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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.
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.
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.
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.
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
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