October 15-17, 2024 at Orange County Convention Center in Orlando, Florida
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Tuesday Oct 15 9 AM — 5 PM
Wednesday Oct 16 9 AM — 5 PM
Thursday Oct 17 9 AM — 4 PM

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Orange County Convention Center

9800 International Drive
Orlando, Florida 32819

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North America's largest metal forming, fabricating, welding and finishing event heads to Orange County Convention Center in October 2024. FABTECH provides a convenient "one stop shop" venue where you can meet with world-class suppliers, see the latest industry products and developments, and find the tools to improve productivity, increase profits and discover new solutions to all of your metal forming, fabricating, welding and finishing needs.

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North America's Largest Metal Forming, Fabricating, Welding and Finishing Event

From the Blog

The Case for Using Low-Hydrogen Covered Electrodes

By Jennifer Dallos on on
With its versatility, ease of use, and capability to reduce harmful hydrogen diffusion in the weld deposit, the low-hydrogen covered electrode is a wise choice By Lisa Byall, portfolio manager, Industrial Products, The Lincoln Electric Co., Cleveland, Ohio. Reprinted with permission: The Welding Journal While mechanized welding is seen as the future for a number of applications, shielded metal arc welding (SMAW) in combination with low-hydrogen electrodes often can prove to be the best choice. Low-hydrogen electrodes are the logical choice for a variety of welding applications. Following is a look at what low-hydrogen electrodes are and why they work so well. Low-Moisture Coating = Hydrogen Control During welding, the arc and its resultant heat release hydrogen from the moisture in the coating, the surrounding atmosphere, and from substances on the base material, among other sources. Of course, moisture at times is a good thing — without it, forming and extruding are not possible. But, sometimes you can have too much of a good thing. Less moisture in the electrode coating reduces the opportunity for diffusible hydrogen to be deposited into the weld metal, which can result in weld failure from hydrogen-induced cracking, also known as hydrogen embrittlement or cold cracking. Low-hydrogen electrodes, most simply defined, are SMAW consumables that contain less than 0.6% coating moisture — compared to 4 to 6% moisture in traditional cellulosic electrode coatings. AWS A5.1/A5.1M:2012, Specification for Carbon Steel Electrodes for Shielded Metal Arc Welding, states that low-hydrogen electrodes must have coating moisture levels of less than 0.6% when tested at 1800°F, but many low-hydrogen electrodes carry much lower moisture levels. The lower moisture levels correspond to relatively lower diffusible hydrogen levels in the deposited weld metal. Typical AWS classifications for SMAW electrodes include EXX15-x, EXX16-x, EXXX18-x, and Exx28-x. Diffusible hydrogen levels, measured in maximum milliliters of hydrogen per 100 g of weld deposit, are often listed as optional supplemental designators at the end of the AWS classification for the electrode. For example, a low-hydrogen electrode may be tested, per the A5.1 specification, as measuring no more than 8 mL/100 g. Therefore, the electrode would carry a designation of H8. Low-hydrogen electrodes typically measure 16 mL/100 g or less, with H8 and H4 as common designators. An example of a full AWS classification is E7018 H4. Certain low-hydrogen electrodes are manufactured with special moisture-resistant coatings. These electrodes can be identified by the addition of an “R” to their classification number. AWS defines the guidelines for testing electrodes to carry this designation. Low-hydrogen electrodes having the ‘R’ designator generally exhibit extended shelf lives and room-air exposure times, and improved resistance to weld defects such as porosity and hydrogen-induced cracking. Generally, the exposure time to room air for low-hydrogen electrodes is limited to approximately four hours, while electrodes with the ‘R’ designator can potentially be exposed for an entire work shift, up to nine hours. There is a limit to how long low-hydrogen electrodes can be exposed to room air before the coatings pick up hydrogen from condensation and can no longer be considered “low hydrogen.” As a result, it is a recommended practice to store the electrodes in an air-tight container at an elevated temperature to prevent condensation. A rod oven (Fig. 1) is commonly used to properly store low-hydrogen electrodes. Electrodes may even require rebaking under strict guidelines if the stock was exposed to the environment for a prolonged time.
Fig. 1 — Low-hydrogen electrodes should be stored in a rod oven (100° to 300°F) to bake out and prevent moisture pickup in the coatings.

Fig. 1 — Low-hydrogen electrodes should be stored in a rod oven (100° to 300°F) to bake out and prevent moisture pickup in the coatings.

