Pipeline operators often deal with the large numbers of dents that require further consideration, and are required to prioritize these dents for further investigation and repair. Code guidance is clear on the relative severity of dents based on a depth or associated with welds, corrosion, gouging or cracking. It allows the pipeline operators to prioritize their dig lists and limit the number of “investigative digs” by omitting plain and shallow dents. However, the dent depth criterion has limitations, experiences learned in the past have shown that a dent prioritization based on depth alone, may still leave a significant number of dents in the pipeline which may pose a threat, particularly from local static strain and fatigue. In recent years, strain and fatigue analyses have been included in the assessment of severity of dents in order to better prioritize and effectively repair dents which represent a threat to the structural integrity of pipelines. However, strain analyses require tedious calculation of dent curvature at each data point from ILI reported dent profile. When a large numbers of dents require to be prioritized by strain severity, using this detail calculation is impractical. Therefore, a screening methodology is required to reliably identify candidate dents that require detail strain assessment. In this paper, an aspect-ratio based screening methodology is developed and applied to over 7,000 dents reported by an In-Line Inspection (ILI) caliper tool for a 265 miles long pipeline section. A total of 263 shallow dents which could have injurious strain level were identified and ranked for detail strain and fatigue calculations. In-ditch investigation of 20 dents with LaserScan profiling showed that the developed screening methodology provides an effective tool to capture all the dents with strain equal and 6.5% at 95% confidence level.
Today’s in-ditch laser scan inspection technology provides pipeline operators with relatively accurate 3D dent profile data. Some of the benefits of using laser scan data are to accurately calculate dent strain and quantify its severity. However, there are some concerns regarding the scan parameters used such as; scanner resolution settings, scan coverage over the dent, and its surrounding area as well as repeatability and reliability of scanned dent data that could affect the accuracy of the calculated dent strains. Therefore, it is important to understand how these parameters affect the accuracy of calculated dent strains, which could lead to either over- or under-estimating equivalent strains and result in unnecessary repairs or leaving critical dents in the pipeline without mitigation. The benefit of this study is to help the pipeline operators to reduce in-ditch dent inspection time without compromising on the accuracy of dent geometry and its strain. In this paper the effect of different scan resolutions on the calculated strain is studied first. Then, using high resolution, the effect of scan coverage on the dent strain is studied. In particular, the difference in the calculated strain among 60°, 90°, 180°, 360° scans coverage circumferentially. The repeatability of dent scan with two different resolutions is then evaluated with two real life dent samples. Finally, the findings from this study are summarized. This serves as the basis for developing an optimal procedure for dent laser scanning with acceptable level of scan parameters for a reliable strain assessment. The benefits and limitations of 3D laser scanning technology from this study are also presented.
Recent failures in seam weld pipe have raised concerns within the pipeline industry over the integrity of such welded pipe. Low-Frequency (LF) Electric Resistance Welded (ERW) pipe manufactured prior to 1970, in particular, can be susceptible to failures caused by hook cracks, lack of fusion and other planar defects should the weld area exhibit low toughness. Integrity management regulations and Pipeline operators are evaluating potential methodologies to address and mitigate the LF-ERW seam weld threat. A program has been initiated at Williams Northwest Pipeline GP (NWPGP) to address the integrity management of its pre-70s ERW pipelines. In this case study, as part of an overall integrity management program, a hydrostatic test and fatigue analysis based methodology for addressing the LF-ERW seam weld threat is presented. The methodology was applied to 15 pre-1970’s natural gas pipelines. The results and findings are summarized in terms of the integrity threat mitigation and maintenance strategies.
New technologies for in-ditch non-destructive evaluation were lately developed and are becoming of mainstream use in the evaluation of external corrosion features for both In-Line-Inspection performance evaluation and pipeline integrity assessment. However, doubt was cast about the reliability and repeatability of these new technologies (hardware and processing software) when compared with those used in the traditional external-corrosion in-ditch measurement and the reliability of the pipeline integrity assessment calculations (PBurst) embedded in their software when compared with industry-wide accepted calculation methods. Therefore, the primary objective of this study is to evaluate the variation and repeatability of the measurements produced by these new technologies in corrosion feature profiling and associated PBurst calculations. Two new 3D scanning systems were used for the evaluation of two pipe samples removed from service which contain complex external corrosion features in laboratory. The reliability of the 3D scanning system in measuring corrosion profiles was evaluated against traditional profile gage data. In addition, the associated burst pressures reported by the systems were compared with results obtained using industry-widely used calculation methods. Also, consistencies, errors and gaps in results were identified. In this paper, the approach used for this study is described first, the evaluation results are then presented and finally the findings and their implications are discussed.
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