The use of COD and plastic instability in crack propagation and arrest in shells

The initiation, growth, and possible arrest of fracture in cylindrical shells containing initial defects are dealt with. For those defects which may be approximated by a part-through semi-elliptic surface crack which is sufficiently shallow so that part of the net ligament in the plane of the crack is still elastic, the existing flat plate solution is modified to take into account the shell curvature effect as well as the effect of the thickness and the small scale plastic deformations. The problem of large defects is then considered under the assumptions that the defect may be approximated by a relatively deep meridional part-through surface crack and the net ligament through the shell wall is fully yielded. The results given are based on an 8th order bending theory of shallow shells using a conventional plastic strip model to account for the plastic deformations around the crack border

Transportation of hazardous materials via pipeline. A historical overview

The transportation of hazardous materials via pipelines is often considered a safer alternative to other transportation modalities such as railway, road and ship. However, pipelines often cross industrial and highly populated areas, so that their failure can pose a significant risk to the surrounding environment and the exposed population: the possible release of flammable and/or toxic materials in such areas can generate catastrophic events with very severe consequences. A number of accidents have actually occurred in the past years, and even when no deaths or injured are reported, significant damages to the surrounding environment often occur. This suggests that, given the extremely wide extension of the network worldwide, and the very high amounts of transported materials, a careful analysis is still required. In addition, the construction of pipelines also involves the contribution of expertise from a range of technical areas. As a consequence, the occurrence of accidents and the impact of their consequences, depend on the combination of a large number of parameters. In the present paper, an analysis of data relative to pipelines transporting hazardous materials has been carried out, and the influence of specific issues connected with their type and operation, has been assessed

Effect of Repeated Loads on the Low Temperature Fracture Behavior of Notched and Welded Plates

The influence of repeated loadings on the susceptibility of weldments to fracture in a brittle manner is studied for an ABS-Class C steel. The test members have consisted primarily of 12, 24 and 36 in. wide notched-and- welded specimens that, at low temperatures, have been known to provide low-stress brittle fractures. The repeated loads or loading history are found to affect the fracture behavior of the weldments. In all but one instance the fracture stresses obtained for the notched-and welded wide plates were greater than the stresses to which the members had been subjected during the repeated loadings. Furthermore, the repeated loadings appeared to eliminate the two-stage fractures observed in some of the tests of as-welded specimens. This latter condition is in general desirable, but only if the fracture stress is raised to a high-stress level.Bureau of Ships - Department of the Navy Contract NObs 88283 Proj ect SR-149 Ship Structure Committe

Low‐income mothers’ feeding goals predict observed home mealtime and child feeding practices

BackgroundMothers’ goals are important for health behavior change, and engagement in child obesity interventions. It is unknown if maternal feeding goals are associated with observed home mealtime or feeding practices. The objective of this study was to examine the association of four common feeding goals (restrict junk food, promote fruit or vegetable intake, promote autonomy in eating and prevent obesity) with mothers’ observed home mealtime and feeding practices.MethodsLow‐income mothers (N = 265) of children (mean child age 70.8 months) participated in a semi‐structured interview about child feeding. A coding scheme was developed and reliably applied to identify mothers’ feeding goals from transcripts. Mothers’ observed home mealtime and feeding practices were reliably coded from home mealtimes and a laboratory eating protocol. Mothers completed a questionnaire and reported demographics. Participant weights and heights were obtained. Regression models were used to test the association of each feeding goal with observed maternal practices, controlling for covariates.ResultsThe goal of restricting junk food was associated with the child always eating at a table (OR 2.87, 95% CI (1.39–5.96) p = 0.005), but not with the mother restricting junk food. The goal of promoting fruit or vegetable intake was associated with observationally promoting vegetables (OR 1.41, 95% CI (1.09–1.84), p = 0.01). The goals of promoting autonomy and preventing obesity were not associated with any observed maternal home mealtime or feeding practices.ConclusionsWhile mothers’ goals to restrict junk food and promote fruit or vegetable intake were associated with observed home mealtime and feeding practices, promoting autonomy and preventing obesity were not. Increased understanding of why low‐income mothers may not translate certain feeding goals into practices may inform childhood obesity interventions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134417/1/cch12396.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134417/2/cch12396_am.pd

