Online Continuous Non-Intrusive Corrosion Monitoring is fast becoming industry best-practice in the Refining Industry globally. This technique involves wireless battery-powered sensors placed in the process units which deliver high-quality data directly to the desk of the corrosion engineer. This paper will present a case study and learnings from various refineries from the deployment of non-intrusive ultrasonic wall thickness monitoring systems in HF alkylation units.

Online non-intrusive automated corrosion monitoring of HF alkylation units is valuable due to the safety risks associated with inspection inside these units, as well as the high probability of corrosion events and grave consequences of leakages. The technology discussed in this paper was developed using information from around 300 thickness monitoring sensors installed across 12 HF alkylation units globally. Traditional expectation is that iron fluoride scale layers that build up will not affect ultrasonic thickness results. However, through monitoring using permanently installed ultrasonic sensors, it was observed that the scale layer did negatively affect the ultrasonic signal. Our field experience has led to the development of an advanced signal processing algorithm, designed to be less affected by the effects of ultrasonic distortion due to the scale build-up.

Data examples will be presented to explain this effect and comparisons between traditional signal processing methods and the advanced methods developed for this application. We close with a case study from a refinery who, via online monitoring of their HF alkylation unit, were able to detect elevated corrosion rates and take action to bring the corrosion under control, before any danger.


In oil refineries, one corrosion issue occurs each week worldwide that leads to a severe incident such as sudden leakages, e.g., resulting from pipe ruptures.[1] These facts emphasize the need for corrosion control in refineries. Corrosion monitoring is one important approach to utilize and can maximize equipment integrity and productivity. Other than traditional monitoring techniques (e.g., intrusive probes or manual ultrasonic wall thickness inspection), new wireless sensors were developed in recent years. They monitor pipe or vessel wall thickness and, thus, corrosion online by ultrasonic testing (UT).

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