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Preventing the Effects of Moisture Contamination on Flux Cored Wire
The Effects of Moisture
During the manufacture of most flux-cored wire, a seam is formed along the length of the wire. It is through this seam that moisture can be absorbed into the flux. This moisture produces hydrogen that will go into solution during welding and settle in the weld’s structural voids.
Plain water alone would not hurt the weld, but the heat and arc break down water into its basic elements, hydrogen and oxygen. Hydrogen in or near the molten weld can pose a significant threat to the weld quality.
Flux-cored arc welding is generally considered to be a low-hydrogen welding process. However, as material susceptibility to the effects of hydrogen increases, the amount of diffusible hydrogen necessary to cause cracking decreases. When welding high-strength, low-alloy steels, it is important to evaluate the amount of diffusible hydrogen produced during welding.
Certain flux-cored wires can absorb significant moisture if stored in a humid environment, in damaged or open packages, or if left unprotected for extended periods of time. In the worst cases of humidity, even overnight exposure of unprotected wire can lead to levels of crack-inducing hydrogen.
In the event the wire has been exposed, the filler metal manufacturer should be consulted regarding probable damage to the low-hydrogen characteristics and the possibility of reconditioning of the wire.
Exposure to moisture can also cause rust, which is detrimental to weld quality. As well as causing problems in the feeder and gun, rust contains oxygen and hydrogen as a result of the rusting process. This hydrogen can enter the weld and cause problems.
The following suggestions include some ways to combat the negative effects of moisture on welding with high-strength, low-alloy flux-cored wire:
- Just-In-Time (JIT) inventory. Proper forecasting techniques for wire usage can aid in ordering what the user requires in a set time frame. This can help limit the amount of wire awaiting use in the shop or field. JIT also limits the amount of inactive wire that might be susceptible to moisture pickup. Damaged wire that has taken on moisture should be reconditioned. Wire that is damaged or rusted should not be used.
- Oven storage. Similar to those used to hold SMAW electrodes, ovens are available for holding spools and coils of flux-cored wire. In an oven, the wire can be held at specified temperatures or reconditioned if the wire has taken on moisture.
Once flux-cored wire is removed from its initial packaging, the unused portion should be stored at temperatures not to exceed 300 degrees Fahrenheit (150 degrees Celsius) for coils, masonite spools, or wire baskets, and 150 degrees F (65 degrees C) for plastic spools. Precise temperatures should be obtained from the wire manufacturer’s technical department.
- Climate control. If the amount of flux-cored wire is large and held in a single location, an investment in a climate-controlled facility might be in order. This option offers inventory tracking as well as custom climate controls.
- Hermetically-sealed packaging. Another option to consider is hermetically-sealed packaging, which decreases the likelihood of moisture contamination. Special care must be taken not to damage the packaging.
Flux-cored wires exhibiting weld metal porosity or "worm tracks" because of moisture absorption by the flux can be reconditioned by rebaking the wire.
The exact time and temperature for rebake are determined by the wire and spool material. Wire coils, masonite spools, or wire baskets are typically rebaked in a range of 230 to 300 degrees F for a minimum of six to 12 hours. Precise temperatures are available from the wire manufacturer.
It is important to note that some flux-cored electrodes are never baked. Reconditioning these types of electrodes may not only destroy the protectant lubricant on the electrode, but may cause chemicals in the flux to react. This reaction may cause arc stability problems and may change the mechanical properties of the weld deposit. Non-baked flux-cored products can be either self-shielded or gas-shielded electrodes.
Wire on plastic spools cannot be rebaked because of plastic’s inability to withstand high temperature.
Another important factor in the storing and rebaking of flux-cored wire is the lubricant on the outside of the wire. Some lubricants can be damaged by high temperatures. The wire manufacturer should be contacted to determine the potential damage.
While bad operator technique does not create moisture, poor technique can allow hydrogen from other elements besides moisture to enter the weld.
By using a shorter stick-out length (the amount of the wire extending from the gun’s end) and higher welding currents, the operator may be promoting higher hydrogen levels. With shorter stick-out, less resistive heating is available to evaporate hydrogen-containing residues from the wire surface. These residues can consist of drawing soaps or other lubricants used in manufacturing the wires. These residues can enter the weld pool, increasing the hydrogen content.
The wire manufacturer’s technical department should always be contacted for specific instructions involving wire storage and reconditioning. Proper storage and rebaking temperatures depend on the wire and its condition.
As with all types of welding wire, it is important that users of flux-cored wire take great care to keep it from taking on moisture. In addition to avoiding hydrogen cracking, moisture-free flux-cored wire will run easier and cleaner.
Article reprinted with permission from the January/February 1998 issue of Practical Welding Today™. FABRICATORS & MANUFACTURERS ASSOCIATION, INTL. 833 FEATHERSTONE RD. ROCKFORD, IL 61107-6302, Phone 815-399-8700