Refining Industry Experience with HF Unit Flange Face Corrosion and Detection for API RP 751

The corrosion of raised face flanges and subsequent build-up of a more voluminous iron fluoride scale has been a historic problem encountered by refining industry Hydrofluoric Acid Alkylation processors.  The iron fluoride build-up, which generally initiates on the inner diameter of the raised face of the carbon steel flange, sometimes progresses sufficiently to cause a leak in that component.  API has addressed the need for inspection of these flanges in API RP 751; however specific inspection procedures are not specified.  Phased Array Ultrasonic has been successfully applied for the inspection of these flanges, both on line and during shutdowns to assess and prioritize the conditions of these flanges for mechanical remediation during turnarounds.  An overview of Phased Array will be presented along with results of actual plant experience employing this methodology for non-invasive corrosion assessment of these critical components.