- Detect high pressure valve leakage even under insulation, liquid or gas
- Instantly check full valve closure & seating
- Look for expensive leaks in compressed air and other gasses
MHC - Monitoring Valves in Power Generation
All valve seats will wear. The maintenance frequency depends upon its operating conditions and its usage. In the case of high pressure water valves there is a strong financial incentives to refurbish any valve starting to pass, fail or otherwise leak. To identify such worn valve seats at the earliest opportunity Nuclear Electric staff at Hartlepool Power Station use Acoustic Emission (AE) from Holroyd. Full details are available on the download data sheet, the main points are:
- Turbulent flow of pressurised fluids escaping past a worn valve seat generates acoustic noise in ultrasonic frequencies. In high pressure systems, the escaping fluid past a worn seal promotes accelerated wear and this provides a greater impetus for its early detection.
- Hartlepool Power Station needed a monitoring technique which was easy and quick to use but would give them meaningful numbers that could be logged and trended over time (as opposed to a ‘listening-stick’ type of instrument with a subjective headphones output).
An MHC instrument was used to take spot measurements on eight major valves over 6 months. Some valves retained steady AE levels whilst some others rose progressively as shown in Fig 1. AE measurements were used as the basis for selecting specific valves on which to carry out detailed inspections. It was confirmed that those valves with increasing Distress® levels had valve seats which were visibly worn when stripped down. Invasive measurements showed that the valve with the degraded seat in Fig 1 for example was passing 2.5 kg per second of water when fully closed at 200 bar. When a valve seat was replaced the Distress® level reduces as shown for a valve in Fig 2. Interestingly, the level soon starts to rise again, presumably indicating that maintenance in this occasion had been insufficient to cure the problem.
On some valves however there was a slight complication in that the progressive wear in the seat of a valve (which was not being monitored as part of the research) was detected and mis-ascribed to a nearby valve which was being monitored. This experience brought home the importance of monitoring the whole of this part of the plant in order to get an AE fingerprint of all the valves.
Hartlepool Power Station continues to use Holroyd MHC sensors in permanent installation for monitoring of large valves critical to their plant operational efficiency.
Click to enlarge