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The article focuses on a study which identified the current capabilities of structural integrity monitoring methods for structural integrity management of offshore installations. A review was made on the key structural monitoring methods related to offshore structures. It noted the limitations of offshore experience of structural integrity monitoring. It also noted the importance of the use of continuous monitoring techniques for offshore structures that operate with their original intended lifetime.

The article presents the elements of a framework for managing the structural integrity of fixed jacket structures in Great Britain. The regulatory requirements for structural integrity management (SIM) in the country are discussed. It identifies the key processes that constitute a good practice in SIM, as well as the appropriate management and documentation structure. The inspections strategy of the Structural Technical Authority (STA) is also explored.

The article addresses the issues related to the life extension of ageing offshore installations in Great Britain. It discusses the regulatory aspects of ageing and life extension of offshore installations in Great Britain, Norway and the U.S. Several definitions of design life according to the ISO standards are given. The structural integrity considerations for ageing offshore installation are explored, including fatigue, system strength and inspection. The initiatives of the Health and Safety Executive (HSE) for ageing installations are also discussed.

The article presents an overview of developing key performance indicators (KPI) for offshore structures, based on the aspects which are important to safety and asset integrity. It cites the hazards to structural integrity including extreme weather, corrosion and fatigue. Details of how to developed KPI based on the hazards of structural integrity are discussed. It illustrates the relationship between KPI and performance standards.

RUNNING HEAD UNNING HEADMA AND SHARP Fatigue design of cast steel nodes in offshore structures based on research data A. Ma, BSc, PhD, MICE, MBCS, FCIArb, Barrister and J. V. Sharp, MA, DPhil, CEng, CPhys Steel castings have been incorporated in the fatigue sensitive zones of North Sea platforms to exploit the superior fatigue performance of cast steel nodes when compared with conventional welded joints. Fatigue assessment and the design of tubular joints in offshore structures are largely governed by three parameters; namely (a) stress concentrations at the joints, (b) the SN relationships of the material used and (c) defects in the material at potential fatigue crack initiation sites...

Carbon fibres heat treated to temperatures in the range 1000-2600°C have been irradiated in the spent fuel pond to gamma doses between 1-1000 Megarads (MI). The mechanical properties of the irradiated fibres have been determined by single filament tests.There is a reduction in strength and modulus for fibres irradiated in air, probably due to radiation enhanced oxidation effects. This produces an increase in fibre diameter (≲10%) for fibre originally heat treated to 1000 and 1500°C. This is probably due to fine scale voidage (∼20 A) for which there is some evidence in thin sections prepared from regions close to the surface of these fibres (irradiated to 1000 Mr).The mechanical properties of fibres irradiated to 1000 Mr in argon were unaffected by the irradiation showing that the displacement damage from the irradiation has had little effect on the processes controlling modulus and strength.

AbstractDislocation loops in irradiated or quenched metal crystals are swept out by the glide dislocations during deformation, leaving cleared channels. The removal of prismatic loops with the same Burgers vector as the glide dislocations can occur by direct recombination (Saada and Washburn 1963) but the annihilation of loops with Burgers vector out of the glide plane has not been explained. A simple mechanism is proposed for their removal in face-centred cubic crystals. This involves the formation of a junction around half the loop followed by the gliding together and coalescence of this with the other half. Both steps are glissile and energetically favourable, and give complete annihilation of the loop at the expense of a change in shape of the glide dislocation. Faulted loops may also be removed in this way if they first unfault in the presence of a glide dislocation. The mechanism is not diffusion controlled, but requires a high loop mobility and may be affected by impurity pinning.

A technique utilizing electroplating is described for the preparation of specimens for transmission electron microscopy, which show the relation between surface detail and internal structure. The cleared channels in deformed neutron irradiated copper crystals have been correlated with surface slip steps indicating that the surface slip bands are a true representation of the bulk deformation behaviour. The slip steps show a uniform distribution of shear within the central region of the cleared channel, with a decreasing shear strain near the edges. The channel is, however, cleared of irradiation produced defects for approximately the full width of the slip step, indicating that the removal mechanism is relatively efficient. This and other features of the slip process are discussed in terms of the observations.

The deformation of neutron-irradiated copper single crystals has been studied by transmission electron microscopy techniques. The width of the defect-free channels formed by the passage of dislocations has been measured as a function of temperature, dose and strain, in sections cut normal to the primary glide plane. The width and spacing of the channels have also been compared with surface replicas. Sections parallel to the primary glide plane have also been examined to provide details of the dislocation structure within a channel. The formation and development of the channels are discussed and the destruction of loops by dislocations is examined. The deformed state of neutron-irradiated crystals is compared with that of unirradiated crystals.

High densities of small defect clusters have been observed in MgO irradiated in the high voltage electron microscope. The threshold voltage at nominal room temperature has been determined as 480 ± 10 kV, corresponding to 64 ± 2 eV for the displacement energy of the magnesium ions. This energy is very similar to the value for oxygen ion displacement from optical absorption studies on accelerator irradiated specimens.1 The similarity of the displacement energy for the two ions is discussed and the values compared with those for other ceramic materials. Calculations of the displacement cross sections show that at 600 kV the rate of production of oxygen ions is a factor ∼1.8 higher than the rate foi magnesium ions, whereas at 1 MV the rates are very similar. The effect of increasing dose and irradiation temperature on the defect clusters has been investigated and the results are compared with neutron irradiation damage in MgO and electron irradiation damage in other materials.

General analytic expressions for the components of the interaction force between two straight skew dislocations with arbitrary Burgers vectors are derived. The interaction between two orthogonal dislocations is considered in detail and used to discuss the interaction between a gliding screw dislocation and an orthogonal forest dislocation. When the two dislocations have parallel Burgers vectors there is a very large, long-ranged force component on the screw dislocation in the cross-slip direction. The significance of this force in relation to dipole formation is discussed and shown to be pertinent to hexagonal and cubic structures.

The interaction force between an edge dislocation and a parallel dislocation dipole has been calculated, assuming an isotropic medium. Both of the 45° positions of equilibrium of the dipole have been considered and also the effect of the rotation of the dipole due to the interaction with the dislocation. The magnitude of the interaction force acting in the direction of the Burgers vector has been compared with the force required to make the dipole glide along its slip cylinder. It has been shown that in a face-centred cubic metal such as copper, the dipole should be swept along by a moving dislocation under a low stress.The sweeping up of dipoles by dislocations has been used to explain the formation of dislocation 'braids' observed in the early stages of the deformation of face-centred and hexagonal metals.

It has been shown by a sensitive parallel plate condenser technique that no deformation (> 1 × 10-6 strain) occurs in neutron irradiated (2.5 × 1018 f. n. cm-2) copper single crystals at stresses lower than the 'critical' shear stress at the appropriate strain rate. When the critical stress is reached the deformation occurs entirely by the formation of prominent slip lines, there being no sign of fine slip, viz. the limited movement of dislocations on a large number of slip planes. This result supports the model of slip in neutron irradiated metals proposed by Makin and Sharp and is contrary to the large microstrain observed by Koppenaal in bend tests.