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Tube Maintenance plugged during the repair , bill of materials , and repair documents should be documented properly for future reference .
Leak detection methods It is advised to take multiple approaches to investigate when a leak is suspected . Relying only on one method of evaluation may not provide all the required information for root cause analysis . In that case it might be difficult to determine corrective actions based on limited assessment . Once all the information regarding the leak ( i . e ., type of the leak , location , severity , etc .) are gathered , along with the heater ’ s internal drawings , archived repair information and unit operating condition , then the correct approach to the repairs ( i . e . plugging ) can be predicted . Upon completion of the task , all the information related to leak and repair ( image taken by video probe , updated tube map , test results , plugs used , etc .) should be documented properly for future reference .
Visual inspection Visual inspection is the primary examination in leak assessment and should be conducted in the accessible areas of the tube side while the heater is open . Early signs of failure can be easily detected by inspecting tube inlets and tube-to-tubesheet joint welds for signs of corrosion or erosion . Visual inspection can only reveal defects in the accessible area of heater . Inaccessible areas of the heater should be inspected through borescope video probes . Areas to inspect include inlet and outlet nozzles , manway area gasket seating surface , all welds , channel barrel area etc .
Tube leaks : Tube side leak test Tube leaks can be detected by simply conducting tube side leak test :
• Leaving the tube side pressurized , and
• Once the steam and drains to the shell side are sealed , opening the shell side drains to check for leakage .
The major limitation of this simple go / no-go check is that it does not locate the leaking tube . Also , where in the span of the heater the tube has failed is critical in determining root cause of the failure . The location of tube failure and length along the tube can be quickly determined by several methods such as inserting a video probe or a tight-fitting probe .
Video probe Video probe is the quickest way to view tube internals , determine leak location and characteristics of defects . Measuring the length of the probe inserted into the tube from tubesheet face provides the length along the tube where leak has occurred . Video inspection can easily reveal the nature of the leak as well such as whether it is a pinhole , circumferential crack , longitudinal crack , ruptured tube , etc . Instead of speculating what the potential problems within a heat exchanger may be , visual evidence obtained from video probe inspections helps to achieve better identification of the problem .
Tight fitting probe An example of a typical tight fitting probe device is shown in Figure 2 . This probe should be inserted into the leaky tube ( s ) and the distance measured at the depth at which air flow pattern changes as the probe plug passes the leak location . The air pressure into the shell side should be adjusted so that only enough air is leaking through the break so that it can readily detected by ‘ feel ’. When probe reaches the leak , the following will happen depending upon the size and type of leak :
• Pinhole or circumferential crack : If the leak is pinhole or circumferential crack , as soon as the main body of the plug ( just beyond the line of the front chamfer ) passes over the leak , the flow will stop or become greatly reduced . This length to the
Generous champher 3 / 16 " x 1 / 8 " Drill hole large enough to accept wire
3 / 4 "
Original tube ID Minus 0.010 - 0.015
Suggest electrician ' s or plumber ' s pulling snake
Bend end of wire and silver solder , braze or weld
Figure 2 : Leak probe device by Foster Wheeler
20 Heat Exchanger World September 2023 www . heat-exchanger-world . com