Platforms are required on towers for access to valves, instruments, blinds and maintenance accesses. Platforms are usually circular and supported by brackets attached to the side of the tower.
Generally access to platforms is by ladder. Following figure shows a typical platform arrangement. Platform elevations for tower are set by the items that require operation and maintenance and by a maximum ladder run of 30 ft (9150 mm).
Following drawing shows a platform and ladder elevation requirements. Platform widths are dictated by operator access. For intermediate platforms with no controls required and platforms with controls located to the side or edge of the platform, the width must be minimum of 3ft (915 mm).
At congested platform with controls located over the platform, the width must be minimum of 3 ft (915 mm) plus the width of the controls or proejctions. Following figure shows these arrangements.
At maintenance access platforms, adequate space must be provided to swing the maintenance access cover flange open for storage against the face of the tower.
Top head mounted maintenance accesses must be from three sides.
Following figure shows typical maintenance access arrangements.
Top head platforms are required for access to vents, instruments, and relief valves and are supported from the head by trunions.
Following figure shows a typical top head platform arrangements.
Access between towers, if layout permits, is provided by common platforming. The platform elevations can be within a maximum difference of 90 in (230 mm) but must be connected by mechanical joint.
Following figure shows a common top head platform arrangement. Brackets for side mounted platforms are evenly spaced around the tower and when possible, straddle both the main axes.
Oddly angled brackets can be used for small platform extensions as long as the bracket clip does not interfer with the adjacent support.
Following figure shows the approximate guide to bracket spacings.
When common ladder serves two or more platforms, the ladder rungs must be level with the platforms they serve.
The platform elevations must be in even increments to suit the standard 12-in (300 mm) ladder rung spacing. Following figure shows this requirement. Ladders at tower transitions sections and at flared skirts may be sloped, if required, to a maximum angle of 15 degree from the vertical.
Offsets in ladders should be avoided.
Following figure shows a typical sloping ladder arrangement.
On very wide platforms, or those that support heavy piping loads, kneee bracing is required in addition to the usual platform steel as shown below.
The potential obstruction immediately under the knee brace must be kept in mind during platform design. For example, the platform elevations shown on the process vessel sketch are the minimum requirements for instrument, valve and mainenance access.
Following diagram displays a platform arrangement for the tower using the information and guidelines in this handbook.