CPVC - ASTRAL PRO

THERMAL EXPANSION AND THERMAL STRESSES 

* For ½" wall thickness minimum is not a function of SDR.

THERMAL EXPANSION AND CONTRACTION:

Like all piping material, Astral CPVC PRO expands when heated and contracts when cools down. CPVC piping (regardless of pipe diameter) will expand about 1 inch per 50 feet of length when subjected to 50° F temperature increase, therefore, allowances must be made for this resulting movement. However, laboratory testing and installation experience have demonstrated that the practical issues are much smaller than the coefficient of thermal expansion would suggest. The stresses developed in CPVC pipe are generally much smaller than those developed in metal pipe for equal temperature changes because of the difference in elastic modulus. Required loops are smaller than those recommended by the Copper Development Association for copper systems.

Expansion is mainly a concern in hot water lines, generally, thermal expansion can be accommodated with changes in direction. However, a long straight run may require an offset or loop. Only one expansion loop, properly sized is required in any single straight run, regardless of its total length. If more convenient, two or more, smaller expansion loops, properly sized, can be utilized in a single run of pipe to accommodate the thermal movement. Be sure to hang pipe with smooth straps that will not restrict movement. For convenience, loop (or offset) length have been calculated for different pipe sizes and different run length with a temperature increase (?T) of about 80°F. The results, shown in table A and B, are presented simply as a handy guide for quick and easy determinations of acceptable loop length for other temperatures and run length can be calculated utilizing the following equations :

Where: 

L = Loop length (in.)
E = Modulus of elasticity at maximum temperature (psi)
S = Working Stress at maximum temperature (psi)
D = Outside diameter of pipe (in.)
ΔL = Change in length due to change in temperature (in.)

Thermal Expansion Formula Where:
ΔL = Change in length due to change in temperature (in.)
Lp = Length of pipe (in.)
C   = Coefficient of thermal expansion (in. / in. /°F) 
     = 3.4 x 10-5 in. / in./°F for CPVC
ΔT = Change in temperature (°F)

TABLE A

Astral CPVC PRO IPS PIPES (ASTM D 2846)
Calculated Loop (Offset) Length with ΔT of approx. 80°F in inches   

TABLE B
Astral CPVC PRO IPS PIPES (ASTM F 441)
Calculated Loop (Offset) Length with ΔT of approx. 80°F in inches

Length of Run in feet 

HORIZONTAL AND VERTICAL SUPPORT :

Horizontal & Vertical runs of Astral CPVC PRO Pipe should be supported by pipe clamps or by hangers located on the horizontal connection close to the riser. Hangers should not have rough or sharp edges, which come in contact with the pipe.

TRANSITION FITTINGS & JOINTS:

Special transition fittings or joints are used whenever CPVC piping is connected to a metal valve, fittings, or other appurtenance such as a filter, or to parts made of another plastic. These special transition fittings can have many forms. One common form is the true union with a metal end and a CPVC end held together with a plastic or metal gland nut and having an elastomeric seal between them. Other forms are the flanged joint, the grooved joint, insert molded metal in CPVC fittings, patented push-on type fittings and finally the CPVC female threaded adapter with an elastomeric seal at the bottom of the thread. The later fittings are designed so that they have no thread interference and rely entirely on the elastomeric seal for water tightness. They require only minimal torque to attain an adequate seal.

Standard compression fittings which utilize brass of plastic ferrules can be used to assemble CPVC. However, Teflon® tape should be applied over the brass ferrule to compensate for the dissimilar thermal expansion rates of the brass and CPVC that could possibly otherwise result in a leak. Care should be taken not to over-torque the compression connection.

Metal fittings with CPVC socket inserts are also available. The tubing is cemented directly into the socket in the same way as all-CPVC fittings.

