malleability, and so forth, are known as metallic properties, and chemical elements that possess these properties are generally called metals. Chemical elements that do not possess these properties are called nonmetals. Oxygen, hydrogen, chloring, and iodine are a few examples of nonmetallic chemical elements. A few chemical elements behave sometimes like metals and sometimes like nonmetals. These elements are often called metalloids. Carbon, phosphorus, sulfur, and silicon are examples of metalloids.
Most types of steel look quite a lot alike, so you cannot go by appearances. On Navy blueprints and on drawings furnished in the manufacturer's technical manuals, materials are usually specified by federal or military specification numbers. In addition, the blueprints and drawings may refer to a commercial classification system, such as the Society of Automotive Engineers (SAE) system or the American Iron and Steel Institute (AISI) system.
Federal or military specifications usually require the tubes to be identified by some marking system. For example, one specification for boiler tubes requires that boiler tubes 1 1/4 inches or greater and 3 feet in length be legibly marked by paint stenciling, while smaller or shorter tubes may be bundled and tagged. Another boiler tube specification requires the tubes to be marked by ink stenciling approximately 3 inches from each end and again in the middle of the tube. As a general rule, boiler tube identification markings must include (1) the name or trademark of the manufacturer, (2) the heat number, (3) the class letter, (4) the specification number, and (5) the outside diameter, the wall thickness, and the length.
Boiler tubes should be replaced when they cannot be made tight, or when they are warped, or otherwise seriously damaged. As a general rule, boiler tubes should not be straightened in place; leaks may develop that could cause permanent damage to other parts of the boiler. Occasionally, however, you may find a screen tube or a wall tube that has bowed out of position for no apparent reason; you can straighten the tube in place and re-roll it if a replacement tube is not available. Tubes that have bowed out of position because of low water SHOULD NOT BE STRAIGHTENED.
To renew tubes in the A row, the corresponding tubes in the B row must also be renewed, regardless of their condition. Similarly, whenever superheated tubes are renewed, remove the superheater support tubes when they are not accessible without removal of the superheater tubes.
General renewal of tubes in a boiler should not be undertaken without approval of the battalion or base commander. The commander's decision as to whether to approve a general renewal of the tubes will be based on the results of inspection and examination of tube samples.
Before beginning to renew tubes, be sure all preparations have been made. Be sure the right types of replacement tubes are available and that all tools and equipment required for the job are on hand and in good working order. Check the cutters, the air hoses, and the fittings for the pneumatic tools, the tube benders, the electric equipment, and the staging.
The steam drum must be opened and some fittings removed to allow access to the ends of the tubes. Also, the water drums and headers must be opened. Any fittings removed from the drums should be carefully set aside and marked, if necessary, to ensure correct replacement.
Before allowing a person to enter the boiler, be sure all safety precautions are observed. Make it your personal responsibility to see that all cross-connecting valves between the boiler being retubed and any steaming boiler are closed and locked or wired shut and are tagged DANGER. DO NOT OPEN. Be sure, also, that the control valves of the steam-smothering system are locked in the CLOSED position. See that enough ventilation is provided; keep portable blowers running at all times while people are working in the boiler. Do not allow unauthorized types of lights in the boiler. Flashlights are preferred for boiler work. If portable lights are used, the electric leads must be thoroughly insulated and the portable fixture itself must be the grounded, watertight type. Before use, portable lights should be checked by an electrician to ensure they are safe.
Using an air-powered side-cutting chisel (fig. 2-7) ground, cut the old tube flush with the drum or header. Carefully work the cutter so as not to damage the surface of the drum or header. When you are removing superheater tubes, it will be impossible to cut the tube flush with the header with a side-cutting chisel. An expandable fly cutter must then be used to cut out the tubes.Continue Reading