Underground pipelines are used in various process piping systems to transport gasses or fluids and are usually subjected to the effects of external corrosion. Corrosion can be defined as the deterioration of a material due to a reaction with its environment or the destruction of the material by means that are not mechanical (Fontana and Greene, 1967:2). External corrosion, due to the interaction between the pipe and the soil, is generally a slow process and the corrosion rate is influenced by a variety of external factors. Some of these factors include the ambient pH and salinity, the presence of moisture and bacteria, temperature, the electrical potential difference between the pipe and other structures and the implementation of preventative measures (such as cathodic protection and wrapping). Although the external corrosion of underground pipelines is generally a slow process in mild environments, pipe degradation as a result of external corrosion remains one of the prevalent reasons for the failure of underground pipelines. As with many mechanical systems that are prone to fail at one time or the other, the high costs involved with unforeseen failure necessitate some quantitative (or qualitative) indication of the condition of the pipe system. Some of the costs that can be expected as a result of unforeseen pipeline failure are, amongst others: • costs as a result of the failure of dependent systems; • costs as a result of the loss of production; • costs as a result of the loss of product (in distribution networks); • the cost of unscheduled maintenance (logistical costs); • costs as a result of damage to public property; • fines imposed by customers (in distribution networks); • costs related to pollution control, and • the loss of life The single most important parameter associated with the condition of a system is its profitable remaining life. This is the time during which a sub-system contributes to the well-being of a larger system and the organisation. Therefore, it is necessary to determine, with reasonable accuracy, the extent of the remaining life of a system so that managerial decisions (i.e. investments, cash-flow analyses, maintenance task scheduling and replacement programmes), based on this figure, can be made. Done correctly, this can directly lead to a decrease in maintenance costs and subsequently to an increase in profit. The extent of a corrosive attack on the pipeline might be highly localised or might be fairly uniform over the length of the installation. The fact of the matter is that, since the pipe is buried, it is very difficult to quantify the external damage caused by corrosion. A variety of techniques are in use to survey pipelines and detect anomalies. However, for large pipelines, most of these techniques are either inefficient or too expensive. There will always remain some uncertainty regarding the integrity of the pipeline. The work presented in this study is explained with valid generic examples and aims: 1. to provide the reader with sufficient background information so that the need for determining the integrity of a pipeline becomes apparent; 2. to indicate why a reliability-centred approach is necessary (Chapter 1); 3. to explain the basic principles of corrosion and the electrochemical nature of corrosion (Chapter 2); 4. to indicate areas, based on the basic principles of corrosion, where severe corrosion can be expected (Chapters 2 and 7); 5. to provide and elaborate on information regarding pipe surveillance techniques that are currently available (Chapter 3); 6. to establish the criteria for pipeline failure, in the form of a limit state Junction, for pipes that are subjected to near-constant internal pressures (static failure domain) as well as for pipes subjected to varying internal pressures (fatigue domain) (Chapters 5 and 6); 7. to indicate the sensitivity of the fatigue domain solution to changes in the system variables and to indicate that a significant reduction in the system variables does not necessarily reduce the solution accuracy (Chapter 6), and 8. to integrate the above-mentioned into a practical and workable guideline that can be used to determine the remaining life of an underground pipe network (Chapter 7). / Dissertation (MEng (Mechanical Engineering))--University of Pretoria, 2002. / Mechanical and Aeronautical Engineering / unrestricted

La présente thèse vise à améliorer l'état des connaissances à l'égard des paramètres influençant les effets de site des barrages en enrochement. Une revue exhaustive des publications liées au comportement et à la modélisation dynamique de ce type de barrage a mis en évidence que le nombre de cas de référence est très limité dans la littérature spécifiquement orientée vers l'étude des effets de site avec des analyses en 3D de barrages en enrochement pour lesquels des données instrumentales sont disponibles. Les travaux réalisés sont très orientés vers les praticiens, car ils établissent des lignes directrices pouvant les aider à évaluer les formulations et algorithmes les mieux adaptés à la réalisation d'analyses en 1D, 2D ou 3D. Ils portent sur l'étude des effets de site du barrage Denis-Perron, un grand barrage en enrochement construit dans une vallée