Low Hydrogen SMAW Electrodes: A History and Best Practices
by Joseph Kolasa, Lincoln Electric Welding School Instructor and Joseph Murlin, SMAW Consumable Product Manager, The Lincoln Electric Company
The steady development of new alloys over the years has shaped the design and specification of arc welding stick electrodes, which 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 an alloy content higher than that of mild steel, such as high carbon and low alloy steels. Electrode Properties
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. This suffix indicates that 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 indicates milliliters of diffusible hydrogen per 100 grams of weld metal. For example, a designation of H4 indicates 4mL 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°F for 9 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" or less), they also can be used on AC polarity. In fact, some EXX18 electrodes are designed specifically for AC polarity, such as Excalibur® 7018 AC stick electrode from Lincoln Electric.
Low Hydrogen Workhorse
Low hydrogen electrodes, incidentally, 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 is easy to remove.
This class of stick electrode also is ideal for use in joints involving high-strength, high carbon or low alloy steels. The E7018 electrode’s wide versatility makes it a workhorse for many SMAW applications.
Techniques and Troubleshooting
Success in achieving X-ray quality welds using E7018 low hydrogen electrodes, or any low hydrogen electrode, in the SMAW process comes down to technique. Porosity and cracking are the most prevalent of these defects.
Another important thing to keep in mind is the fact that electrodes last only so long. You will get only so many inches of weld with a single electrode before you need to restart your work with a new one. Be aware that restarting can cause a variety of problems if not done with care.
One of the most common issues occurring with restarting is that the welder gets too much of an upward rod angle and creates fingernailing or a long arc situation. Many people start too high and drag it above the crater. To avoid these scenarios when restarting an electrode, start about ¼" to ½" above your work or the previous weld.
Think of it this way: if you had an 8" plate and weld 3", many people would try to strike the arc at the top and drag down to where the weld ends. Instead, start no more than ¼" to ½" above the crater to keep the joint as clean as possible. You want to angle the electrode directly into the joint at no more than 5 or 10 degrees.
Sometimes, you might not have burned up the entire rod and want to restart with that same electrode at another time. It’s likely, however, that the electrode’s tip has hardened, leaving the covering brittle and tough. If you’re like most people, you’re going to want to put the electrode in a holder and bang it on the plate like a hammer. Don’t, because it can chip the electrode’s coating, affect slag production and cause the weld to go off center and crack.
Instead, disconnect the electrode from the stinger and roughly rub it on the surface of the welding table. Do not bang it. Scratch it to get the core wire to show so you can make a good connection and have proper conditions for good arc shielding.
Additionally, proper storage of low hydrogen electrodes is critical once the container has been opened to prevent moisture pick up. Low hydrogen electrodes can be re-dried if proper care and technique is used. Please consult the electrode manufacturer for their recommendations.
In short, proper training in SMAW techniques is crucial for achieving good results, particularly when work involves low hydrogen electrodes. Understanding how these electrodes function and exploring the techniques required to deliver X-ray quality welds will pay big dividends in better weld quality and fewer porosity defects.