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Chapter 22

Damage Control

Damage control is based on the premise that the safety and life of a ship depends on watertight integrity. This chapter describes some emergency procedures that can be used in the event the ship's hull has been punctured and watertight integrity has been lost. The procedures described are emergency measures taken by the damage control team to maintain watertight integrity of the ship in the event of accident, collision, or grounding.


  22-1. If a ship's hull is punctured, watertight integrity is lost. If enough water is allowed to enter the hull and is uncontrolled, the ship will sink. There is no such thing as a "little leak". Any size leak is a cause for alarm. Through damage control, this "leak" may be either stopped or reduced to a point where the ship's pumps can control any excess water.
  22-2. Along with other emergency duties (fire and lifeboat), certain crew members are also assigned to an emergency squad or damage control team. This team may consist of the chief officer, an engineer, bosun, and two or more seamen and enginemen. There should be sufficient skills among the team members to perform the tasks required in an emergency.
  22-3. Army vessels are authorized to carry specified damage control kits. These damage control kit items should be set aside and used only for their intended purpose.
  22-4. In the event of fire, collision, grounding, or hostilities, one of the damage control team's missions is to assist in maintaining the watertight integrity of the ship. Many ships have been lost because no real effort was made to save them.
  22-5. When plugging leaks, the ultimate aim is to stop the leak permanently. The amount of water entering a vessel through a hole varies directly with the area of the hole and with the square root of its depth. Realistically, if you can reduce the flow of water by more than 50 percent, it is a job well done. Also, the ship's pumps should be able to handle whatever water is left. The values in Figure 22-1 show how important it is to put some kind of plug into any hole right away.
  22-6. Damage control also consists of either shoring up decks that are weakened or strengthening bulkheads between flooded compartments. Although all damage control work is temporary, it must be strong enough to allow the ship to make it back to port safely.

Figure 22-1. Flooding Effect Comparison: Unpluggd Holes Versus Partially Plugged Holes


  22-7. The term "shoring" involves two phases:
  • Stopping or reducing the inflow of water.
  • Bracing or shoring up the damaged or weakened members of the ship's structure by transferring and spreading the pressures to other portions of the ship.
  Shoring also includes the processes of patching and plugging.
  22-8. The first step in effective shoring is to clear the decks. Damage serious enough to produce a hole in the hull usually leaves wreckage scattered about the area. The damaged area should be cleared quickly to permit the damage control team to do a quick, adequate, and safe job.
  22-9. Most loose wreckage can be removed by hand. At other times cutting and breaking are required. This requires the use of mauls, sledges, axes, heavy cold chisels, pinch bars, power drills, power chisels, and air hammers.
  22-10. If fire accompanies the damage, burning bedding, stores, and supplies must be removed. A devil's claw (a homemade long-handled rake device) made of steel is handy for this purpose.
  22-11. Shoring tools such as saws, 2-foot squares, hammers, and hatchets are stowed in the ship's damage control locker. Additional equipment may be devised, limited only by the ingenuity of the ship's crew.
  22-12. Step two in shoring is speed. Seconds count, especially if there is a hole below the waterline. Each member of the damage control team must be able to think fast and improvise shoring with whatever material is available. More than once; items such as life jackets, mattresses, pillows, and mess tables have proven to be satisfactory temporary shoring material.
  22-13. The third step is preparation. Only through regular drills can skills be developed that will enable each man to do a fast, effective shoring job under adverse conditions. A thorough training program should be established to train all crew members. Damage control lockers must be clean and orderly. All tools should be placed in secure mountings, yet be readily detachable.
  22-14. Observe the following basic principles when shoring damaged or weakened members of a ship's structure.
  • Spread the pressure. Make full use of strength members by anchoring shores against beams, stringers, frames, stiffeners, and stanchions (see Figure 22-2). Place the legs of shoring against strongbacks at angles from 45° to 90° (see Figure 22-3).
  • Plan shoring to hold the bulkhead as it is (see Figure 22-4). Do not attempt to force a warped, sprung, or bulged bulkhead back into place.
  • Secure all shoring. Use nails and cleats to ensure that shoring will not work out of place.
  • Inspect shoring periodically. The motion of the ship often can produce new stresses that will cause even carefully placed shoring to work free. Inspect all shoring regularly, particularly when the ship is underway.

