FAC Inspection
Date: 26/11/2022 | read: 140

Carbon steel and low-alloy steel are often used in the manufacture of transportation pipes, and pipes made of these steels are often used in nuclear, fossil and other energy industries. During the operation of nuclear power plants and the transportation of liquid fossil fuels, Flow accelerated corrosion (FAC) means that the corrosion progress of pipelines will be accelerated due to contact with flowing liquids, which increases the risk of leakage events and safety accidents. The accelerated corrosion process of the fluid will be affected by the physical and chemical state of the fluid such as temperature, acidity value, temperature, oxygen content, and flow rate; from the perspective of raw material smelting and product manufacturing, if the steel contains a small amount of chromium, copper, molybdenum, the corrosion rate will be significantly reduced. Therefore, the content values of trace elements are often used in the risk assessment of steel FAC, which is also an integral part of positive material identification (PMI).

What is FAC (Flow Accelerated Corrosion)

Flow-accelerated corrosion (FAC), is a corrosion mechanism in which a normally protective oxide layer on a metal surface dissolves in a fast flowing water or fluid. The underlying metal corrodes to re-create the oxide, and thus the metal loss continues. As the water flows against the carbon steel material, the surface oxide layer, Fe3O4 is dissolved into the flowing stream. As a result, it make the wall of piping thinner over time.FAC was the cause of several high-profile accidents in nuclear and power plants.

What Are the Factors Influencing FAC

FAC often affects carbon steel piping carrying ultra-pure, deoxygenated water or wet steam. Stainless steel does not suffer from FAC. FAC of carbon steel halts in the presence of small amount of oxygen dissolved in water. FAC rates rapidly decrease with increasing water pH.
In a summary, the FAC process is mainly influenced by the following factors:
(a)The chemical composition of the steel, mainly the elements of Cr, Cu and Mo in the piping made of carbon steels and alloy steels
(b)Water or fluid chemistry like temperature, Ph, Oxygen and etc.
(c)Flow variables, like the velocity, fitting geometry etc.
Among these, the chemical composition material of the piping, especially the Cr concentration is the most important.

How to Do FAC Inspection

Chemical analysis of carbon steel piping in FAC inspection has traditionally been performed by laboratory analysis s or by use of spark-based Optical Emission Spectrometer, due to the need for detection of very low levels of chromium. Spark OES technology, although very reliable but it is not very friendly for onsite analysis because it will need to damage the sample and do sample preparation. In addition, it is heavy and is not convenient to move to onsite to do analysis. Further more, it requires the operator of OES be qualified and well trained to do some calibrations.
But now there is much more convenient and reliable FAC inspection with a non destructive way and efficient onsite testing method. That is handheld XRF analyzer.
Using the AXR Terra series handheld XRF alloy analyzer can accurately determine the content of various metal elements and improve the reliability of the determination results of trace element content in alloys. The instrument has good portability and ease of use, and the analysis results are highly readable, enabling on-site analysis under different conditions.

Handheld XRF Solution for FAC Inspection

In low alloy steels, metal elements other than iron are usually present at trace (0.01% - 1%) or trace (<0.01%) levels. The AXR Terra900 series analyzer has a lower element detection limit, which solves the problem that traditional methods are difficult to quickly and accurately analyze trace and trace elements in samples; while the instrument has high accuracy, it also has the following advantages:
(a) The instrument is portable and easy to use in different occasions
(b) No sample preparation required for non-destructive testing
(c) Short time required for quantitative analysis and reliable results
Terra900 series analyzers provide a relatively complete solution for the composition analysis and reliability identification of alloy materials. The instrument is equipped with a high-performance X-ray tube and Si-PIN detector to provide users with fast and accurate element content analysis; an optional large-area silicon drift detector is provided to further improve the resolution of the instrument and reduce the time required for analysis .

Use AXR Scientific Handheld XRF to Analyze Chromium on Flow-Accelerated Corrosion

During the analysis, standard samples were used to establish a working curve to achieve quantitative analysis. Quantitative analysis is realized by the fundamental parameter method (Fundamental Parameter, FP), so in the actual quantitative analysis of elements, no additional standard sample calibration work is required.
Before analysis, according to the detection limits of chromium Cr, copper Cu, and molybdenum Mo in iron-based alloys (30 seconds analysis time), the analyzer has the ability to accurately determine low-level elements in samples.

During the analysis, set the test time to 30s, and analyze the contents of Cr, Cu and Mo in the sample. A low-alloy steel sample with known content was tested 10 times under the same conditions, and the test time for each test was 30s. The repeatability test shows that the analysis results of the instrument are stable, accurate and repeatable, with good reliability.


AXR Terra900 series handheld XRF analyzer has good trace element detection capabilities and can accurately measure the composition and content of alloy elements. With the improved analytical capability for trace quantities of Cr, Cu and Mo make it comparable in performance to spark optical emission spectrometer for the FAC application. So they can be used as the main analysis tool for FAC determination for nuclear and fossil fuel power plants and also can be ideal tool for quality control and grade identification of alloy materials.

AXR Scientific is a high-tech manufacturer focusing on the development and application of X-ray technology products. It is committed to becoming a world-class supplier of X-ray industrial inspection solutions.AXR Scientific currently offer handheld XRF analyzer, handheld alloy analyzer, handheld soil analyzer, handheld lithium battery analyzer, precious metal analyzer, coating analyzer, gold analyzer and online XRF analyzer etc. to global customers. We keep serving global customers in the fields of machinery manufacturing, metal processing, aerospace, petrochemical, mining and geology, food safety, environmental protection, scientific research and etc. AXR Scientific keeps improving product performance and user experience with R&D advantages and innovative designs, and continues to provide global users with reliable X-ray measure solutions to solve various challenges from routine testing tasks to complex customized measure requirements. To contact us, please send email to market@axr-scientific.com