Tue, 07 October, 2025
Effective Baseline Inspection as a Foundation for Development of Preventive Maintenance Strategies
An effective asset integrity management (AIM) begins with the establishment of a comprehensive initial condition of the assets which can be achieved through a comprehensive baseline inspection program. This baseline data serves as a technical benchmark for developing a targeted and efficient preventive maintenance (PM) plans in the future.
TWI Services recently completed a baseline inspection study for a Combined Cycle Gas Turbine (CCGT) power plant in Malaysia prior to its commissioning. The scope of work included:
- Identification of potential threats and damage mechanisms
- Development of Condition Monitoring Locations (CMLs)
- Execution of on-site inspection activities
- Establishment of a preventive inspection program for the Heat Recovery Steam Generator (HRSG) unit and its associated piping and pressure parts/components
Using available design and operating data, the study first determined the susceptibility of the HRSG components to various degradation mechanisms through a systematic review of relevant codes, standards, and published technical literatures e.g. API 571, ASME PCC-3, and EPRI guidelines. The assessment considered multiple parameters, including:
- Material of construction
- Type of process service (particularly for internal degradation)
- Environmental conditions (for external degradation)
- Protective measures and design features
- Operating parameters such as temperature and pressure
- Historical and experiential data from plant engineers and comparable units
The key damage mechanisms identified included high-temperature degradation (creep and thermal fatigue), corrosion under insulation (CUI), and flow-accelerated corrosion (FAC). The CML were then established based on the identified damage mechanism.
These CML are crucial for gaining information on the condition, corrosion, erosion, wear, and/or other issues that could affect the integrity of the components and further guide the inspection plan. For this case, CML were marked on the drawings and inspection templates of the HRSG components. They were selected to monitor factors like wall thickness loss, stress cracking, CUI, high-temperature damage, and more. The CML were mainly placed where damage is most likely to occur, such as elbows, tees, reducers, caps, and straight pipe sections. Based on the data collected from these CMLs, decisions can be made about necessary maintenance, repairs, or replacements to ensure safe and efficient operation.
Next TWI Services conducted the baseline on-site visual inspections and ultrasonic thickness measurements (UTTM) in accordance with the established CML and inspection plan. A baseline inspection is a crucial initial assessment carried out before an asset is commissioned or placed into service. The followings are the key properties that must be verified through quality assurance/quality control (in this case, by the owner) and on-site inspection activities, to ensure compliance with the intended design and project requirements:
- Materials of construction
- Design and installed wall thickness.
- Condition of coating or insulation
Performing this inspection upon receipt of the asset is considered best practice, as it provides a clear reference point for future condition assessments and supports long-term asset integrity objectives.
Finally, a preventive maintenance and inspection plan was developed based on the results of the baseline inspection, taking into account the early-life stage of the components. The plan outlined recommendations for inspection methods, coverage, locations, and frequencies for each HRSG component.
In addition, the implementation of a Risk-Based Inspection (RBI) program was recommended for all HRSG components, and to be expanded across other parts of the plant. RBI evaluates the likelihood and consequence of potential failures to calculate the risk, allowing for prioritization of inspections, optimization of maintenance efforts, extension of asset life, and effective risk mitigation. This approach also aligns with regulatory expectations for transitioning toward a self-regulated plant management system.
The baseline inspection completed by TWI Services has laid a strong foundation for effective asset integrity management at the CCGT power plant. By identifying potential damage early, setting up the CML, and creating a tailored maintenance and inspection plan, the plant is better prepared for safe and reliable long-term operation throughout its lifecycle. The recommendation to implement an RBI program further supports a proactive approach, helping to prioritize inspections, reduce risks, and meet regulatory goals for self-regulation. This baseline program not only protects the assets from the start but also helps improve performance and extend the life of the plant.