Offshore piping systems may be subject to low temperatures due to operation related scenarios and are cause for brittle fracture concern. The analyses included in this work consider probable events leading to low temperature conditions such as auto-refrigeration. In such circumstances, brittle fracture assessments of piping are typically carried out using API 579-1/ASME FFS-1, latest referred as API 579, procedures. The assessment of piping systems are in many cases very involved, requiring extended piping system information followed by stress analysis and MAT calculations depending on the material type, thickness of the piping analyzed, and stress levels. In addition, the component-by-component assessment approach recommended in API 579 leads to tedious calculations.
In this paper, approaches used for static and dynamic low temperature scenarios are presented. Static cases involve constant pressures and temperatures. Dynamic cases involve varying pressures and temperatures as the low temperature events unfold (e.g., blowdown of a valve or a vessel). Dynamic cases warrant the requirement of a safe operating envelope or MAT curve similar to those developed for pressure vessels. Case studies involving the influence of the extent of the system analyzed and the restraint conditions on the results are also presented. In addition, the importance of separately assessing the rated components such as flanges and valves away from the stress analysis is discussed. Based on the assessments carried out, a discussion on the toughness rules defined in ASME Section VIII Divisions 1, 2, and the original piping code of construction is provided.