Item:
- Stainless steel transition piece between the outlet of the gas turbine and the inlet of the heat recovery steam generator
- Transition joint allows significant expansion between turbine and HRSG
Problem:
- Severe cracking of transition piece within months of commissioning of the unit
- Design of transition piece not in the scope of supply of either the gas turbine or the HRSG supplier.
- Third party design and installation of transition piece
Objective:
- Identify the mechanism of cracking
- IPropose design modifications to alleviate the cracking
Findings:
- Internal pressure identified as being negligible and not a cause for concern
- Thermal analysis of steady state condition indicates stresses not great enough to cause cracking
- Thermal transient analysis of start-up predicts large thermal difference between the flanges of the transition piece on the gas turbine and HRSG sides. These differences result in stresses which demonstrably predict cracking in the timescales observed
- The analysis identifies the design features which are at the root of the problem
Outcome:
- Design modification proposed which significantly reduces the stresses during start-up, thus greatly reducing the likelihood of cracking
Benefits:
- Design modification implemented which successfully eliminated the cracking
- Analysis and proposed design modification undertaken in short timescales
- Minimum downtime for the CCGT plant
- Cost effective solution implemented
Published:
Brear, J.M. and Jarvis, P
“Cracking of a gas turbine to HRSG transition piece”
IMechE HRSG User Group, Warwick, 11-12 Nov 2009