HSRG Feed Water Regulator Case Study done by SpiralWeld™

Introduction

The many elements of a heat recovery steam generator (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 due to replacement of prematurely failed critical components. With around 4000 litres passing through the drum 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. If the water levels are too high then the risk of carryover increases, which will risk the steam turbine blade integrity. Either of these scenarios can have maintenance intensive consequences for plant operators and engineers.

The Challenge

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. 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.

Solving the Problem

SpiralWeld Ltd was approached by a CCGT / CHP power plant on the south east coast to review operating issues on thier 30% & 100% FWR valve. They had noticed these valves were failing to maintain drum level control within 6 months of installation. SpiralWeld Ltd inspected the components to understand the wear mechanisms, analysed the parent and seat materials and operating conditions. It was evident that the operating control surfaces were being heavily erroded by the high pressure and temperature flows across these surfaces. The critical dimensions at the seats were effected after only a short period of operation. 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.

A Successful Outcome

These used components were returned to standard dimensions ready for a further operating cycle. The enhanced seat performance successfully increased the mean time to failure from 6 months to 6 years, well within the standard outage cycle of the CCGT plant.

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.

Our ReManufacture+ service WILL extend the life of your components. The below images provide comparison between OEM components from service BEFORE and AFTER SpiralWeld™ ReManufacture+ upgrade. There is clear indication of errosion of the control surfcaces prior to upgrade, with only faint witness marks evident on SpiralWeld enhanced components. Those components that have undeegone our process were removed as part of a standard outage cycle and sent for clean and inspection.