This calculation can be used to assess resistance to internal pressure for piping not subject to significant external loads. This calculation takes a single minimum thickness reading along with flaw dimensions. As it does not apply to components operating in the creep range, the B31 'W' factor does not apply. Note: Equation 5.13 of API 579 (2016) is in error - we have inversed the weld efficiency fraction given in that formula. Calculation should be carried out by a qualified mechanical engineer.