When engineers design a steel gas line, they designate a required pipe minimum yield strength, often called the specified minimum yield strength or SMYS. This is the level of stress the pipe must be capable of experiencing without permanent deformation. Manufacturers specify a SMYS for each type and grade of pipe they sell. By doing so, they certify that their pipe can, at a minimum, be safely subjected to the certified SMYS.
Minimum yield strength is a factor in determining the maximum allowable operating pressure or MAOP of a pipe. It also determines the allowable external loading. The SMYS for a specific pipe is impacted by the grade of steel used and how it was manufactured. Stronger steels are more expensive but can provide higher stress resistance.