What does the 'X' in the electric identification ER70S-X indicate?

The 'X' in the electric identification ER70S-X signifies a specific classification designation within the filler metal's standard. It indicates that the filler metal has special attributes or characteristics that may enhance its performance or suitability for specific applications. In this context, the 'X' typically denotes different chemical compositions or mechanical properties that vary according to the requirements outlined in the ANSI/AWS A5.18 specification.

The use of 'X' allows for differentiation among various wire types made for similar applications but designed to work under diverse conditions or with particular requirements in mind. This classification is crucial for welders to select the correct material based on the specific needs of their welding projects, such as strength, ductility, or resistance to certain environmental factors. Understanding this designation helps ensure that the filler metal will perform adequately in the intended application, thereby contributing to the overall integrity of the welded structure.