The many elements of a HRSG feed water system combine to supply and control critical drum levels. Loss of drum level control is costly in lost generation and maintenance downtime to replace prematurely failed critical components. With around 4000 litres passing through it per hour, the variable safe limits of the water levels are relatively small in relation to the size of the drum. If the water levels get too low the tubes will burn out and if the water levels are too high then the risk a of carryover increases the risk to the turbine. Either of these scenarios can have maintenance intensive consequences for plant operators and engineers.
Typical erosion pattern common to all feed water regulator valve components caused by high velocity – turbulent feed water at low aperture opening.
High operating pressure and flow rates across the relatively small control edges and apertures of the feed water control system components, cause a high rate of attrition to these critical control edges, resulting in a loss of control particularly at low aperture opening.
30% Feed-Water Regulator Valve General Assembly and Weld Map
The material compositions of the parts installed are not usually sufficient to stop the erosion and other damaging processes from taking place. The associated downtime for repairing or replacing these parts outside of a planned maintenance outage is costly in both down time and maintenance cost.
30% FWR Components from a 4000MW CCGT Power Station
Masoneilan 5 ” FWR
Masoneilan 5 ” components pre-recovery
Masoneilan 5 ” components post-recovery
SpiralWeld ™ was approached in 2011 by a CCGT / CHP power plant on the south east coast to review and recommend upgrades to 30% & 100% FWR valve internals which were failing to maintain drum level control within 6 months of installation. Following review of the materials and operating conditions, and using our combined 85 years of experience in the power industry we recommended a SpiralWeld™ ReManufacture+ service and upgrade for these components using our advanced Cobalt/Chromium Alloy overlays to the seat areas of the control plug and body seats. Not only were these used components returned to standard dimensions ready for a further operating cycle but we successfully increased the mean time to failure from 6 months to 6 years.
At SpiralWeld™ we can provide remanufacture services returning worn components to standard dimensions using equivalent material overlays. We can also provide ReManufacture+ services based on extensive power station maintenance and operating knowledge which not only recovers used components to an as new standard, but also upgrades the original design to resist wear and erosion to increase the mean time to failure.
Repairing of Feed Water Regulator Components
The recovery process that the components undergo is based around a similar set of procedures. This can differ depending on whether we are repairing a component (ReManufacture) or improving it (ReManufacture +). The following is a generalised process of what the FWR components received:
- XRF analysis of the original component.
- Full inspection including 3D co-ordinate measurement.
- Technical review to determine the damage and how to implement the recovery processes.
- Pre machine and NDT.
- SpiralWeld™ overlay.
- Proof machine and NDT.
- Finish machine and NDT.
- Final inspection and packaging for transportation and storage.
The following examples are components from the feed-water regulator system which have been recovered at SpiralWeld™ to the highest quality and with a short lead time:
As proof that our ReManufacture+ service will extend the life of your components here are some components that have had a ReManufacture+ service and have been in service for the last 12 months. You can notable see the decrease in damage compared to components shown above which have not been through our processes.
Ex-U3A4 Original design after 9 months and 83 starts- seat failure.
EX-U4A4 AD107 Ultimet overlay after 12 months and 142 starts- no failure.
Min leak off valve orifices before Remanufacture+ service.
Min leak off valve orifices after Remanufacture+ service.
Schroedahl min leak off control head before ReManufacture+ service.
Schroedahl min leak off control head after ReManufacture+ service.