1. How can a tube rupture or perforation in a coil-type heat exchanger be repaired?
On the corresponding tube sheet, mark the numbers of the damaged tubes. To ensure balanced heat distribution, tubes should be plugged in pairs during the plugging process. The procedure for tube plugging is as follows: mill both tube ends flat—drill holes—tap threads—machine the thread plugs—prepare the adhesive—clean the threaded holes with a solvent—apply adhesive to the thread plugs—and finally cure by heating.

2. How can leaks at the tube-to-tubesheet connections of a spiral-wound heat exchanger be repaired?
For leaking pipe ends, drill and tap the area, then insert a threaded plug with a central hole. Apply adhesive before tightening the plug into place, and finally heat it to cure the bond. This repair effectively stops leaks without affecting the pipe's heat transfer performance afterward. If leakage reoccurs at the same spot where the plug was installed, simply repeat the process.

3. What are the typical causes of leaks in coiled-tube heat exchangers?
(1) During the coiling process, excessive bending of the heat transfer tubes created an initial hidden defect. Under unstable operating conditions, cumulative fatigue eventually led to the expansion of this flaw, ultimately causing the tube to rupture. (Therefore, when coiling the heat transfer tubes, it’s essential to use flexible tooling and carefully control the winding speed.)
(2) After sudden braking followed by an immediate resumption of driving, the exhaust volume is reduced, causing a liquid column to form inside the pipe. Under the impact of the high-pressure air flow, this leads to a hammering effect, ultimately resulting in pipe rupture.
(3) During equipment start-up and shutdown, the equipment was not properly thawed. As a result, trace amounts of water accumulated and supercooled into ice particles, which, under the impact of airflow, repeatedly struck the curved sections of the pipes, leading to pipe rupture or perforation.

4. What are the key considerations for starting up and shutting down a coil-type heat exchanger?
(1) When parking, the separator liquid level should be drained to prevent cold fluid from flowing downward, which could otherwise lead to a hammering effect during startup.
(2) Before starting the operation, use ambient-temperature nitrogen to purge the heat exchanger and connected pipelines, removing any trace amounts of moisture that may have accumulated inside the equipment and pipes.
(3) For equipment that has been running continuously for more than 3 months, perform defrosting procedures before restarting after a shutdown.
(4) During driving, the cooling rate should be strictly controlled, typically at 10 degrees per hour.

5. In the manufacturing of coiled-tube heat exchangers, the most critical step is winding the tube bundle. What are the specific requirements for tube winding?
(1) Spacing must be uniform—specifically, the gap between each tube after winding should be maintained within a consistent range. Variations in spacing, where some gaps are larger than others, can lead to uneven methanol flow and negatively impact heat transfer efficiency.
(2) The bends at the tube ends should transition smoothly and naturally. Before threading the tubes through the tube sheet, they must undergo multiple bends to reach their final position. During this bending process, it’s crucial to maintain smooth, seamless curves to prevent excessive internal stress in the tubes or compromise their aesthetic appearance.
(3) The special-shaped strip serves to position the tube; it must be evenly divided and maintain the same helix angle as the tube, with a smooth transition at the contact point.
(4) Since the tubes are supplied in coil form, a straightening mechanism must be installed before they enter the coiling position. This straightening process also serves as a pre-tensioning function, helping to prevent springback from occurring during the winding process.
(5) Heat exchange tubes in different tube passes are properly routed to their corresponding tube sheet areas.
(6) The most common issue in coil winding is the "dumbbell"-shaped tube bundle, where the ends are larger while the middle section remains narrow. Therefore, during the winding process, it’s crucial to prevent the tubes from bulging outward at both ends, as this can make threading the core particularly challenging.