Openings must commonly be cut or drilled in structures for the installation of plumbing systems. To accomplish this task, you will need a fundamental knowledge of how buildings are constructed (structural design), and what tools are necessary for performing the tasks. When you cut or drill structural openings for the installation of pipe, you will need to support the pipe to prevent it from sagging or vibrating, and consequently developing leaks.

This course introduces the various types of piping material used in the accomplishment of your job. Part of your job will be the installation of steel and plastic piping, and copper tubing. You will also discover the advantages and disadvantages of each material, as well as the preparation, installation, joining, and support structure requirements associated with each of these materials.

When you have completed this course, you will be able to:

  1. Describe the design and types of structural openings.
  2. Describe the different types of steel pipe assemblies.
  3. Describe the different types of plastic pipe assemblies.
  4. Describe the different types of copper tubing assemblies.


1.0.0 Structural Openings

2.0.0 Steel Pipe Assembly

3.0.0 Plastic Pipe Assembly

4.0.0 Copper Tubing Assembly

Review Questions


1.1.0 Structural Design

Buildings are constructed of wood, masonry products, metal, or a combination of these materials. Other materials such as drywall, asphalt shingles, paneling and plaster are also used in the construction of buildings. However, wood, masonry products, and metal are the primary materials used to build the major structural components of a building. We will address the most common types of structural design.

1.1.1 Wood

Buildings are constructed using either box or frame type construction. The type of construction will determine how your plumbing system is installed.

Box Type

Box type construction uses only a single board thickness in the walls and has only enough framework to support the floor and roof. The studs inside the building are exposed. Most plumbing is exposed. This is considered a temporary building.

Frame Type

The frame type is a more permanent type of construction. This type of structure has a framework of studs, usually 2 x 4 inch or 2 x 6 inch, covered on both sides to form a double wall. All water supply and drainage piping located above the floor level are usually concealed within the framework.

1.1.2 Masonry

Most permanent structures are built of some type of masonry material. It may be solid concrete, stone, brick, brick veneer, or cement block. In most masonry buildings, the water piping is exposed because of the possibility of leakage. The drainage system, which is not pressurized, may be covered by a concrete floor after it has been properly inspected. You must, however, install an access point for cleaning in case of stoppages. This access is called a cleanout. If a pipe must pass through a masonry wall, a sleeve (section of plastic pipe) is set in place while the wall is being constructed. This sleeve prevents corrosion between the metal pipe and masonry materials. The pipe can also be wrapped in insulation to prevent corrosion.

1.1.3 Metal

Metal buildings have a framework of structural steel or pipe and are covered with sheet metal. Most water piping in this type of structure is exposed. If metal buildings have a concrete floor, the drainage system may be covered after it has been inspected.

1.2.0 Locating Structural Openings

Building Construction Plans. Since most piping, either supply or drainage is installed to directly serve some type of fixture, you must know the location of all fixtures. You can obtain this information from the floor plans. See Figure 1.

Figure 1 — Floor plan.

Specification Sheets. The specification sheets will indicate the exact model or type of fixture to be used.

Manufacturer’s Rough-In Specifications. These show the required location of all supply and drainage pipe openings. You must know this information when locating the structural openings for the waste and supply piping. One reason for this is because you may need to cut holes through structural members to align the pipe with the fixture location.

Working Drawing. After you check the construction plans, specification sheets, and manufacturer’s rough-in specifications, you will prepare a working drawing. This drawing should indicate the location of all fixtures and the routing of all supply and waste pipes.

1.3.0 Stages of Construction

During the construction of a building, the UTs complete the plumbing installation in two major phases. The first phase is referred to as rough-in plumbing. The second phase is referred to as finish plumbing.

1.3.1 Rough-In

Before the concrete slab is poured, you will install horizontal water and drainage piping below ground in trenches. From the horizontal piping in the trench, you will “stub up” vertical piping for each fixture to a height that will terminate at least 12 inches above the proposed finished floor. Then you will wrap any portion of vertical metallic pipe that comes in contact with concrete with insulation to prevent corrosion between the pipe and the concrete. Another method to avoid corrosion is to install a sleeve (short piece of plastic pipe) while the wall is being constructed. The newly installed pipe is tested for leaks and inspected before the trenches are backfilled. The concrete slab is then poured.

Once the building is framed and the exterior walls are installed, you will return to extend vertical and horizontal rough-in piping. It is at this time that most of the structural openings are cut. Portions of water and waste lines will be “stubbed out” past the walls for fixtures that will be installed later.

1.3.2 Finish Plumbing

Once the rough-in plumbing is completed, you will continue with finishing interior and exterior wall coverings. When the job is nearly complete, you will return to install the fixtures and connect the water and drain piping to each fixture. This final stage of plumbing installation is referred to as "finish plumbing.”

1.3.3 Hole Cutting Tools

Most often, you will be using power tools to cut structural openings for the installation of pipe. There are a variety of tools available for this purpose. On occasion, you may have to cut these openings with hand tools.

Electric Drills and Hole Saws  — Electric drills and hole saws are most often used when cutting holes in wood because the tool cuts a perfectly round hole for pipe installation. The hole saws used with the electric drill are available in diameters to accommodate most sizes of pipe. See Figure 3.

Figure 3 — Electric drills and hole saws.

The electric drill can be used with a variety of bits to drill through wood, steel, and masonry.

Paddle bits are used with electric drills to make round holes in wood. This type of bit only comes in sizes that will accommodate smaller diameter pipe. Carbide bits can be used to drill holes through steel and some masonry materials.

Reciprocating Saw  — Reciprocating saws may be used to create large openings for the installation of pipe. Blades for reciprocating saws are available to cut through wood and many types of metal. See Figure 4A.

Jigsaw  — Jigsaws are used to cut irregular shaped openings in wood. For a circular shaped opening, a pilot hole is drilled within the area to be cut out of the lumber. The jigsaw is then used to cut out the circular shaped opening. See Figure 4B.

Figure 4 — Reciprocating and jigsaws.

Hammer Drill  — A hammer drill is used to drill an opening in masonry materials. The drill bit reciprocates and turns simultaneously to bore the hole. See Figure 5A.

Tin Snips — Tin snips are used to cut curved or circular shaped openings in sheet metal. See Figure 5B.

Brace and Bit  — A brace and bit is used to manually drill holes in wood when electricity is not available for power tools. See Figure 5C.