Figure 22-2. Anchoring Fit

Figure 22-3. Correct Shoring Angles

Figure 22-4. Shoring for Bulging Plate


  22-15. In addition to breaks and cracks in the hull, severe damage to a ship can impose stresses on bulkheads adjacent to the damaged area. The internal bulkheads of a ship are not designed to withstand a great amount of internal water pressure and must be immediately braced. It is unlikely that any two bracing jobs will ever be handled in the same manner, even among the same class ships. The location and extent of damage present individual problems to test the common sense and good judgment of the shoring party. Each case is different. The following fundamentals serve as a starting point.
  22-16. Brace weakened or damaged bulkheads against decks, overhead beams, stanchions, and hatch coamings. It is important to allow a three-point distribution of pressure. At the same time it is equally important to avoid damage to flanges, stiffeners, and deck beams.
  22-17. Place shores, so the pressure they receive produces direct compression. However, never place a shore deliberately below the point of compression so that bowing results. It is better to install several shores at close intervals because a bowed shore is dangerous to personnel and ship safety. When relatively long shores support heavy pressures, there is an even greater tendency of the shores to bow. Figure 22-5 shows shoring against horizontal pressure.
  1. Never use a shore that is longer than 30 times its minimum thickness. Therefore, the maximum length of a standard 4- by 4-inch shore must not exceed 10 feet (120 inches).
  2. Sometimes it is impossible to foresee where new stresses will cause bowing. If a timber begins to bow, the pressure should be relieved immediately to prevent snapping. If there is danger of a shore jumping out as the ship works, the shore should be held in position with nails and cleats.
  22-18. Secure the butt ends of shores against only undamaged members of the ship's structure such as hatches, stanchions, machinery foundations, frames, and coamings. Strongbacks may help distribute pressure on a bulkhead or deck. Each strongback must be supported with a number of shores placed to exert pressures perpendicular to the bulkhead.

Figure 22-5. Shoring Against Horizontal Pressure

  22-19. Use wedges to anchor and tighten shores in place. They should be driven in uniformly from both sides so the end of the shore will not be forced out of position (Figure 22-6). When the butt of a shore is anchored against a joint having protruding rivet heads, the shore is anchored with a shole (a plank or plate with pockets chiseled out for the rivet heads). This prevents the end of the shore from splitting. As the shoring job progresses, it must be checked carefully to ensure that all wedges are exerting the same amount of force on the member being shored in place. The desired force should be obtained by using as few wedges as possible.

Figure 22-6. Driving Wedges

  22-20. About half the shoring job is getting the right size shore. Practice in using the measuring batten will help in an actual emergency. The ends of the batten should be fitted firmly into the recesses selected for anchoring the timbers, and the exact measurement from each leg should be transferred carefully to the shoring. The most rapid and accurate way to measure shores for cutting is by using an adjustable shoring batten similar to the one shown in Figure 22-7. To use the shoring batten, extend it to the required length and lock it with the thumbscrews on the length locking device. Then measure the angles of cut by adjusting the hinged metal pieces at the ends of the batten and lock the angle locking device in place. Lay the batten along the shore. Mark and cut the timber to the proper length and angle. Shores should be cut 1/2 inch shorter than the measured length to allow space for wedges.

Figure 22-7. Adjustable Shore Measuring Batten

  22-21. Shoring may be confined to one compartment of the ship. However, if the pressure on a deck or bulkhead is so great that the next deck or bulkhead anchorage cannot safely withstand the pressure, place the shoring in adjacent areas to distribute pressures (see Figure 22-8). The work of bracing often can be expedited by having chainfalls, blocks and tackles, and jacks available for use in moving heavy weights back into their original position. Dry sand can be sprinkled on oily decks as a safeguard against slipping.

