2. If the spider rods under the roof have corroded, remove them, as they are needed only during erection.

3. Paint the roof, selecting the proper paint for the particular location.

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.

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 connections 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