Corrosion and erosion-corrosion behaviour of lean duplex stainless steels in marine and oilfield environments

Lean duplex stainless steels are becoming attractive for applications in oilfield and marine environments due to their economic advantages, very good mechanical properties and relatively good corrosion resistance. One such application is in the production of the carcass of flexible pipes. However, materials selection for such oilfield applications becomes more complex as a result of the interactions between corrosion and erosion. Much effort has been directed towards the study of erosion-corrosion behaviour of carbon steels and other passive alloys. However, the subject of erosion-corrosion of lean duplex stainless steels is still rarely reported. Moreover, data available in the literature on the localized corrosion resistance of the lean duplex stainless steels are limited to alkaline environments. Efforts have been made in this thesis to add to the existing data and to the understanding of the subject of localized corrosion and erosion-corrosion resistance of lean duplex stainless steels UNS S32101, UNS S32304 and UNS S82441 in oilfield environments. The lean duplex alloy UNS S32101 has been studied in detail because of its combination of high strength and good corrosion resistance. This research also compared the corrosion and erosion-corrosion resistance of lean duplex stainless steels with standard austenitic stainless steels UNS S30403 and UNS S31603 as well as duplex stainless steel alloy UNS S32205. Aerated 3.5% NaCl and synthesized CO2-saturated oilfield brines were considered as the corrosion media. Extreme erosion-corrosion conditions were simulated to design for severe environments often encountered in sand-containing oilfield pipeline systems. Breakdown potentials, under static conditions, were found to be more positive in the aerated 3.5% NaCl than the CO2-saturated oilfield brine solution. Also, lean duplex stainless steels and standard austenitic stainless steels exhibited similar resistance in both environments. X-ray Photoelectron Spectroscopy (XPS) analysis of the passive film indicated higher chloride incorporation in the CO2-saturated oilfield brine. This, in addition to lower pH of the CO2-saturated oilfield brine appeared to be the reason why the breakdown potential was more negative in this environment. Erosion-corrosion results showed that lean duplex stainless steels, UNS S32101 and UNS S32304, have higher resistance to pure-erosion damage than UNS S30403 and UNS S32205; better erosion-corrosion resistance than UNS S30403 austenitic stainless steel; and equivalent erosion-corrosion resistance to UNS S32205 standard duplex stainless steel. There was also a correlation between the erosion-corrosion resistance of the alloys and the sub-surface crystallography, microstructure and phase transformation. This, together with repassivation kinetics of the passive film, may be used to explain the erosion-corrosion behaviour of UNS S32101 and UNS S30403 in the oilfield slurry

Associations between Academic Stressors, Reaction to Stress, Coping Strategies and Musculoskeletal Disorders among College Students

Background: The adverse health effects of stress are enormous, and vary among people, probably because of differences in how stress is appraised and the strategies individuals use to cope with it. This study assessed the association between academic stress and musculoskeletal disorders  (MSDs) among 1365 undergraduates.Methods: This was a cross-sectional study conducted in a Nigerian university at the beginning of the 2010/2011 academic session with the same group of participants. The Life Stress Assessment Inventory, Coping Strategies Questionnaire, and Short Musculoskeletal Function Assessment were administered as tools of data gathering.Results: Students’ stress level and associated MSDs were higher during the examination period than the pre-examination periods. Stressors were significantly associated with increased risk of MSDs in both sexes were those related to changes (odds ratio (OR) = 1.7, p = 0.002) and pressures (OR = 2.09, p = 0.001). Emotional and physiological reactions to stress were significantly associated with MSDs in both sexes, with higher odds for MSDs in females, whereas cognitive and behavioral reactions showed higher odds (though non-significant) in males. The risk of MSDs was higher in respondents who adopted avoidance and religious coping strategies compared with those who adopted active practical and distracting coping strategies.Conclusions: Stress among students could be significantly associated with MSDs depending on individuals’ demographics, stressors, reactions to stress, and coping methods. Interventions to reduce stress-induced MSDs among students should consider these factors among others.Keywords: Academic stressors, Coping strategies, Musculoskeletal disorder

