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Heat exchanger tube plugs are a routine maintenance task that improves efficiency and increases the lifetime of exchangers.
By plugging a leaking tube, the fluid mixing is arrested which improves the downstream efficiency of the unit. Most exchangers are built with approximately 20% excess tubes so the throughput will remain intact even after plugging. Additionally, tube plugging prevents tube leaks from damaging adjacent tubes via direct spray and/or increased vibration. But most importantly, tube plugging can increase the amount of time between costly and complicated re-tube and replace projects.
Heat exchanger tube plugging is fast, simple and effective. Once determined that plugging is the correct process, there are a few things to consider to get it done right. First comes the temperature and pressure of the exchanger. This will determine which types of plugs can be used and narrow down to the correct plug. Second is the plug material selection which will ensure the plug are compatible with the exchanger in question and avoid common pitfalls in material selection. And third is simple but often overlooked, the sizing of the tube plugs. Getting this right from the start is critical for a successful project.
Pressure. This variable will quickly narrow down the plug selection between high, medium and low-pressure tube plug options. Exchangers with maximum allowable working pressure (MAWP) and test pressure below 250 psi are often condensers and HVAC related. These can often utilize rubber-based condenser plugs like the TNS-ECP plugs. These provide excellent expansion range and material compatibility. When pressure is between 250 and 1,000 psi, this is the medium pressure range for exchangers, where the majority of exchangers tend to be. The medium pressure TNS-MP plugs are the best option in this band, providing a confident metal to metal seal while still maintaining a huge expansion range. Finally, supercritical and other process exchangers above 1,000 psi are candidates for the signature TNS high pressure mechanical plugs. These plugs will seal tubes up to 7,000 psi with the simple ease of a torque wrench.
Material. At low pressures where a rubber plug will work, material consideration does not come into play. However, for the medium and high-pressure options, material compatibility is an important consideration. The three properties to look at for materials with mechanical plugging are relative hardness, thermal expansion and risk of galvanic reaction. A good example is a recent customer with 410 stainless steel tubing that wanted to use 316 stainless steel plugs:
Relative hardness: The relative hardness for 316SS (Brinell = 190) and 410SS (Brinell = 190 to 240) are very similar and on average tends to be the same. Hardness is okay.
Thermal expansion: Both materials have a very low coefficient of thermal expansion, between 11 and 16 microns/m-K. Thermal Expansion is okay.
Galvanic reaction: There is a small gap on the chart between the two materials. However, since the relative surface area of the tube is so much greater than the relative surface area of the plugs, and the tube is the more anodic material, the risk of a damaging galvanic reaction is basically 0. Galvanic risk is okay.
Thus, the use of 316 stainless steel plugs was approved for use within the 410 Stainless Steel tubes and provided a quick off the shelf solution for this customer.
Sizing. The final variable is straightforward but critical. A proper measurement of the tube ID using a caliper is the best way to ensure an accurate sizing. However, it is also possible to calculate the tube ID by taking the tube OD and subtracting two times the wall thickness. Either way you go, it is best to verify the size by also using the alternative method. Selecting a plug size where the tube ID is within the expansion range of the plug will provide the final part number.
With the correct heat exchanger plugs specified and procured ahead of any outage or turnaround, the tube plugging process is fast, simple and effective.
For more information, visit torq-n-seal.com/bic, call (201) 641-2130 or email sales@torq-n-seal.com.
