2. 3. As pointed out earlier, standpipes are, in effect, ground level storage tanks. Inspection and main- tenance procedures for standpipes are the same as those for ground level steel storage tanks. If the spider rods under the roof have corroded, remove them, as they are needed only during erection. Paint the roof, selecting the proper paint for the particular   location. UNDERGROUND STORAGE.—When   steel storage tanks are constructed belowground or are surrounded by an earth embankment, the semiannual inspection and repair include only the interior of the tank, the roof, and the accessories. The inspection and maintenance procedures are the same as given for ground storage steel tanks. ELEVATED   STORAGE.—Besides the inspection  and  maintenance  procedures  set  forth  above for  ground  storage  steel  tanks,  the  following  specific procedures apply to elevated storage steel tanks. Semiannually, tower structures should be checked for rust and corrosion, loose, missing, bowed, bent, or broken members; loose sway bracing; misalignment of tower legs; and evidence of unstableness. Items that must be covered are as follows: 1. Inspect the back surface of the lattice bars and anchor  bolts,  the  inside  of  boxed  channel columns,  and  pockets  where  batten-plate connections  and  column  bases  form  pockets  for collecting trash and water. Clean and paintthese enclosures, and fill with concrete as necessary to shed  water. 2.   Check the bases and the baseplates for evidence that water has collected at that point; if water is found,  drill  a  1  1/2-inch  hole  through  the channel-boxed  section  to  allow  complete drainage.  Then  grout  the  baseplate  with  a mixture of sand and asphalt to prevent water from running under the plates. Taper the grout from the top edge of the plate to the pier. 3.   Check  the  sway  bracing  and  tighten  the turnbuckles if necessary. Examine under clevis pins and rod loops where corrosion may be greatest. Drill holes in the bal cony floor to eliminate stand ing water. Besides general roof inspection and repair, as described for ground storage steel tanks, obstruction and  navigation  lights  should  be  inspected  and relamped if necessary. Additional items that should be covered are as follows: 1. Check the operation of all other lights; check hoods, shields, and receptacle fittings; look for missing or damaged parts. Repair or replace parts as necessary. 2. Check lightning rods, terminals, cables, and ground  connections. In cold climates, potable water storage tanks (with small riser pipes) and elevated storage tanks (for fire protection  only)  usually  have  heating  equipment  to prevent freezing in severe low temperatures. Checks that must be conducted are as follows: 1.   Annually, 2 months before the freezing season, inspect the riser for deterioration of the frost covering. Seal any openings to reduce heat loss. Also, check the heating system to ensure proper operation during the next cold season. 2. Annually, 1 month before the freezing season, operate the heating system for 8 hours to check all elements under operation. CATHODIC  PROTECTION  EQUIPMENT.—Only impressed  current  cathodic  protection  systems  are  used for protecting steel water storage tanks against corrosion. This system of protection may be applied to all types of steel  water  tanks-ground  level  standpipe,  underground, and elevated. Refer to the material presented earlier in this chapter for a discussion of inspection and maintenance procedures for impressed current systems. Also, other applicable  procedures  are  as  follows: Annually, note and record the current flow during the operation. If the current does not flow, check the fuses, electrodes, which contact the tank, ground wire connection to the tank, and the immersion of electrodes. If the equipment is operating at voltages or  amperages  above  those  listed  on  the  nameplate, the rectifier may be damaged. CAUTION Make  certain  that  the  connections  to  the rectifier are not reversed. Reversed connec- tions will result in tank damage. Annually,   check   the   operating   record   to determine if the electrodes are immersed at all times, or almost all the time. If the electrodes are not immersed, there will be no damage to the 8-30