Analyzing Existing Flanges

The reasons for flange leakage and the decision to repair, insulate, or replace the flanges can be determined by visual inspection of the flange, by comparing the existing flange thickness against the ASME and Company recommended thickness, and by relating the onset of leakage to some significant event (i.e., startup, upset, or rain storm).

Inspection
The following inspection techniques can be used to analyze existing flanges:
• Check for flange rotation. Are the flanges “metal-to-metal” around any part of the circumference?
• Inspect the gasket. See Figure 1000-2 for problems that examination of the
gasket can point out.
• Inspect the gasket seating surface for damage or corrosion.
• Measure the flange thickness to determine if it is at or below ASME tmin.
• Measure the critical dimensions and compare them with the original exchanger and TEMA tolerances. Figure 1000-3 can be used for this purpose.

Determining the Cause of Leakage by Examining the Gasket

The following procedure can be used for analyzing existing flanges:
• Check the flange thickness versus ASME tmin and Chevron Method tmin using the PCFLANGE program for the existing gasket design. If existing thickness is less than ASME tmin then flange will need to be replaced.
• Determine if a different gasket will solve the problem. Use Figure 500-15, in Section 540, to choose the optimum gasket. Determine the ASME tmin for the new gasket. If the existing flange is not thick enough to properly compress the gasket consider replacing the flange.

Exchanger Flange Tolerances

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