the  FASTENING  attaches  the  insulating  material to  the  piping  and  to  the  lagging. Insulation  covers  a  wide  range  of  temper- atures,  from  the  extremely  low  temperatures  of the refrigerating plants to the very high temper- atures  of  the  ship’s  waste  heat  boilers.  No  one material  could  possibly  be  used  to  meet  all  the conditions  with  the  same  efficiency. INSULATION   MATERIALS The  following  QUALITY  REQUIREMENTS for the various insulating materials are taken into consideration by the Navy in the standardization of  these  materials: 1.    Low  heat  conductivity 2.   Noncombustibility 3.    Lightweight 4.  Easy molding and installation capability 5.  Moisture repellant 6.    Noncorrosive,  insoluble,  and  chemically inactive 7.   Composition,   structure,   and   insulating properties  unchanged  by  temperatures  at which it is to be used 8.    Once  installed,  should  not  cluster,  become lumpy, disintegrate, or build up in masses from  vibration 9. Verminproof 10.  Hygienically  safe  to  handle Insulating material is available in preformed pipe coverings, blocks, batts, blankets, and felts. Refer  to  NSTM,  Chapter  635,  “Thermal,  Fire, and  Acoustic  Insulation,”  for  detailed  informa- tion on insulating materials, their application, and safety  precautions. The  insulating  cements  are  comprised  of  a variety  of  materials,  differing  widely  among themselves  as  to  heat  conductivity,  weight,  and other  physical  characteristics.  Typical  of  these variations  are  the  asbestos  substitute  cements, diatomaceous  cements,  and  mineral  and  slag  wool cements.  These  cements  are  less  efficient  than other high-temperature insulating materials, but they are valuable for patchwork emergency repairs and for covering small irregular surfaces (valves, flanges,  joints,  and  so  forth).  Additionally,  the cements are used for a surface finish over block or   sheet   forms   of   insulation,   to   seal   joints between  the  blocks,  and  to  provide  a  smooth finish over which asbestos substitute or glass cloth lagging  may  be  applied. REMOVABLE  INSULATION Removable  insulation  will  be  found  on  the bleed air systems and waste heat boiler systems. Removable  insulation  is  also  installed  in  the following   locations: .   Flange pipe joints adjacent to machinery or equipment that must be broken when units  are  opened  for  inspection  or  overhaul .    Valve  bonnets  of  valves  larger  than  2 inches  internal  pipe  size  (IPS)  that  operate at 300 psi and above or at 240°F and above .   All  pressure-reducing  and  pressure-regu- lating  valves,  pump  pressure  governors, and strainer bonnets GENERAL  INSULATION PRECAUTIONS You   should   observe   the   following   general precautions   relative   to   the   application   and maintenance  of  insulation: 1.  Fill  and  seal  all  air  pockets  and  cracks. Failure to do this will cause large losses in the  effectiveness  of  the  insulation. 2.  Seal  the  ends  of  the  insulation  and  taper off  to  a  smooth,  airtight  joint.  At  joint ends  or  other  points  where  insulation  is liable  to  be  damaged,  use  sheet  metal lagging  over  the  insulation.  You  should cuff flanges and joints with 6-inch lagging. 3.  Keep  moisture  out  of  all  insulation  work. Moisture is an enemy of heat insulation just as much as it is in electrical insulation. Any dampness increases the conductivity of all heat-insulating   materials. 4. Insulate all hangers and other supports at their  point  of  contact  from  the  pipe  or other unit they are supporting; otherwise, a considerable quantity of heat will be lost via  conduction  through  the  support. 5.  Keep  sheet  metal  covering  bright  and unpainted unless the protective surface has been damaged or has worn off. The radia- tion  from  bright-bodied  and  light-colored objects  is  considerably  less  than  from rough  and  dark-colored  objects. 6.  Once  installed,  heat  insulation  requires careful   inspection,   upkeep,   and   repair. Replace  lagging  and  insulation  removed  to make repairs as carefully as when originally 9-48