Failure assessment of corroded pipes buried in partially saturated soils

Pipelines are used to provide variety of services in modern community and have grown rapidly in past few decades due to ever increasing needs of socio-economic aspects. Most of the water pipelines are buried in unsaturated soils where the behaviour of pipes is significantly different when compared to the pipes buried in dry/fully saturated soils. The internal and external loading act on buried pipes in such non-dry soil medium can lead towards undesirable failures as the current approach of pipe failure assessments overlook soil moisture effect (i.e. suction). The risk of pipe failure can be further triggered by aging effects as these pipelines have been laid sometime in the last century or earlier (i.e. highly corroded). As failures of water mains can have negative consequences on economy, society and environment in various ways, accurate prediction of remaining service life incorporating realistic soil and pipe condition can facilitate better asset management by water utilities while providing enhanced service to their customers. In this study, buried pipe response under operational loads (internal water pressure and external traffic loads) was investigated using a comprehensive large-scale pipe-soil testing methodology. Pipe deformations as well as soil stresses were evaluated in reference to a cast iron pipeline buried in low plasticity clay under different soil saturation levels. The results obtained from large scale experiments are compared with those from 3-dimensional finite element models that were calibrated against unsaturated soil sample tests conducted in the current study. The calibrated 3-dimensional (3-D) finite element model then formed a basis for detailed investigation of buried pipe behaviour under various loadings in unsaturated soil conditions. Results from large scale tests revealed that the backfill soil saturation can significantly affect the pipe deformation under internal and external loadings. The behaviour of buried pipe response in unsaturated soils was then simulated using 3-D Finite element (FE) method with advanced constitutive soil models. The models were first validated using experimental and reported field test data using calibrated soil properties. A series of 3-D FE analysis is used to develop an analytical model for predicting maximum stress in pipes (new and uniformly corroded condition) considering soil saturation effects. Results from the FE analysis reveal that the maximum pipe stress can be lowered by 10-80% depending on the partial saturation condition when compared to dry condition. The proposed formula shows a good agreement with the field data and FE results, so that the expression can be used in calculation of maximum pipe stress when they are buried under realistic (i.e. non-dry) soil conditions. Further studies were conducted to investigate the behaviour of corroded pipes subjected to internal and external loadings in partially saturated soil medium. Number of 3-D finite element studies was conducted using advanced soil constitutive models to analyse the behaviour of pipes with various corrosion patch geometries (corrosion patch depth, width and longitudinal length) which were identified on the basis of exhumed pipe sections in Australia. Results of the analyses were rigorously analysed by considering both stress intensity factor and stress concentration factor approach to determine the failure state of buried corroded pipes in unsaturated soils subjected to service loads. Study revealed that corrosion geometry (size & shape) and location can be highly significant in predicting the pipe failures in unsaturated soils. Analysis results were used to develop an analytical model on predicting the maximum pipe stress incorporating corrosion characteristics in addition to pipe and soil parameters. The model can be the backbone in failure assessment of buried pipes which are undergone inevitable corrosion during its service life

Observation of the Helium 7 Lambda hypernucleus by the (e,e'K+) reaction

An experiment with a newly developed high-resolution kaon spectrometer (HKS) and a scattered electron spectrometer with a novel configuration was performed in Hall C at Jefferson Lab (JLab). The ground state of a neutron-rich hypernucleus, He 7 Lambda, was observed for the first time with the (e,e'K+) reaction with an energy resolution of ~0.6 MeV. This resolution is the best reported to date for hypernuclear reaction spectroscopy. The he 7 Lambda binding energy supplies the last missing information of the A=7, T=1 hypernuclear iso-triplet, providing a new input for the charge symmetry breaking (CSB) effect of \Lambda N potential.Comment: 5 pages, 4 figures, submitted to PR

Multimodel assessment of the factors driving stratospheric ozone evolution over the 21st century

The evolution of stratospheric ozone from 1960 to 2100 is examined in simulations from 14 chemistry‐climate models, driven by prescribed levels of halogens and greenhouse gases. There is general agreement among the models that total column ozone reached a minimum around year 2000 at all latitudes, projected to be followed by an increase over the first half of the 21st century. In the second half of the 21st century, ozone is projected to continue increasing, level off, or even decrease depending on the latitude. Separation into partial columns above and below 20 hPa reveals that these latitudinal differences are almost completely caused by differences in the model projections of ozone in the lower stratosphere. At all latitudes, upper stratospheric ozone increases throughout the 21st century and is projected to return to 1960 levels well before the end of the century, although there is a spread among models in the dates that ozone returns to specific historical values. We find decreasing halogens and declining upper atmospheric temperatures, driven by increasing greenhouse gases, contribute almost equally to increases in upper stratospheric ozone. In the tropical lower stratosphere, an increase in upwelling causes a steady decrease in ozone through the 21st century, and total column ozone does not return to 1960 levels in most of the models. In contrast, lower stratospheric and total column ozone in middle and high latitudes increases during the 21st century, returning to 1960 levels well before the end of the century in most models

