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Avec plus de 30 ans d'expérience dans les services de production d'électricité et de vapeur industrielle, Tetra Engineering a une longue histoire de projets.
An assessment of the susceptibility of HRSG piping components was performed according to Tetra Engineering’s FACRisk™ methodology which includes the use of thermal modelling simulation software (PPSD). From each system, sub groups are ranked using both time to minimum wall thickness and wear rate. The highest risk components (such as elbows, tees and valves) are identified. Overall, due to relatively high operating pH level (>9.2), the overall risk of FAC failures at the CCGT plant in question was considered to be relatively low, with few specific areas showing increased risk. Three separate load cases were simulated and analysed to determine the potential FAC risk. The results of each simulation were incorporated into the final locations recommended for inspection.
After several tube failures in recent years in the 1st row of LTRH hanger tubes, Tetra was tasked with performing a Root Cause Analysis (RCA) to determine the underlying cause of the failures. A detailed review of operating data, failure reports and design information was carried out and potential causes investigated. The tube failure mechanism as determined by metallurgy was short-term overheating, with temperatures likely exceeding 700°C prior to failures. Two contributing causes were identified by elimination of all other possibilities: temporary loss of steam flow in affected leading row tubes coupled with high flue gas temperatures in certain tubes at the side of the boiler gas path. Unfortunately, the underlying root cause of the loss of flow could not be confirmed, whereas the asymmetric flue gas temperature distribution is a known issue since commissioning.
During a recent condenser tube leak at a CCGT Power Station in the Middle East, two trips occurred on the boiler feedwater pumps leading to trips of one of the HRSGs. During that time, three tubes failed on the HP Evaporator. Tetra Engineering performed an investigation into the failures with the aim of determining the failure mechanism, to estimate the root cause of failure, and to identify inspection priorities in case damage may have gone undetected. This work included metallurgical analysis and a review of key operating data. Failures were located directly under the risers at extreme ends of the HP Drum. The most probable source of tensile overload is tube quenching when flow restarted
In 2015, it was discovered that the thermal sleeve in the attemperator in a client’s power station hot reheat line had failed, resulting in fracture around the circumferential weld in the sleeve’s mid section. For this reason, Tetra was engaged by the owner to investigate. The investigation showed failure from fatigue cracking. There were no signs of thermal fatigue damage, hence quenching from over-spraying was discounted as the root cause. The cracked area showed signs of high cyclic local strain, and given the moderate number of starts low-cycle fatigue was thought to be the root cause. Differential thermal expansion between the Grade 22 sleeve and the Grade 91 pipe, combined with lock-in of the sleeve on the pin locations, would raise sufficiently high stresses
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