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Duplex stainless steels are commonly used in environments that are expected to produce hydrogen i. e. in sour environments and sea water applications, often under cathodic protection. Under these conditions there is a concern about their susceptibility to hydrogen embrittlement. The effect of hydrogen, both external and internal, on the mechanical properties and the fracture characteristics of duplex stainless steels Type 2205 and 2507 have been studied by slow strain rate techniques using smooth tensile specimens. Specimens were strained to failure in air after high pressure hydrogen thermal charging, in a hydrogen atmosphere, in a hydrogen sulphide environment under open circuit potential condition, and whilst cathodically polarized at different potentials in distilled water with 100 wppm potassium sulphate added, in 3.5% aqueous sodium chloride, or in NACE solution. All the environments produced a major reduction in ductility that increases linearly with decrease in strain rate. The severity of the embrittlement depended upon whether the supply of hydrogen was external or internal. Internal hydrogen, as in thermally charged specimens, produced a more profound loss in ductility than straining in a hydrogen atmosphere and prolonged room temperature aging of these specimens, for up to 3 years, resulted in insignificant recovery of ductility, emphasizing the role of the austenite as a hydrogen reservoir. Provision of hydrogen at very high fugacities (cathodic polarization) during straining indicated that the potential at which loss in ductility is first noted corresponds to the hydrogen evolution potential for the particular solution involved. The presence of chloride ion seems to have no significant effect on the loss in ductility- The presence of hydrogen sulphide in the environment, however, introduced the complication of extensive chemical attack during and after crack propagation. The loss in ductility increased as the pH of the solution decreased and, irrespective of pH, maximum embrittlement occurred at some particular temperature between 20 and 90'C. The latter is attributed to the two competing processes of hydrogen ABSTRACT embrittlement and corrosion. A minimum chloride ion concentration of 300 wppm seems necessary to maintain the maximum embrittlement. The ultimate tensile strength of the steel is not affected by hydrogen since cracking only occurs after it is exceeded. Cracks initiate and grow preferentially through the ferrite phase, with fracture surfaces exhibiting quasi-cleavage features; the austenite often failed in a ductile mode. The proportion and distribution of the two phases has a significant effect on the degree of embrittlement. The presence of greater amounts of austenite seems to inhibit crack propagation, but may act as a hydrogen source or reservoir for the embrittlement of the ferrite phase. Straining of the as received weldments, which had been annealed after welding, showed no evidence of hydrogen embrittlement, but an attempt was made to simulate via heattreatment the structures that could occur in the heat affected zone of the weld and these structures had inferior mechanical properties in the presence of hydrogen.

The research is concerned with bond failures found during the manufacture of rubber-to-metal bonded bushes, the bond being formed using a polymeric adhesive intermedium and completed concurrently with the vulcanisation of the bulk rubber. Failure occurs when stresses developed as the composite parts cool after moulding act on the comparatively weak "hot" bond. Three techniques are utilized for measuring the shrinkage stress i) a finite element method which shows the distribution of the direct stresses, ii) an empirical calculation which indicates the average direct stress acting on the bond, iii) an experimental method serving as a confirmation of the theoretical approach. The main factors influencing the hot bond strength immediately after moulding are identified and include:- Rubber hardness Rubber moisture content Adhesive type (reactivity) Heat input during vulcanisation These are quantified using a specifically developed test-piece. Bush cooling characteristics are studied to allow a direct comparison of shrinkage stress with bond strength and to predict the theoretical likelihood of bond failure. The research shows that, under ideal conditions, only in a few products is the shrinkage stress sufficient to cause bond rupture. Bond failure rates are greater than the theory suggests and the main causes are identified as being due to lack of process and management control on the shop-floor. Recommendations are made as to methods required to obtain better control. A new adhesive was evaluated and introduced into the company giving potential for a 40% reduction in oond failure levels with a cost saving of £50,000 p.a.

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The stabilisation of archaeological iron is considered as one of the major problems facing the archaeological conservator today. Free chlorides, held as counter ions at the metallic anode, act as electrolytes and promote corrosion of metallic iron This study examines and compares the efficiency of a range of aqueous wash methods currently used to remove chloride ions from archaeological iron and determines how these various treatments work. It also investigates the effect of selected aqueous wash treatments on the chloride rich metastable corrosion product 0-FeOOH. The amount of Cl'removed from 0-FeOOH and any transformations to new compounds are recorded. Iron objects were treated using aqueous Soxhlet extraction with nitrogen, aqueous sodium hydroxide and aqueous alkaline sulphite solutions. Synthetic O-FeOOH and PFeOOH1Fe3Om4 ixtures were washed in aqueouss odium hydroxide, aqueousa lkaline sulphite solution, aqueous sodium sulphite, hot and cold deionised water. The outcome of the work showed that: (1) For archaeological iron objects: O. SM nitrogen de-aerated aqueous NaOH solutions are very efficient chloride extractors, often approaching a 100% efficiency. Almost as efficient were 0.5M aqueous... NaOH/Na2SO3 treatment solutions. Nitrogen de-aeration of treatment solutions improves their cr extraction efficiency, by freeing Cl' from its counter ion role. Hydroxide ions improve extraction efficiency of Cl- from iron objects in nitrogen and Na2S03 de-aerated environments. The de-aerated aqueous Soxhlet extraction method, as suggested by Scott and Seeley (1986), is a less efficient chloride extractor than either nitrogen de-aerated 0.5M NaOH or 0.5M NaOH/Na2SO3. De-aerated NaOH treatment solutions are to be preferred to NaOH/Na2SO3 solutions, as they do not introduce residual electrolyte ions (SO 42). (2) For O-FeOOH samples: Pure O-FeOOH and P-FeOOH/Fe3O4 mixtures reacted differently during washing. Pure 0-FeOOH completely transformed to cc-FeOOH in the alkaline environments provided by NaOH and NaOH/Na2SO3. This released all the chloride from the PFeOOH. In NaOH solutions within the range pH8.5 to 10.5 0-FeOOH/Fe3O4 transformed mostly to Fe304. Above pH1 1 there was limited conversion. Improved release of Cl' from P-FeOOII/Fe3O4 mixture correlated with the transformation of PFeOOH to Fe304.

