Thermal power plants are the backbone of India’s energy sector, contributing over 65% of the nation’s electricity. These facilities operate under extreme conditions, with steamlines designed to sustain pressures around 4.5 MPa. Over time, these critical components can deteriorate due to wear and tear, compromising their structural integrity. Regulatory authorities often recommend either replacing the compromised parts or shutting down the plant altogether—both options being far from ideal.
- Replacement Challenges: Some components are too large, complex, or expensive to replace.
- Shutdown Consequences: Halting operations can result in massive losses and disrupt power supply.
However, Fitness-for-Service (FFS) analysis offers an alternative solution, enabling the evaluation of damaged components without interrupting operations.
A prime example of this is the Kalisindh Thermal Power Plant in Rajasthan, operated by Rajasthan Vidyut Utpadan Nigam. The plant’s main steamline, which transports high-pressure steam (up to 4 MPa) to the boiler, had developed four visible dents over time. A failure in this steamline could halt the boiler and shut down the entire plant. With the steamline in service for over 25 years and originally designed by a Chinese company, the plant faced a daunting challenge requiring immediate attention.
Fig – Dent in boiler steamline
Challenges
Replacing the damaged steamline wasn’t a feasible option due to its size and location. The steamline, measuring 1067 mm in diameter and positioned at a high elevation, required meticulous measurements for accurate modeling. To proceed with FFS, Finite Element Analysis (FEA) was essential, demanding precise dent modeling based on on-site laser scans.
Fig – actual visuals of dent in steamline.
Solution
Comprehensive FEA and MAWP Analysis
The steamline had four dents located in various sections, including the pipes and elbows. Using 3D measurement data from on-site laser scanning, a detailed CAD model was developed. FEA simulations were then conducted under three critical load cases:
- Internal Design Pressure.
- Operating Pressure.
- Maximum Allowable Working Pressure (MAWP).
Fig- concept of MAWP
Understanding MAWP
Maximum Allowable Working Pressure (MAWP) is the highest pressure a vessel can safely sustain as defined by design codes.
- MAWP: Slightly higher than the design pressure but below the Maximum Allowable Operating Pressure (MAOP).
- MOP: The regular working pressure under standard operations.
Fig- equivalent stress representation
Analysis Results
Dent Locations and Elevations:
- Dent-1: 4.495 m
- Dent-2: 16.6 m
- Dent-3: 21.7 m (near the nozzle)
- Dent-4: 47.9 m
- Elbow Dent: 48.2 m
Fig- representation of dent formation in elbow.
Design Parameters:
The FEA analysis was performed according to ASME Section VIII, Division 2 Edition 2013 standards. Stress analysis revealed maximum stress concentrations around the dents.
Design and Operating Pressures:
- Design Pressure: 4.631 MPa
- Operating Pressure: 4.07 MPa
- At design pressure, Dent-2 and the elbow passed, but Dent-1, Dent-3, and Dent-4 failed.
- At operating pressure (4.07 MPa), Dent-2, Dent-4, and the elbow passed, but Dent-1 and Dent-3 still failed.
This indicated that 40% of the dents posed a future failure risk.
Setting MAWP to 3.5 MPa:
To ensure safety, the MAWP was recalibrated to 3.5 MPa, reducing operational stress. At this pressure:
- All dents passed the stress analysis.
- Primary and secondary stresses ranged from 72.108 MPa to 385.17 MPa, remaining within the allowable stress limit of 385.58 MPa.
Conclusion
Dents and flaws in industrial components are inevitable due to prolonged use and operational stress. While minor damages can be repaired or replaced, larger and more complex components often require innovative solutions to avoid costly shutdowns.
Fitness-for-Service (FFS) analysis offers a sustainable, cost-effective alternative by leveraging numerical simulations to assess and extend the life of damaged equipment. At the Kalisindh Thermal Power Plant, this approach enabled safe operations to resume, preventing a potential shutdown and ensuring continued power supply.
Thanks to FFS and meticulous engineering analysis, the plant is back in action, demonstrating how technology can keep our essential infrastructure running smoothly.