control either by requiring electrodes with low hydrogen cover or by placing specific limits on diffractive hydrogen.

AWS D1.1 / D1.1M: 2010, Structural Welding Code - Steel, for example, includes several provisions that use hydrogen designers, such as H8, and AWS D1.8 / D1.8M: 2009, Structural Welding The code -Matic complement specifies the use of low-hydrogen electrodes when using the SMAW process for demand critical welds. Additionally, AASHTO / AWS D1.5M / D1.5: 2010, Fracture Control Plan of Bridge Welding Code, requires the following electrode specs for welding fracture-critical members: H16, H8, or H4 when the minimum specified yield strength is 50 Is how or less; And H8 or H4 when the minimum specified yield strength exceeds 50 ksi.

Other agencies, such as the US Army and the Bureau of Shipping, also set limits on variable-hydrogen levels. Both use limits of 15, 10, and 5 mL / 100 grams for some applications, and the military specification has a strict limit of 2 mL / 100 grams or H2.

Record engineers can override these codes to make them more restrictive, but not infrequent. And if the application code does not call for low-hydrogen weld deposits, engineers of record can issue that required to provide a safety margin.

Code and engineers recognize the value and importance of low-hydrogen-covered electrodes, which is why they are consumables and will continue to be a popular choice.