Understanding the Basics of Low-Hydrogen Stick Electrodes
Knowing the basics about E7018 low-hydrogen stick electrodes can be helpful in understanding how to maximize their operation, their performance and the welds they can produce.
Posted: August 1, 2014
Stick welding remains key for numerous welding jobs, in part because the materials used in many applications continue to lend themselves to the process and it’s one that many welding operators know well. When it comes to stick welding, American Welding Society (AWS; Miami, FL) E7018 stick electrodes are a common choice because they provide suitable mechanical and chemical properties for a variety of applications, along with low hydrogen levels to help prevent hydrogen-induced cracking.
Knowing the basics about E7018 low-hydrogen stick electrodes can be helpful in understanding their operation, performance and resulting welds. As a general rule, E7018 stick electrodes offer low spatter levels and a smooth, stable and quiet arc. These filler metal characteristics give the welding operator good control over the arc and minimize the need for post-weld cleanup — both important factors in applications that require careful attention to weld quality and heat input, and those on strict deadlines.
These electrodes offer good deposition rates and good penetration, which means welding operators can add more weld metal into the joint in a given time than many other stick electrodes (such as E6010 or E6011), and can still typically avoid weld defects like lack of fusion. The addition of elements like iron power, manganese and silicon to these electrodes provide distinct advantages, including (but not limited to) the ability to successfully weld through some dirt, debris or mill scale.
Good arc starts and restarts, which help eliminate issues like porosity at the start of the weld, are an additional benefit of E7018 stick electrodes. For good restrikes (initiating the arc again), it is necessary to first remove the silicon deposit that forms at the end of the electrode. It is important, however, to verify all requirements prior to welding, since some codes or procedures don’t permit the restriking of stick electrodes.
As noted in their AWS classification, E7018 stick electrodes provide a minimum of 70,000 psi tensile strength (designated by “70”) and can be used in all welding positions (designated by “1”). The “8” refers to the low-hydrogen coating, as well as the medium penetration the electrode provides and current types it requires for operation. Along with the standard AWS classification, E7018 stick electrodes can have additional designators such as and “H4” and “H8” that refer to the amount of diffusible hydrogen the filler metal deposits in the weld. An H4 designation, for example, indicates the weld deposit has 4 ml or less of diffusible hydrogen per 100 g of weld metal.
Electrodes with an “R” designator — such as E7018 H4R — have undergone specific testing and have been deemed moisture-resistant by the manufacturer. To obtain this designation, the product must resist moisture within a given range after being exposed to 80 deg F temperature and 80 percent relative humidity for nine hours.
Lastly, the use of “-1” on a stick electrode classification (e.g. E7018-1) means the product offers improved impact toughness to help resist cracking in critical applications or at lower temperatures.
E7018 low-hydrogen stick electrodes can operate with a constant current (CC) power source that provides either alternating current (AC) or direct current electrode positive (DCEP). E7018 filler metals have additional arc stabilizers and/or iron powder in the coating to help maintain a stable arc when welding using AC current. The primary advantage of using AC with E7018 electrodes is the elimination of arc-blow, which can occur when DC welding using less-than-ideal grounding or when welding magnetized parts. Despite having additional arc stabilizers, the welds made using AC may not be quite as smooth as those made with DC, however, due to the continuous changes in current direction that occur up to 120 times per second.
When welding with a DCEP current, these electrodes can provide easier control of the arc and a more appealing weld bead, since direction of the current flow is constant. For best results, follow the manufacturer’s recommendations for operating parameters for the electrode diameter.
Like any process and electrode, proper technique when stick welding with E7018 stick electrodes is important to ensure good weld quality. Hold a tight arc length — ideally keeping the electrode just above the weld puddle — to maintain a stable arc and minimize the chance for porosity.
When welding in the flat and horizontal positions, point/drag the electrode 5 deg to 15 deg away from the direction of travel to help reduce the chance of trapping slag in the weld. When welding in the vertical-up position, point/push the electrode upwards 3 deg to 5 deg while traveling upwards, and employ a slight weaving technique to help prevent the weld from sagging. The weld bead width should usually be two and half times the diameter of the electrode’s core wire for flat and horizontal welds, and two and a half to three times the core diameter for vertical-up welds.
E7018 stick electrodes typically ship from the manufacturer in a hermetically sealed package to protect them from moisture damage and pick up. It’s important to keep that package intact and stored in a clean, dry area until the products are ready for use. Once opened, the stick electrodes should be handled with clean, dry gloves to prevent dirt and debris from adhering to the coating and to eliminate the opportunity for moisture pickup. The electrodes also should be held in an oven at the temperatures recommended by the manufacturer after being opened.
Some codes dictate how long a stick electrodes can be outside of sealed packaging or a storage oven and if or how often the filler metal can be reconditioned (i.e. through a special baking to remove absorbed moisture) before they must be discarded. Always consult applicable specifications and codes for the requirements of each job.
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