Figure 5 — (A) Hammer drill
(B) Tin snips
(C) Brace and bit.

Keyhole Saw — The keyhole saw can be used to cut irregular shaped openings in wood when electricity is not available for power tools. See Figure 6A.

Hammer and Star Drill — When creating openings in concrete it may be necessary to use a hammer and chisel or a hammer and star drill. Using these tools to cut through concrete requires more time and labor than using power tools. See Figure 6B.

Figure 6 — (A) Keyhole saw, (B) Hammer and star drill.

1.4.0 Structural Openings

A structural opening is an opening cut in a structural member that allows the piping to pass through it. When openings are properly reinforced, they can also help to support the pipe. Structural openings are created when notching or drilling holes in a wooden structural member during the installation of pipe. You may need to reinforce structural members whenever you cut them if the cut or hole compromises the strength of the structural member. The following are four basic types of structural openings.

1.4.1 Center Cut

The most desirable type of structural opening to use is the center cut (Figure 7A). A center cut is a round hole cut in the center of the board. It causes less damage to the structural member than any other type of cut. The diameter of the opening should not exceed one-third the width of the board. If a larger hole is cut, the board loses its ability to support weight and stress.

Figure 7 — Types of structural openings.
(A) Center cut, (B) Over cut, (C) Under cut

1.4.2 Over Cut

If a center cut cannot be made, an over cut (Figure 7B) is acceptable. An over cut is made by notching the top of the board. The piping is installed through the notch and the beam provides some support to reduce movement of the pipe. Wedge a block of wood and nail it into the notch. This prevents the beam from sagging.

1.4.3 Under Cut

The under cut (Figure 7C) is a notch in the bottom of the structural member. Again, the piping is installed through the notch. To support the bottom of the pipe and the beam, install strap iron and lag screws on the notch to reinforce the beam. It is important to note that an over cut or an under cut should never be more than 1/2 the width of the beam or it will be weakened considerably.

1.4.4 Notch

A notch is a cut similar to an over cut or an under cut. If the opening (cut) is on a vertical structural member, it is referred to as a notch. See Figure 8.

Figure 8 — Notch cut.

1.5.0 Vertical Supports

Vertical piping must be supported to prevent stress on joints and potential leaking. Listed below (Table 1) are some of the general guidelines for supporting vertical piping. Support can be provided by structural openings that have been reinforced, or by the installation of pipe supports. Refer to your project specifications for locations. For additional information, refer to the International Plumbing Codebook 2009, Section 308. 

1.6.0 Horizontal Supports

Horizontal water and waste piping must also be supported to prevent sagging and potential leaking. Again, supports can be in the form of reinforced openings or pipe support materials. Criteria for supporting various types and diameters of pipe are listed below in Table 1. For additional information, refer to the International Plumbing Codebook 2009, Section 308.

Table 1 — Piping Support Spacing.

Piping Material  Maximum Horizontal Spacing
Maximum Vertical Spacing (Feet)
ABS pipe  4 10
Aluminum pipe and tubing  10 15
Brass pipe  10 10
Brass tubing, 1 1/4 inch diameter and smaller 6 10
Brass tubing, 1 1/2 inch diameter and larger   10 10
Cast iron pipe 5 15
Copper or copper alloy pipe 12 10
Copper or copper alloy tubing, 1 1/4 inch diameter and smaller 6 10
Copper or copper alloy tubing, 1 1/2 inch diameter or larger 10 10
CPVC pipe or tubing, 1 inch and smaller 3 10
CPVC pipe or tubing, 1 1/4 inch and larger 4 10
Lead pipe Continuous 4
PB pipe or tubing 2 2/3 feet or 32 inches 4
PEX tubing 2 2/3 feet or 32 inches 10
Polypropylene (PP) pipe or tubing, 1 inch or smaller 2 2/3 feet or 32 inches 10
Polypropylene (PP) pipe or tubing, 1 1/4 inches or larger 4 10
 PVC pipe 4 10
Steel tubing 8 10
Steel pipe 12 15



The maximum horizontal spacing of cast iron pipe hangers must be increased to 10 feet where 10 foot lengths of pipe are installed.

1.7.0 Support Materials

A variety of pipe support materials and devices are available. Specialized supports or pipe hangers are made for almost every possible situation you will encounter during your duties. See Figure 9.

Figure 9 — Types of supports.


Test Your Knowledge

1. Which of these structural opening cuts is most desirable for support of piping?

A. Center cut
B. Over cut
C. Under cut
D. Notch

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2.1.0 Measuring Procedures

Before you can thread the pipe, it must be measured and cut to length. There are different methods of measuring steel pipe: (1) end-to-end, (2) end-to-center, (3) centerto-center, and (4) face-to-face.

2.1.1 Thread Engagement (TE)

When trying to obtain the end-to-end measurement from one of the other measurements listed previously, you will add or subtract some different measurements. One of the measurements is referred to as the thread engagement. Thread engagement is the amount of pipe that will be screwed into a fitting to make a watertight seal. This measurement differs depending on the diameter of the pipe to be installed. The common thread engagements that you will encounter are for 1/2 inch and 3/4 inch diameter pipe. The rule of thumb for TE on 1/2 inch and 3/4 inch pipe is approximately the diameter of the pipe. For all other sizes, measure the thread engagement of individual fittings.

2.1.2 Methods

In plumbing systems, measurements must be obtained before you can cut, thread, or ream the pipe to be installed. End-to-end measurement is the measurement that you will use to cut the length of pipe. To find the end-to-end, you must take other measurements first.

During the rough-in of piping systems, structural openings are made for the installation of the piping. The center-to-center is a common measurement used. This measurement is used when two structural openings are made for pipe to be run through. The centerto-center is measured from the center of the two openings. This is also the center of the two fittings to be installed. To convert a center-to-center measurement to an end-to-end measurement, measure the distance from the center of one fitting to the center of the other fitting; subtract the thread engagement from each end, and this will give you the end-to-end measurement for the pipe.

Face-to-face is also used to determine a length of pipe to be installed. The face refers to the opening of the fitting. Often you may have two fittings in place and must obtain a measurement for pipe to be installed between them. This measurement does not allow for thread engagement. To convert a face-to-face measurement to an end-to-end measurement, first measure the distance from the face of one fitting to the face of the next fitting. Next, add one thread engagement for each fitting.