Предсказательное техническое обслуживание трубопроводов на основе экспресс-оценки степени опасности дефектов

The paper describes a tested and proven practical methodology of predictive maintenance of pipelines with two types of defects — “loss of metal” and “pipe wall lamination”, detected by the ILI technology. The laminations are caused by the steel and pipe manufacturing technology, and may also appear during pipeline operation. The laminations can be further classified as metallurgical laminations, hydrogen induced cracking (HIC), non-metallic inclusions, and such. For the defects of the “pipe wall lamination” type the assessment of their level of danger is conducted only after they are converted to surface “loss of metal” type defects. The paper presents models on how to adequately convert the “pipe wall lamination” type of defects to the “loss of metal” type defects. A methodology is described on how to rank the defects according to their level of danger (with respect to the rupture type of failure), and how to perform the probabilistic assessment of the pipeline residual life. In order to account for “leak” and “rupture” types of failure, a computer based express assessment is developed of the level of severity of each defect. This defect assessment is based on graphs, which restrict the permissible sizes of defects and allow making operative decisions as to which maintenance measures should be taken, regarding pipeline segment as a whole. The pipeline defects are ranked according to their potential danger, which depends on their location on the graphs. The probabilistic assessment of the residual pipeline life is performed taking into account the stochastic nature of defect growth. In order to achieve this, the maximal γ-percentile corrosion rate is defined over all detected defects. As the main decision parameter the gamma-percent operating time is chosen. It is characterized by: the safe operating time, and the percentile probability that during this time the pipeline limit state will not be reached. A detailed example of implementation of the described methodology to a real product pipeline segment operating in a severe corrosion environment is given. The economical effect of the implementation is outlined.Статья описывает проверенную практическую методологию предсказательного технического обслуживания (мейнтенанса) трубопроводов с двумя типами дефектов — «потеря металла» и «несплошность металла стенки трубы — расслоение», обнаруженных с помощью технологии внутритрубной диагностики (ВТД). Несплошности металла стенки трубы возникают в процессе сталеплавильного и прокатного производства, а также в процессе эксплуатации. К этим дефектам относятся: металлургические расслоения, водородные расслоения, закаты и плотные неметаллические включения. Для дефектов, относящихся к этому типу, оценка степени опасности производится только после приведения дефекта к поверхностному дефекту типа «потеря металла». В работе представлены модели приведения несплошности металла к поверхностным дефектам типа «потеря металла». Методика описывает способ ранжировки дефектов по уровню их опасности (относительно отказа типа «разрыв») и вероятностную оценку остаточного ресурса трубопровода. Для учета обоих сценариев отказа «течь» и «разрыв» строится компьютерная экспресс-оценка степени опасности дефектных участков трубопровода путем построения графиков, ограничивающих размеры дефектов трубопровода и позволяющих принимать оперативные решения о мерах по дальнейшей эксплуатации трубопровода. Осуществляется классификация потенциальной опасности дефектов трубопровода в зависимости от области их расположения на графиках. Расчет вероятностной оценки прогнозирования остаточного ресурса трубопровода проведен с учетом вероятностного подрастания дефектов. Для этого определяется максимальная, с заданной вероятностью γ, скорость коррозии по всем дефектам. В качестве основного показателя определяется гамма-процентный ресурс, задаваемый двумя численными значениями: наработкой и выраженной в процентах вероятностью того, что в течение этой наработки предельное состояние не будет достигнуто. Данная работа описывает пример применения описанной методологии к наземному участку трубопровода, транспортирующему сильнодействующий коррозионный конденсат. Также обсуждается экономический эффект от реализации представленной методологии

