Piping

All the elements of piping are under regulations for manufacturing, fabrication, building and construction. These are the Codes, standards, Manufacturers specifications , recommended practices, and specifications. Every industry develops codes and standards for specific applications. In addition, every country, state or province, or community,  establishes minimum rules in their jurisdiction.

Requirements are mandatory only if said Code is law in your country.  If not, Code serves as generally accepted guidelines for design, fabrication, construction and installation.  An example is ASME BPVC Code.

ASME - American Society of Mechanical Engineers 

ASME was founded in 1880 to provide a setting for engineers to discuss the concerns brought by the rise of industrialization and mechanization.

Having established the Boiler Testing Code in 1884, ASME formed a Boiler Code Committee in 1911 that led to the Boiler & Pressure Vessel Code (BPVC) being published in 1915. The BPVC was later incorporated into laws in most US states and territories and Canadian provinces.