Inspectioneering Journal

Utilizing TFM/FMC for Detection of Flange Face Corrosion

By Mark Schramm, Advanced NDE Services Manager at Pro-Surve Technical Services. This article appears in the May/June 2020 issue of Inspectioneering Journal.


Regular inspections can be very beneficial to industrial processes. However, choosing the right inspection method and the right inspection percentage/frequency can be a challenging task. When choosing an inspection method, there are several things that must be considered, such as:

  • the cost of inspection vs. the risk of not performing inspections,
  • the value of the inspection, (i.e., will it provide the information needed to make effective decisions regarding run/repair/replace status of the equipment?),
  • which types of inspections will yield the best results for the application and type of damage expected,
  • when inspections should be performed, and
  • what the acceptance criteria for the inspections should be.

With new advancements in technology emerging rapidly, tools for customizing an inspection to address special requirements are becoming more available, feasible, and powerful. Each damage mechanism is unique and sometimes customized tools are necessary to achieve the desired result. One such tool and technique is utilizing Total Focusing Method/Full Matrix Capture (TFM/FMC) to inspect in-service flange faces for corrosion. Specifically addressed in this article is the detection and quantification of Hydrofluoric (HF) acid corrosion of flange faces.

Because the risk of bodily injury to personnel or the environment is so high in the case of an HF acid leak, it is necessary to regularly inspect all of the flanges in HF acid services (even trace HF acid services) to prevent leaks from happening. The most common method used to inspect flange faces is to schedule regular shutdowns of the pressure equipment followed by opening, cleaning, and visual inspection of each flange pair, often performed on a rotation. The corrosion damage is oftentimes not visible without the use of a straight edge ruler and a flashlight (See Figure 1) because of its slight, smooth tapering corrosion appearance in lieu of the rough, carbuncle looking corrosion seen with other damage mechanisms.

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