Engineering guide
Module DECK calculates covers for access openings (dome covers, manhole covers) on tanks for the carriage of dangerous goods to DIN EN 14025, clause 6.3.6. Calculated are the required cover thickness and the required bolt cross-section of the bolting — optionally for flat or domed cover designs.
Access openings are unavoidable on tank vehicles and rail tank wagons and at the same time safety-critical: the bolted cover must withstand the design and test pressures, compress the gasket reliably, and also carry the dynamic loads of transport service. Anyone who wants to calculate a manhole cover to EN 14025 therefore verifies both the plate or shell load-bearing capacity of the cover and the bolt forces from the pressure and gasket loads.
The module supports the design of new dome covers as well as the re-rating of existing components, for example for changed tank codes or higher test pressures. The domed design exploits membrane action and manages with a considerably smaller wall thickness than a flat cover of the same size.
Scope
- Covers for manholes
Typical workflow
Select the design
First the cover design is chosen: flat plate or domed cover. The design determines the calculation model — plate bending with calculation coefficients for the flat cover, membrane action with a knuckle coefficient for the domed one.
Enter geometry and loads
The opening diameter, the gasket geometry, the number of bolts and the bolt circle are entered together with the design and test pressures per EN 14025.
Calculate the required cover thickness
From the pressure, the allowable stress of the cover material and the design-dependent coefficients follows the required cover thickness, supplemented by corrosion and tolerance allowances.
Verify the bolt cross-section
From the pressure force on the gasket face and the required gasket contact pressure, the bolt forces are determined and the required stress cross-section per bolt is compared with the available one.
Frequently asked questions
When is a domed cover worthwhile instead of a flat one?
The domed cover carries the pressure predominantly through membrane stresses and therefore needs a considerably smaller wall thickness than the bending-loaded flat plate — for large opening diameters and higher pressures it is the more economical and lighter solution. The flat cover, in turn, is easier to manufacture and offers a plane mounting surface for fittings.
Why is the bolt cross-section verified separately?
Besides the pressure force on the projected cover area, the bolts must also ensure the gasket contact pressure — in the bolting-up condition without any relieving internal pressure. Depending on the gasket type, the bolting-up condition can yield the larger bolt force. Too few or too small bolts lead to leakage before the cover plate itself becomes critical.
Do the same pressures apply to dome covers as to the tank shell?
Yes, the cover is part of the pressure-retaining wall and is verified with the design pressure and the test pressure of the tank per EN 14025. In addition, the dynamic loads of transport service are covered, which are already included in the pressure assumptions of the standard.
Technical content source: LV-Solved-Problems-Content 628d313247e7