Extra Strong

Extra Strong, abbreviated as XS, also described as extra heavy (XH), is a term used to classify a certain category of pipe thickness and pressure ratings in the context of pipe sizing and specifications.  The term is often associated with steel pipe used in industrial applications, particularly in the petrochemical, oil and gas, and process industries.  It's a designation that indicates that the pipe is thicker and can handle higher pressure compared to standard pipes.

In the United States, pipe dimensions and specifications are governed by standards established by organizations such as the American National Standards Institute (ANSI) and the American Society of Mechanical Engineers (ASME).  These standards provide guidelines for pipe materials, dimensions, wall thickness, pressure ratings, and more.

In the ASME B36.10 and ASME B36.19 standards, which deal with steel pipe sizes and stainless steel pipe sizes respectively, you'll find pipe schedules.  Each pipe schedule is associated with a specific wall thickness and pressure rating.  Extra Strong (XS) is a designation for a thicker pipe wall compared to the standard wall thicknesses.  The exact dimensions, wall thickness, and pressure ratings for XS pipes can vary depending on the material, industry standards, and specific application.

It's important to consult relevant standards and engineering specifications to determine the appropriate pipe schedule and thickness for your specific needs.  In some industries, the use of XS pipes might be necessary to accommodate higher pressures, corrosive environments, or other specific requirements.