A Segment Test Validation Program for Reeling ECA of Partially Over-Matching CRA Girth Welds

Abstract A segment test validation program for reeling ECA of partially over-matching girth weld is presented. Conventional ECA references to the FAD concept and is limited to weld strength that at least even-matches the parent pipe material. For girth weld strength that is partially over-matching, reeling ECA validated in this paper is based on FEA and utilizes a tearing-low cycle fatigue model. Fatigue crack growth from low cycle fatigue in reeling cycles is calculated based on Paris’s law. If crack driving force due to straining of pipe in reeling is less than blunting limit, tearing is not initiated and does not contribute to flaw growth. If crack driving force exceeds blunting limit, then tearing is initiated and contributes to flaw growth. In the presented validation test program, segment specimens were machined from welded pipe pups composed of carbon steel parent pipe with 3mm thickness of CRA clad. Two welding procedures were selected in test program. A pre-testing ECA was performed based on the same reeling ECA by FEA method to determine the suitable initial notch size for segment tests. EDM notches with pre-determined sizes were fabricated in segment specimens, at the weld center line, from the external cap. Segment tests included five straining cycles, from zero strain to target strain. The maximum final notch height growth was measured using SEM. Post-testing ECA was then performed based on segment specimen setup measurements and segment and weld specific material testing data. The reeling ECA by FEA method is validated by the excellent agreement between the measured notch height growth and flaw growth calculated from post-testing ECA. In two welding procedures, a detailed comparison demonstrated a marginal over-prediction of flaw growth by the described reeling ECA method.