A tube-sheet is a plate, sheet, or bulkhead which is perforated with a pattern of holes designed to accept pipes or tubes. Perhaps the best known use of tube-sheets are as supporting elements in heat exchangers and boilers. These devices consist of a dense arrangement of thin walled tubes situated inside an enclosed, tubular shell. Tubes are supported on either end by sheets which are drilled in a predetermined pattern to allow the tube ends to pass through the sheet. The ends of the tubes which penetrate the tube-sheet are expanded to lock them in place and form a seal.

The tube arrangement forms a contained unit between the tube-sheets. The tube-sheets are then bolted to flanges inside the shell. The shell extends beyond each tube-sheet and is sealed, thereby forming two closed chambers on the non-tube ends of the tube-sheets. Heated fluid is then passed from one end chamber to the other through the tubes where cold fluid in the cavity between the tube-sheets absorbs the heat energy. Large exchangers may have several thousand tubes running through them arranged into precisely calculated groups or bundles.

The design of tube-sheets is a fairly precise and complex process; the exact number of tubes needs to be established and a pattern of holes calculated to spreads them evenly over the tube-sheet surface. In order to prevent galvanic action between tubes and tube-sheets, the obvious selection of tube-sheet material for new units is the use of same material as the tubes. However, this may be prohibitively expensive. The next best choice is to use materials that are as close as possible to one another in the galvanic series or ensure satisfactory performance by using coatings or cathodic

protection.