2.2.0 Hand Threading

2.2.1 Cutting Pipe

The purpose for cutting pipe is to obtain the correct length for installation and/or repair of piping systems. After the pipe has been measured and marked, it should be inserted into the pipe vise with the section to be cut extending beyond the face of the vise. To cut pipe with a pipe cutter, open the jaws of the cutter by turning the handle counterclockwise. Then, place the pipe cutter around the pipe and align the cutting wheel with the mark where the cut is to be made. Tighten the handle until the cutter wheel is forced slightly into the pipe. Revolve the cutter around the pipe one complete turn. Tighten adjustment handle 1/4 turn for every revolution of the cutter. Repeat this procedure until the pipe is cut.

2.2.2 Reaming

The purpose of reaming pipe is to restore the inside diameter of the pipe by removing any burrs which are created by the cutting of a pipe. Removal of these burrs will prevent flow restriction in the piping. The tool used to remove burrs could be a pipe reamer or a file.

2.2.3 Threading

The threads used on steel pipe are a standard size called the American Standard Pipe Thread. The process uses a 1/32 inch per inch taper with a 60° angle on the upper and inner threads. The angle and taper provide for a watertight seal when tightened. The diameter of the pipe determines the number of threads per inch on the pipe.

2.2.4 Dies

Nonadjustable hand dies with a ratchet type handle may be used to thread pipe from 1/ 8 inch to 2 inch diameter. Adjustable hand dies can thread pipe 1 inch to 2 inches. Three-way hand dies will thread from 1/2 inch to 1 inch diameter.

2.2.5 Procedures

Before you thread a pipe, inspect the dies to see that they are sharp and free from nicks and excessive wear. Then insert the pipe into the vise. Place the round guide end of the pipe die stock on the pipe (Figure 10) and push the pipe-threading dies against the pipe with the heel of the hand. (You must wear gloves to do this). Exert strong pressure with the heel of the hand against the pipe die and make three or four short turns in a clockwise direction to start the dies.

Figure 10 — Placing die stock on pipe.

When the dies are started, turn the handle of the pipe die (Figure 11). Apply cutting oil after every two or three downward strokes of the die handle. The oil prevents the pipe-threading dies and threads from overheating, and the threads from becoming dulled and marred. Continue to turn the dies until approximately two newly cut threads project beyond the end of the die segments. When the proper number of threads are cut on the pipe, reverse the ratchet on the die handle and turn the pipe dies counterclockwise until they are free of the threads.

Figure 11 — Threading pipe with ratchet and die.

The procedure for threading with an adjustable hand die is similar to the nonadjustable hand die. Adjustable dies have an automatic release that will allow only the correct number of threads to be cut.

2.3.0 Assembling Threaded Joints

2.3.1 The following steps describe how to make a leak-proof threaded joint. 

  1. Clean the threads. Use a wire brush to clean the threads of the fitting and pipe
  2.  Apply pipe-joint compound. There are several reasons for using pipe-joint compounds. They may be used as a lubricant, a corrosion protection agent, or an anti-seize compound. The anti-seize compound is used in case the joints must later be disassembled. The two most common types of pipe joint compound are Teflon tape and pipe dope.
  3. Fit the connection. Screw the fitting onto the pipe by hand, and tighten about two more turns with the correct size pipe wrench. Do not over-tighten the joint. If you over-tighten, the fitting may stretch or crack, and the joint might leak. Use a backup wrench to keep existing joints from turning and possibly causing a leak (Figures 4-12 and 4-13).

Figure 12 — Tightening a coupling using two wrenches.

Figure 13 — Tightening a pipe using two wrenches.

2.3.2 Wrench Selection

Pipe wrench sizes to be used for the several pipe sizes are as follows:

2.3.3 Pipe Nipples

Pipe nipples are also used in water systems. Nipples are short pieces of pipe. They come in the same diameter as long pipe, from 1/ 2 inch to 12 inch diameter.

There are three types of nipples: the close nipple or all-thread nipple (Figure 14A); the shoulder nipple, which has a short space between threads (Figure 14B); and the long nipples (Figure 14C) which are made in graduations of 2, 2 1/2, 3, 3 1/2, 4, 4 1/2, 5, 5 1/2, 6, 7, 8, 9, 10, 11, and 12 inches long.

Figure 14 — Pipe nipples.

2.4.0 Cold Water Distribution System Installation

2.4.1 Installations Procedures

After you have cut, reamed, and threaded the pipe, you are ready to assemble the threaded joint. Whenever you are assembling threaded joints, be sure to apply joint compound to the male threads. This makes it easier to disassemble the connection. There are many different types of joint compound. The most popular is Teflon tape. After applying the compound, screw the fitting onto the pipe hand tight, then turn the fitting two more revolutions with a pipe wrench.

The proper size wrench is important to the user because of the leverage needed to assemble or disassemble a joint. A back-up wrench is sometimes needed to ensure that the remaining pipe will not turn as you tighten or loosen the joint that you are working on.

Galvanized steel pipe was often used on the water distribution systems of older buildings. However, it will gradually corrode and is difficult to fit and work with. Since much of the work you will do as a UT will involve repairing, replacing, and maintaining in-place systems, you will need to be skilled at working with galvanized piping and fittings.

When assembling a cold water line using galvanized iron pipe, always start at the end of the service line to create the distribution main. Branch lines to individual fixtures are connected to the distribution main by using a reducing tee and nipple and a 90° elbow. The fixture supply risers are vertical pipes connected to the branch lines by means of a 90° elbow. Risers should be supported at each floor level and at joints. Refer to Figure 15 for installation of a branch line and risers.

Figure 15 — Installation of a branch line and risers.

The cold water inlet is normally located at the top (right side) of the tank. It will have a dip tube extending from it to direct the cold water to the bottom of the tank. The cold water inlet is 3/4 inch in diameter and has a shut-off valve installed on it.

2.4.2 Supporting Steel Pipe

There are many ways to support steel pipe. You can use pipe hangers, plumbing tape, and other support materials. Be sure to consult the engineer for structural strength. Supporting steel pipe is very important because if the pipe is not supported correctly, the appearance is bad and more importantly, the pipe will sag, possibly damaging the pipe. Commonly you want to support steel pipe horizontally: 3/4 inch and smaller – every 10 feet; 1 inch and larger – every 12 feet. Vertically, support pipe every other floor not to exceed 25 feet. Always refer to the International Plumbing and Mechanical Code books.