Особливості зварювальних робіт на діючих газопроводах

Описано технологічні особливості зварювальних робіт на газопроводах під тиском газу. В рамках теорії теплопровідності при зварюванні сформульовано вихідні положення для постановки крайової задачі. Зварювальна дуга моделюється як розподілене джерело тепла з коефіцієнтом зосередженості k і плямою нагріву dн. Наведено залежність параметрів дуги від зварювального струму. Описано порядок розрахунку коефіцієнта теплообміну на внутрішній поверхні труби за наявності в ній потоку газу, наведено теплофізичні дані газу. Побудовано математичну модель зварювання кругового шва на трубі. Наведено аналітичний розв’язок задачі. Виведено співвідношення розподілу теплової потужності дуги при зварюванні кутових швів. На прикладі розрахунку температурних полів при зварюванні кругових швів, відмічено асиметрію процесу поширення тепла в ділянці металу усередині кругового шва і за його межами. Максимуми температур на внутрішній поверхні труб послідовно зміщуються в сторону центру обертання. Процес нагрівання внутрішньої поверхні труби в зоні зварювання продовжується і після завершення кругового шва. Відзначено охолоджувальну дію потоку газу на формування температурного поля. Намічено шляхи удосконалення математичної моделі для розрахунку процесів розподілу тепла при зварюванні кругових швів.The technical specifications are described while conducting the welding works on gas-pipelines under gas pressure. In accordance with the theory of welding heat conduction the assumptions for boundary-value task setting is formulated. The welding arc is modeled as a distributed heat source with concentration coefficient k and heating spot dн. The dependence of arc parameters from the welding current is shown. The calculation of heat transfer coefficient on the inner surface of the pipe with the gas flow is also described; the thermo-physical gas data are presented. A mathematical model of circular welding seam on the pipe is developed. The analytical solution to the problem is offered. The correlation of arc heat capacity distribution under fillet welts welding is calculated. By the example of the temperature fields calculation under circular joints welding, some asymmetry of the heat distribution process in the metal area inside the circular weld and beyond is detected. Temperatures maximum on the inner surface of the pipe is consistently shifted towards the center of rotation. The heating process on inner surface of pipes within the welding zone continues after the circular seam process is over. Cooling effect of the gas flow on the temperature field formation is observed. Some ways to improve the mathematical model of distributed heat of circular welding seam on the pipe are suggested

Quantification of Uncertainties in Inline Inspection Data for Metal-loss Corrosion on Energy Pipelines and Implications for Reliability Analysis

One of the major threats to the oil and gas transmission pipeline integrity is metal-loss corrosion. Pipeline operators periodically inspect the size of the metal loss corrosion in a pipeline using in-line inspection (ILI) tools to avoid pipe failure which may lead to severe consequences. To predict pipe failure efficiently, reliability-based corrosion management program is gaining popularity as it effectively incorporates all the uncertainties involved in the pipe failure prediction. The focus of the research reported in this thesis is to investigate the unaddressed issues in the reliability-based corrosion assessment to assist in better predicting pipe failure. First, a methodology is proposed to facilitate the use of RSTRENG (Remaining Strength of Corroded Pipe) and CSA (Canadian standards association) burst pressure capacity models in reliability-based failure prediction of pipelines. Use of RSTRENG and CSA models require the detail geometric information of a corrosion defect, which may not be available in the ILI reports. To facilitate the use of CSA and RSTRENG models in the reliability analysis, probabilistic characteristics of parameters that relate the detailed defect geometry to its simplified characterizing parameters was derived by using the high-resolution geometric data for a large set of external metal-loss corrosion defects identified on an in-service pipeline in Alberta, Canada. Next, a complete framework is proposed to quantify the measurement error associated with the ILI measured corrosion defect length, effective length, and effective depth of oil and gas pipelines. A relatively large set of ILI-reported and field-measured defect data is collected from different in-service pipelines in Canada and used to develop the measurement error models. The proposed measurement error models associated with the ILI reported corrosion defect length, effective length, and effective depth is the weighted average of the measurement errors of the corresponding Type I and Type II defects and the weighted factor is the likelihood of ILI reported corrosion defect being a Type I defect (without cluster error) or a Type II defect (with clustering error). A log-logistic model is proposed to quantify the weighted factor. The application of the proposed measurement error models is demonstrated by evaluating probability of failure of a real corroded pipe joint through system reliability analysis