BEST PRACTICES FOR USING LOW HYDROGEN SMAW ELECTRODES
Follow the guidelines in this primer for applications where base metals have a tendency to crack, where thick sections are to be welded or where the base metal has an alloy content higher than that of mild steel, such as high carbon and low alloy steels.
The steady development of new alloys over the years has shaped the design and specification of the arc welding stick electrodes that were first used in shipbuilding during World War I. As increasingly demanding welding applications became standard operating procedure in fab shops and in the field, the need for durable, low hydrogen stick electrodes became more prevalent across a variety of industries involved in welding.
As a result, low hydrogen stick electrodes emerged in the marketplace. These versatile consumables have become a primary electrode for a variety of welding applications and have gained wide acceptance in the industry. They are ideal for use in other applications where base metals have a tendency to crack, where thick sections are to be welded or where the base metal has alloy content higher than that of mild steel, such as high carbon and low alloy steels.
Stick electrodes feature a conductive core wire that in many cases is steel. This wire conducts electrical current from the electrode holder to the work. It also melts to become the filler metal.
During the manufacturing process, the chemical coating that forms the flux layer is extruded onto the steel core wire. The electrodes are then baked in a controlled oven to achieve optimum moisture content so the flux can perform its primary task – vaporizing to form a shielding gas and slag system that protects the weld puddle from nitrogen, hydrogen and oxygen. The electrode coating also can provide alloy and properties to the weld deposit.
Today there are many types of low hydrogen electrodes available for use in shielded metal arc welding (SMAW) applications. These electrodes, which include EXX15, EXX16, EXX18, EXX18-X, EXX28 and EXX48, are often specified to reduce the likelihood of hydrogen-related cracking during the stick welding process.
Low hydrogen electrodes are recommended for three broad areas of application:
- On steels with poor weldability: low alloy, high carbon, high sulfur, or other steels where cracking can be a problem.
- When specified by governing codes.
- For high-deposition, out-of-position welds on heavy plate.
Low hydrogen electrodes offer fast-fill (high-deposition) or fill-freeze (out-of-position) characteristics and are designed to produce sound welds of X-ray quality with excellent notch/impact properties and high ductility.
Some low hydrogen stick electrodes have a “-1” suffix in the AWS classification that indicates the stick electrode meets the requirements for improved toughness.
Welding consumables can be classified with an optional diffusible hydrogen designator. These designators include an H4, H8 and H16 designation. The “H” and corresponding number indicate milliliters of diffusible hydrogen per 100 grams of weld metal. For example, a designation of H4 indicates 4 mL of diffusible hydrogen per 100 grams of weld deposit.
The “R” designation for an electrode indicates that it has a moisture-resistant coating. To qualify for an “R” designation, electrodes that have been removed from freshly opened packages or have been reconditioned are exposed to 80 percent relative humidity and a temperature of 80 deg F for nine hours. Moisture content after this exposure cannot be more than 0.4 weight percent. Even a small amount of moisture over this level can cause weld porosity and other defects.
While low hydrogen electrodes ideally should run on DCEP polarity (especially if the size is 5/32 in or less), they also can be used on AC polarity. In fact, some EXX18 electrodes are designed specifically for AC polarity, such as the Excalibur® 7018 AC stick electrode.
Low hydrogen electrodes are the most widely used class of welding consumables for such applications as power generation, general fabrication, shipbuilding, hard-to-weld, out-of-position and pipeline (ASME vertical up) welding.
The popular E7018 electrode, for example, has certain characteristics that separate it from other classes. An ideal choice for all position welding (with the exception of vertical down), these low hydrogen electrodes have a high iron powder content that facilitates a smoother, quieter arc with very low spatter, medium arc penetration and high deposition rates. The E7018 electrode exhibits moderately heavy slag that is easy to remove.
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About the Author: Joseph Kolasa is a welding school instructor and Joseph Murlin is the SMAW consumable product manager at The Lincoln Electric Company, 22800 Saint Clair Avenue, Cleveland, OH 44117-8542, www.lincolnelectric.com.