 A Variety of Applications The low-hydrogen class of electrodes is the most widely used for SMAW. Common applications include welding thick metal sections, restrained joints, and making critical welds for bridge and building construction, offshore, and power generation. Low-hydrogen electrodes are also growing in use for nontraditional applications to provide an additional safety measure against weld defects. There are many reasons contributing to this widespread use. Most notably, shielded metal arc is considered the easiest welding method to learn and employ. In comparison, semiautomatic wire electrode welding demands more extensive training and higher initial capital investment. Low-hydrogen covered electrodes also provide a smooth low-spatter arc that simplifies welder training. These versatile electrodes can be used to weld virtually anything. Consider process piping fabrication. An alternate choice may be mechanized wire electrode welding. However, given the potential for inconsistent fitup and constricted space, mechanized welding generally is not a good option. Manual shielded metal arc welding, on the other hand, allows for flexibility in tackling highs and lows on the pipe weld joint and other poor-fitup issues. Covered electrodes can be “bent” to permit welding pipe in confined spaces. Often, in these applications, a manual welder can maintain a level of productivity that matches the mechanized processes. Another benefit of SMAW is its portability. The covered electrode eliminates the need for external shielding gases. When welding is performed outdoors or in difficult-to-access spaces, the transport, footprint, and care required for shielding gas bottles is not a concern. The AWS E7018 electrode is the most popular low-hydrogen covered electrode type in use today. It features certain characteristics that separate it from other classes. This class of covered electrode 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 E7018 a desirable electrode to use by welders of all skill levels. They provide weld deposits with medium penetration levels, ensuring good fusion to the base metal. Another benefit, made possible with the addition of iron powder in the coating, is a relatively high deposition rate. The robust deposition rate can make covered electrode welding cost effective for a wider range of applications. Finally, under most conditions, these low-hydrogen electrodes provide good arc starting and restriking capabilities. These start and restrike characteristics minimize starting and striking porosity. Defense against Cracking But why should you specifically choose low-hydrogen electrodes? The answer is simple: To avoid cracking. Low-hydrogen covered electrodes are ideal for use in crack-sensitive applications since they reduce the risk of hydrogen-induced cracking. This phenomenon occurs when elevated levels of hydrogen, which is naturally soluble or diffusible in liquid metal, becomes trapped in the hardened, highly stressed weld material or heat-affected zone (HAZ). The trapped hydrogen seeks an escape route and eventually produces voids and cracks in the substrate, ultimately leading to failures of the welded material. This is especially true for higher-strength steels, which are more susceptible to cracking due to their higher carbon content. Today, engineers specify higher-strength steels for a greater number of applications. Often, a part can be made from a lighter-weight, thinner metal if the material’s strength is higher. These thinner materials commonly have lower transport costs and a reduced volume of weld metal with fewer weld passes — and all of the associated reductions in labor expenses. In addition, higher strength steels, correctly used, can hold up well to environmental and force stresses. Most importantly, weld or HAZ cracking in high-strength, high-carbon-content steels resulting from trapped hydrogen is an unacceptable defect that requires gouging out the weld and rewelding — adding significant cost. Eliminating one variable that can contribute to cracking, by specifying low-hydrogen electrodes, can provide a safety margin in some applications. Battling diffusible hydrogen levels in higher-strength steels has led to a marked rise in use of low-hydrogen electrodes. 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 by either requiring low-hydrogen covered electrodes or by placing specific limits on diffusible hydrogen. The AWS D1.1/D1.1M:2010, Structural Welding Code — Steel, for example, includes several provisions that use hydrogen designators, such as H8, and AWS D1.8/D1.8M:2009, Structural Welding Code —Seismic Supplement, specifies the use of low-hydrogen electrodes when using the SMAW process for Demand Critical welds. Additionally, the Fracture Control Plan of AASHTO/AWS D1.5M/D1.5:2010, 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 ksi or less; and H8 or H4 when the minimum specified yield strength is greater the 50 ksi. Other agencies, such as the U.S. military and the American Bureau of Shipping, have also set limits on diffusible-hydrogen levels. Both use limits of 15, 10, and 5 mL/100 g, and the military specification has a stricter limit of 2 mL/100 g, or H2, for certain applications. The engineer of record can override these codes to make them more restrictive, but not less. And if the applicable code does not call out for low-hydrogen weld deposits, the engineer of record can issue that requirement to provide a safety margin. Codes and engineers recognize the value and importance of low-hydrogen covered electrodes, which is why these consumables are, and will remain, a popular choice.

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