ABSTRACT
The installation of plastic pipe is by far the most important consideration for a successful piping system, for it is in the installation that most of all problems occur. Part of this problem stems from the lack of formal training provided to trade groups. Keeping in mind that plastics are a relative newcomer to industrial piping systems, their metal counterparts have been around for hundreds of years. Most trade apprenticeship programs go into great depth on brazing, welding, orbital joining, and soldering, and just about every means of joining metallic pipe is covered in great detail. Another part of the problem is that the standards that have been adopted over the years have drawn upon the many years of experience and an understanding of the materials. Plastics, on the other hand, are constantly changing and are treated with much less detail. It is generally left to the plastic manufacturer to provide the bulk of training on installation of its product. As a result, there can be variation between what is generally accepted installation practice from manufacturer to manufacturer.Plastics have very different joining methods. There is solvent cementing, thermal fusion, modified butt fusion, electrofusion using high-resistance wire to conduct heat between two parts, and ever-changing ways of introducing heat to joining surfaces. In this chapter we will attempt to delve into as much detail as possible to provide the most recent successful joining methods in the industry today. More traditional joining methods such as solvent cementing and mechanical joining will be straightforward, while newer methods will draw upon specific manufacturers to provide details installation methods from which the reader will be able to understand the appropriateness of the particular joining method for a specific application. II. GENERAL INSTALLATION GUIDELINES
Storage of plastic pipe is the first critical step in a successful installation. Proper storage and handling of plastics is more than neatly stacking pipe. Common sense must be exercised when handling plastics. Rough handling, dragging on a rack, 126
or just dropping on the ground can damage some plastic pipe simply through small scratches.Some plastics are notch sensitive, which is measured by the Izod impact test. A low Izod value means that scratches or small cuts in the pipe can weaken the pipe and result in a potential failure if stress is induced. A notch can be generated through mishandling before the pipe is installed or during or after installation. Certain products, PVC and CPVC, for example, are more notch sensitive than other thermoplastics (Table 1). Other materials such as polyethylene have much higher Izod values and can be readily buried or impacted without concern about failure due to notch sensitivity. This property must be taken into consideration for a buried application.To prevent sagging or drooping, particularly of the longer sections, pipe should be stored on racks that provide close or continuous support. Any sharp edges or burrs that protrude on the racks should be removed or covered. To prevent excessive deflection, loose stacks of pipe should not exceed a height of 3 ft. (1 m). Bundled pipe can be stacked twice as high. Pulling a length of pipe off a truck bed and letting the free end fall to the ground should be avoided. So should dragging the pipe over rough ground, dropping heavy objects on it, or using any kind of chains. The resulting scratches, splits, or gouges can reduce the pressure rating. If damage from careless handling does occur, one of the advan-
tages of plastic pipe is that damage is readily apparent. The damaged section can be quickly cut out and the pipe ends rejoined. B. Weathering
A few thermoplastics have excellent resistance to weathering and can be stored outside for long periods. However, many thermoplastics oxidize and should be covered if stored outside for any period of time. For extended storage, the piping components should be covered with a light-colored tarp or kept under cover in a warehouse or shed that is well ventilated to prevent excessive temperature buildup and possible warping. The storage area should not be located near steam lines or other high heat sources.Fittings and flanges should be kept in their original packaging or in separate bins until they are needed. They should never be mixed in with metal piping components, as scratches are possible.The thermoplastics that should be covered with a tarp, shed, or anything that will keep direct sunlight from the exposed surface at all times if stored outside are: Olefin plastics such as polyethylene, polypropylene, and polybutylene,Vinyls such as PVC and CPVCCompounded thermoplastics like ABS Thermoplastics that are not affected by ultraviolet (UV) light would be: Fully fluorinated plastics like PTFE (Teflon)Partially fluorinated plastics like PVDF and ECTFE
Cutting plastic pipe is important to ensure a successful installation. In most cases cutting is critical to the successful outcome of the joint. For instance, in high-purity applications saw cutting will generate particles that will adhere to the pipe walls (due to static buildup) and could result in contamination. Plastic pipe can easily be cut at the job site by any of several methods. These include a radial cutoff saw (which is how pipe fabricators efficiently cut large volumes of pipe), a circular saw, a band saw, and the conventional hand saw. A wheel-type pipe cutter (shown Fig. 1) with special blades for plastic pipe is available and is the recommended cutting method.The guillotine cutter is often used for large-diameter polyethylene pipe service lines (shown in Fig. 2). An interlocking multiwheel cutter is used for field cuts in tight spaces (shown in Fig. 3).A more recent plastic pipe cutting tool is the ratchet-type knife or shear
cutter (shown in Fig. 4), which is suitable for small-bore compound or some polyolefin thermoplastics. These cutters are not recommended for heavy walls or highly crystalline plastics, which could crack when cut with ratchet-type cutters.To ensure square-cut ends (which allow the pipe to “bottom out” in the socket of the fitting), a miter box should be used with the hand-sawing method.Fine-tooth blades (16-18 teeth per inch) with relatively little set (maximum 0.025 in.) are recommended for use with power saws. For circular saws, the speed should be about 5000 ft./min (1500 m/min), and about 3000 ft./min (900 m/min) for band saws. Standard steel blades soon become dull, so carbide-tipped saw blades are preferred where large quantities of pipe are cut. Some of the more abrasion-resistant plastic (i.e., PVDF) will dull blades faster than vinyls or compound plastics.
