Low Hydrogen electrodes, Their Storage & Baking Procedure?
Low-hydrogen electrodes are SMAW electrodes that contain less than 0.6% coating moisture — as per ASME Section IIC, SFA 5.1- Table 10, compared to 4- 6% moisture in cellulosic types electrode (E6010, E7010, etc.) coatings. AWS A5.1/A5.1M: Specification for Carbon Steel Electrodes for Shielded Metal Arc Welding, states that low-hydrogen electrodes must have coating moisture levels of less than 0.6% when tested at 1800°F (980°C), but many low-hydrogen electrodes carry much lower moisture levels. The lower moisture levels correspond to relatively lower diffusible hydrogen levels in the deposited weld metal.
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Requirements for Welding Electrode Storage
- Stored the welding electrode at temperatures well above the dew point always. This can be kept safely in a heated room at a temperature above 15° Celsius (in cold places) and at ambient temperature in hot & humid places and a relative humidity below 50%.
- Storage at very high temperature (> 25° Celsius) shall be avoided as well, due to the fact that the lubricant on the wire (e.g. GMAW wire spools) may volatilize too early.
- Follow FIFO rules for electrode withdrawal from store: When material is taken from the storage always choose the product with the oldest manufacturing date (FIFO)!
- Welding Electrodes or wire spools that are not fully consumed have to be packed prior to storage.
- Drying of wet welding wires or electrodes is not possible and they should be discarded.
- A maximum duration of storage cannot be specified in general for welding electrodes. In doubt a qualification by welding tests must be performed.
the maximum permitted moisture content in Electrode Coating
Electrodes of the low-hydrogen classifications E6018 [E4318], E7015 [E4915], E7016 [E4916], E7018 [E4918], E7018M [E4918M], E7028 [E4928], and E7048 [E4948]) are made with inorganic coverings that contain minimal moisture. The covering moisture test such as specified in AWS A4.4M, Standard Procedure for Determination of Moisture Content of Welding Fluxes and Welding Electrode Flux Coverings, converts hydrogen-bearing compounds in any form in the covering into water vapor that is collected and measured. The test thus assesses the potential hydrogen available from an electrode covering. All low-hydrogen electrodes, in the as-manufactured condition or after conditioning, are expected to meet a maximum covering moisture limit of 0.6% or less, as required in Table 10 of SFA 5.1 as given below:
Benefits/ Advantages of low hydrogen electrodes
Low hydrogen electrodes are recommended for three broad areas of application:
• On steels with poor weldability: low alloy, high carbon, high sulfur, or other steels where cracking can be a problem
• When specified by governing codes
• For high-deposition, out-of-position welds on heavy plate.
So, 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. 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.
Optional diffusible hydrogen designator in Low Hydrogen Electrodes
Welding electrodes 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. Below table shows the maximum permissible hydrogen level in Low hydrogen electrodes.
low hydrogen electrode baking/reconditioning procedure
In order to maintain low-hydrogen electrodes with minimal moisture in their coverings, these electrodes
should be stored and handled with considerable care. Electrodes which have been exposed to humidity may absorb considerable moisture and their low-hydrogen character may be lost. Then conditioning can restore their low-hydrogen character. Temperature details for baking and holding are given in below table.
Storage of Low Hydrogen Stick Electrodes
Low hydrogen stick electrodes must be dry to perform properly. Unopened hermetically sealed containers provide excellent protection in good storage conditions. Opened cans should be stored in a cabinet at 250 to 300°F (120 to 150°C). Low hydrogen stick electrode coatings that have picked up moisture may result in hydrogen induced cracking, particularly in steels with a yield strength of 80,000 psi (550 MPa) and higher.
Moisture resistant electrodes with an “R” suffix in their AWS classification have a high resistance to moisture pickup coating and, if properly stored, will be less susceptible to this problem, regardless of the yield strength of the steel being welded. All low hydrogen stick 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 9 hours.
When containers are punctured or opened, low hydrogen electrodes may pick up moisture. Depending upon the amount of moisture, it will damage weld quality in the following ways:
1. A greater amount of moisture in low hydrogen electrodes may cause porosity. Detection of this condition requires x-ray inspection or destructive testing. If the base metal or weld metal exceeds 80,000 psi (550 MPa) yield strength, this moisture may contribute to under-bead or weld cracking.
2. A relatively high amount of moisture in low hydrogen electrodes causes visible external porosity in addition to internal porosity. It also may cause excessive slag fluidity, a rough weld surface, difficult slag removal, and cracking.
3. Severe moisture pickup can cause weld cracks in addition to under-bead cracking, severe porosity, poor appearance, and slag problems.
How many times baking of a low hydrogen electrode is allowed?
This is the most common question that arises with many welding engineers/ QA-QC personnel. While the Codes and electrodes specifications are silent on this query, precautions must be taken care not to bake electrodes more than twice. The obvious reason is ‘Each baking sequence will remove the essential moisture required in the coating and additive substances which hold the coating strong on the core wire of the electrode. To be precise, any low hydrogen electrode should be discarded if excessive redrying 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.
Welding consumable storage and handled guidelines should be in accordance with the consumable manufacturer’s instructions and guidelines and as given in the AWS A5.XX series of filler metal specifications. To reduce exposure to moisture, certain welding consumables should be stored in warm holding ovens after they have been removed from the manufacturer’s packaging. Low-hydrogen SMAW electrodes supplied in non-hermetically sealed containers should be baked according to manufacturer’s instructions prior to use.