HOTSCAN

Long range ultrasonic system for continuous in service inspection and structural health monitoring of high temperature superheated steam pipes in power generation plant with 100% coverage

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 Obiettivo del progetto (Objective)

'A typical electricity power plant of 500MW (both nuclear and conventional) has up to 4 kilometres of pipe work carrying superheated steam at pressures of up to 400 bars and temperatures up to 580 oC. The extreme pressures produce hoop stresses in a pipe causing the pipe welds to creep continuously in time until weld creep cracks are generated which, if undiscovered, may grow until the pipe ruptures. The pipes also suffer continuous cyclic loading through vibrations which produces fatigue cracks in the welds which if undetected are another cause of pipe rupture. Worldwide, failure to detect steam superheated steam pipe cracks results in a catastrophic failure every year or two with loss of life, appalling injuries, widespread power cuts and massive financial losses for the operators, typically with a cost impact of €120m per event. The project goal seeks to overcome the serious problems of superheated steamline integrity through the use of a high frequency long range ultrasonic condition monitoring system, permanently installed on pipe work, which will continuously inspect all welds in a plant during the entire plant design life whilst in service at 580oC (HotScan). Once installed at an outage there will be no need to remove lagging and perform inspection at subsequent outages, thus reducing planned outage time by 5% with a total saving €162 Million per annum (nuclear sector and €374 Million per annum (fossil fuel sector) if the HotScan system was deployed throughout the entire stock of EU power plant. The system will identify all creep and fatigue cracks of length greater than 1% of the pipe circumference, reducing the weld failure probability to below, eliminating forced outage time due to weld failure. So the forced outage time from all causes will be reduced by 10% thus saving €0.352 Billion per annum (nuclear sector) and €2.53 Billion per annum (fossil fuel sector) in the EU assuming widespread HotScan deployment.'

Introduzione (Teaser)

In electric power plants, pipelines carrying steam can fail due to corrosion fatigue. To retain the reliability and extend the life time of plants, EU-funded researchers have developed techniques for in-situ condition monitoring.

Descrizione progetto (Article)

A typical electric power plant of 500 megawatts (either nuclear or conventional) can have up to 4 kilometres of pipe work carrying superheated steam at pressures up to 400 bars and temperatures up to 580 degrees Celsius. The stresses produced by the extreme pressures and temperatures can result in cracks leading to pipe ruptures. Failure to promptly detect cracks once initiated can cause catastrophic accidents with appalling injuries and widespread power cuts.

During scheduled outages when the power plants shut down for maintenance and repair, pipelines are inspected with non-destructive testing techniques. The http://www.hotscan.eu/ (HOTSCAN) project received funding under the Seventh Framework Programme (FP7) to develop a monitoring system that would be permanently installed on pipelines. Once installed during a scheduled outage, the new system would continuously inspect all welds while the plant is in service.

Ultrasonic guided wave testing was identified as the most suitable method to detect structural defects and monitor their growth. In particular, guided waves can propagate in cylinders and different elongated structures, enabling inspection of a large area. This technique had been successfully employed at ambient temperatures, but the extremely high temperatures in power plants presented a great challenge for HOTSCAN researchers.

The long range ultrasonic technique proposed by HOTSCAN researchers is based on an array of transducers placed around a pipe to transmit sound waves and receive the echoes. The transducers were manufactured using a special type of lithium niobate crystal that retains its piezoelectric behaviour at temperatures as high as 600 degrees Celsius. Dedicated software was also developed to analyse the data received from the array of transducers.

The HOTSCAN system can identify cracks having cross section greater than 1 millimetre. This reduces the probability of a power plant failure due to steam pipe ruptures to below 1 in 10 000. Such continuous inspection of all welds reduces the planned outage time by up to 5%, resulting in significant cost savings.