Equation which, based on production measurements or specifications, provides a performance property useful in design calculations. NOTE A design equation can be defined by applying reasonable extremes to the variables in a limit state equation to arrive at a conservative value of expected performance. When statistically derived, the design equation corresponds to a defined lower percentile of the resistance probability distribution curve.
Source: API TR 5C3, Technical Report on Equations and Calculations for Casing, Tubing, and Line Pipe Used as Casing or Tubing; and Performance Properties Tables for Casing and Tubing, Upstream Segment, First Edition, December 2008. Global Standards