Les habiletés manifestées par des éducateurs d'adultes dans l'adaptation d'une activité globale d'apprentissage

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal

Flow-induced corrosion behaviour of low alloy steel in the presence of mono-ethylene glycol

Abstract: The flow-induced corrosion behaviour of welded low ally steel in 1 wt. % NaCl environment containing monoethylene glycol at 0oC and 25 oC respectively, was investigated. A modified submerged impinging jet rig was adopted to simulate the low temperature environment. Varying speeds between 1 and 3 m/s were used to study the degradation mechanism of the welded steel. Also, the ratio of MEG: 1 wt. % NaCl was kept at 1:4 for the MEG/NaCl solution. Static corrosion condition was also studied and compared with the flowing conditions. Results indicated that the alloy degraded with observable weight loss in pure 1wt. % NaCl at both temperatures whereas there was very negligible weight loss in all the samples in MEG/NaCl solution

Fabrication of forced air cool austempered ductile iron and exploring its corrosion behaviour in a simulated mine water

Abstract: The production of austempered ductile iron (ADI) with uniform microstructure and properties is constrained by the austempering process vis-à-vis the quenching medium. This is as a result of the stringent operating parameters with costly facilities. This limitation has restricted the application of ADI, despite its inherent mechanical and chemical properties. An emerging technology of overcoming this limitation is by austempering with force air cooling equipment, which is accessible, available and cost-efficient. This work characterizes the behaviour of the forced air cool ADI in simulated mine water due to the strategic importance of the mining industry in the global economy. The study establishes the influence of sample section thickness on the corrosion performance. The sample’s thickness were 5, 15, and 20 mm. Electrochemical experiments were performed on the forced air cool ADI at atmospheric pressure and room temperature with method such as open circuit potential (OCP). The post-corrosion analyses were performed using X-ray diffractometry (XRD) and field emission scanning electron microscopy (FESEM). The research highlighted that small section thickness has a more favourable performance compared with larger section. Consideration is also accorded to the capability of the ADI in the studied environment

Erosion-corrosion behaviour of dual phase medium carbon steel using a designed slurry pot

Abstract: A slurry pot has been designed, fabricated and evaluated for erosion-corrosion investigations. A variable voltage controller was used to vary the input voltage into the one-horse-power motor that controls the slurry pot. The actual speed of the slurry pot shaft was also calibrated using a non-contact digital tachometer. Voltages of 100 and 200 V resulted in rotational speeds of 1100 and 2100 rpm, respectively employed for the subsequent erosion-corrosion tests. Erosion-corrosion of a dual-phase carbon steel was investigated with the aid of the slurry pot in aerated 3.5 wt.% NaCl environments. The sample was normalised at 850 oC and then cooled in air to room temperature. Prior to the test, the normalised samples were heated to 700, 725, 750, 775, 800 and 825 oC, respectively and quenched in oil. Erosion-corrosion rates of between 0.027 to 1.26 g/cm2.hr at 1100 rpm and 0.57 to 1.9 g/cm2.hr at 2100 rpm were recorded. It was also observed that as hardness increased there was reduction in weight loss of the heat treated alloy