escarpée. L'emplacement exceptionnel de cet ouvrage et le fait qu'il a été muni d'accéléromètres pendant sa construction en font un sujet d'étude particulièrement intéressant. Le premier volet des travaux a consisté à analyser les signaux détectés par les accéléromètres pendant trois petits séismes. Les résultats de cette analyse mettent en évidence qu'il est possible de déduire les caractéristiques dynamiques d'un grand barrage, et ce, même avec des signaux faibles. Les fonctions de transfert et les rapports spectraux obtenus à partir de ces séismes fournissent en fait de nouvelles connaissances sur la directionnalité des fréquences de résonance, les modes de vibration et les effets de site. Puisqu'à travers le monde, il existe très peu de barrages instrumentés dont les données sont disponibles et que les séismes de moyenne et de forte amplitude se produisant dans des zones de faible sismicité sont rares, ces données sismologiques se sont avérées très précieuses pour valider les résultats obtenus au cours des travaux subséquents. Le deuxième volet des travaux a servi à évaluer le potentiel de la technique du bruit ambiant pour déterminer les caractéristiques dynamiques du barrage Denis-Perron. Des mesures de bruit ambiant ont été prises à l'aide de vélocimètres à trois composantes adaptées aux conditions d'un grand barrage. Ces données expérimentales ont permis d'établir la fréquence des modes de vibration de ce grand barrage. Les résultats obtenus d'analyses simples effectuées pour traiter les signaux individuels sont aussi concluants que ceux provenant d'une analyse modale réalisée à partir d'un ensemble de signaux synchronisés entre eux tout en étant cohérents avec les résultats issus de l'analyse des données sismologiques. À partir de la fréquence des modes de vibration fondamentaux calculée avec les données sismologiques et expérimentales, une analyse modale numérique effectuée avec un modèle tridimensionnel a permis d'ajuster le profil de rigidité moyen par rétro-calculs représentatifs du milieu 3D. Dans le cadre du troisième volet, des analyses paramétriques ont été réalisées avec des modèles simplifiés, conçus pour étudier des aspects spécifiques en lien avec les effets de site du barrage Denis-Perron. Les résultats obtenus de ces analyses indiquent que la forme de la vallée, le contraste d'impédance ainsi que le contenu fréquentiel et l'orientation de la sollicitation sont les paramètres qui influent le plus sur les effets de site. Bien que ces résultats illustrent l'importance des effets de site du système vallée barrage étudié, ils font également ressortir certaines limitations entourant la réalisation d'analyses dynamiques en 2D et 3D pour un tel système. De plus, conformément à la littérature, ils indiquent que la forme de la vallée et le rapport entre la hauteur maximale d'un barrage et sa longueur en crête agissent fortement sur sa réponse dynamique. Après que les modèles aient été améliorés pour mieux refléter les conditions du barrage, ils ont été validés à l'aide des données sismologiques disponibles. Les signaux du séisme le plus fort de 1999 ont permis de vérifier et valider ces modèles avancés à l'aide des résultats de simulations obtenus tant dans le domaine temporel que fréquentiel, de même que de conclure qu'il n'est pas requis de recourir à une dé convolution pour ajuster des signaux à la base des modèles. Des analyses dynamiques faites à partir d'un séisme de plus forte intensité (0,3 g), représentatif de la sismicité de l'Est du Canada, a aussi permis d'extrapoler ainsi que de prévoir les phénomènes dynamiques et leurs impacts sur la stabilité et les déplacements permanents du barrage Denis-Perron. / This thesis aims at improving the state of knowledge regarding the parameters that influence the site effects of rockfill dams. A comprehensive literature review related to the behavior and dynamic modeling of this type of dam has highlighted that the number of reference cases specifically oriented towards the study of site effects with 3D analyses of rockfill dams for which seismological data are available is very limited in the literature. The research effort is very practitioner-oriented, as it establishes guidelines that can help engineers evaluate the most appropriate formulations and algorithms when performing 1D, 2D or 3D analyses. It focuses on the study of the site effects of the Denis Perron Dam, a large rockfill dam built in a steep valley. The exceptional location of this structure and the fact that it was equipped with accelerometers during its construction make it a particularly interesting case study. The first phase of the project consisted in analyzing the signals detected by the accelerometers during three small earthquakes. The results of this analysis show that it is possible to deduce the dynamic characteristics of a large dam, even with weak signals. The transfer functions and spectral ratios obtained from these earthquakes provide new insights into resonant frequency directionality, vibration modes, and site effects. Since there are very few instrumented dams worldwide for which seismological data are available and as medium and large magnitude earthquakes occurring in areas of low seismicity are rare, the available seismological