A fouled PTFE tube bundle has been chemically cleaned, soaked, and flushed. The circulation is stopped, and the cleaning solution is drained. But is the bundle truly clean? Is its thermal performance restored, or does a thin, insulating layer of biofilm or scale still cling to the hidden inner walls? Before the bundle is valved back into service, a simple, two-part verification can provide the objective, documented proof of cleanliness.
Borescope Inspection: Visual Verification
The first step in verifying post-cleaning cleanliness is a borescope inspection. A flexible scope is inserted into multiple tubes, and the inner walls are visually examined. A clean tube is a bright, white, open highway for both the fluid and the light of the scope. Any residual dark scale, biofilm, or chemical residue indicates that additional cleaning may be required. The borescope also provides a permanent digital image record for the maintenance log, serving as visual evidence of cleanliness.
Pressure Drop Comparison: Hydraulic Verification
The second step is a quantitative check through a pressure drop measurement. Clean water is circulated at a known, standard flow rate, replicating the conditions used when the bundle was first commissioned. The tube-side pressure drop is measured and compared directly to the original baseline recorded when the exchanger was known to be clean. If the pressure drop returns to within a few percent of the baseline, the hydraulic path is fully restored. Together with the borescope inspection, this measurement confirms that the cleaning was successful.
Technical Considerations
Consistent Conditions: The pressure drop test must be performed at the same flow rate, fluid, and temperature as the original baseline measurement.
Documentation: Both the borescope images and pressure drop data should be recorded in the exchanger's maintenance log for traceability.
Two-Pronged Verification: Visual and hydraulic evidence provides definitive proof, eliminating any guesswork regarding post-cleaning cleanliness.
Conclusion
True post-cleaning cleanliness is not a guess; it is a proven, documented fact. A combination of borescope inspection and validated pressure drop comparison returns the PTFE exchanger bundle to its as-built performance. A successful chemical cleaning restores both the visible condition of the tubes and the hydraulic characteristics, ensuring the exchanger operates at full efficiency and reliability.