Multimodel projections of stratospheric ozone in the 21st century

Simulations from eleven coupled chemistry-climate models (CCMs) employing nearly identical forcings have been used to project the evolution of stratospheric ozone throughout the 21st century. The model-to-model agreement in projected temperature trends is good, and all CCMs predict continued, global mean cooling of the stratosphere over the next 5 decades, increasing from around 0.25 K/decade at 50 hPa to around 1 K/ decade at 1 hPa under the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES) A1B scenario. In general, the simulated ozone evolution is mainly determined by decreases in halogen concentrations and continued cooling of the global stratosphere due to increases in greenhouse gases (GHGs). Column ozone is projected to increase as stratospheric halogen concentrations return to 1980s levels. Because of ozone increases in the middle and upper stratosphere due to GHGinduced cooling, total ozone averaged over midlatitudes, outside the polar regions, and globally, is projected to increase to 1980 values between 2035 and 2050 and before lower stratospheric halogen amounts decrease to 1980 values. In the polar regions the CCMs simulate small temperature trends in the first and second half of the 21st century in midwinter. Differences in stratospheric inorganic chlorine (Cly) among the CCMs are key to diagnosing the intermodel differences in simulated ozone recovery, in particular in the Antarctic. It is found that there are substantial quantitative differences in the simulated Cly, with the October mean Antarctic Cly peak value varying from less than 2 ppb to over 3.5 ppb in the CCMs, and the date at which the Cly returns to 1980 values varying from before 2030 to after 2050. There is a similar variation in the timing of recovery of Antarctic springtime column ozone back to 1980 values. As most models underestimate peak Cly near 2000, ozone recovery in the Antarctic could occur even later, between 2060 and 2070. In the Arctic the column ozone increase in spring does not follow halogen decreases as closely as in the Antarctic, reaching 1980 values before Arctic halogen amounts decrease to 1980 values and before the Antarctic. None of the CCMs predict future large decreases in the Arctic column ozone. By 2100, total column ozone is projected to be substantially above 1980 values in all regions except in the tropics

Stress Prediction of Buried Pipes Subjected to Operational Loadings in Unsaturated Soils

Pipelines are used to provide variety of services in modern community and have grown rapidly in past few decades due to growing socio-economic requirements. Most of the water mains are buried in shallow depths where the soil is partially saturated with significant spatial and temporal variations. Even though the behavior of buried pipes in such unsaturated soil condition is substantially different when compared to dry or fully saturated soil, the effect of soil saturations is overlooked in the current pipe stress prediction methods, leading to unrealistic predictions of the pipe stresses. In this study, three-dimensional (3D) finite element (FE) method was employed with advanced constitutive soil models to analyze the behavior of pipes buried in unsaturated soil condition. Having validated the FE model using reported field test data, an analytical model was proposed to predict the maximum stress in buried pipes considering soil saturation effect using a series of 3D FE analyses. Results from the FE analyses reveal that the maximum pipe stress can be significantly different when soil is in unsaturated condition when compared to dry condition. The proposed formula shows a good agreement with the field data and FE results, so that the expression can be used in the prediction of maximum pipe stress when they are buried under realistic (i.e., nondry) soil conditions

Manufacturing polymer/carbon nanotube composite using a novel direct process

A direct process for manufacturing polymer carbon nanotube (CNT)-based composite yarns is reported. The new approach is based on a modified dry spinning method of CNT yarn and gives a high alignment of the CNT bundle structure in yarns. The aligned CNT structure was combined with a polymer resin and, after being stressed through the spinning process, the resin was cured and polymerized, with the CNT structure acting as reinforcement in the composite. Thus the present method obviates the need for special and complex treatments to align and disperse CNTs in a polymer matrix. The new process allows us to produce a polymer/CNT composite with properties that may satisfy various engineering specifications. The structure of the yarn was investigated using scanning electron microscopy coupled with a focused-ion-beam system. The tensile behavior was characterized using a dynamic mechanical analyzer. Fourier transform infrared spectrometry was also used to chemically analyze the presence of polymer on the composites. The process allows development of polymer/CNT-based composites with different mechanical properties suitable for a range of applications by using various resins

The <i>Escherichia coli</i> BolA Protein IbaG Forms a Histidine-Ligated [2Fe-2S]-Bridged Complex with Grx4

Two ubiquitous protein families have emerged as key players in iron metabolism, the CGFS-type monothiol glutaredoxins (Grxs) and the BolA proteins. Monothiol Grxs and BolA proteins form heterocomplexes that have been implicated in Fe–S cluster assembly and trafficking. The <i>Escherichia coli</i> genome encodes members of both of these proteins families, namely, the monothiol glutaredoxin Grx4 and two BolA family proteins, BolA and IbaG. Previous work has demonstrated that <i>E. coli</i> Grx4 and BolA interact as both apo and [2Fe-2S]-bridged heterodimers that are spectroscopically distinct from [2Fe-2S]-bridged Grx4 homodimers. However, the physical and functional interactions between Grx4 and IbaG are uncharacterized. Here we show that co-expression of Grx4 with IbaG yields a [2Fe-2S]-bridged Grx4–IbaG heterodimer. <i>In vitro</i> interaction studies indicate that IbaG binds the [2Fe-2S] Grx4 homodimer to form apo Grx4–IbaG heterodimer as well as the [2Fe-2S] Grx4–IbaG heterodimer, altering the cluster stability and coordination environment. Additionally, spectroscopic and mutagenesis studies provide evidence that IbaG ligates the Fe–S cluster via the conserved histidine that is present in all BolA proteins and by a second conserved histidine that is present in the H/C loop of two of the four classes of BolA proteins. These results suggest that IbaG may function in Fe–S cluster assembly and trafficking in <i>E. coli</i> as demonstrated for other BolA homologues that interact with monothiol Grxs