Lined Expansion Joints

Expansion joints provide a flexible connection between components such as piping, pumps, and vessels to counter expansion, contraction, bending, torsion, and other operational forces such as vibration (Fig. 8.39). PTFE is the material of choice. Unlike hoses, an expansion joint is used either with a cover, usually elastomeric, or merely with rib supports between the convolutions. Expansion joints are available in two or three convolutes. The choice depends on the requirements of the installation. 

PTFE convolutes are manufactured by either tape wrapping or the isostatic molding process. 

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Fired Heaters Incinerators FCC Transfer Lines FCC Flue Gas Lines Expansion Joints... 

All of these systems share to some degree several typical design problems associated with cryogenic liquid transfer. One class of difficulties results from cooling the system down from ambient to cryogenic temperature. Evidence of cooldown is in the form of two-phase flow, thermal contraction, and line bowing. Thermal contraction of a transfer line must not result in contact between the inner and outer lines, a condition most frequently encountered at changes in direction of the transfer lines. Expansion joints, bellows, and U-bends have been employed to solve the problem of thermal contraction. 

Furnace linings, refractory blocks , gaskets, expansion joints, very high-temperature work. 

One of the expansion joints accidentally failed while being cleared with a steam supply. Investigators determined the sponsors of this modification did not address the fact that sometimes process lines were blown clear with 150 psig ( 1,040 kPa gauge) steam. The robust piping system was compromised by an expansion joint that could not withstand I lie heat. Fortunately, there were no injuries. 

The coefficient of linear expansion of these alloys in the temperature range of 21 to 100°C (70 to 212°F) is 12.2 X 10- /°C (6.8 x 10" /°F), which is slightly above that of cast iron (National Bureau of Standards). Since these alloys have practically no elasticity, it is necessary to use expansion joints in relatively short pipe lines. Connections for flanged pipe, fittings, valves, and pumps are made to 125-lb American Standard drilling. 

All of these materials-brick, mortars and membranes-will be fully discussed in later chapters along with (1) Castables, grouts, and polymer concretes (2) Monolithics (troweled, sprayed and gunned linings) and (3) Expansion joint compounds, plus rigid plastic fabrications such as polyethylene, polypropylene and PVC. These components made from a whole host of materials are effectively used in a wide variety of industrial applications requiring superior chemical and thermal resistance. 

If a thermal difference will exist between the CRM lining and the shell and expansion joints are not provided in the lining, then NACE Publication 6K157 "Acidproof Vessel Construction With Membrane and Brick" suggests using the... 

The designer should note that if this type of rigid membrane is used, it will be because no flexible membrane can accept the exposure to the anticipated chemical environment. Therefore, there is no flexible expansion joint material that can accept this exposure either. Consequently, any vessel that must be lined with such a membrane should be so designed that no expansion joints are required. For such design, see the section on design elsewhere in this volume. 

It should be noted that, if interlocking expansion joints are to be used, it is generally advisable to go to an 8" lining. The reasons for this will be discussed under that heading. 

This is the first law of expansion joints-every expansion joint in chemically resistant masonry must end in a sliding joint or another expansion joint. If it is not so designed, the expansion joint will not function. See Drawing 4 of the wall of a brick-lined trench, below. 

The upper right-hand sketch shows the way a draftsman first designed the expansion joint. Note that the joint is totally immobilized because where the joint ends in the concrete above the brick lining, the concrete abuts the brick and holds the top course of brick in a fixed position. If the top brick cannot move, then neither can the brick below it. 

A thrust block may be defined, for our purpose, as a ceramic anchor, set in the substrate to prevent the movement of a brick facing placed over it. It is used to direct the expansion of a brick lining (or surfacing) in one direction only, rather than in both. On a floor, this may be used to prevent damage to the capping and brick lining of a trench or pit when it is undesirable to place an expansion joint adjacent to it. 

In 20 ft. trenches, with squared ends, it is often possible to eliminate intermediate expansion joints by the use of end pads of closed-cell foam rubber as shown in Drawing 8. This, in effect, "floats" the brick lining between the two foam pads, absorbing its expansion in both directions. The thickness of the two pads must be calculated to accept the maximum movement anticipated in one-half the thickness to be employed in the end pads. 

In placing expansion joints, it must be remembered that drains and pipe entries are both points of no movement, and that they should be centered between expansion joints to prevent the existence of any unbalanced stresses in the lining. 

Interlocking expansion joint in vessel lining ends at rubber inverted "T" (T) at brick cap. Shaft of rubber "T" shear pad permits lateral movement at this point independent of brick veneer on outside of vessel. Cross bar of "T" is set flat on membrane covering top of tank wall, and brick are laid up to and against the shaft on both sides. 

Where this 20 ft. linear distance is exceeded, therefore, it is wise to install "stress relief joints." These are, quite simply, cuts through the topping to the surface of the slab filled with elastomeric expansion joint sealer. The stress lines in the topping cut in this manner prevent the accumulation of sufficient stresses to exceed the strength of the bond of the topping to the substrate. If there are expansion joints at 15 to 20 ft. intervals, obviously there is no need for such stress relief joints. But if the expansion joints are at 30 ft. intervals, then a stress relief joint of this kind should be placed at the midpoint of this 30 ft. span to prevent such stress buildup. 

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