When “ISO” is selected in FTOPT2 (columns 51–53), SACS performs the fatigue assessment in accordance with the ISO fatigue framework (ISO 19902).
However, ISO 19902 does not provide a closed-form equation for calculating the in-line Stress Concentration Factor (SCF) for tubular-to-tubular girth welds.
Therefore, SACS evaluates the in-line SCF using an internally implemented industry-based parametric equation that accounts for parameters such as diameter ratio, thickness ratio, and eccentricity of the connected tubulars.
This formulation originates from legacy offshore industry fatigue guidance that has historically been adopted in offshore structural design practice and incorporated into early SACS implementations.
Summary:
- ISO 19902 does not publish a formula number for calculating in-line SCF for tubular girth welds.
- SACS applies an established industry parametric SCF equation embedded within the software.
- Selecting “ISO” in FTOPT2 governs the fatigue assessment methodology, but does not change the girth weld SCF formulation.
See also