Piping Tierods

The absence of tierods where they should be used is one of the most frequent hazards in existing piping systems. This section will show the conditions which require tierods to make a piping system safe and provide the tools to simplify the design of tierods and other anchor systems. 

Where tierods support a dead load in a long-vertical run-of-pipe, the effect of the dead load on the design conditions of the tierods should be checked. 

The longitudinal force in a pipe joint, caused by internal pressure is 

The effective area of a sleeve coupling, or bell and spigot-type joint is considered to be the area of a circle having a diameter equal to the outside diameter of the pipe. The effective area of convoluted expansion joints is determined by pressure tests, which are made by the manufacturer and published in his catalogs. The effective areas given in Table 7-18 are representative of the product of several manufacturers. 

With this design force, enter Table 7-19 and select the number smd size of tierods most suited to the operating conditions. The joints which are required to have a hinge action should have two tierods. 

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Piping tierods are used to restrain the anchor force produced by the particular group of pipe-joints which tend to pull apart when subjected to internal pressure. Figure 1-135 shows a typical tierod design. 

Doyle, W.E. Piping Tierod Design Made Simple. Hydrocarbon Processing Petroleum Refiner, August 1965, p. 118. 

Enter Table 7-20 with the size of the tierod selected, which determines the size of the tierod anchor required. The required section modulus of the anchor, given in the second column, has been determined using an allowable fiber stress of 10,000 psi and a distance of 3-1/2 inches from the rod to the pipe, which is adequate for all joints in common use. The structural member size and shape given in the third column is merely a suggestion, other structural members may be used provided their section modulus is adequate. 

Sufficient weld-metal should be used to develop the full strength of the tierod anchor where it connects to the pipe. 

Where an expansion joint is used in a vacuum line, or where any other compressive force is required to be restrained, a pipe sleeve should be placed over each tierod to span the distance between the anchors, with the expansion joint in the free condition, as shown in Figure 7-136. 

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