This project was carried out to develop a better understanding of "Electrochemical Chloride Removal (also known as Desalination), a relatively new technique for rehabilitating reinforced concrete structures suffering from chloride induced corrosion. The factors influencing chloride removal were investigated and a mathematical model for predicting the spatial distribution of chloride in the concrete at the end of the treatment was developed. To investigate the factors influencing chloride removal, concrete prisms containing varying levels of admixed sodium chloride and number of steel bars were tested. The amount of chloride removed during the treatment was assessed by analysing the anolyte. It was found that chloride removal increased with increasing applied potential, number of reinforcing bars at a particular depth, water/cement ratio, chloride contamination depth and initial chloride content. Chloride removal was unaffected by concrete strength but decreased with increasing percentage of cement replacement material. A greater percentage of chloride was removed from prisms where the thickness of the chloride bearing layer of concrete was less than the depth of cover to the reinforcement. Where the thickness of the chloride bearing layer exceeded the cover to the reinforcement, the use of an external cathode significantly increased the total amount of chloride removed. Chloride removal from a face remote from the source of the chloride contamination (soffit desalination) was shown to be feasible. In prisms containing 2, 3 and 4% Cl (by weight of cement), it was found that the amount of chloride remaining in the prisms reached a limiting value irrespective of the initial admixed chloride content. This value was believed to be approximately equal to the amount of bound chloride in the concrete. Analysis of ground samples of concrete showed, however, that in a few cases bound chloride was removed locally to the reinforcing bars. Even though significant amounts of chloride remained in the concrete after completion of the treatment, the reinforcement remained passive for periods exceeding 30 months. Towards the second aim of predicting the spatial chloride distribution in the concrete, a mathematical model for electrochemical chloride removal from concrete based on the Nernst-Planck and Laplace equations was developed. The model relies on experimentally derived chloride transport number profiles. The predicted quantities of chloride removed into the anolyte and chloride remaining in concrete correlate well with data obtained by testing prisms containing one bar and dosed with 2, 3 and 4% Cl. The model shows that all parts of the concrete prisms undergo chloride removal albeit at different rates. Concrete directly between the anode and cathode undergoes the highest rate of chloride removal while concrete below the cathode, the lowest. It would appear, therefore, that there are no 'dark spots' in the concrete where chloride removal is prevented.

Fixed jacket offshore structures. which react environmental wave loading. are generally constructed using tubular steel members. When subject to load. severe surface and through-thickness stress gradients occur due to local bending of the tubular wall. The cyclic nature of the environmental wave loading results in high stress concentration at the joints. which can lead to fatigue cracking. British Gas currently operates twelve fixed offshore structures. two of which. the Rough A-Complex structures. are now ageing and showing signs of fatigue cracking. The objective of the work described in this thesis is the development of a fracture mechanics-based methodology for the assessment of fatigue cracking in these structures. The fracture mechanics approach uses the stress intensity factor (SIl) to characterise crack-tip conditions. and provides a means of analysing the behaviour of cracks. The SIF is defined in terms of the crack site stress distribution and the change in structural compliance with crack size. Difficulties in the application of fracture mechanics lie in the derivation of accurate solutions for the SIF. The tubular joints of offshore jacket structures present particular difficulties due to their complex loading and geometry. The current work starts with a review and assessment of tubular joint fracture mechanics models. followed by a numerical study of cracked tubular joints using shell finite element (FE) models incorporating line spring crack representation. Based on the results of this study. a general fracture mechanics model for the prediction of SIF solutions for tubular joints. is derived and assessed. The general fracture mechanics model is incorporated into a crack growth model. which is best implemented using sophisticated commercial software. Crack growth and fatigue life predictions obtained are validated against full scale tubular joint fatigue data. Finally. a complete methodology for the assessment of fatigue cracks in any tubular joint is proposed, and applied to the assessment of fatigue cracking in the Rough A-Complex structures.

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No description available.