A steel slide plate or low-friction slide plate assembly should typically be provided at the sliding end of every exchanger or vessel, regardless of the flexibility inherent in the structural support. Small, lightly loaded exchangers or vessels may not require slide plates. Low-friction manufactured slide
plate assemblies should be used to reduce high-frictional resistance, especially in cases of heavy exchangers or for exchangers with significant thermal growth. For exchangers with bundle pull, steel slide plates instead of low-friction slide plate assemblies may be more cost efficient.
Typically, a low-friction slide plate assembly consists of multiple individual slide plate components spaced out along the length of the saddle. Each slide plate component consists of an upper element and a lower element, and the sliding surface is at the interface of the upper and lower elements. The elements should be fabricated with a carbon steel backer plate attached to the elements to facilitate welding of the upper elements to the saddles and the lower elements to the steel bearing plate.
Typical coefficients of friction are as follows. For low-friction slide plate assemblies, the manufacturer’s data sheet should be read carefully, as the coefficients of friction vary with slide plate material, temperature, and pressure. Use the following figures for coefficients of friction:
1. No slide plate (steel support on concrete): 0.60
2. Steel slide plate: 0.40
3. Low-friction slide plate assemblies: 0.05 to 0.20
It is suggested that the criteria for sizing low-friction slide plate elements should be as follows. The manufacturer’s data sheet and specifications should be consulted for temperature restrictions, pressure limitations, and other requirements that may affect the size and types of materials used for the slide plate elements. These data should be available to the mechanical department, which is always responsible for delivering these data. By considering Д as the total thermal growth between exchanger or vessel saddles, the element widths will be defined by the following limits:
1. Upper element = saddle width + 25 mm minimum to allow for downhand welding on the element-to-saddle weld (a larger upper element width may be required for exchangers or vessels with large Д values).
2. Lower element = upper element width – 2(Д) – 25 mm (minimum of 25 mm narrower than upper element).
Element lengths should be defined as follows (use a 450-mm maximum clear distance between lower elements):
1. The lower element is based on the allowable contact pressure, in accordance with the manufacturer’s literature and the lower element width.
2. Upper element = lower element length + 25 mm.
Plates should be aligned with saddle stiffeners where practical. A continuous steel bearing plate should be provided under the lower elements so that the lower elements can be welded to the bearing plate. The minimum width of the bearing plate should be 25 mm larger than the width of the lower elements. The minimum length of the bearing plate should be 25 mm larger than the saddle length. Bearing stress on concrete should be checked in accordance with ACI 318-05/318R-05.
In summary, the suggested criteria for sizing steel slide plates are as follows:
1. Minimum width = saddle width + 2Д + 25 mm
2. Minimum length = saddle length + 25 mm
Bearing stress on concrete should be checked in accordance with ACI 318- 05/318R-05.