Welding is the process of joining materials together by melting the two pieces and adding a third melted material. Electrodes provide a current to the materials and are made of a variety of difference materials. Electrodes are manufactured for different purposes and welding types and are classified by a five-digit number like E7011-M. Each number and letter corresponds with a piece of information, including recommended welding position, tensile strength and penetration depth. The "E" in the classification stands for electrode.

Strength

The first two digits of an electrode classification indicate the strength of the electrode. This strength is measured in thousands of pounds per square inch (psi). For example, an electrode classified as E80xx has a tensile strength of 80,000 psi. This number also determines the yield strength or point of deformation for low alloy steel electrodes. Subtract 13,000 from the electrode tensile strength to determine the approximate minimum yield strength. For example, the E80xx electrode has yield strength of 63,000 psi.

Welding Position

The third digit of the electrode classification determines the appropriate welding positions. Welds are performed in four major positions: flat, horizontal, vertical and overhead. Exx1x electrodes can be welded using all four positions with the vertical position moving up. Exx2x electrodes use only flat and horizontal positioning. Exx4x electrodes may use all positions with the vertical position moving down.

Classification Type

The fourth digit represents the classification type. The classification type states the electrode’s coating, penetration depth and required current type. Penetration depths range includes light, medium or deep. Current types include alternating current (AC), direct current electrode positive (DCEP) and direct current electrode negative (DCEN), though some electrodes use multiple types depending on the type of weld. For example, an Exxx7 electrode is coated with iron powder and iron oxide, has a penetration depth of medium and uses AC or DCEN power.

Additional Requirements

Certain electrode classifications include a suffix which identifies any additional requirements or information. Low alloy steel coated electrode requirements differ from the requirements of mild steel coated electrodes. Some common suffixes include M, which signifies military-grade electrodes, and G, which signifies that the electrode has no required chemistry.