2.4.3 Pressure

Testing After the water supply system has been installed and checked for evidence of shifting, the system must be tested to ensure there are no leaks before they are concealed within the walls or under slabs. This is especially important where pipe is to be concealed in walls or ceilings. If a leaking pipe is sealed in the building framing, the water would probably run for a considerable length of time before being discovered. This could result in costly damage to the building. To reduce the possibility of this happening, all pipes in the system are tested at least twice, once after the rough-in, and again after the water supply system is installed. One method of testing is to close off the entire system using plugs or caps screwed onto the nipples and open the supply valve. Another way to test is to close off the entire system, install an air gauge and fill the system with air. Inspect the system for leaks and monitor the air gauge.

Test Your Knowledge

2. When conducting end–to-end measurements for piping, what value is needed to establish a correct length?

A. Nipple joint length
B. Thread engagement
C. Joint length
D. Nipple engagement

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Plastic is a very versatile material. It can be formed into almost anything. Cars, boats, homes, and of course plumbing have many components made of plastic. Plastic pipe has rapidly become one of the more popular piping materials. It can be used for numerous plumbing installations, including water distribution and the drainage of wastewater.

3.1.0 Install Plastic Piping

3.1.1 Types Used for Water Distribution

Polyvinyl Chloride (PVC) — Plastic pipe is often used for distribution mains and building service lines. It has an exceptionally smooth interior surface and, therefore, low friction losses. This enables large diameter plastic pipe to convey water with little or no pressure loss. The material is chemically inert, which makes it completely corrosion proof. Corrosion is probably the biggest contributing factor to the destruction of underground metallic piping systems. The use of plastic eliminates this factor. Plastic pipe commonly comes in 20 foot lengths.

Chlorinated Polyvinyl Chloride (CPVC) — In recent years, the use of plastic pipe for the distribution of water in buildings has been widely accepted, especially in domestic homes. Since water distribution system will commonly be concealed in the walls of the building, the piping used must be able to withstand a variance of temperature and pressure and remain completely leak proof. CPVC was formulated to withstand higher temperatures and pressures than PVC. CPVC can withstand temperatures as high as 180 degrees and pressures up to 100 pounds per square inch (psi) depending on the manufacturer.

3.1.2 Joining Plastic Pipe

Usually compression joints (O-ring joints) or solvent welded are used. Figure 16 shows a compression joint. These are simple joints to assemble. Water mains may be equipped with rubber O-rings and a spigot end. The spigot end is beveled to allow the joining pipe to slide into the O-ring and bell. The spigot is lubricated and inserted into the bell. The O-ring compresses around the pipe to seal the joint.

Figure 16 — Compression joint.

3.2.0 Applications and Restrictions

The weight of the pipe is basically a description of the thickness of its walls. Plastic pipe comes in two weights, schedule 40 and schedule 80.

3.2.1 PVC Schedule 40

Schedule 40 plastic pipe has the thinnest walls of the two. This lightweight material can be used on most applications systems discussed above, as long as the codes allow it. PVC Schedule 40 is joined by cement, PVC, CPVC, or ABS cement, as it is too thin to be threaded. It can be installed in exterior water lines only.

3.2.2 PVC Schedule 80

Schedule 80 plastic pipe has a thick wall. It is more rigid than schedule 40 plastic so it can withstand higher pressure. PVC pipe cannot be installed in an interior system. PVC Schedule 80 pipe can be joined by cement, PVC, CPVC, or ABS cement or it can be threaded. For more information, reference the International Plumbing Code book for additional information.

3.2.3 CPVC Schedule 40

This is normally installed in interior water distribution systems. The plastic material looks and feels like PVC pipe except for the coloring, which is commonly beige. Schedule 40 can be joined only by solvent glue.

3.2.4 CPVC Schedule 80

It can be joined by solvent glue or threaded into valves and fittings using male adapters. Solvent-welded and threaded plastic (PVC and CPVC) connections will be discussed in depth later in this course.

3.3.0 Advantages and Disadvantages

3.3.1 Advantages

There are many advantages to using plastic piping. It is lightweight, takes few tools to assemble, and requires very little maintenance once it has been installed. Plastic pipe is chemically inert so it will not rot or corrode. It is strong and durable material that has an accepted service life of 20 to 50 years, depending on the application, and an indefinite shelf life if stored properly. Keep away from open flame and heat. Keep and store in original container. Keep container closed.

3.3.2 Disadvantages

There are very few disadvantages to using plastic pipe. Small diameter plastic piping can be very flexible and may require substantial means of support. When plastic pipe is assembled using solvent weld, the fumes from the cement, PVC, CPVC, or ABS cement can be harmful and dangerous.

3.3.3 Safety When Using Solvent Glue and Primers

Take great care when using these products. They contain chemicals that can be toxic, flammable, and combustible. Ventilate the area and try to avoid breathing the fumes. Keep solvent glue and primers away from all sources of ignition, heat, sparks, and open flames. Keep all containers tightly sealed and safely stored when not in use. Avoid contact with your eyes. You may be required to use proper eye protection when solvent gluing overhead piping. Avoid contact with your skin, and always wash your hands after use.

3.4.0 Methods of Installation

There are four methods of joining plastic pipe: solvent welding, fusion welding, fillet welding, and threading.

3.4.1 Solvent Welding

Before solvent welding PVC and CPVC plastic pipe, clean the pipe and fittings. Use a clean, dry cloth and wipe away all loose dirt and moisture from inside the fitting and from the outside of the plastic pipe. Ensure the fittings and the pipes are of the same temperature for at least an hour before welding; this will assure they are thermally balanced. With a bristle brush, apply a coating of primer to the outside of the pipe. This removes surface gloss and etches the pipe.

Do the same to the inside of the fittings. If the pipe is so hot the primer evaporates or if the pipe is above 90°F, move it to a shaded area before priming the surfaces. Use notched boards to keep the pipe ends out of the dirt. Clean the pipe ends before cement application.

Dip a brush in cement and apply it to the entire active surface of the pipe to a width slightly more than the depth of the socket of the fitting, as shown in Figure 17, View A. Then brush a light coating in the depth of the socket. (Avoid excess cement to eliminate the buildup inside the fitting when the pipe is socketed.) Apply the second coating of cement to the end of the pipe to ensure no voids exist. (There should be no problem of too much cement on the pipe because the excess will bead out on the surface of the face of the fitting and can be easily wiped away.)

Figure 17 — Making solvent weld joints on plastic pipe.

