With over 30 years of experience in power and industrial steam generation services, Tetra Engineering has along history of projects.
For more information on any of these projects or Tetra capabiltites contact your regional Tetra office here.
During the 2018 shutdown at a CCGT in Europe several of the HRSG HP drum riser nozzle and downcomer nozzle welds were checked and all were found to be cracked on the inside of the drum, at the weld toe or between weld beads, with the cracks following the fusion line back to the nozzle. The drum feedwater inlet and steam outlet nozzles (above drum waterline) were both undamaged. The drums were removed and all welds were repaired in the workshops. Tetra performed Finite Element Analysis (FEA) and operational data analysis and could conclude that the operational stresses were high enough given the current cycling regime to cause the cracking observed. The quality and design of the original welds is also likely to have contributed to the cracking.
Client region: Europe
Caustic soda is injected into the product water in order to raise the pH as required by the specification. Inspection of GRP piping has often shown large amounts of deposition inside these pipes. Deposition is mostly observed downstream of the injection point of sodium hydroxide and can therefore be attributed to unsuitable chemical injection. Typical injection setups utilise four simple (no nozzle) injection ports at 90° from one another causing ineffective mixing of the flows, leading to the observed precipitation. Tetra performed a CFD analysis of the caustic injection process to investigate the degree of mixing of the two flows and simulate the effects of modifying the volumetric flow rate.
Client region: Middle East.
Tetra was engaged by a client to investigate the recently observed cracking on the diverter damper actuator. The design documentation and failure mode was reviewed. From this initial review it could be concluded that the shaft cracking is most likely a result of the operating procedure, where the damper is kept in an open position for an extended period of time. The exposure to hot flue gas in combination with the load acting on the toggle arms is the most likely source of the cracking
Client region: Middle East
Caustic soda is injected into the product water in order to raise the pH as required by the specification. Inspection of GRP piping has often shown large amounts of deposition inside these pipes. Deposition is mostly observed downstream of the injection point of sodium hydroxide and can therefore be attributed to unsuitable chemical injection. Typical injection setups utilise four simple (no nozzle) injection ports aStaff at a CCGT plant engaged Tetra to investigate the root cause of the cracking and damage appearing on the Main Steam Valve (MSV) stellite seat ring(s). The metallurgical analysis identified iron dilution from the F91 valve seat into the hard-facing alloy as the root cause of the debonding. The extent of the iron dilution is a sign of excessive heat input, most likely caused during the welding process. This points towards the welding during fabrication as the actual root cause of the failure. The driving force for failure / debonding of the Stellite hardfacing could also include residual stresses from welding and/or transient heat transfer stresses and/or thermal shock during operation.t 90° from one another causing ineffective mixing of the flows, leading to the observed precipitation. Tetra performed a CFD analysis of the caustic injection process to investigate the degree of mixing of the two flows and simulate the effects of modifying the volumetric flow rate.
Client region: Middle East.
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.
Client region: South East Asia
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.
Client region: Asia
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
Client region: Middle East
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
Client region: Europe