After primary liquid-transfer line connections have been located, roof access ladders (or stairways) and side shell and roof maintenance access connections should be located.
Following figure addresses these issues.
If tank heaters are employed, mobile maintenance equipment should be located in the most convenient area.
Tank maintenance includes such activities as internal inspection, cleaning, and repairs to internals, roof supports, and level instruments.
Setting entrances to stairway or ladder areas at grade is the most convenient choice for operations personnel. It should be noted that stairways are not recommended for tanks whose diameters are less than 15 ft 6 in (4.7 m).
For safety, handrails should be added along the tank roof edge on both sides of the ladder or stairway.
Level instruments with internal floats are usually located in this area, as are roof maintenance access openings, which are convenient for inspections, re-pairs, and cleaning of instruments.
Two types of tank-shell maintenance access opening are shown in Exhibit 15- 21.
The standard, round opening is a minimum of 18 in (0.460 m) in diameter. The larger, oval-shaped, flat-bottom opening is more commonly used on large tanks or those that use internal heaters.
The layout designer must keep the area immediately around access openings free of such obstructions as large pipe supports, piping, and light poles. Valve access catwalks can be seen in following figure.
It is of utmost importance to give operations person-rid adequate access to primary tank valves. Consideration must be given to the elevation of all valve hand-wheels in relation to the catwalk.
Adding extension stems to smaller valves will facilitate opening or closing such valves. Tank mixers A tank mixer, shown in below, is another auxiliary piece of equipment found in tanks with highly viscous fluids.
Adequate area must be provided for removal of tank mixers. Tank heaters Tank heaters come in various sizes and shapes, as shown below.
Sufficient unobstructed space must be provided outside access openings to permit removal of heaters.