Immediately, upon finishing the cement application, insert the pipe to full socket depth and rotate one quarter turn to ensure complete distribution of cement, as shown in Figure 17, View B. Hold the pipe together for 10 to 15 seconds so it does not move out of its socket. After joining, immediately wipe the excess cement from the pipe and fitting and gently set the pipe on a level surface. Do NOT move the pipe for about 2 minutes. (As the pipe size increases, it takes longer for the joint to set up.) The pipe SHOULD NOT be joined in temperatures below 40°F and above 90°F or when it is exposed to direct sunlight. The drying time should be at least 48 hours before the joint is moved or subjected to internal or external pressure. The drying time is shorter in hot weather and longer in colder weather.


Do not attempt to speed the setting or drying of the cement by applying heat to solvent-welded joints.

Forced rapid drying by applying heat causes cement solvent to boil off‘, forming bubbles and blisters in the cement film. During cool weather, the setting of the cement can be speeded by pre-warming the cement, the pipe, and the fitting, or by shielding the joint from the wind.


Check the shelf life of the cement.

Do NOT use cement that is lumpy or stringy. Do NOT try to thin it out with a thinner or primer. Always follow the instructions on the cement container; the above estimates should in no way be used in the place of application instructions. Always use the specific glue for the piping to be joined i.e. PVC cement for PVC pipe, CPVC cement of CPVC pipe.

3.4.2 Fusion Welding

Fusion welding requires either a gas- or an electric-heated welding tool, as shown in Figure 18. As the tool warms up, spray its contact surfaces lightly with a silicone-releasing agent. This prevents the pipe from sticking to the surface of the welding tool. Check the temperature of the tool. Ensure the tool reaches the proper temperature range before placing the pipe on the heating element. Be sure the pipe is squarely on the element. Hold onto the pipe, until a bead appears on the pipe at the entrance of the female tool piece. After the bead appears, remove the pipe and insert it into the fitting, squarely and completely.

Figure 18 — Fusion welder


Do not rotate the pipe while it is being joined with the fitting.

3.4.3 Fillet Welding

In fillet welding of plastic pipe, as shown in Figure 19, maintain uniform heat by using a specially designed heat gun (hot air welder), which produces a jet of hot air that softens both the parts to be joined and a plastic filler rod, all of which must be of the same or a very similar plastic. The plastic welding rod is an extruded rod that is used to weld plastic. Suitable rod materials include ABS, PVC, Polypropylene, polyethylene, PVDF and many other types of thermoplastic. Plastic welding rods are available in a wide range of colors to match a project's color. Along with a uniform application of heat, a uniform pressure needs to be maintained on the rod while welding. Too much pressure on the rod stretches the bead and causes the weld to crack as it cools. The rod should be held at a 90-degree angle to the joint. The rod bends in an arc when proper pressure is applied. When finishing a weld, make the bead overlap the top, NOT alongside itself, for at least 3/8 to 1/2 inch. Never overlap alongside when welds are being spliced.

Figure 19 — Fillet welding plastic pipe.

3.4.4 Threaded

Threading reduces a pipes wall thickness and results in lower pressure ratings. Only schedule 80 or heavier pipe should be used when plastic pipe is being threaded. You should never use pipe wrench to tighten plastic pipe; use a strap wrench. However if you must use a pipe wrench to tighten be sure to use an insert within the vise jaws to prevent scoring of the pipe. Use a wood or aluminum plug while the pipe is being threaded to prevent distortion of the pipe and to avoid off-center threads. The dies should be sharp, and for best results with power tools, use a 5-degree negative front rake. When tightening threaded joints, avoid too much torque. One or two turns past hand-tight is sufficient. Teflon tape should be used as an anti seize pipe joint compound.

Test Your Knowledge

3. What is the minimum temperature at which plastic piping should be joined?

A. 60°F
B. 55°F
C. 45°F
D. 40°F

- To Table of Contents -


The hot water system is the part of the plumbing installation that heats water and distributes it to various fixtures. There are a number of ways to heat water, but whichever system is used must be able to supply maximum demand. Copper tubing and pipe is the most popular material used for the installation of a hot water supply system. Using copper in a hot water system is especially desirable because of its ability to resist corrosion, which increases in proportion to the temperature of the water.

There was a time when hot water delivered to plumbing fixtures was a luxury and very few people, even those who were considered affluent, were provided with this convenience. Current sanitation standards require some type of hot water system for all residences, so that even the humblest dwelling is provided with this convenience.

Part of your job will be the installation of copper tubing. You should enjoy working with this product, because it is lightweight and easy to install. The joints, easily made using fittings, are as permanent as the tubing itself. Copper tubing and pipe are less resistant to water flow as compared to galvanized steel pipe. Therefore, when you install copper tubing and pipe instead of galvanized steel pipe, you can use smaller tubing and pipe, and still deliver the same amount of water to the point of discharge.

4.1.0 Hot Water Distribution System

4.1.1 Types of Copper Tubing and Pipe

There are four types of copper tubing and pipe: K, L, M, and DWV. These classifications are based on tubing wall thickness.

Type K — A green band or green stenciling on the tubing and pipe surface identifies the pipe as type K. It is recommended for underground installation and high-pressure systems. It is ideal for building service lines and compressed air systems. Type K has the thickest wall of the four types of tubing. Type K copper can be purchased in standard lengths of 20 feet for hard drawn copper, or coils of 25 feet to 100 feet for soft drawn copper. Type K can be buried.

Type L — A blue band or blue stenciling on the surface of the tubing and pipe identifies the tubing and pipe as type L. It has a medium wall thickness and is recommended for interior use in plumbing and heating installations. Type L copper also can be purchased in standard lengths of 20 feet for hard drawn, or coils of 25 feet to 100 feet for soft drawn.

Type M — Type M has a light wall thickness and is used in low-pressure installations. It is identified with a red band or red stenciling on its surface. Both hard and soft drawn are available in 20 foot lengths.

Type DWV — The Drain, Waste, and Vent (DWV) have the thinnest wall of all types of copper tubing and pipe. DWV is used in above and below ground installations. It is available in hard drawn only in lengths of 20 feet. It is identified by a yellow color or stencil on its surface.

4.1.2 Measuring Copper Tubing and Pipe

When you measure copper tubing and pipe, be sure that the measurement that you want is correct. If the measurement is too short, the joint will be weak. If the measurement is too long, the joint will be put under strain and the service life of the pipe will be affected.

