Welders accustomed to using a low-hydrogen electrode with a particular classification are sometimes puzzled when they receive electrodes with added designations like "H4R." Low-hydrogen electrodes are generally used in more critical applications to begin with, and their concern is understandable. However, it’s simply a case of the manufacturer providing more information on the same electrode as before.
The added characters are optional designators, permitted by the AWS classification system, to clarify the low-hydrogen characteristics of carbon steel and low alloy steel manual electrodes. Nothing in the electrodes themselves has changed.
Low hydrogen is defined as less than 16 milliliters (ml.) per 100 grams of weld metal. This classification has now been stratified into three levels, so the added designators make it easier to quickly determine how "dry" a particular electrode is. The levels are H16, H8, and H4, corresponding to 16, 8, and 4 ml. per 100 grams of weld metal. These represent the maximum diffusible hydrogen levels obtainable with a specific product.
One additional designator may also be added. This is an optional moisture resistant designator (R), which indicates a low-hydrogen electrode’s ability to meet specific low-moisture pickup limits under controlled humidification tests. This generally indicates that the electrode’s coating has been formulated with non-hygroscopic materials and will resist picking up moisture longer than electrodes with standard low-hydrogen coatings. This can be important when welding in humid areas, since a standard coating will be affected by moisture in about two hours, while a moisture-resistant coating can be safe to use for as long as 10 hours.
When these suffixes are used, they must be imprinted on the electrode itself, in addition to appearing on the label. The actual AWS classification does not change when they are added, however. For example, an E7018 H4R product will still be classified as E7018, although the product is identified by the full designation.
With any low-hydrogen consumable, it is important to observe proper storage procedures. Products such as the H4 electrodes come in a hermetically sealed can. Once opened, they should be stored in a rod oven until used, since they may not meet specifications if left open in high humidity. In case of doubt about low-hydrogen electrodes and their application, the supplier should be consulted for recommendations.