What does the 'X' in the electrode identification ER70S-X signify?

The 'X' in the electrode identification ER70S-X signifies a classification specification that allows for various types of alloying elements within the filler metal. The 'ER' stands for "electrode or rod," and the '70' indicates the minimum tensile strength of the weld metal in thousands of pounds per square inch (psi). The 'S' denotes that it is a solid wire and the suffix 'X' provides flexibility in the composition of the filler metal based on the specific needs of the welding application. This means that various chemical compositions can comply with the same classification, allowing the welder to choose an electrode that best fits the requirements of the welding application while still meeting the relevant codes and standards. This adaptability is significant in ensuring that the welding process achieves the desired mechanical properties and characteristics for different materials and conditions.