Figure 22-8. Shoring Spread to Adjacent Compartments

  22-22. Most shoring is used to support bulkheads endangered by structural damage or weakness caused by concussion or by the pressure of floodwater. Shoring up a flooded compartment requires that particular attention be given to the heavier pressures existing at the lower sections of the bulkheads. These pressures increase with the height of water in the compartment. The area of greatest pressure can also move from one area to another due to pitching and rolling of the ship.
  22-23. When a hatch or door is used to support shoring, the entire hatch cover or door should be shored over. Never place shoring ends and wedges directly against such openings, as they are the weakest parts of the bulkhead or deck. The pressure should be spread over the hatch or door and onto supporting structures.
  22-24. Closely allied with shoring are the other basic damage control operations. Emergency lighting and lines for submersible pumps must be rigged. Ruptured fire mains and other liquid-carrying lines must be isolated or repaired. The entire operation must be attacked with determination and with an open mind to cope with conditions that never seem to parallel those in a reference book.


  22-25. If a shoring batten is not available, measure the shores for length by using a folding rule or a steel tape and a carpenter's square. The step-by-step procedure for measuring shores is as follows:
  • Measure the distance A from the center of the strongback to the deck. Then measure the distance B from the edge of the anchorage to the bulkhead, subtracting the thickness of the strongback.
  • Lay off the measurements A and B on a carpenter's square, using the ratio 1 inch to 1 foot. Rule measurement is taken to the nearest 1/16 inch. To maintain the ratio of 1 inch to 1 foot, use the information in Table 22-1.
  • Measure the diagonal distance between A and B. Figure 22-9 shows this distance as 7 7/8 inches. Because of the 1 inch to 1 foot ratio, the distance in feet would be 7 7/8 feet or 7 feet 10 1/2 inches.
  • Subtract a 1/2 inch since shore should be cut 1/2 inch shorter than the measured distance. The final length of the shore should be 7 feet 10 inches.
  The carpenter's square may also be used to measure the angles of cut and to mark the shore for cutting (see Figure 22-10).

Table 22-1. Ratio Conversion Table

Actual rule

Measurement on
carpenter's square

3/4 inch
1 1/2 inches
2 1/4 inches

1/16 inch
1/8 inch
3/16 inch

3 inches

1/4 inch

3 3/4 inches
4 1/2 inches
5 1/4 inches

5/16 inch
3/8 inch
7/16 inch

6 inches

1/2 inch

6 3/4 inches
7 1/2 inches
8 1/4 inches

9/16 inch
5/8 inch
11/16 inch

9 inches

3/4 inch

9 3/4 inches
10 1/2 inches
11 1/4 inches

13/16 inch
7/8 inch
15/16 inch

12 inches

1 inch

Figure 22-9. Measuring Length of Shore

Figure 22-10. Cutting the Angles of a Shore


  22-26. Plugging is a technique used for filling small holes with a suitable material to stop the flow of water until permanent repairs can be made. Holes up to 6 inches in diameter can usually be plugged by driving in wooden plugs or wedges.
  22-27. Plugs made of bare, soft wood perform best because they soak up water, swell, and hold firmly in place.
  • Painted wood does not swell, and should be used only in emergencies.
  • Square-end plugs hold better than conical plugs.
  • Additional sealing properties can be obtained by wrapping the plugs with cloth.
  • Use "oakum" (a black sticky fibrous material made from old hemp) if carried aboard ship. Coat the plugs with oakum before putting them in the hole.
  22-28. Plugs cut from sheet lead are effective in stopping leaks when a plate has pulled loose from its rivets. Often small leaks can be stopped by driving in lead slugs, strips, or plugs.
  22-29. Cracks are dangerous because they may enlarge and spread. If time permits, drill a small hole at each end of the crack (see Figure 22-11). This will prevent it from cracking any further.
  22-30. The drilled holes should be plugged with either machine or wood screws.
  22-31. A flat piece of rubber or canvas backed up with a board should be laid across the crack and held in place with shoring (see Figure 22-12). This type of patch should be inspected frequently as it tends to shift and slip as the ship works.


