Metals analyser pinpoints power plant failure

London - A hired out, portable XRF (x-ray fluorescence) alloy analyser has enabled engineering consultants at Tetra Engineering to investigate and pinpoint failures within a power plant’s complex pipeline network.

Flow-assisted corrosion (FAC) has long been a common problem for nuclear and fossil fuel power plants, in which steel piping and its components are degraded due to flowing water or steam-water mixes. As the water flows, the surface layer of the piping is dissolved, resulting in the pipe walls thinning over years of use.

Research has shown that FAC is a function of temperature, velocity, pH, dissolved oxygen, the geometry of the component, and the material properties of the pipe. While most of these variables can be measured or inferred it is the material properties that are most elusive.

Researchers have also found that the presence of the alloying elements of chromium (Cr) and molybdenum (Mo) has a big impact on the pipe resistance to FAC, and that even small amounts can make a difference. Specifications for carbon steel piping often exclude these elements or simply set an upper limit. When trying to predict wear on pipes engineers often have to guess at suitable Cr and Mo levels.

To tackle this problem, Tetra Engineering contacted Ashtead Technology to hire the handheld Niton XL3t XRF analyser as part of a project focussing on degrading pipework at a combined cycle power plant in the UK.

With the XL3t analyser, the elusive variables are now field measurable, and the results can be fed back into the predictive calculations. Areas suggesting signs of possible future damage can be better identified and then monitored using ultrasonic thickness testing, allowing engineering experts to replace any pipes found to be at risk and to modify the design or plant operations.

Prior to the advent of XRF technology, spark-based OES (optical emission spectroscopy) instrumentation was traditionally used but this was typically larger equipment which also required complex and time-consuming sample preparation in contrast to the small, easy-to-use XL3t.

Mark Taylor, a senior engineer at Tetra, said: “The new XL3t analyser enabled us to easily identify the Cr and Mo content of components in the piping system. As a result of this we were able to refine our engineering calculations and to re-rank the risk of failure of susceptible components.

“In addition to FAC work we have also used [analyser] on general plant inspections, and for practical purposes it is far superior to using the services of an analytical laboratory.

The XL3t enables users to carry out on-site positive material identification (PMI) and elemental analysis of alloys quickly and easily. It has increased precision and lower detection limits than was previously achievable with XRF technology. Several hundred alloys are stored on the instrument's library and customised settings are available for unique alloys, including a 'pass/fail' mode.

Supplied with the Niton Data Transfer software to generate reports, the XL3t also features a tilting colour touch-screen display for easy viewing and can give laboratory quality results in a matter of seconds.

Ashtead’s General Manager James Carlyle said: “The Niton XRF XL3t analyser provides fast and easy access to high-quality test data. However, they are highly sophisticated and costly tools to purchase outright, making them ideal for renting.

“Instrument hire is ideal for project work of this nature; we have a full range of the latest PMI equipment which means that customers are able to use exactly the right technology for the period of the work and no longer. This ensures that the inspection is undertaken as quickly and effectively as possible with minimal costs.”