Boiler condition assessment surveys are aimed at quantification of the current condition of boiler components and the estimation of the remaining safe operating life. A combination of non-destructive evaluation, post-exposure thermo-mechanical testing and metallographic evaluation is utilized to determine the current condition of the material. Non-destructive evaluation reveals life-limiting damage mechanisms, of which the rate determining factors are subsequently quantified through post-exposure testing and/ or metallography.
The most prevalent degradation mechanisms associated with boilers are creep, softening and metal loss. SecMet’s suitably qualified personnel and extensive experience in creep testing and assessment, enables the accurate in-house evaluation of replicas, classification of microstructures and measurement of scale deposits in accordance with internationally accepted creep and softening classification systems.
SecMet’s world-class creep testing enables determination of creep life expended and remaining safe operating life. A combination of experimental and calculative procedures is used, in accordance with internationally accepted methods. Our many satisfied clients globally can attest to the financial benefits resulting from our boiler condition surveys.
The slow and continuous deformation of metals at high temperatures below the yield stress is defined as creep. Therefore, it is a time dependent deformation process of a stressed component and all metals and alloys are susceptible to it. Creep behaviour is relevant above four-tenths of the melting point (0.4 Tm).
The general rule of thumb is that an increase of 12°C or increase of 15% in stress can reduce the remaining creep life by half or even more – depending on the alloy. Increased stress due to loss of thickness due to corrosion will reduce the creep life exponentially with time.
Remaining Life Estimation for Assets
A Remaining Life Assessment (RLA) can be performed at any given stage of the equipment life in order to establish a retirement or replacement plan for equipment nearing the end of their life cycle or equipment that has been operated longer than its original design life.
The creep rupture life assessment procedure provided in API 579-1/ASME FFS-1 2007 Fitness-for-service provides a systematic approach for evaluating the creep damage for each operating cycle that may be applied to a component as a result of multi-axial stresses in the component. The total creep damage is computed as the sum of the creep damage calculated for each cycle.
Furthermore, for equipment that operates in the creep range (typically above 427 °C), temperature excursions may be experienced and as a consequence, the creep life may be significantly reduced. In such cases, a fitness-for-service and remaining life assessment is performed to verify that the component or equipment is still fit for continued service and to determine the revised creep life.