REGIONAL CLIMATE MODEL PERFORMANCE AND PREDICTION oF SEASONAL RAINFALL AND SURFACE TEMPERATURE oF UGANDA

Knowledge about future climate provides valuable insights into how the challenges posed by climate change and variability can be addressed. This study assessed the skill of the United Kingdom (UK) Regional Climate Model (RCM) PRECIS (Providing REgional Climates for Impacts Studies) in simulating rainfall and temperature over Uganda and also assess future impacts of climate when forced by an ensemble of two Global Climate Models (GCMs) for the period 2070-2100. Results show that the models captured fairly well the large scale flow signals influencing rainfall and temperature patterns over Uganda. Rainfall and temperature patterns were better resolved by the RCM than the GCMs. The rainfall and temperature patterns differed among the three seasons. Rainy season March to May (MAM) is likely to experience increment in both surface temperature (0.9\ub0 C) and rainfall (0.2 mm day-1). For September to october (SON) rainy season, an opposite trend in the two climate parameters, temperature and rainfall, will be registered with the former increasing by 0.9 \ub0C and the latter dropping by 0.7 mm day-1. For the dry season, June to August (JJA), both temperature and rainfall are projected to decrease by 0.3 \ub0 C and 0.4 mm day-1, respectively.La connaissance du climat de demain fournit un aper\ue7u sur la mani\ue8re dont les d\ue9fis pos\ue9s peuvent \ueatre adress\ue9s. Cette \ue9tude a \ue9valu\ue9 la comp\ue9tence du Mod\ue8le Climatique R\ue9gional (RCM) PRECIS du Royaume Uni (fournissant des climats r\ue9gionaux pour des \ue9tudes d\u2019impacts) dans la simulation de la pluviom\ue9trie et la temp\ue9rature en ouganda et, d\u2019autre part, \ue9tudier les impacts des climats une fois forc\ue9e par un ensemble de deux Mod\ue8les Climatiques \ue0 l\u2019\ue9chelle de l\u2019Univers (GCMs) pour les p\ue9riodes 2070-2100. Les r\ue9sultats montrent que les mod\ue8les ont raisonnablement saisi une large \ue9chelle du flow des signaux qui influencent la tendance de la pluviom\ue9trie et la temp\ue9rature en ouganda. Les tendances de la pluviom\ue9trie et la temp\ue9rature \ue9taient mieux d\ue9termin\ue9es par RCM que GCMs. Les tendances de la pluviom\ue9trie et la temp\ue9rature diff\ue9raient au cours des trois saisons. La saison pluvieuse Mars \ue0 Mai (MAM) connaitra probablement une augmentation de la temp\ue9rature (0.9 \ub0C) et de la pluviom\ue9trie (0.2 mm jr-1). Pour la saison de pluie de Septembre \ue0 octobre, une tendance contraire dans les deux param\ue8tres climatiques sera enregistr\ue9e avec la m\ueame augmentation de 0.9 \ub0C et une diminution de 0.7 mm jr-1de pluie. Pour la saison s\ue8che de Juin \ue0 Ao\ufbt (JJA), les projections montrent une diminution de la temp\ue9rature et de la pluie de 0.3 \ub0C et 0.4 mm jr-1, respectivement

