Dislodgement Resistant Trays
Mapesa "D.R." (DISLODGEMENT RESISTANT) trays are specifically designed for applications where unusual uplift surges exist so that mechanical failure is prevented. These trays are equipped with special heavy duty features which allow the individual tray components to act as a network, whereby, the fully assembled tray is capable of withstanding pressure surges of up to one, two or even three p.s.i., without permanent deformation or dislodgement of any of the components. Depending upon the specific design criteria, such as vessel design temperature, anticipated magnitude of pressure surge, consideration of possible pulsation or excessive vibration, material analysis, corrosion allowance and tower diameter, any combination of the following Mapesa D.R. features may be utilized in tray design:
- Increased tray thickness (trays which are normally 14 ga. for stainless are increased to 12 ga.,10 ga., 3/16" or even 1/4" thick as needed). - Thru-bolted integral beams (normal design allows for a frictional holddown of tray panel edges). - Increased quantity of bolting and hardware assemblies to utilize 3" spacing (normal spacing for hold down on tray panel edges is approximately 6"). - Lock washers or double nuts (for use when excessive vibration is anticipated).
Thru-bolted clips at ends of integral beams for attachment to adjacent beams (see figure a below) or tray support ring (see figure b below).
Thru-bolted clip angles at ends of integral beams for attachment to downcomer truss (see figure c below).
Welded tray design (for use when installation time and future removal considerations allow).
Additional major beams or support channels (these beams are bolted to welded-in attachments at tower shell).
Plate and angle lattice trusses (see figure d). This configuration often provides the necessary requirements for maximum strength and vapor equalization with minimum weight and use of material.
D.R. Hardware (heavy duty, extra thick washers and clamps which greatly resist dislodgement).
Mapesa does not recommend D.R. trays for all applications because of minor problems such asincreased installation time and effort due to the extra bolting and hardware assemblies required and additional tray purchase price. Under normal liquid and vapor loadings most trays will operate adequately without D.R. features. In cases where there is a history of tray mechanical failure (particularly aboveand below vapor feeds), D.R. tray design will substantially increase their operating life. This extended tray operation can often result in extended service life and reliability in a vessel and even the entire plant by eliminating the necessity for unplanned shut downs.