4.1.3 Bending Copper Tubing

Hand Method — Probably the simplest method of bending tubing is the hand method. The copper tubing is filled with sand and gripped with your hands apart as shown in Figure 20. Bend the tubing a little at a time, starting from the outside, and working your thumbs toward the center of the bend. Do not try to make the complete bend by applying pressure from only one position. This procedure will probably kink the tubing some, even though it is filled with sand.

Figure 20 — Bending tubing filled with sand.

Bending Block — Another method of bending soft copper tubing is using a bending block, as shown in Figure 21. Mount the block on a table or some other solid structure. During the bending operation, insert one end of the tubing in the loop, and, using both hands; gradually form the tubing over the contour of the block. Hard drawn tubing can be bent with this method if it is annealed (softened by heat) first.

Figure 21 — Bending tubing over a block.

Spring Bender — Still another method a UT uses to bend copper tubing without buckling is to use a flexible bending spring. Soft drawn copper tubing must be used when using the spring bender because of the flexibility of the tubing. Bend the tubing by placing the correct size flexible bending spring over the tubing. Then gradually form the tubing with your thumbs while holding it against a table or solid surface. See Figure 22.

Figure 22 — Types of spring benders.

Mechanical Bender — Mechanical tube benders are considered the most practical and most accurate method of bending copper tubing. These benders are manufactured in many different sizes. When you place tubing in the bender, raise the right handle of the bender as far as it will go so that it rests in a horizontal position. Raise the clip and place the tubing in the space between the handle and slide block and the bending form. Now place the slip over the tubing and turn the handle slide bar about its pin and to the right. Note that the zero mark on the bending form will line up with the mark on the slide bar. Next, continue to pull the handle to the right (clockwise), until the tubing is bent to the desired angle. When using the mechanical bending tool, you may make bends up to 180° without buckling or kinking the tubing. See Figure 23. 

Figure 23 — Mechanical bender.

4.2.0 Joining Copper Tubing

4.2.1 Ferrule Joints

A compression type joint has three parts: the fitting, nut, and ferrule. First, cut the copper tubing to the correct length. Then ream the inside of the tubing to remove the burr. Slip the nut over the tubing, followed by the ferrule. Next, slide the end of the tubing into the fitting and slide the ferrule up against the fitting. Screw the nut onto the fitting. Use either an open-end or adjustable jaw wrench to finish tightening the nut. Tightening the nut compresses the ferrule onto the tubing and against the fitting. This action results in a watertight and airtight seal. Always use a backup wrench when assembling ferrule joints to protect the tubing from damage. See Figure 24.

Figure 24 — Cross section of a ferrule joint.

4.2.2 Flaring

Another joint is flaring. Flaring is an easy and satisfactory method of joining copper tubing. Flare the ends of the tubing and press them against the tapered surface of the flared fitting. Next, screw the flare nut over the end of the fitting as shown in Figure 25.

Figure 25 — Flaring block and cone.

An advantage of this type of connection is that it is easily disassembled when repairs are necessary. The only thing required to disassemble this connection is to select the correct size wrench, unscrew the flare nut that makes up the compression-type connection, and separate the fittings. When you make a flare on copper tubing, you must take every precaution to produce an airtight and watertight joint. First, measure and cut the tubing to the proper length with a tubing cutter or hacksaw. Then remove the burr within the tubing by reaming. Copper tubing can be flared with a flaring cone and flaring block or with a plug type flaring tool. Figure 25 shows a flaring block and cone.

Before a flare is made, slip the compression nut on the tubing and insert the end of the tubing into the correct size hole in the flaring block. Then extend the end of the tubing above the face of the block twice the wall thickness of the tubing.

Next, attach the flaring yoke to the flaring block and center the flaring cone over the end of the tubing as shown in Figure 26. Force the cone against the flaring block by rotating the handle on the flaring yoke clockwise. This causes the end of the tubing to expand just enough to fit into the compression nut and over the end of the flare fitting.

Figure 26 — Positioning the flaring yoke and making the flare.

After the tubing has been flared properly, assembly of the joint is simple. Place the flare against the fitting. Next, slip the compression nut against the flare and screw it on the fitting. This operation compresses the flare of the tubing between the fitting and nut. When these joints are properly constructed and tightened, they will withstand 3,000 psi of internal pressure.

4.2.3 Swedging

Swedging is the process of expanding the end of the tubing to receive the same size tubing. The joint is then sealed by soldering. By swedging, one fitting is eliminated, normally a coupling.

The swedging kit (Figure 27) consists of a swedging tip that can be changed out to swedge different size pipe. It fits easily inside of the tubing. The kit contains a block that holds the tubing in place while making the swedge. The yoke with a handle is attached to the block. When the handle is turned clockwise, the swedge tip will be forced into the pipe, enlarging the pipe. The swedge kit is very similar to the flaring kit. It uses the same flaring block that was used for flaring copper tubing.

Figure 27 — Swedging kit.

Procedures. The flaring block has several holes of various sizes (Figure 28, View A). On the front side of the block the holes are beveled for flaring. On the back side of the block, there are no bevels. This side of the block is used for swedging. To swedge, select the proper size hole in the block and insert the tubing. The distance the tubing should extend above the face of the flaring block is the diameter of the tubing plus 1/8 inch. Select the correct size swedging tip and attach it to the yoke with the handle. Slip the clamp on the block and twist to lock it in place (Figure 28, View B). Turn the handle clockwise to drive the swedging tip down, forcing the pipe to expand. Once the swedge tip has been completely inserted, then retract the swedge by turning the clamp handle counterclockwise. Inspect the pipe by inserting the same size copper tubing into the end of the swedge (Figure 28, View C). The fitting should be snug. Then follow the procedures for soldering that will be explained next.

Figure 28 — Swedging process.

4.2.4 Soldering (Sweat)

Soldering (sweating) is a method of joining two metals together by allowing molten solder to run between them and cool. The law of capillary attraction governs the force responsible for bonding in solder joints.

Preparing a Soldered Joint — The copper tubing and fittings must be properly prepared before assembling a soldered joint. The metallic surfaces must be cleaned thoroughly to remove oxidation. This can be done by using emery cloth, steel wool, sandpaper or a fitting brush. When cleaning copper tubing, clean the exterior of the tubing and the interior of the fittings. Flux is then applied to the exterior of the tubing, and the interior of fittings. The flux will prevent oxidation from occurring during the soldering procedure. If oxidation occurs, the solder will not bond to the copper.

