98.154 Figure 12-7.—Tube corrugation resulting from oil on waterside. Waterside Inspection of Drums and Headers Whenever a boiler is opened for cleaning and overhaul,  the  internal  surfaces  of  the  drums  and headers should be carefully inspected for evidence of  cracking.  Particular  attention  must  be  given  to steam    drum    manhole    knuckles,    knuckles    at corners of drum heads, corners of cross boxes and headers,   superheater   header   vent   nozzles,   and handhole   openings.   Any   defect   found   must   be recorded  in  the  boiler  water  treatment  log  and  in the maintenance log. These defects should also be reported    to    the    maintenance    office    so    that appropriate repair action can be taken. Hydrostatic Tests Boilers  are  tested  hydrostatically  for  several different purposes. In each case, it is important to understand why a test is being made and to use— but NOT to exceed—the test pressure specified for that     particular     purpose.     In     general,     most hydrostatic  tests  are  made  at  one  of  three  test pressures:  boiler  design  pressure,  125%  of  design pressure,  or  150%  of  design  pressure.  Other  test pressures may be authorized for certain purposes. For example, a test pressure of 150 psi is required for   the   hydrostatic   test   given   before   a   boiler undergoes chemical cleaning. The   hydrostatic   test   at   design   pressure   is required   upon   the   completion   of   each   general overhaul, cleaning, or repair that affects the boiler or  its  parts  and  at  any  other  time  when  it  is considered necessary to test the boiler for leakage. The   purpose   of   the   hydrostatic   test   at   design pressure  is  to  prove  the  tightness  of  all  valves, gaskets, flanged joints, rolled joints, welded joints, and boiler fittings. The   test   at   125%   of   design   pressure   is required after the renewal of pressure parts, after chemical cleaning of the boiler, after minor welding repairs  to  manhole  and  handhole  seats,  and  after repairs  to  tube  sheets,  such  as  the  correction  of gouges   and   out-of-roundness.   The   “renewal   of pressure  parts”  includes  all  tube  renewals,  rolled or  welded,  except  downcomers  and  superheater support tubes. The   test   at   150%   of   design   pressure   is required   after   welding   repairs   to   headers   and drums,   including   tube   sheet   cracks   and   nozzle repairs,  after  drain  and  vent  nipple  repairs,  and after renewal or rewelding of superheater support tubes  and  downcomers.  The  hydrostatic  test  at 150%  of  design  pressure  is  basically  a  test  for strength. This test may be (but is not necessarily) required at the 5-year inspection and test. Before making a hydrostatic test, rinse out the boiler   with   freshwater.   Using   at   least   50-psi pressure,  play  the  hose  onto  all  surfaces  of  the steam   drum,   the   tubes,   the   nipples,   and   the headers.  Examine  the  boiler  carefully  for  loose scale,  dirt,  and  other  deposits.  Be  SURE  that  no tools or other objects are left in the boiler. Remake all  joints,  being  sure  that  the  gaskets  and  the seating  surfaces  are  clean.  Replace  the  handhole and manhole plates and close up the boiler. Gag   all   safety   valves.   Boiler   safety   valves must  NEVER,  under  any  circumstances,  be  lifted by  hydrostatic  pressure.  When  gagging  the  safety valves, do not set up on the gag too tightly or you may  bend  the  valve  stems.  As  a  rule,  the  gags should be set up only handtight. Close  all  connections  on  the  boiler  except  to the air vents, the pressure gauges, and the valves of the line through which water is to be pumped to the   boiler.   Be   sure   the   steam-stop   valves   are completely closed and that there will be no leakage of water through them. After  all  preparations  have  been  made,  use the feed pump to fill the boiler completely. After all air has been expelled from the boiler, close the air vents and build up the hydrostatic pressure 12-13