Slip-Type Joints

In one design, the gun-packed joint (Fig. 113. packing can be inserted into the stuffing box a any time with full temperature and pressure on the line. This eliminates shutdown and minimizes maintenance time. 

A slip joint fitted with a sliding member at only one end is known as a single-end joint. When sliding members are used at both ends, the joint can absorb twice the expansion of a single-end joint and is known as a double-end joint. 

---

The slip-type joint (Figure 7-112) is particularly useful in steam and hot-water transmission lines where expansions and contractions are frequent and of large magnitude. Slip joints contain no highly-stressed flexing element subject to failure after a finite number of cycles. 

Except for some specialized applications of the corrugated type, expansion joints and bends require good pipe alignment to perform satisfactorily. Guides serve two important purposes. When installed near an expansion joint they prevent cocking of the sleeve in a slip-type joint or distortion and possible buckling of a corrugated-type joint or an expansion bend. 

Slip-type expansion joints (Fig. 10-178) substitute packing (ring or plastic) for bellows. Their performance is sensitive to adequate design... 

FIG. 10-178 Slip-type expansion joint. (From Kellogg Design of Piping Systems, Wiley, New York, 1965.)... 

Anchors for Expansion Joints Anchors (such as those of the corrugated, omega, disk, or slip type) shall be designed to withstand the algebraic sum of the forces at the maximum pressure and temperature at which the joint is to be used. These forces are ... 

Pressure thrust, which is the product of the effective thrust area times the maximum pressure to which the joint will be subjected during normal operation. (For slip joints the effective thrust area shall be computed by using the outside diameter of the pipe. For corrugated, omega, or disk-type joints, the effective thrust area shall be that area recommended by the joint manufacturer. If this information is unobtainable, the effective area shall be computed by using the maximum inside diameter of the expansion-joint bellows.)... 

Three proven means for absorbing pipe expansion and contraction are (1) expansion bends, (2) corrugated or bellows-type expansion joints and (3) slip-type expansion joints. 

All expansion bends, whether fabricated or not, require more installation space than either corrugated or slip-type expansion joints. This is often an important consideration in crowded refinery or petrochemical plant areas but can usually be overlooked on tank farms and other locations where a large amount of space is available. 

The first cost of a fabricated expansion bend may exceed the first cost of a bellows or slip-type expansion joint. A built-up expansion bend usually costs less than a fabricated bend or either type of expansion joint, unless a great deal of labor is required to build the bend. 

The curves in Figure 7-115 illustrate the comparative magnitude of end and intermediate anchor loads for slip-type expansion joints, and they also provide reasonably accurate anchor load... 

Figure 13.33. Flange types (a) Welding-neck (b) Slip-on (c) Lap-joint (d) Screwed...

If unbalanced layouts cannot be avoided, appropriate analytical methods must be apphed to assure adequate flexibility. If the designer determines that a piping system does not have adequate inherent flexibility, additional flexibility may be provided by adding bends, loops, offsets, swivel joints, corrugated pipe, expansion joints of the bellows or slip-joint type, or other devices. Suitable anchoring must be provided. 

---