data have proven to be very valuable invalidating the results obtained in the subsequent work. The second phase of the project was meant to evaluate the potential of the ambient noise technique to determine the dynamic characteristics of the Denis Perron Dam. Ambient noise measurements were recorded using three-component velocimeters adapted to the conditions of a large dam. These experimental data were used to establish the frequency of the vibration modes of this large dam. The results obtained from simple analyses conducted to process individual signals are as conclusive as those from a modal analysis based on a set of signals synchronized with each other while being consistent with the results from the analysis of the seismological data. From the frequency of the fundamental vibration modes calculated with the seismological and experimental data, a numerical modal analysis was conducted using a three-dimensional model to fit the average stiffness profile by retrofit calculations representative of the 3D medium. In the third and last phase, parametric analyses were conducted using simplified models designed to study specific aspects related to the site effects of the Denis-Perron dam. The results obtained indicate that the valley shape, impedance contrast, frequency content, and solicitation orientation are the parameters that have the most influence on the site effects. These results illustrate the importance of site effects for the studied valley-dam system, but they also emphasise some limitations surrounding the performance of 2D and 3D dynamic analyses for such a system. Further, in accordance with literature, they show that the ratio of the maximum height of a dam to its crest length and the valley shape strongly affect its dynamic response. After the models were refined to better reflect dam conditions, they were validated based on seismological data. Signals from the strongest 1999 earthquake were used to verify and validate these advanced models from simulation results in both time and frequency domains and conclude that deconvolution is not required to fit the signals at the base of the models. Dynamic analyses based on an earthquake of higher intensity (0.3 g), representative of the seismicity of eastern Canada, were conducted, from which the dynamic phenomena and their impacts on the stability and permanent displacements of the Denis Perron dam were extrapolated and predicted.

No description available.

The use of engineered wood products (EWP) in residential construction has increased in recent years. Most specifications for the installation of these components are found in proprietary manufacturer literature rather than in the building code. Although some home inspections include EWP prescriptive compliance, very little applied and academic literature addresses this practice. This lack of practical information and the lack of standardized inspection methods can result in undetected non-compliant EWP installations that fail to meet the minimum safety provisions of the building code. The goal of this project was to develop a visual inspection methodology, associated knowledge base, and software application for the inspection of EWPs and connector hardware (CH) in new residential construction at the pre-drywall stage. The methodology was based upon subject matter expert (SME) inputs and validation was derived from the use of a modified Delphi method that was able to the gather, collate, refine, and validate the research process and outputs based on the expertise of the subject matter experts. The concept of high face validity was used to establish project validity. Installation problems with EWPs and CH were noted by the SMEs partly because the use and installation instructions for proprietary products are not found in building codes. Building code officials (BCO) and home inspector (HI) SME responses indicated a need for a methodology and software to aid in the inspection process. Although authoritative reference materials for prescriptive installation are available, the scope of material is not consistent between manufacturers, and is presented in different formats for different brands. The developed software application provides ready access to reference materials needed for EWP and CH installations. No widely accepted inspection methodology is available, although the HI SMEs used systematic inspection methods. Inspection methods such as the top-down method and sighting along the patterns of repetitious framing elements can improve the detection of non-compliant installations. BCO and HI SMEs identified both component-specific and zone-specific techniques as a part of the systematic inspection methodology. Definable high risk areas for each EWP and CH were identified and the associated inspection methods may help the inspector reduce the incidence of undetected problem areas. Knowledge of the high-risk areas may also enhance the inspection. The developed software application was found to be a useful inspection tool. BCO and HI SMEs determined that functions of the computer software necessary for use included ease of use, onboard reference materials, specific inspection techniques, prepared comments, and technical illustrations. / Ph. D.

