Material degradation, corrosion, cracking, and particularly catastrophic failure are undesirable, but they are intolerable when it comes to turbine and generator components. AMCO’s experienced technical staff from UK, USA & Japan is knowledgeable in all aspects of turbine/generator asset integrity management, including advanced NDE inspection, finite element analysis, reliability centered maintenance (RCM), component life assessment, metallurgical investigation of damaged and failed components and evaluation of turbine material properties by removing and testing small samples without the need for repair or replacement. We at AMCO, use our advance technology like Electric Discharge Sampling Equipment (EDSE) for removing the sample without heating or damaging the turbine component.
The engineers in our laboratory have the ability to conduct a full range of metallurgical assessments, whether as an individual service in support of a root cause analysis (RCA) team at the corporate level or plant site, or as part of a multidisciplinary approach to failure investigation that involves a range of engineering services from AMCO.
Evaluating Material Condition and Damage Mechanisms
The need for material evaluations can result from inadequate knowledge of the properties or details of the materials of construction, from identified conditions in which some level of material damage is suspected, from direct identification of damage, or from a component failure. Metallurgical and mechanical testing can be performed on large samples, or testing can be performed on small samples removed from the component(s) in question. For example, turbine wheels may be evaluated by removing small “scoop” samples, which allow for metallography, hardness testing, and estimates of strength and toughness properties without having to remove the wheel from service. Alternatively, components such as turbine blades (buckets), rotors or rotor sections, bolts
shims, etc. can be evaluated individually or in groups. In the case of material properties, testing can include chemical composition analyses and alloy verification, microstructural evaluation and associated hardness testing, and detailed mechanical testing to obtain tensile strength and fracture toughness properties. When material damage is suspected, or when damage or failure has occurred, testing can include property evaluations, as described above, in addition to fractography (optical and scanning electron microscopy), elemental analysis of contaminants that might be associated with material degradation such as stress corrosion cracking, metallography for evaluation of damage morphology, and identification of the damage mechanism. Metallurgical (destructive) testing is often performed as part of a formal Root Cause Analysis (RCA), with the testing results feeding into the RCA Team’s information database.
General categories of failure mode that are typically considered include overload, stress corrosion cracking, and fatigue failures. Since material properties can affect component behavior within each of these failure modes, evaluation of the component’s material condition and comparison to appropriate material specifications is also important. Once the failure mode is identified, an RCA team can combine information regarding the machine’s operating history, vibration data, cycle chemistry, and stress distribution to ultimately determine why the turbine failed. Our team of experts understand these goals, and can provide a full range of failure analysis testing and analysis methods to assist with causal analysis.