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Calorifier Maintenance Checks
Without regular planned maintenance, a calorifier’s efficiency may reduce over time. This may be for any number of reasons including: leaking tubes; passing of the primary fluid across the header division web; a build-up of scale on the heat transfer surfaces. Early detection is needed in order to avoid extended downtime and excessive remedial costs. This is critical for public buildings, as water temperatures for HW services of less than 60°c for extended periods could lead to the growth of Legionella bacteria.
A typical inspection would involve a visual check of the calorifier to spot any obvious problems, however most problems will be found internally. The most reliable method for testing a calorifier tube bundle is ,to remove it from the calorifier shell and carry out a hydraulic pressure test to the recommended pressure. The header should also be inspected for pitting and corrosion of sealing faces and erosion of the inner surface.
A common issue with tube bundles is thinning of the tube walls, particularly at the inlet and outlet where they are expanded into the tube sheet. If the tubes start to leak, the calorifier should be isolated until repairs can be carried out.
Valveforce's sister company Heatxforce Limited is able to manufacture replacement tube bundles or carry out repairs to existing bundles, depending on the condition of the tubes and tube sheet. The tube sheets are usually manufactured from rolled Naval Brass plate and Copper “U” formed tubes with plain or extended surfaces. Where only the ends of the tubes have suffered a reduction in wall thickness, it is often possible to “crop” the tubes. This involves cutting the tubes close to the back of the tube sheet, thus removing the affected parts of the tubes. The cropped tubes can now be refitted, and although this will slightly reduce the tube length, it is unlikely to have a significant effect on thermal performance but will be far less costly than full tube replacement.
The shell side inspection, though mainly visual, will include a measurement of the wall thickness, as this is safety critical. In the case of unlined steel shells, there is generally, corrosion of the inner surface over time. Steel shells are designed to include a corrosion allowance, however, once the minimum wall thickness is exceeded, the shell must be replaced. It is good practice to remove any accumulation of loose debris from the shell whilst the tube bundle is removed.