Plant Life Assessment
hrl: use a well proven methodology to assess the residual life of materials from knowledge of creep properties, degradation processes, material condition, thermal history and operating stress.
For more precise prediction on critical components, accelerated creep tests can be carried out either on miniature samples removed non-destructively from the operating component, or on full size samples.
hrl: has been involved in life assessment investigations and research studies for over thirty years. Techniques for assessing life degradation have been developed and evaluated in laboratory test programs. This has established the reliability of microstructural changes, carbide transition and development of cavitation as an indicator of the creep condition of various alloy steels. Creep testing techniques utilising miniature samples (that can be taken from operating plant non-intrusively) tested under argon have greatly improved the reliability of assessments.
Plant studies have been carried out involving the detailed collection and analysis of data on the thermal histories of components, and various data reduction methodologies have been developed to assist in the process. Plant instrumentation and other indirect techniques such as using the measured bore oxide thickness have also been used to understand the thermal history and thus determine the remaining life of creep damaged materials. Studies into the creep behavior of weldments, and the weld repair of creep damaged steels are also keeping our engineers at the forefront of knowledge of creep and life assessment.
How we can help
Plant Life Assessment
The assessment of remaining life of high temperature components generally requires creep analysis, which is very sensitive to temperature. In most cases limited data on operating temperatures is available, however, in steam plant the thickness of the protective internal oxide layer provides a good indicator of thermal history. Using ultrasonic techniques, from the outside of tubing, we are able to measure wall thickness and the oxide thickness nondestructively and from this infer tube metal temperature.
Using various correlations for specific alloys the average operating temperature and remnant life can be predicted. In addition, the temperature distribution across a boiler can be gauged and advice offered on the effective modifications to improve the temperature distribution. Detailed microstructural analysis of carbide transitions, spheroidisation or cavitation are used to characterise the materials and impact of service on the remaining life.
Integrity of Components
Plant failures result from overload, fatigue, propagation of cracks, creep deformation or various combinations of these processes often complicated by corrosion activity. hrl: has a range of assessment packages covering fracture mechanics, fatigue and creep to determine the significance of known defects in components and structures. We use a run-repair-replace strategy to assess the severity of defects, to specify criteria for acceptance of plant during inspection and compliance with design codes.
We use a well proven methodology to assess the residual life of materials from a knowledge of creep properties, degradation processes, material condition, thermal history and operating stress. For more precise prediction on critical components, accelerated creep tests can be carried out either on miniature samples removed non-destructively from the operating component, or on full size samples.
Detailed inspections are an essential component of asset management and hrl: has carried out inspections at several cogeneration stations, smaller power plant and to base load power stations operating around the country. hrl: has experienced and qualified inspectors to visually assess plant in accordance with statutory requirements, such as AS3788. We develop plant inspection manuals and risk-based inspection programs. Technicians with highly developed skills in the non-destructive evaluation of components identify any cracks or defects and estimate thermal history of plant. Our laboratories are NATA registered for these inspection activities. hrl: also provides management and resourcing of inspection outage programs including the necessary audit and interpretation.
Using strain gauges and thermocouples affixed to plant components we obtain data to calculate residual and operating stresses resulting from mechanical loading, thermal gradients, thermal cycling and vibration. We operate sophisticated 3D finite element analysis software to determine the stresses in structures and components of complex geometries. The analysis makes allowances for creep relaxation and cracking and is applied to single components and integrated systems. The distribution of stress, strain and temperature within a structure and their variation with time is calculated from the finite element models.