This research is intended to better understand the structural behavior of steel bridge beams that have experienced section loss near the bearings. This type of deterioration is common in rural bridges with leaking expansion joints, which exposes the superstructure to corrosive road deicing solutions. Seventeen beams from 4 decommissioned structures throughout Virginia were tested to induce web shear failure near the bearing locations and measured for load, vertical displacement, and web strain behavior. The strain was measured using a digital image correlation (DIC) system to create a digital strain field at equal loading and beam displacement intervals during testing. The data recorded during these large-scale tests was compared to several existing methods for calculating the shear capacity of the damaged beams. Finally, the most appropriate method of these approaches was identified based on accuracy, conservatism, and ease of implementation for load rating. When using load rating methods to determine a steel beam's capacity, this study also recommends that the effective area of the web used in determining the percentage of remaining thickness should consist of the bottom 3 inches of the web and should extend the length of the bearing plus one beam height excluding any areas without any noticeable section losses. / Master of Science / Older bridge structures typically include a rubber joint near the ends to allow for expansion and contraction of the bridge due to heating and cooling from the weather. In many cases, these joints will get damaged due to impacts from vehicle tires and other environmental disturbances. Damage to these joints allows for water to leak through, which, while not in of itself harmful, also allows melting snow to carry road salts laid in the winter to spread onto the underlying bridge steel. These salts cause aggravated corrosion of the steel beams below the bridge's deck, resulting in damage or collapse of the bridge itself. The goal of this study was to characterize this damage and determine how it affects the remaining capacity of the bridge. This objective was achieved by testing 17 beams from 4 out of service bridges with varying damage levels. A load was applied near the damaged ends to determine their behavior during loading, to locate areas of high strain resulting from corrosion, and find the beam's capacity. Several methods to predict the remaining strength in corroded steel beams were compared and recommendations made based on accuracy and conservatism.

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Bridges are amongst the most important structures of any highway network. Once the bridge construction is complete and a bridge is put into service, it is subjected to deteriorations. An effective condition assessment, as a component of bridge management system, is therefore necessary to keep bridges in admissible conditions of safety and serviceability. In South Africa, some bridge authorities do not have sufficient funds to carry out bridge inspections at required intervals. In the case where bridge authorities have enough funds, a systematic inspection is performed, covering a number of bridges that are not in need of inspection. Inspection and maintenance for a limited number of bridges randomly chosen may result in an increase of the number of bridges in critical conditions. A bridge inspection prioritisation method that takes into account the need of inspection of bridges is therefore needed for South African highway bridges. This research provides a prioritisation method for concrete bridge inspections by integration of nonprofessional inspectors, imagery inspection and deterioration models. To achieve the research objectives of this study, a literature study has been carried out to understand bridge inspection practice in general and South African practice in particular. The literature helped also to identify previous works on bridge inspection prioritisation, the use of information from informal sources, imagery inspection and involvement of non-professionals in bridge inspection and use of deterioration models in bridge management. A survey has been conducted amongst South African bridge authorities in order to fill the literature gaps. Inventory and inspection data of bridges managed by South African National Roads Agency Limited (SANRAL) was used to develop a deterioration model by considering bridge characteristics such as bridge age, number of spans, and bridge type. Based on the literature review, results of surveys and estimated regression parameters, a bridge inspection prioritisation method has been developed. This method comprises three phases. The first phase is the initial screening that consists of an identification of bridges with critical defects that have not been repaired yet. These bridges, to which are added bridges that have not been inspected in the previous inspection, constitute the first inspection priority category. The second phase is an imagery screening which is an analysis of digital photographs for detection of defects that need urgent assessment by professional inspectors. The analysed photographs are taken by non-professional inspectors and uploaded to the Bridge Management System. The third phase is a grouping of bridges in inspection priority categories as a function of their physical characteristics and deteriorating factors using deterioration modelling. The method has been applied on SANRAL bridges using inspection ratings of 2011-2012. 