Advantages of the Plastic Patch

From the damage control viewpoint, the main advantages of a plastic patch are versatility, simplicity, effectiveness, speed of application, and durability.

The plastic patch can be used on a variety of damaged surfaces with smooth or jagged

Figure 7-24.-Resin temperature vs. the kick-over time.

protruding edges. The plastic has excellent adhesive qualities. It can be readily applied to steel, cast iron, copper, copper-nickel, brass, bronze, and galvanized metals.

It is relatively easy to apply a plastic patch. Inexperienced people can do it. If they follow instructions carefully, the patch will be 100-percent effective. If the patch leaks, then it is likely that proper preparation and applications procedures were not followed.

The speed of application will vary somewhat with the size and the type of rupture and also with local working conditions. A simple patch can be applied to a 4-inch pipe in 10 minutes or less by an inexperienced crew with the minimum amount of training and indoctrination. The type and the size of the rupture, or the shape and the size of the structure to which the patch is applied, have little effect on the time involved in patching. However, some types of damage may require more initial preparation.

There is no known time limit on the life of a plastic patch. It will certainly last until permanent repairs can be made. The patch is relatively inert, being seriously affected only by excessive heat and concentrated acids.

Application of Plastic Patches

The following discussion will help you apply different types of plastic patches (simple, elbow, severed, and others). You will see that as the individual patch materials are applied, the patch

becomes progressively wider. Figure 7-25 illustrates the positions of the patch materials in relation to one another. You must consider the buildup in the length of the patch when you plan the application. When possible, allow the patch to extend at least 4 to 5 inches on either side of the rupture.

In addition to the size of the rupture, the width of the patch may also depend upon the location of the rupture in the pipe system. For example, an elbow rupture may require a patch of greater width than would the same size rupture in a straight section of pipe.

You must make the following preparations before you apply the plastic patch:

1. Secure or isolate the ruptured area in the piping system.

2. Remove all lagging.

3. Clean the area around the rupture and remove all grease, oil, dirt, paint, and other foreign matter. If grease or oil is present, use an approved solvent, such as methyl chloroform. If an approved solvent is not available, scrape and wipe the surface until it is clean. The surface may then be further abraded for better adhesion. An abrasive cloth is furnished with the kit.

4. Make sure that the entire pipe surface is dry.

5. Where practical, simplify the rupture by bending or removing irregular projections. This may be done by cutting or burning.

CAUTION: IT IS OF THE UTMOST IMPORTANCE THAT NO EXPLOSIVE CONDITIONS EXIST BEFORE USING SPARK-PRODUCING TOOLS OR BURNING EQUIPMENT.

6. Determine the amount of materials you will need. For example, a 2-inch rupture in a 2-inchdiameter pipe will require 500 grams of activated resin and a length of woven roving cloth that is at least 25 inches long. Cut the woven roving cloth, in width, to extend at least 3 to 4 inches on either side of the rupture.

SIMPLE PIPE PATCH.- Use these stepby-step procedures to apply the simple pipe patch.

1. Put on the eyeshields and the gloves. Then open the liquid resin can and the liquid hardener can.

Figure 7-25.-Relative positions of patch materials.

2. Add the hardener to the resin and mix thoroughly for approximately 2 minutes or until it is a uniform gray color. (Note that all of the liquid hardener in the smaller can is the correct proportion to mix with all of the liquid resin in the larger can.)

3. Coat both sides of the void cover with the resin-hardener mixture. Tie the void cover over the rupture with a chalk line (view A of fig. 7-26.).

4. Lay the woven roving cloth on a clean, flat surface. Starting at one end of the cloth, pour on the resin-hardener mixture and spread it evenly over the entire surface of the cloth using the spatula provided in the kit. It is only necessary to impregnate one side of the woven roving cloth. However, you must ensure that the edges are well impregnated with the resinhardener mixture.

5. Center the woven roving cloth over the void cover with the impregnated side toward the pipe. Wrap the cloth around the pipe not less than three turns and preferably not more than four turns. (See view B of fig. 7-26.)

6. Wrap the PVC film at least two complete turns around the entire patch. Tie the PVC film with the chalk line, starting from the center of the patch and working toward one end, making 1/2-inch spacings between spirals (view C of fig. 7-26). Tie this end securely, but do not sever the line. Make one spiral back to the center of the patch. Then working to the opposite end from the center of the patch, make 1/2-inch spacings between spirals and again secure the line. After 30 to 40 minutes the patch should be sufficiently cured to restore the pipe to service.

Remember, for best results the temperature of the liquid resin and the liquid hardener before

mixing should be approximately 70F. With a temperature of 70F at the time of mixing, the patch will cure approximately 1 hour from the initial mixing time. After this hour, pressure may be restored to the piping system. In emergencies, if the temperature of the resins and hardeners is below 50F, you can accelerate kick-over by applying external heat with hot-air heaters. However, the heat must be applied gradually. Too much heat will cause the plastic patch to be extremely porous and fail.

Figure 7-26.-Simple pipe patch.