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. RENEWING  TUBES 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 b e c a u s e    o f    l o w    w a t e r    S H O U L D    N O T    B E 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. REMOVING  TUBES 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. 2-8