VEGETATION BIOMASS PREDICTION IN THE CATTLE CORRIDOR OF UGANDA

Pastoralists in Sub-Saharan Africa face complex problems notably frequent and severe droughts. This study was conducted in the cattle corridor of Uganda, a largely semiarid area to estimate the likely vegetative biomass production under the 2O71-2100 projected rainfall conditions. Spatio-temporal pattern of vegetative biomass production were determined by analysis of the seasonal variation of Normalised Difference Vegetation Index (NDVI) for 10 years from 2001-2010. A biomass relationship was established between the NDVI and the Standardised Precipitation Index (SPI); and used to project the period 2071-2100 NDVI using downscaled rainfall for the cattle corridor. A change trajectory performed on the annual means revealed the highest increase in vegetation in 2008 (0.031) and decrease in 2009 (-0.022). The SPI revealed two main droughts that were established to have occurred in the years of 2004 - 2005 and 2008-2009. The wettest year was 2003 and corresponded with the increase in NDVI. A strong positive correlation of rainfall and vegetation was established (r=0.99). Precipitation has influenced vegetative biomass in the cattle corridor as there is a positive correlation between precipitation and the vegetative biomass production. Secondly, vegetation is likely to be concentrated in areas that will have high precipitation in 2070-2100, such as Luwero and the districts south of it of the cattle corridor compared to those in the north of the cattle corridor of Uganda.Les \ue9leveurs en Afrique Sub-saharienne se confrontent aux probl\ue8mes complexes notamment les s\ue9cheresses fr\ue9quentes et plus graves. Cette \ue9tude a \ue9t\ue9 men\ue9e dans le corridor du b\ue9tail de l\u2019ouganda, une r\ue9gion largement semi-aride pour estimer la production susceptible de biomasse v\ue9g\ue9tale sous les conditions pluviom\ue9triques projet\ue9es en 2071-2100. Le mod\ue8le spatio-temporel de production de biomasse v\ue9g\ue9tale a \ue9t\ue9 d\ue9termin\ue9 par l\u2019analyse de la variation saisonni\ue8re de l\u2019Indice de V\ue9g\ue9tation par Diff\ue9rence Normalis\ue9e (NDVI) pendant 10 ans dans l\u2019intervalle de temps 2001-2010. Une relation de biomasse a \ue9t\ue9 \ue9tablie entre l\u2019indice de v\ue9g\ue9tation NDVI et l\u2019indice de pr\ue9cipitations normalis\ue9 (SPI), et elle est utilis\ue9e pour projeter le NDVI de la p\ue9riode 2071-2100 en utilisant les pr\ue9cipitations \ue0 \ue9chelle r\ue9duite pour le corridor du b\ue9tail. Une trajectoire de changement effectu\ue9e sur les moyennes annuelles a r\ue9v\ue9l\ue9 la plus forte augmentation de la v\ue9g\ue9tation en 2008 (0.031) et une diminution en 2009 (-0.022). Le SPI a r\ue9v\ue9l\ue9 deux principales s\ue9cheresses qui ont \ue9t\ue9 \ue9tablies pour avoir eu lieu dans les ann\ue9es 2004 - 2005 et 2008-2009. L\u2019ann\ue9e la plus humide \ue9tait 2OO3 et correspondait \ue0 une augmentation de l\u2019indice de v\ue9g\ue9tation NDVI. Une forte corr\ue9lation positive entre les pr\ue9cipitations et la v\ue9g\ue9tation a \ue9t\ue9 \ue9tablie (r = 0.99). Les pr\ue9cipitations ont influenc\ue9 la biomasse v\ue9g\ue9tale dans le corridor du b\ue9tail, car il existe une corr\ue9lation positive entre les pr\ue9cipitations et la production de la biomasse v\ue9g\ue9tale. Deuxi\ue8mement, la v\ue9g\ue9tation est susceptible d\u2019\ueatre concentr\ue9e dans les zones qui auront de fortes pr\ue9cipitations en 2070-2100, comme Luwero et les districts du Sud de celui-ci du corridor du b\ue9tail par rapport \ue0 ceux dans le nord du corridor du b\ue9tail de l\u2019ouganda

Wear behaviour of cast aluminium silicon (Al-Si) alloy in dot 4 brake fluid

Abstract : The frictional sliding behaviour of cast Al-Si alloy was investigated with and without DOT 4 hydraulic brake fluid lubrication/environments. Cast Al-Si specimen was produced from wrought alloy and the specimen surface was metallurgically prepared. The as- cast product was characterized with aid of micro-hardness tester, the chemical composition was analysed by X-ray fluorescence (XRF), while X-ray diffraction (XRD) was used to identify phases present, microstructures and surface examinations were done on a high resolution metallurgical Optical Microscope. The properties of the polished and worn sample surfaces were examined by Scanning electron microscope (SEM) equipped with Energy dispersive X- ray (EDS) facilities. A 6mm diameter alumina ball under varying normal loads (3-10 N) was rubbed against the surface of the cast Al-Si coupon specimen. The dry and wet sliding wear behaviour was assessed based on the CoF-sliding time behaviour. From the results, the average CoF values of 0.9064 for dry and 0.2038 for wet contacts were obtained. Comparatively, 1.03E-06 and 4.21E-07 minimum wear intensities; and 467290 and 132170 wear resistances were obtained for dry and wet contacts respectively. Behaviour of cast Al-Si in DOT4 were compared with its performance in DOT3 regarding the hydraulic brake system application