  22-32. Patching is used to cover larger holes with sections of improvised or prefabricated material. This FM only describes the procedures for applying a soft patch because in damage control you are only interested in stopping or controlling the inflow of water. The soft patch is for temporary repair only.

Figure 22-11. Cracks With Holes

Figure 22-12. Shoring Over a Crack

  22-33. Pillows, mattresses, and blankets can be rolled up and shoved into holes. They can be rolled around a wooden plug or a timber to increase their size and to provide rigidity. Such plugs cannot be relied upon, as they have a tendency to be torn out of the holes by action of the sea. This is an expedient to retard the flow of water entering the vessel until a more suitable patch can be applied. Figure 22-13 shows the use of mattresses installed inside and outside the hull as a patch. Placing mattresses inside will reduce the possibility of the patch being knocked away by the sea. If innerspring mattresses are used, at least two thicknesses of blanket should be used as a facing. Over a period of time, feather pillows are not as effective as folded blankets for patches. Feathers in the pillow get wet and tend to lump at one end.
  22-34. A variation of the plate patch is called a hinged plate patch (see Figure 22-14). This is a circular plate, 18 inches or less in diameter, cut in two, and so hinged that it can be folded and pushed through a hole from inside the vessel. The plate should be fitted with a gasket, such as a pillow, and also a line for securing to the vessel. Using water diving equipment, this patch can be applied over a submerged hole without going outside the vessel. This patch is for use over relatively small holes, as it has no vertical support to hold it in place.

Figure 22-13. Example of Hull Patching Using a Mattress

Figure 22-14. Hinged Plate Patch

  22-35. An ordinary galvanized bucket can be used in a variety of ways to stop leaks. It can be pushed into a hole, bottom first, to form a metal plug, or it can be stuffed with rags and put over a hole. It can be held in place by shoring or by using a hook bolt.
  22-36. A hook bolt is a long bolt having the head end shaped so that the bolt can be hooked to plating through which it has been inserted. The common types are the T, J, and L (see Figure 22-15). The long shanks are threaded and provided with nuts and washers. Steel or wooden strongbacks are used with them. The bolt has no regular head. The head end of the bolt is inserted through a hole and the bolt rotated or adjusted until it cannot be pulled back through the hole. A pad or gasket, backed by a plank or strongback, is then slid over the bolt and the patch secured in place by taking up on the nut. It is generally necessary to use these bolts in pairs. Figure 22-16 shows an installed patch using two J-type hook bolts. Hook bolts can be used in combination with various patches such as the folding plate and the bucket. Figure 22-17 shows how to patch a hole using the folding T-type hook bolt.

Figure 22-15. Types of Hook Bolts

Figure 22-16. Patching Using Hook Bolts

Figure 22-17. Patching Using the Folding T-type Hook Bolt


  22-37. Piping system leaks usually accompanies any large hole in the hull. Soft patches can seal holes and cracks in low-pressure lines and water lines. Install a soft patch on a pipe as follows (see also Figure 22-18):
  • Opening is plugged with soft wood plugs or wedges (the flow of water must not be retarded by driving an excessive amount of wood into the pipe).
  • Trim plugs and wedges flush with the outside of the pipe.
  • Wrap rubber sheeting over the damaged area and back it with light sheet metal held in place with bindings of wire or marline.
  Stop minor pipe leaks with a jubilee patch (an adjustable strap with a flange on each edge). These can be made up as needed. The patch is shaped by bending sheet metal around a cylinder and turning out the flanges and then clamped in place (see Figure 22-19). The flanges may have to be reinforced as pressure increases (Figure 22-20).

