Electrode Storage and Porosity on a Rainy Day
A workshop stores its covered electrodes in an open rack near the roller door. The rainy season has started, and the shop is humid. A student welding a 10 mm fillet on mild steel with E7018 electrodes notices porosity scattered along the whole bead, plus a rough, uneven surface. The electrodes were opened from a sealed pack two weeks ago and have been sitting on the rack since. The machine is set at 130 A with a 3.2 mm electrode, and the student's travel speed looks normal. The instructor suspects the consumables rather than the machine settings.
1. Explain why E7018 electrodes are particularly sensitive to this storage problem, and how the observed porosity fits that explanation.
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E7018 is a low-hydrogen electrode. Its coating contains a significant amount of material that must stay dry; if it absorbs moisture from humid air, that water breaks down in the arc and releases hydrogen into the weld pool. The hydrogen cannot escape before the metal freezes, so it forms gas pores, which show up as scattered porosity along the bead.
Two weeks in an open rack in a humid shop is exactly the wrong storage. Sealed packs protect the coating, but once opened, the electrodes need a holding oven or a heated quiver, typically around 100-150 degrees Celsius for low-hydrogen types, to keep them dry. Electrodes left on an open rack are not protected.
The porosity pattern fits: it is distributed along the whole bead rather than concentrated in one spot, which points to the consumable rather than to a single arc strike or a dirty patch of plate. The rough surface is also consistent with a coating that has softened or partly broken down.
2. The student proposes drying the electrodes on top of the welding machine, which gets warm during use. Evaluate this idea and state what should actually be done.
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Drying electrodes on top of the machine is not acceptable. The machine top reaches an uncontrolled temperature, often only warm rather than hot enough to drive off moisture, and it can also get much hotter in spots. There is no way to hold a specified temperature, so the result is unpredictable: the coating may stay damp, or it may be overheated and cracked. The top of a machine is also exposed to grinding dust and spatter.
The correct action is to remove the suspect electrodes from service, store low-hydrogen electrodes in a proper holding oven at the recommended temperature, and if the coating is damaged or the electrodes have been damp for a long period, follow the manufacturer's re-drying procedure or discard them. For everyday work, keep only a small amount in a heated quiver at the job and return the rest to the oven. The instructor should also check the storage rack and move it away from the roller door.
3. Describe how the student could confirm that the electrodes, rather than the base metal, caused the porosity, using only materials already in the shop.
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Run a controlled comparison. Clean a fresh piece of the same mild steel to bright metal, then weld a short bead with a new electrode taken straight from a sealed pack, using the same current, polarity, and travel speed. Then weld an identical bead on the same prepared plate with one of the suspect electrodes from the rack.
If the new electrode gives a clean bead and the suspect one gives porosity, the consumable is the cause. If both beads show porosity, look elsewhere: base metal contamination, gas flow if using a shielding gas process, or a machine fault. Keep the two test plates labelled so the instructor can inspect them. This isolates one variable at a time and costs only a few electrodes and a scrap plate.