Figure 29 illustrates a acetylene torch that is ideal for soldering small copper lines. The torch will heat the tubing quickly and evenly. An acetylene torch can be used to solder larger diameter copper tubing and brass fittings.

4-29 — Acetylene torch.

What about the solder? 95/5 solder is used to solder copper tubing. It is 95% tin and 5% antimony and melts at 452° F. It replaced the old 50/ 50 solder that had a very high lead content. Usually, the solder is 1/8 inch in diameter and comes in rolls.

Soldering Procedure — After cleaning and fluxing the piping and materials, insert the tubing inside the fitting. Apply heat to the fitting with the torch. When soldering small diameter piping and materials, you can hold the flame at one spot on the fitting. With large piping and materials, you will have to move the flame all over the fitting to ensure the heat is applied evenly. Frequently touch the solder to the fitting to see if the melting point has been reached. Once the solder melts and begins to free flow, remove the flame from the fitting. The solder will be drawn into the joint by capillary action. The amount of solder needed will be equal to the diameter of the tubing being joined. For example, it would take 3/4 inch of solder to assemble a 3/4 inch joint. Once enough solder is in the joint, wipe the joint with a wet rag. The rag makes the joint cool faster and will remove any excess solder and flux residue.

Silver Solder Procedures are the same as with regular solder. Clean the tubing and fitting thoroughly, and then apply flux to them. Use air acetylene or oxygen acetylene torch to apply heat because of the high temperature required to silver solder. See Figure 30.

Figure 30 — Air acetylene torch.

Solder made of silver alloy comes in many sizes, compositions, and strengths. To determine the type of solder to use, follow the manufacturer’s specifications. The melting point for silver solder is from 1145° F to 1650° F, enabling it to withstand more pressure and temperature than 95/5 solder, which is why it is used on high pressure lines.

4.3.0 Supporting Copper Tubing

During the installation of copper piping you must consider several factors. First consider the weight of the pipe, and then the length of the pipe that will be installed. Will the pipe be supported in a vertical position or a horizontal position? Always refer to the International Plumbing Code and project specifications when you are not sure of the support requirements.

Pipe that is supported horizontally and is 1 1/2 inch or less in diameter is supported every 6 feet. Pipe that is 2 inches and larger is supported every 10 feet. Pipe that is supported vertically will be supported at each floor level, not to exceed 10 feet between supports.

4.4.0 System Layout

When you are ready to determine the system layout, the following items will help you create a successful layout. First, use the building construction plans to determine where the piping system will need to be installed. Working and isometric drawings that you create will help guide your thoughts when considering different aspects of the job. Refer to the building construction plans when creating your working and isometric drawings. Refer to the manufacturer's rough-in specifications for details. (Example: drain line installed 16 inches above the finished floor, and supply lines installed 20 inches above the finished floor). Develop a bill of materials using the working and isometric drawings. This will be a shopping list of the parts that will be needed for the job.

4.5.0 Safety

4.5.1 Safety Equipment

Always wear your safety equipment. Neglecting to wear safety items will increase the chance of injury. All it takes is one slip up for you to receive a permanent injury that could have been prevented. Safety gloves help protect your hands against hot flux and molten solder that can cause burns to the skin. Eye protection, such as goggles or face shields, protect your eyes and face. Long sleeves will protect your arms.

4.5.2 Safety Precautions

All safety precautions directed by the manufacturer or your supervisor will be followed to ensure your safety and the safety of your shipmates. Fire extinguishers should be close by in case of fire, and the area should be well ventilated.

Heat shields are provided to prevent any wood from catching fire. This is a small sheet of metal that you place behind the copper pipe when you are soldering in a tight location and the flame would touch the wood. After you are finished soldering, remove the heat shield. Inspect the job site for any smoldering wood whenever you have finished soldering in tight places.

Test Your Knowledge

4. Which of the following processes is used to expand the end of the tubing to receive the same size tubing?

A. Ferruling
B. Flaring
C. Sweating
D. Swedging

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Buildings and facilities are constructed from a number of different products, but all require entry and exit of utilities through structural openings. Your knowledge of proper location, construction, and materials utilized in structural openings is key to the successful completion of any project. Steel, copper, and plastic pipe assembly were covered in this lesson, including methods, material, and component selection. The responsibility of the proper material selection and location for the different distribution systems encountered begins with you.


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Review Questions

1. What is a feature of the box type structural design method?

A. Plumbing is exposed.
B. Water supply piping is located above floor level.
C. Studs inside the building are not exposed.
D. Drainage piping is located within the box type framework.

2. What is required for piping to pass through a masonry wall in a frame type structural design method?

A. Pipe hangers are required within masonry walls.
B. Sleeve or plastic pipe is placed around the piping.
C. Metal sheaving 4 inches wide is placed around piping.
D. No actions are required for this design method.

3. Where can the locations of plumbing fixtures to be placed inside a storage facility be located prior to construction?

A. Site plans
B. Rough- in specifications
C. Floor plans
D. Working drawing

4. During the construction of a building (berthing), UTs complete the plumbing installation in how many phases?

A. 5
B. 4
C. 3
D. 2

5. Before the concrete slab foundation is poured, what needs to be installed first?

A. Horizontal drainage piping below ground
B. Corporation stop
C. Vertical water piping below ground
D. Curb box

6. When piping is stubbed up, what is the minimum termination height of the pipe in inches?

A. 6
B. 12
C. 18
D. 24

7. Which of these tools is used to make round holes in wood with an electric drill?

A. Carbide bit
B. Keyhole saw
C. Paddle bit
D. Star drill

8. If electricity is not available, which of these tools would be utilized to make irregular shaped holes?

A. Hole saw
B. Reciprocating saw
C. Jigsaw
D. Keyhole saw

9. What type of structural opening is made by notching the top of the structural member?

A. Over cut
B. Notch cut
C. Under cut
D. Center cut

10. What is the maximum size of an under cut on a beam?

A. 1/4 the width of the beam
B. 1/2 the width of the beam
C. 1/4 the length of the beam
D. 1/2 the length of the beam

11. Horizontal water and waste piping must be supported to prevent what condition?

A. Stress
B. Cracking
C. Sagging
D. Pressure drop

12. During the rough-in process, which type of measurement is most commonly used?

A. End-to-center
B. End-to-end
C. Face-to-face
D. Center-to-center

13. When cutting pipe with a pipe cutter, how do you open the jaws of the cutter?

A. Turn the handle in a counterclockwise direction.
B. Loosen set screw and turn handle in downward direction.
C. Turn the handle in a clockwise direction.
D. Loosen set screw and turn handle in upward direction.

