Clean exchangers subject to fouling (scale, sludge deposits, etc.) periodically, depending on specific conditions. A light sludge or scale coating on either side of the tube greatly reduces its effectiveness. A marked increase in pressure drop or a reduction in performance usually indicates cleaning is necessary. Because the difficulty of cleaning increases rapidly as the scale thickens or deposits increase, the intervals between cleanings should not be excessive.
Neglecting to keep tubes clean may result in random tube plugging. Consequent overheating or cooling of the plugged tubes, as compared to surrounding tubes, will cause physical damage and leaking tubes due to differential thermal expansion of the metals.
To clean or inspect the inside of the tubes, remove only the necessary tube-side channel covers or bonnets, depending on type of exchanger construction. If the heat exchanger is equipped with sacrificial anodes or plates, replace these as required.
To clean or inspect the outside of the tubes, it may be necessary to remove the tube bundle. (Fixed tubesheet exchanger bundles are not removable.) When removing tube bundles from heat exchangers for inspection or cleaning, exercise care to see that they are not damaged by improper handling. Table 1 shows safe loads for steel rods and eyebolts.
- The weight of the tube bundle should not be supported on individual tubes but should be carried by the tubesheets, support or baffle plates or on blocks contoured to the periphery of the tube bundles.
- Do not handle tube bundles with hooks or other tools that might damage tubes. Move tube bundles on cradles or skids.
- To withdraw tube bundles, pass rods through two or more of the tubes and take the load on the floating tubesheet.
- Rods should be threaded at both ends, provided with nuts, and should pass through a steel bearing plate at each end of the bundle.
- Insert a soft wood filler board between the bearing plate and tubesheet face to prevent damage to the tube ends.
- Screw forged steel eyebolts into both bearing plates for pulling and lifting.
- As an alternate to the rods, thread a steel cable through one tube and return through another tube.
- A hardwood spreader block must be inserted between the cable and each tubesheet to prevent damage to the tube ends.
Lift tube bundles horizontally by means of a cradle formed by bending a light-gauge plate or plates into a U-shape. Make attachments in the legs of the U for lifting. Do not drag bundles because baffles or support plates may become easily bent. Avoid any damage to baffles so that the heat exchanger will function properly.
Some suggested methods of cleaning either the shell side or tube side are listed:
- Circulating hot wash oil or light distillate through tube side or shell side will usually effectively remove sludge or similar soft deposits.
- Soft salt deposits may be washed out by circulating hot fresh water.
- Some commercial cleaning compounds may be effective in removing more stubborn deposits. Use in accordance with the manufacturer's instructions.
Some tubes have inserts or longitudinal fins and can be damaged by cleaning when mechanical means are employed. Clean these types of tubes chemically or consult your heat exchanger manufacturer for the recommended method of cleaning.
If the scale is hard and the above methods are not effective, use a mechanical means. Neither the inside nor the outside of the tube should be hammered with a metallic tool. If it is necessary to use scrapers, they should not be sharp enough to cut the metal of the tubes. Take extra care when employing scrapers to prevent tube damage. Do not attempt to clean tubes by blowing steam through individual tubes. This overheats the individual tube and results in severe expansion strains and leaking tube-to-tubesheet joints.