DISCUSIÓN DE RESULTADOS

There are general above-ground recommendations for the installation of plastic pipe. But, never make assumptions based on average installations.

Confirm manufacturer’s recommendations for all of your installation projects.

The anchoring, support spacing, and hanger designs used with plastic pipe can dif-fer from the procedures used with other types of pipe. Another special considera-tion with plastic pipe is the potential risk of damage from different types of impact.

Let’s go over some of these basics.

Support Spacing

The rules for support spacing when working with plastic pipe are different than those used for metal pipe. Both the tensile and compression strengths of plastic pipe are lower than those of metal pipe. Recommended spacing is illustrated in Table 5.2.

This means that additional support is needed for plastic pipe. Additionally, the tensile strength of thermoplastic pipe decreases when the pipe gets hot. Therefore, more support is needed. Conditions can exist when temperature ratings are so high that thermoplastic pipe will require continuous support.

Thermoset requirements for support are not as extensive as those used with thermoplastic pipe. In fact, thermoset installations are much more in line with the requirements set forth for metal pipes. Check your local code requirements for spe-cific spacing data on supports.

PLASTIC PIPING HANDBOOK 5.6

Hangers

The types of hangers used with plastic pipe can be critical to the success of the pipe’s function. Using the wrong type of hanger can cause stress on a pipe that will shorten the useful life of the conduit. Overall, most designers choose hangers that have a large bearing area to disperse the load of the pipe over the largest area feasible. A variety of hangers are illustrated in Figures 5.3, 5.4, 5.5, 5.6, and 5.7.

Hangers that are manufactured for metal pipe can often be modified and used with plastic pipe. Horizontal pipe is often hung with either a sling clamp or a cle-vis hanger.

Shoe supports can be used when conditions are favorable for them. Remem-ber to choose hangers that offer the largest area of support that is practical.

It is not unusual to find a sleeve of sheet metal installed between the pipe and its hanger. Why is this done? The sheet metal spreads the load over a larger area of the pipe to reduce stress on the pipe.

When U-bolt hangers and roller hangers are used, the plastic pipe should be fitted with a protective sleeve. Medium-gage sheet metal is often used to fabri-cate these sleeves. Another type of sleeve is a section of plastic pipe that has been cut in half to fit over the pipe being secured. A rule-of-thumb for plastic pipe installations where excessive temperature calls for continuous support is to use a smooth structural angle or channel.

ABOVE GROUND PIPE DESIGN 5.7

TABLE 5.2 Recommended Support Spacing (in feet)

(Courtesy George Fischer Engineering Handbook)

Roller hangers are recommended when a pipe might move axially.

Thermal expansion is possible due to fluid or environmental temperature vari-ations. This may cause movement that is best handled by roller hangers. In such cases, the pipe should be fitted with a protective sleeve.

Plastic pipe that rubs against a steel support can be damaged to a point that the useful life of the pipe is reduced. Any abrasive surface can be destructive to plastic pipe. Wood is sometimes used to protect plastic pipe from abrasive sur-faces, but wood can deteriorate. A thermoplastic pad, such as PVC or polyethylene

PLASTIC PIPING HANDBOOK 5.8

FIGURE 5.3 Band hanger with protective sleeve. (Courtesy George Fischer Engineering Handbook)

FIGURE 5.4 Clevis hanger. (Cour-tesy George Fischer Engineering Handbook)

FIGURE 5.5 Adjustable solid ring swivel type.

(Courtesy George Fischer Engineering Handbook)

FIGURE 5.6 Single pipe roll. (Courtesy George Fischer Engineering Handbook)

makes a better protective surface. Pipe roll plates as illustrated in Figure 5.8 are also effective supports.

Your local code will dictate where hangers must be installed, but remember to install them as close as possible to all 90-degree bends.

Vertical installations must be supported in compliance with code regulations.

The support intervals are not as frequent as those used for horizontal piping, but they are just as necessary. The base of all stacks must be supported. From there, the vertical intervals vary, so check your local code requirements.

It is preferable to avoid heavy weight loads on the base of vertical runs. The weight load can be controlled with riser clamp or double-bolt pipe clamps, illus-trated in Figures 5.9 and 5.10.

ABOVE GROUND PIPE DESIGN 5.9

FIGURE 5.7 Roller hanger. (Courtesy George Fischer Engineering Handbook)

FIGURE 5.8 Pipe roll and plate. (Courtesy George Fischer Engineering Handbook)

FIGURE 5.9 Riser clamp. (Courtesy George Fischer Engineering Handbook)

FIGURE 5.10 Double-bolt clamp. (Courtesy George Fischer Engineering Handbook)

When using these devices, you must avoid tightening the supports to a point where they will compress the wall of the pipe being secured. It’s common to install these supports directly beneath couplings. In this way, the shoulder of the coupling rests on the support for maximum results. A trick of the trade when you need a support in a location where there is no fitting is to cut the hub of a fitting from the fitting and bond it to the vertical pipe. The shoulder of the hub can then rest on your support. Placing your supports under the shoulders of fittings makes it easier to maintain support without compressing the pipe too much. Continuous support arrangements are illustrated in Figure 5.11.

Valves are a common part of a piping installation. When the valves are larger than 2 inches in diameter, they should be supported. Unsupported valves can put stress on the joints between the valve and the pipe ends. In horizontal installa-tions, it’s a good idea to support the pipe on both sides of a valve, near the point of connection. Support arrangements are illustrated in Figure 5.12

Pipe movement must be controlled. This is most often done with the use of anchors and guides. These devices can direct the motion of a pipe within a defined range. Once an anchor is installed, there is no axial or transverse movement of the pipe. When axial movement is allowable, but transverse movement is not, guides are installed. Achorage methods are illustrated in Figures 5.13 and 5.14.

The use of anchors and guides should be designed in a way to function with-out point loading the pipe. You can expect to find anchors and guides whenever expansion joints are used. Long runs or piping are logical places to install anchors and guides. Directional changes in piping also call for anchors. When 90-degree bends are installed, anchors should be installed as close to the offsets as possible.

These are illustrated in Figure 15.5.

PLASTIC PIPING HANDBOOK 5.10

FIGURE 5.11 Continuous support arrangements. FIGURE 5.12 Typical support arrangements.