Two wrinkle-like features were discovered in two girth welds of an onshore, horizontal directionally drilled (HDD) 42-inch OD x 0.438-inch wall thickness, Grade X70 pipeline using a high resolution in-line inspection (ILI) tool. The HDD pipeline was buried at a depth of approximately 30 feet. The data from the ILI tool revealed a wrinkle feature encompassing the full circumference of the pipeline, in contrast to a traditional wrinkle, which typically encompasses a third to half the circumference. The high resolution ILI data was then used to generate a finite element model of the pipeline sections of interest to calculate stress concentration factors (SCFs) under combined loading conditions representative of buried transmission gas pipelines. The FEA results showed that stress concentration factors ranging from 1.03 to 7.5 existed in the pipeline section under certain loading conditions, which warranted additional assessment of the features.
In addition to the numerical analyses, full-scale experimental efforts were conducted to fabricate anomalies having characteristics similar to the ones found in the field on pipe sections of the same characteristics as those of the HDD pipeline. The wrinkle anomalies were generated by applying external compression loads in the lab, followed by pressure cycling representative of a 20 year service life, and burst testing.
This paper addresses these pipeline anomalies using both numerical and experimental methods, following the guidelines of the API-579-ASME-FFS-1 standard, which is used to evaluate if affected equipment is fit for continued service. In addition to the steps encompassed by API-579-ASME-FFS-1, elements of the Engineering Based Integrity Management Program, or EB-IMP® (IPC2008-64492), were also utilized in order to determine the operability of the pipeline, and the expected factors of safety relative to static strength, fatigue and crack propagation.
The conclusion from this study is that the wrinkle-like features by themselves (i.e., without cracks) do not pose an immediate threat to the actual pipeline considering that the testing survived 20 years of simulated cyclic pressure. However, the Sample did not survive the pressure ramp to 72% SMYS after pressure cycling, and it leaked via a circumferentially-oriented through-wall crack at 69% SMYS. This ultimately led to an appropriately scheduled replacement of the pipe section in question.
Capeto, J., Bedoya, J. J., Alexander, C. R., “Numerical and Experimental Assessment of Girth Welds Interacting with Wrinkle Anomalies,” Proceedings of the Rio Pipeline Conference & Exhibition 2017, Rio de Janeiro, Brazil, October 24 – 26, 2017.
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