14. What is the purpose of reaming a pipe after the initial cut?

A. Ensure threads are perpendicular to each other
B. Remove burrs from the inside diameter of the pipe
C. Ensure threads are parallel to each other
D. Remove burrs form the outside diameter of the pipe

15. What is the desired angle of a locally manufactured piece of pipe threads?

A. 40°
B. 50°
C. 60°
D. 70°

16. Which of these prevents the threads from becoming dulled during the pipe threading process?

A. High pressure water
B. Antiseize compound
C. Pipe compound
D. Oil

17. What two pipe-joint compounds are most commonly used?

A. Teflon tape and pipe dope
B. Pipe dope and pipe glue
C. Teflon tape pipe glue
D. Pipe putty and Teflon tape

18. What is the result of over tightening the joint when connecting fitting connections?

A. Fitting will sag.
B. Joint might leak.
C. Water flow will be reduced.

19. What size pipe wrench is used with a 1 inch pipe?

A. 8 inch
B. 10 inch
C. 14 inch
D. 18 inch

20. What size pipe wrench is used with a 1/8 inch pipe?

A. 8 inch
B. 10 inch
C. 14 inch
D. 18 inch

21. How many different types of pipe nipples will you work with as a UT?

A. 1
B. 2
C. 3
D. 4

22.  Whenever you are assembling threaded joints, be sure to apply joint compound to the female threads.

A. True
B. False

23. What is the size of the cold water inlet line for a cold water distribution system installation?

A. 1/4 inch
B. 1/2 inch
C. 3/4 inch
D. 1 inch

24. At what interval is 3/4 inch steel pipe horizontally supported?

A. Every 3 feet
B. Every 5 feet
C. Every 6 feet
D. Every 10 feet

25. By how much space and how many feet is 1/2 inch steel pipe vertically supported?

A. Every other floor not to exceed 25 feet
B. Every floor not to exceed 10 feet
C. Every other floor not to exceed 15 feet
D. Every floor not to exceed 12 feet

26. Before water is applied to a structure, how many pressure tests of the piping are conducted?

A. One
B. Two
C. Three
D. Four

27. Which type of plastic pipe is used for distribution mains?

A. PVC 50
D. CPVC 50

28. What size does Polyvinyl Chloride piping come in?

A. 5 foot lengths
B. 10 foot lengths
C. 15 foot lengths
D. 20 foot lengths

29. What is the maximum temperature that CPVC piping can withstand?

A. 180° F
B. 200° F
C. 220° F
D. 250° F

30. PVC schedule 40 piping is used in which type of piping system?

A. Exterior drainage lines
B. Exterior water lines
C. Interior waste lines
D. Interior water lines

31.  PVC schedule 80 can withstand a higher pressure than PVC schedule 40.

A. True
B. False

32. PVC schedule 80 piping can be joined by which two materials or methods?

A. Teflon tape and threading
B. Welding and solvent glue
C. Threading and welding
D. Solvent glue and threading

33. Which of these distribution systems utilizes CPVC schedule 40 piping?

A. Interior water
B. Exterior water
C. Interior waste
D. Exterior waste

34. Before solvent welding operations are conducted, how long do the fitting and pipe temperatures need to remain the same?

A. One-half hour
B. One hour
C. Two and one-half hours
D. Four hours

35. At what temperature should the pipe be placed in a shaded area prior to priming the interior of the pipe threading?

A. 70° F
B. 80° F
C. 90° F
D. 100° F

36. When solvent welding, how long do you need to hold the two ends welded together to achieve a good adhesion?

A. 45 seconds
B. 2 minutes
C. 5 seconds
D. 10 to 15 seconds

37. During the solvent welding process, what is the result of rapid drying the connection?

A. Blisters in the cement film
B. Increased cure time
C. Cracking of fitting joint
D. Thread retraction

38. Which type of agent is applied to the contact tip of the fusion electric welding tool?

A. Heat releasing
B. Silicone releasing
C. None

39. During fillet welding operations, what is the result of too much pressure on the rod while welding?

A. Weld will not hold when temperature reaches above 90°F.
B. Bead will form condensation.
C. Weld will crack as it cools.
D. Turbidity will occur at weld point.

40. What is the most popular material used in hot water supply installation operations?

A. CPVC schedule 40 piping
B. Steel piping
C. PVC schedule 80 piping
D. Copper tubing

41. What color designates Type K copper tubing?

A. Green
B. Blue
C. Red
D. Yellow

42. Which type of copper tubing is recommended for use in heating installations?

A. K
B. L
C. M

43.  Type M copper tubing is identified with a red band or red stenciling on its surface.

A. True
B. False

44. Type DWV tubing is available in what size?

A. 5 foot lengths
B. 10 foot lengths
C. 15 foot lengths
D. 20 foot lengths

45. Which method of bending tubing is the simplest?

A. Hand
B. Bending block
C. Spring bender
D. Mechanical bender

46. When using a mechanical bender, you can make bends up to how many degrees?

A. 270°
B. 180°
C. 90°
D. 45°

47. How many parts make up a compression type joint?

A. 1
B. 2
C. 3
D. 4

48. What is an advantage of using a flaring type of copper tubing connection?

A. Cost
B. Ease of assembly
C. Material availability
D. Ease of disassembly

49.  When flared joints are properly tightened, they will withstand 4,000 psi of internal pressure.

A. True
B. False

50. What scientific principle governs the force responsible for bonding in solder joints?

A. Law of increased entropy
B. Law of capillary attraction
C. Law of motion
D. Law of physical attraction

51. Which of the following solder types is used to solder copper tubing?

A. 90/10 solder
B. 50/50 solder
C. 95/5 solder
D. 25/75 solder

52. What is the melting point of silver solder?

A. 1675° to 2165°
B. 945° to 1132°
C. 1145° to 1650°

53. Solder used in joining copper tubing melts at what temperature?

A. 452°
B. 697°
C. 945°
D. 1145°

54. When horizontally supporting copper tubing that is 1 1/2 inch or less in diameter, what are the spacing support requirements?

A. Every 3 feet
B. Every 6 feet
C. Every 10 feet
D. Every 12 feet

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