BEST PRACTICE IN PIPELINE DEFECT ASSESSMENT
Defects in pipelines can be introduced during manufacturing (e.g. laminations), transportation (e.g. fatigue cracking), fabrication (e.g. weld defects) and installation (e.g. dents), and can occur both due to deterioration (e.g. corrosion) and due to external interference (e.g. gouges and dents). To ensure the integrity of the pipeline, operators must be able to both detect and assess the significance of pipeline defects. Furthermore, the importance of accurate engineering models, for which the model uncertainty has been quantified, is important when applying risk-based (structural reliability) methods to pipelines. The past 40 years has seen the development of 'fitnessfor-purpose' methods for assessing the significance of pipeline defects. However, there is no definitive guidance that draws together all of the assessment techniques, or assesses each method against the published test data, or recommends best practice in their application. This paper describes the findings of a recent literature review and defines the objectives of the next phase of a Joint Industry Project which is being sponsored by thirteen international oil and gas companies (BG Technology, BP, CSM, DNV, EMC, Gaz de France, Health and Safety Executive, MOL, PII, SNAM, Statoil, Toho Gas and Total Oil Marine). The deliverable will be a Pipeline Defect Assessment Manual, which will provide the best available techniques for the assessment of pipeline defects.
Introduction and background to DNV RP-F101 Corroded Pipelines
In this paper an introduction and background to the new DNV RP-F101 Corroded Pipelines is given. The RP (Recommended Practice) gives recommendations for the assessment of corroded pipelines subject to internal pressure, and internal pressure combined with longitudinal compressive stresses and covers single defects, interacting defects and complex shaped defects. The RP is a result of co-operation between BG Technology and DNV. The results from their respective joint industry projects have been merged, and form the technical basis for RP-F101. Several oil companies and regulating authorities have sponsored the development of the RP. RP-F101 describes two alternative approaches with different safety philosophy for the assessment of corrosion in pipelines. The first approach is in accordance with the safety philosophy adopted in the DNV Offshore Pipeline Standard (DNV OS-F101). Uncertainties associated with the sizing of the defect and the material properties are specifically considered in determination of the allowable operating pressure. The second approach is based on the allowable stress design format, where the allowable operating pressure is determined from the capacity and multiplied with a single usage factor based on the original design factor. In this paper, focus is on the single defect in the first approach, being in accordance to the safety philosophy adopted in the DNV Offshore Standard OS-F101. The burst capacity equation is described, and the acceptance equation, the calibration of partial safety factors, and an example are given.
Magnetic properties of Lu2Fe17 crystals
Abstract We present the results of crystal structure and magnetization studies of three single crystals grown from melts of different nominal compositions in the vicinity of the Lu2Fe17 stoichiometry. The ferromagnetic state of the crystals is strongly dependent on the real sample composition and the local atomic ordering. A drastic difference is observed in the behaviour of the ferro–antiferromagnetic transition, even in crystals for which almost identical composition and crystal parameters were determined by microprobe and X-ray analysis.