The uptake of renewable energy sources has increased dramatically in recent decades, in response to the contribution to climate change attributed to CO2 emissions from the burning of fossil fuels, the need for governments to maximise the use of domestic energy forms with depleting conventional sources, and to reduce exposure to fuel price volatility. Renewable energy targets set by the European Union have been supported by legislation and economic incentives, and have resulted in a sharp increase in installed wind power capacity in particular. Wind power is seen as a particularly attractive source of renewable energy capacity in the UK due to favourable resources and a competitive cost of energy for onshore sites, with 8.8 GW of capacity currently installed [1]. Constraints from visual and environmental impacts, together with improved wind resources, have led to the acceptance of greater financial costs and the exploitation of offshore sites, with over 5 GW installed to date [1]. Both onshore and offshore, the wind industry now has significant operational experience, with some of the earliest wind farms approaching the end of their design life. Material fatigue is a design critical factor which dictates the safe operational life of wind turbines, but is subjected to numerous areas of uncertainty in the level of environmental loading and structural response, as well as material properties and manufacturing methods. Therefore, a conservative design must be ensured from the outset, which presents the potential for fatigue life extension of installed assets if improved knowledge of their operational experience can be obtained. This thesis details the methodology for a fatigue load assessment of operational offshore wind turbine support structures using measured data, and attempts to quantify areas of loading which contribute to total fatigue damage. The methodologies developed build on existing recommendations for onshore wind turbines to incorporate the additional effects of the offshore environment. Results from measured loading suggest that design fatigue levels can be reduced if operational monitoring is included. Operational experience can allow design conservatism, which is necessary due to uncertainties in structural properties and in levels of stochastic loading, to be more accurately quantified.

This thesis is focused on the application of advanced methods for evaluating damage to boiler tubes, specifically temperature related damage. The aim of this work is to develop an improved damage evaluation procedure utilizing capabilities of modern approaches. This work describes various types of industrial boiler damage. The main focus is on the most exposed and often the most damaged parts of boilers, which are tube bundles (for example, superheaters). Equipment damage is undesirable and often leads to leakages or even to the boiler shutting down. Therefore, it is necessary to find the problem as soon as possible and make the required changes to prevent further damage. The damage types are divided into five categories based on the damage mechanism. Temperature has one of the biggest influences on damage and it may cause short-term or long-term overheating in the tube bundles. This type of damage occurs when the designated temperature is exceeded and results in reduced creep life. It is necessary to know the real surface temperature history of the tube bundle to estimate temperature related damage, however this is often not available. Therefore, it is necessary to calculate those temperatures based on the available data (i.e. inlet and outlet temperatures and pressures). This is real challenge due to the combination of complex flows of the working substances (mainly flue gasses) and heat transfer. Considering available data, new approach is proposed in order to obtain information required for residual creep life estimation. In the first step, thermal – hydraulic calculation is performed followed by a thermal load estimation of a superheater tube bundle in a natural gas fired boiler, using CFD simulations. In the next step, the surface temperature is evaluated and used to determine the temperature related damage, specifically the creep life estimation. The life expectancy is in some ways influenced by imperfections, and therefore at the end of this thesis the influence of the oxide layer on the inner side of tube and fouling on outer side of tube is described.