Uses of Compensators

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Lateral, Angular and Combined Deflection Examples

Example 1

In this example, if the pressure and deflections are low enough, an

inexpensive single expansion joint is able to absorb the thermalexpansion of both the pipe run in which the expansion joint is located, andthe perpendicular pipe. The growth of the perpendicular pipe produceslateral deflection in the expansion joint, while axial deflection absorbs thegrowth of the horizontal run. This combination of movements is, therefore,handled by a single expansion joint. The pressure thrust cannot beresisted by the expansion joint and a "directional" anchor must beprovided at the elbow to permit the elbow to deflect vertically. The pipeguiding required follows that of Example 1from the Axial Deflectionsection.

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Example 2

Example 1, a single expansion joint absorbs, as lateral deflection, thethermal expansion of the long horizontal pipe run. The benefit of this

arrangement is that the anchoring to restrain the pressure thrust isconfined to the short pipe leg that contains the expansion joint. The longpipe is in tension from its pressure thrust and does not require extensiveguiding. A directional anchor is located at the lower elbow, with thefreedom to permit the growth of the horizontal pipe. The upper elbow isattached to a main anchor, and is the fixed point from which all thedeflections are calculated. At the left elbow, an intermediate anchor isadded to fix the end of the portion of pipe from which the expansion jointis accepting movement.

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Page 1 of 4EJ Guide: Lateral, Angular and Combined Deflection Examples

10/5/2006http://www.usbellows.com/ejguide/applications/combine.htm


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If lateral deflections will be larger than a single expansion joint can accept,a universal type can be used as shown above.

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Example 3

When anchoring to absorb the pressure thrust shown in the previousexample is impractical, or uneconomical, an arrangement using a tiedsingle expansion joint can be used as shown above. The tie rods aretension devices which act the same as the pipe wall in resisting or

carrying the pressure thrust. As a result, the length of the expansion jointbecomes fixed, and the unit cannot absorb the axial deflection producedby the thermal expansion of the pipe in which it is installed. Theexpansion joint will absorb, as lateral deflection, the thermal expansion ofthe long horizontal pipe. Since the short vertical pipe length will changedue to the rotation of the tie rods and the thermal expansion of it's elbowsand hot pipe, the horizontal pipe will bend. Therefore a planer guide isprovided as shown. This arrangement will only work if the horizontal pipecan accept the bending. Usually it is practical and economical for smallvertical movements and/or long horizontal pipe runs.

if large lateral deflections must be absorbed, tied universal expansionjoints should be provided as shown above.

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Example 4

This arrangement is similar to Example 3, except that the need for thelong horizontal pipe to accept bending is reduced or eliminated, by theattachment of the tie rods from elbow to elbow. Thus, the length of thevertical pipe between the elbows, including the expansion joint, is fixed.

All the thermal expansion of the vertical leg is absorbed by the bellowswithin the tie rods. Some bending of the long pipe will occur due to therotation of the tie rods during the lateral deflection. However, since therods now cover a longer distance, the angle they must rotate for a given

lateral deflection is considerably reduced.

Example 5

The previous examples dealt with all the piping and deflections in a singleplane. Often, however, pipe runs change planes as well as direction, andthe resulting thermal expansion can appear to be complicated. In thisexample, a tied universal expansion joint is shown accepting the thermalgrowth of two horizontal pipes in two different planes. The example isalmost identical to Example 3, except that the lateral deflections must beanalyzed as vectors. The real deflection of the expansion joint is a singleresultant lateral deflection in a single resultant plane. The axial thermalexpansion of the pipe length that includes the expansion joint is absorbed

within the expansion joint and by bending the pipes just as in Example 3.

The expansion joint can also have the tie rods attached to the elbows, asin Example 4, and achieve the same benefits, but the deflections must stillbe determined as vectors, as above.

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Example 6




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In this example two vessels are connected by a straight inclined orhorizontal pipe. As shown, each vessel is assumed to be an anchor,wherein the vessel supports must be capable of accepting the pressurethrust developed in the pipe, in the direction of the axis of the pipe. Thepurpose of the expansion joint is to accept the thermal expansion of thedistance between the centerlines of the vessels. Even though the pipe isattached to the right vessel at its wall, the growth of the diameter of thevessel itself adds to the connecting pipe growth. The growth from anchorpoint to anchor point must be used for the thermal expansion calculation.Here we have used an untied universal expansion joint, since the growth

of the pipe is accepted as axial compression by the bellows. When thepipe is inclined, or the elevation of the anchor of each vessel is different,the vertical thermal expansion creates a lateral deflection vector, which iseasily accepted by the universal type of expansion joint.In this application, because the pipe and expansion joint are horizontal, orinclined, the weight of pipe spool between the bellows must be consideredin the final design. Tie rods which do not restrain the thrust or controlrods, can be added to suspend the center spool. Similarly, slotted hingescan be added over each bellows. Another mechanism for the samepurpose is a pantographic linkage.The advantage of the pantograph is that it automatically distributes theaxial deflection equally between the two bellows without the addition ofother devices.

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Uses of Compensators

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