422 SANRAL bridges have been categorised in the first inspection priority group by considering hydraulic related defects as critical. The third phase allowed to rank 522 possible combinations of bridges based on their characteristics. The developed method would help bridge authorities where inspection budget is limited, to prioritise bridge inspection as a function of needs of inspection. / AFRIKAANSE OPSOMMING: Brûe is ʼn belangrike deel van enige snelweg netwerk. Wanneer brugkonstruksie voltooi is en dit in diens gestel word, is die brug onderhewig aan skade en verval . 'n Doeltreffende toestandsassessering, as 'n komponent van ʼn brug bestuurstelsel, is dus nodig om brûe in ʼn toestand van veiligheid en diensbaarheid te hou. In Suid-Afrika het sommige brugowerhede nie genoeg fondse om bruginspeksies teen vereiste intervalle uit te voer nie. In die geval waar ʼn brugowerhede wel genoeg fondse het, word stelselmatige reekse inspeksies uitgevoer, waar brûe wat nie lukraaknoodwendig op daardie stadium inspeksie nodig het nie, ook soms ingesluit word. Inspeksie en onderhoud vir slegs 'n beperkte aantal brûe wat gekies word kan 'n toename veroorsaak in die aantal brûe wat in ʼn kritiese toestand is. 'n Bruginspeksie prioritiseringmetode wat brûe identifiseer vir inspeksie is dus nodig vir Suid-Afrikaanse brugowerhede. Hierdie navorsing stel 'n metode voor wat bruginspeksies prioritiseer deur gebruik te maak van nieprofessionele inspekteurs, inspeksie van foto’s en brugtoestandsvervalmodelle. Om die navorsings doelwitte van hierdie projek te bereik, is 'n literatuurstudie uitgevoer oor die praktyk van bruginspeksie in die algemeen, en meer spesifiek om die praktyk in Suid-Afrika te verstaan.. 'n Opname is voorts onder Suid-Afrikaanse brugowerhede uitgevoer om gapings in die literatuur aan te vul. Inventaris en inspeksie data van brûe wat bestuur word deur die Nasionale Padagentskap (SANRAL) is daarna gebruik om 'n toestand agteruitgangsmodel te ontwikkel deur die eienskappe soos brug ouderdom, aantal spanne en die tipe brug in ag te neem Gebaseer op die literatuur, resultate van opnames en beraamde regressie parameters is 'n brug inspeksie prioritiseringsmetode ontwikkel. Hierdie metode bestaan uit drie fases. Die eerste fase is die aanvanklike siftingsproses wat bestaan uit die identifisering van brûe met 'n kritiese defek wat nog nie herstel is sedert ʼn vorige inspeksie nie. Hierdie brûe, wat ingesluit word by ander brûe wat nie geïnspekteer was in die vorige inspeksie nie, is die eerste kategorie van inspeksie prioriteit. Die tweede fase is 'n ontleding van digitale foto's vir die opsporing van defekte wat dringende assessering deur professionele inspekteurs nodig het. Die foto's word geneem deur nie-professionele inspekteurs en dit word gelaai op die brug bestuurstelsel. Die derde fase is die groepering van brûe in inspeksie prioriteit kategorieë as 'n funksie van hul fisiese eienskappe en vervalfaktore met die hulp van agteruitgangsmodelle. Die metode is toegepas op die SANRAL brûe met die hulp van inspeksie graderings van 2011-2012. Deur die aanname van hidrouliese defekte as van kritiese belang, is 422 SANRAL brûe in die eerste inspeksie prioriteit gegroepeer. Die derde fase prioritiseer 522 moontlike kombinasies van brûe op grond van hul fisiese eienskappe. Die metode sal brugowerhede waar inspeksie begrotings beperk is, help om bruginspeksies te prioritiseer as 'n funksie van die noodsaaklikheid van inspeksie.

This study was a follow up to P. C. Dams' (1996) unpublished University of North Texas masters thesis, The effect of defect probability during training on inspection accuracy in a quality control simulation. Graphics of computer circuit boards were presented in dyads with an error free sample on the left and a comparison on the right. Comparisons had either a rotation or transposition defect, or were error free. Subjects had 10-s to accept or reject the comparison as identical to the sample. They were trained using two different stimulus fading procedures (using descending defect probabilities) and immediate feedback. Defect probabilities for the Tens were 0.60, 0.50, 0.40, and 0.30 and for the Twenties were 1.00, 0.80, 0.60, and 0.40. The last 4 pretraining and posttraining sessions were compared and the posttraining performance of the Twenties, as compared to the Tens, demonstrated greater improvement over pretraining performance. No firm conclusions could be drawn as to the effectiveness of either training procedure. The significance of the current investigation and suggestions for future research are discussed.