The standard practice is to thread a male thread adapter into the female threaded part, such as a valve of stop, and then solvent cement to the CPVC pipe. However, when using the male thread adapter, there are two limitations that the installer must consider when deciding where and how to use it. First, the male thread adapter may develop a drip leak if the joint is subjected to very broad temperature range. And second, some thread sealants intended to minimize leak problems may chemically attack the CPVC and cause stress cracking of the adapter (see Thread Sealants section). The preferred method of transitioning between metal and CPVC plumbing component is to use an insert molded metal-in-CPVC fitting or true union with a metal and a CPVC end.

CPVC pipes and fittings can be installed underground. Since these piping systems are flexible systems, proper attention should be given to burial conditions. The stiffness of the piping system is affected by sidewall support, soil compaction, and the condition of the trench. Trench bottoms should be smooth and regular in either undisturbed soil or a layer of compacted backfill. Pipe must lie evenly on this surface throughout the entire length of its barrel. Excavation, bedding and backfill should be in accordance with the provision of the local Plumbing Code having jurisdiction.

TRENCHING :

The following trenching and burial procedures should be used to protect the piping system.

The trench should be excavated to ensure the sides will be stable under all working conditions.
The trench should be wide enough to provide adequate room for the following:
- Joining the pipe in the trench.
- Snaking the pipe from side or side to compensate for expansion and contraction.
- Filling and compacting the side fills. 
The space between the pipe and trench wall must be wider than the compaction equipment used in the compaction of the backfill. Minimum width shall not be less than the greater of either the pipe outside diameter plus 16 inches or the pipe outside diameter times 1.25 plus 12 inches. Trench width may be different if approved by the design engineer.

The trench bottom should be smooth, free of rocks and debris, continuous, and provide uniform support. If ledge rock, hardpan or large boulders are encountered, the trench bottom should be padded with bedding of compacted granular material to a thickness of at least 4 inches. Foundation bedding should be installed as required by the engineer.

Trench depth is determined by the pipe’s service requirements. Plastic pipe should always be installed at least below the frost level. The minimum cover for lines subject to heavy overhead traffic is 24 inches.

A smooth trench bottom is necessary to support the pipe over its entire length on firm stable material. Blocking should not be used to change pipe grade or to intermittently support pipe over low sections in the trench.

BEDDING AND BACKFILLING:

Even though sub-soil conditions vary widely from place to place, the pipe backfill should be stable and provide protection to the pipe.

The pipe should be surrounded with a granular material which is easily worked around the sides of the pipe. Backfilling should be performed in layer of 6 inch with each layer being sufficiently compacted to 85% to 95% compaction.

A mechanical tamper is recommended for compacting sand and gravel backfill which contain a significant proportion of fine grained material, such as silt and clay. If a tamper is not available, compacting should be done by hand.

The trench should be completely filled. The backfill should be placed and spread in fairly uniform layers to prevent any unfilled spaces or voids. Large rocks, stones, frozen clods, or other large debris should be removed. Heavy tampers or rolling equipment should only be used to consolidate only the final backfill.

 HANDLING :

The pipe should be handled with reasonable care. Because thermoplastic pipe is much lighter in weight than metal pipe, there is sometimes a tendency to throw it around. This should be avoided.

The pipe should never be dragged or pushed from a truck bed. Pallets for pipe should be removed with a fork lift. Loose pipe can be rolled down timbers as long as the pieces do not fall on each other or on any hard or uneven surface.

In all cases, severe contact with any sharp objects (rocks, angle irons, forks on forklifts, etc.) should be avoided.

 STORING:

If possible, pipe should be stored inside. When this is not possible, the pipe should be stored on level ground which is dry and free from sharp objects. If different schedules of pipes are stacked together, the pipes with the thickest walls should be at the bottom.

The pipes should be protected from the sun and be in an area with proper ventilation. This will lessen the effects of ultraviolet rays and help prevent heat built-up.

If the pipes are stored in racks, it should be continuously supported along its length. If this is not possible, the spacing of the supports should not exceed three feet (3’).

When storage temperatures are below 0°C (32°F), extra care should be taken when handing the pipe. This will help prevent any problems which could be caused by the slightly lower impact strength of PVC pipes at temperature below freezing.