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Composition of Boiler Tubes

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9. 10. 11. Apply  water  pressure  of  1  1/2  times  the maximum   allowable   working   pressure.   To avoid rapid shock and strain, bring this pressure up in 10 equal increments, inspecting for leaks and deformities at each increase. Inspect   tube   ends,   boiler   seams,   pressure fittings, and connections. Make the corrections and   repairs   wherever   possible.   In   case   of unusual  conditions,  DISCONTINUE  the  test IMMEDIATELY   and   NOTIFY   YOUR SENIOR  PETTY  OFFICER.  Do  NOT  exceed the test pressure. NEVER apply more than 10 pounds  of  pressure  above  the  maximum working   pressure   on   a   low-pressure   boiler. Consult the ASME code for testing procedures for other than welded steel boilers. Secure pressurizing connections at the required test   pressure.   Continually   inspect   the   boiler tubes,  seams,  fittings,  and  connections.  If  the boiler and fittings are tight, the pressure should NOT drop more than 1.5 percent in 4 hours. If loss  of  pressure  is  over  1.5  percent,  find  the leak(s) and make the repairs. Following all hydrostatic testing, steam pressure is raised to lift safety valves and to determine the fitness of the boiler for use. Q1. Q2. Q3. Q4. Most cases of major boiler damage is caused by what operating condition? What could happen if "loose packing" is used on a  gauge  glass? What are the four reasons for using blowoff or blowdown valves? What is the purpose of a hydrostatic test on a boiler? BOILER  TUBES Learning   Objective:   Recognize   and   understand methods  for  renewing,  repairing,  and  cleaning  boiler tubes and sheets. For   any   boiler   retubing   job,   it   is   absolutely essential to use tubes that conform in every way to the tube requirements of the particular boiler. Boiler tubes are   NOT   identical.   They   differ   in   such   important characteristics  as  composition  of  the  metal,  outside diameter, wall thickness, length, and curvature. Much  of  the  required  information  on  sizes, thickness, and number of tubes per boiler is given in the   manufacturer’s   technical   manual.   Some   of   the information is under the heading of "Tube Data." More detailed information is usually given on the drawings included in the manual. COMPOSITION OF BOILER TUBES Generating tubes are usually made of low carbon s t e e l .   T h e y   m a y   b e   e i t h e r   s e a m l e s s   o r resistance-welded.   Seamless   tubes   were   once definitely preferred for naval use. However, improved methods of manufacturing the welded tubes have led to - - an  increased  use  of  welded  tubes  in  naval  boilers. Repair  ships,  tenders,  and  other  naval  activities  that use, handle, or issue plain carbon steel tubes have been instructed to make no distinction between the seamless and  the  welded  tubes,  but  to  stock,  issue,  and  install them interchangeably without regard to the method of manufacture. Superheater  tubes  usually  are  not  made  of  plain low  carbon  steel.  On  boilers  where  the  superheated steam   temperature   reaches   850°F   or   higher,   the superheater   tubes   may   be   made   of   carbon- molybdenum  steel,  chromium-molybdenum  steel,  or an 18-8 chromium-nickel (stainless) steel. To find detailed information on the composition of the  metals  used  for  generating  tubes  and  superheater tubes  in  any  particular  boiler,  check  the  manufacturer’s technical manual. The information may be given on the drawings, or it may be included in the text. Once  you  have  found  information  on  the composition of the metals used for boiler tubes, your next problem is to understand it. Do you know what it means when you see "mild steel" on a blueprint? Can you identify metals by their chemical symbols? Do you know  what  an  "alloy  steel"  is,  or  anything  about  the different kinds of alloy steels? Do you know anything about the various systems of classifying steels? Do you know why different steels are used for different kinds of  tubes?  Answers  to  these  questions  are  necessary before you can make much sense out of the information you are likely to find on blueprints on the composition of boiler tubes. Although  we  all  have  a  general  idea  of  what  we mean by the word metal it is not easy to give a simple, accurate  definition.  Chemical  elements  are  metals  if they  are  lustrous,  hard,  good  conductors  of  heat  and electrcity,  malleable,  ductile,  and  heavy.  In  general, these   properties   of   hardness,   conductivity, 2-7



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