While executing proper welding technique is the most obvious way to avoid porosity or other defects in low hydrogen SMAW welding, the success of the job actually starts well before the first arc is struck.
Low hydrogen electrodes must be dry to perform properly. Unopened hermetically sealed containers provide excellent protection in good storage conditions. Opened cans or electrodes should be stored in a cabinet at 120 deg C to 150 deg C (250 deg F to 300 deg F). Moisture resistant electrodes with an “R” suffix have a high resistance to coating moisture pick-up. However, all low hydrogen electrodes should be stored properly, even those with an “R” suffix.
Standard EXX18 electrodes should be supplied to welders twice per shift. Moisture resistant types may be exposed for up to nine hours. Specific code requirements may indicate exposure limits different from these guidelines. Depending on the amount of moisture absorbed and other factors, moisture pickup can degrade weld quality in various ways:
- Moisture in low hydrogen electrodes may cause porosity. This porosity could be completely subsurface and require x-ray inspection or destructive testing. The porosity could also be visible, external porosity.
- High moisture can also lead to excessive slag fluidity, a rough weld surface, and difficult slag removal. Excessive moisture in low hydrogen electrodes will lead to elevated levels of diffusible hydrogen, which can lead to hydrogen-induced weld cracking and/or underbead cracking.
Re-drying, when done correctly, restores the electrodes’ ability to deposit quality welds. Proper re-drying temperature depends upon the electrode type and its condition. One hour at the listed final temperature is satisfactory. DO NOT dry electrodes at higher temperatures. Several hours at lower temperatures is not equivalent to using the specified requirements.
Electrodes of the E8018 and higher strength classifications should be given no more than three one-hour re-dries in the 370 deg C to 430 deg C (700 deg F to 800 deg F) range. This minimizes the possibility of oxidation of alloys in the coating which would result in lower than normal tensile or impact properties.
Any low hydrogen electrode should be discarded if excessive re-drying causes the coating to become fragile and flake or break off while welding, or if there is a noticeable difference in handling or arc characteristics, such as insufficient arc force.
Electrodes to be re-dried should be removed from the can and spread out in the oven because each electrode must reach the drying temperature.
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