Design analysis and laboratory testing
All ASEplas cable cleats have been subjected to rigorous design analysis and laboratory testing to ensure that they are fit for their purpose of supporting cables safely for a long period of time in a variety of conditions. Design analysis uses the Finite Element Method for stress and displacement calculations. We are fortunate in having links with the Civil Engineering Department at the nearby University of Wales Swansea which is one of the premier FEM research units in the world.
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Stress analysis of a C120 cleat. |
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Corresponding deformation pattern for the C120 cleat.
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Model
The mesh plot (Figure 1) shows the FE mesh used. The blue region represents the SS vessel clip and flange, the green is the insulation and the cyan is the carbon steel flange with a token extension to represent the outboard CS cantilever beam. The model for simplicity looks at one quarter of the circular system (with a small hole at the centre to ease modelling - will not have any influence).
The SS tube is 230 mm long within the vessel insulation and extends a further 75 mm beyond. Thus, with a 25 mm SS flange the SS system extends 100 mm outside the vessel insulation into the ambient air.
Loading
The vessel end of the SS tube is 'grounded' at -160°C. No heat transfer is assumed to take place across the external surface of the SS within the region covered by the vessel insulation, or, in this case across the interior surfaces of the SS tube and flange. All the external surfaces of the model outboard of the vessel insulation were assumed to 'see' an ambient temperature of -9°C with a heat transfer rate of 12 W/sq m/deg C (my thermodynamics colleagues indicated that this is a reasonable value for this situation)
Materials
The Atplas 1010SWC insulation is taken to have a thermal conductivity of 0.2 W/m/deg C. The K for SS was taken as 20 W/m/deg C and that for CS 50 W/m/deg C.
Results
The 'temp image (Figure 2) shows the temperature distribution through the system. The 'temp plot image (Figure 3) shows a graph of temperature through the two flanges and the Atplas block along the line of the SS tube. In this case plot the minimum CS temperature is -11.65°C. It can be seen that the CS temperature falls slightly towards the centre of the flange, but the change is less than 0.25°C.
This study ignores the influence of the bolts passing through the insulation block. It can be seen that these bolts will pass through the marginally warmer part of the flanges. Provided that they are insulated on the CS side as quoted then past studies suggest that they will not lower the CS flange temperature by more than 3°C.
Properties & Characteristics of ASEplas 1010 SWC material |
Figure 1: 30mm Insulation Mesh
Figure 2: 30mm Insulation Temperature Gradient
Figure 3: 30mm Insulation Plot
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Overview
A series of finite element thermal models were run to look at the thermal behaviour of insulation configurations below the Saddle supports of the Jetty and Flare KO drums shown in a Clients Engineering drawings.
The FE Model
The SS saddle and associated drum steel were modelled to scale with the zone of saddle steel within the vessel insulation modelled as a separate entity to enable different boundary conditions to be applied to the steel exposed to the atmosphere. Modelling was simplified by noting the two fold symmetry of the relevant structures so that only one quarter need be generated. Below the saddle was placed a block of ASEplas insulation which initially rested on a steel plate placed on top of the concrete plinth. In later analyses the model was modified to include the addition of the larger lower insulation block over the reduced height concrete plinth shown in the latest drawings. The PTFE layer on the sliding supports was not included in the majority of the runs. Figure 1 shows the mesh used at an intermediate stage of the analysis. The mesh was subsequently modified to include the additional insulation placed on the concrete plinth.
Boundary Conditions
For the final series of analyses of the production drawings the inside of the drum steel fixed at -196°C, no heat input into saddle steel for 220 mm down from drum (to simulate vessel insulation). The rest of the external steel and ASEplas insulating blocks was subject -9°C ambient temperature with a surface convective heat transfer of 5 W/m2. The concrete plinth was modelled for 150 mm below the insulating block and its exposed later surfaces given the same ambient temperature and convection state as the other exposed surfaces. No heat transfer was allowed across the base of the concrete. Further runs were carried out varying the surface convective heat transfer between 4 and 6 W/m2. The temperature profile of the model was not significantly sensitive to this variation. These values of surface convection are probable for very still air conditions. The effect of any wind will increase the rate of heat flow into the system and will tend to increase (make less severe) the temperatures at the concrete interface.
Results
For the fixed end supports the temperature at the insulation/concrete plinth interface should not drop below -15.3°C to -16.0°C for worst-case ambient conditions. At the sliding end the PTFE layer provides extra insulation and the models suggest a worst case of -14.5°C at the concrete level. The temperature at the PTFE interface on the sliding supports should not fall below -42°C for the worst-case ambient conditions.
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Figure 1: Model mesh - one quarter of saddle modelled due to twofold symmetry
Blue = Saddle Steel
Green = Insulating Block
Cyan = Steel Baseplate on Insulating Block
Red merging to white = Concrete Plinth
Figure 2: Typical analytical result – temperature contours
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