A research report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Engineering, 2016 / Wax deposition in sub-sea pipelines is a major concern in the oil industry. Wax precipitates in a pipeline when the temperature falls below a certain temperature called the Wax Appearance Temperature. As wax precipitates and deposits in a pipeline, the wax deposit can cause oil flow problems and reduce production efficiency. At critical conditions wax deposits in pipelines may damage production equipment or cause a production stoppage. In the past two or three decades, the challenge has been to develop and apply high-fidelity models for wax deposition. In this context, two promising models have recently been developed: that of Eskin et al. (2014) and that of Haj-Shafiei et al. (2014). This research report tries to solve and elucidate some of the key assumptions of these wax deposition models, through implementing them in the Python Programming Language. In investigating the significance of the shape of the Solubility Curve on wax deposition, a concave shaped solubility curve was found to exhibit the highest average deposition and the convex shaped solubility curve the lowest average deposition. The shape of the solubility curve also drastically affects the peak wax height with a concave shaped solubility curve forming the greatest wax peak. The results have shown that the description of the phenomenon of Wax deposition in undersea pipelines is difficult to grasp for anyone not familiar with the topic because of the complexity of the mechanisms involved. Often, the models are difficult to visualise owing to their multi-dimensional solution procedure and the interdependence of parameters. The resultant programs could be utilised to help illustrate the process of Wax deposition to Engineering students or professionals who do not have access to expensive proprietary software or who are less proficient with programming but interested in the field. / GS2016

This thesis explores the professional discretion in relation to national inspections by focussing on the Swedish national school inspection (SNSI) and how the inspections made can affect the professional discretion. During the last decades the Swedish welfare sector has gone through a remarkable shift towards using new public management (NPM) reforms, implementing market solutions with the aim to increase cost efficiency and quality. These reforms have caused a huge impact on the education system in Sweden, such as the privatisation of schools and shifting responsibility from the state to the local municipalities. The development of the NPM has also increased the auditing in order to assure that welfare service produces high quality services, where national inspection has been an increasingly popular method of auditing. Extensive research studying the relationship between auditing and de-professionalization is available and many argue that auditing decrease the professional discretion. Despite the research, there is an empirical gap to how national inspection affects professional discretion. This is surprising as national inspections at least theoretically should be able to both undermine and support professional discretion. The controlling inspection type can from this view be argued to undermine professional influence by using top-down steering not considering professional knowledge and experience. The supporting inspection type uses more bottom-up strategies in dialogue with the professions and can theoretically thus be seen as more supporting of professionalism. The aim of this thesis is to initiate the bridging of this gap by analysing the SNSI different inspection types in relation to professional discretion. The results of the study suggest that the SNSI uses two controlling type of inspections as well as one new supporting type of inspection. The supporting inspection type is found to undermine professional discretion, while the two different controlling inspections both support and undermine the professional discretion depending on how the inspection is conducted. This gives evidence to how a supporting inspection type actually can undermine professional discretion more than the controlling inspection types.

Useful processes, that are independently repeatable, are utilised in all branches of science and traditional engineering disciplines but seldom in software engineering. This is particularly so with processes used for detection and correction of defects in software systems. Code inspection, as introduced by Michael Fagan at IBM in the mid 1970's is widely recognised as an effective technique for finding defects in software. Despite its reputation, code inspection, as it is currently practiced, is not a strictly repeatable process. This is due to the problems faced by inspectors when they attempt to paraphrase the complicated semantics of a unit of computer code. Verification based software inspection, as advocated by the cleanroom software engineering community, requires that arguments of correctness be formulated with the code and its specification. These arguments rely on the reader being able to extract the semantics from the code. This thesis addresses the requirement for an independently repeatable, scalable and substantially automated method for yielding semantics from computer code in a complete, unambiguous and consistent manner in order to facilitate, and make repeatable, verification based code inspection. Current literature regarding the use of code inspection for verification of software is surveyed. Empirical studies are referenced, comparing inspection to software testing and program proof. Current uses of formal methods in software engineering will be discussed, with particular reference to formal method applications in verification. Forming the basis of the presented method is a systematic, and hence repeatable, approach to the derivation of program semantics. The theories and techniques proposed for deriving semantics from program code extend current algorithmic and heuristic techniques for deriving invariants. Additionally, the techniques introduced yield weaker forms of invariant information which are also useful for verification, defect detection and correction. Methods for using these weaker invariant forms, and tools to support these methods, are introduced. Algorithmic and heuristic techniques for investigating loop progress and termination are also introduced. Some of these techniques have been automated in supporting tools, and hence, the resulting defects can be repeatably identified. Throughout this thesis a strong emphasis is placed on describing implementable algorithms to realise the derivation techniques discussed. A number of these algorithms are implemented in a tool to support the application of the verification methods presented. The techniques and tools presented in this thesis are well suited, but not limited to, supporting rigorous methods of defect detection as well as formal and semi-formal reasoning of correctness. The automation of these techniques in tools to support practical, formal code reading and correctness argument will assist in addressing the needs of trusted component technologies and the general requirement for quality in software.