Figure 22-18. Installing a Soft Patch On a Pipe

Figure 22-19. Jubilee Pipe Patches

Figure 22-20. Three Types of Reinforced Clamps


  22-38. Most water, fuel, and gas lines can be repaired and restored to the system within 30 minutes if the contents of the emergency damage control metallic pipe repair kit are applied properly. In addition to repair or patching of piping, certain materials, which may be used to patch small cracks and ruptures in flat metal surfaces, are included in the kit. Materials in the kit may be obtained separately through appropriate supply channels whenever a need arises to replace them. You do not need to obtain another completely new kit. A complete kit contains the following materials:
  • Four cans epoxy, resin, 400 grams each.
  • Four cans liquid hardener, 100 grams each.
  • Four cans paste resin, 300 grams each.
  • Four cans paste hardener, 75 grams each.
  • One piece woven roving cloth 24" x 10 ".
  • One piece void cover, 8" x 36".
  • One piece polyvinyl chloride (PVC) film, 36" x 72".
  • One chalk line, 1/8 pound.
  • Four pairs of gloves.
  • Two eyeshields.
  • Four wooden spatulas.
  • One sheet of emery cloth, 9" x 11".
  • One instruction manual.
  22-39. The following describes the basic materials found in the kit. The discussion of factors related to plastics are given to help you gain a better understanding of the kit and its use.
Void Cover
  22-40. The void cover is a resin-treated glass cloth that can be cut and formed to cover the damaged area. It is sufficiently rigid to give support to the patch.
Woven Roving Cloth
  22-41. The woven roving cloth is made of a short-staple, glass fiber woven into a thick, fluffy cloth. During the application of a plastic patch this cloth is coated with the resin-hardener mixture and either wrapped around or placed over the damaged area. The glass cloth provides the main strength of the patch and also provides a means of applying the resin-hardener mixture.
Film (PVC)
  22-42. The plastic film, referred to as PVC, is a thin transparent polyvinyl chloride material. It is used as a separating film for the flat patch to prevent the patch from sticking to the backup plate or other supports. In the pipe patch, it is used to cover the entire patch and retain the activated resin around the patch. Kraft wrapping paper may be used as a substitute if necessary.
Resins and Hardeners
  22-43. The liquid and paste resins are of the epoxy type. The liquid and paste hardeners are chemical compounds used to harden the resins. The resins and the hardeners are packaged in premeasured amounts. For proper mixture and better results, mix the complete contents of the hardener in the smaller can with the complete contents of the resin in the larger can.
  CAUTION: DO NOT mix hardener with resin until all preparations have been completed. DO NOT intermix liquid resin and paste hardener or paste resin and liquid hardener.
  22-44. When the resins and the hardeners are mixed together, a chemical reaction occurs which causes the mixture to harden (liquid mixture, approximately 12 minutes; paste mixture, approximately 17 minutes). This reaction is exothermic, which means that heat is given off. For approximately 12 to 17 minutes the temperature increases gradually until it reaches 120° F to 135° F. At this point a sudden sharp rise in temperature is known as kick over. It is at this temperature that the resin-hardener mixture begins to solidify and change color from gray to light brown. The peak temperature (350° F) can be observed through the external change of the patch.
  22-45. The resin-hardener mixture begins to cool slowly due to the poor thermal conductivity of the materials. After kick over, the mixture continues to harden and increase in strength. This process is referred to as curing. Approximately 30 minutes after kick over (the sharp rise in temperature) the patch is strong and hard and cool enough to use. Pressure should not be restored to the system until the patch has cured. The patch is considered sufficiently cured when the bare hand can be placed on it without discomfort from heat.
  22-46. Several factors contribute to the control of kick over. The most important factor is the temperature. Both the initial temperature of the activated resin mixture and the temperature of the atmosphere, affect the kick over time. However, of these two temperatures, the initial temperature of the activated resin has the greater effect. When the temperature of the resin and the hardener prior to mixing is increased, the kick over time decreases. Conversely, when the temperature of the resin and hardener prior to mixing decreases, the kick over time increases.
  22-47. Knowledge of controlling kick over is necessary since it corresponds to application of working time. This means that when the initial temperature of the mixture is 73° F, the patching material must be placed over the rupture within 12 minutes. Once the resin and the hardener are mixed together, the chemical reaction cannot be stopped. Therefore, the patch should be completely applied before kick over occurs.
  22-48. Figure 22-21 shows the relationship of the kick over time of the resin temperature. If you know the resin temperature at the time of mixing, you will be able to determine the amount of time available to apply the patch before kick over occurs. You can see that if the resin temperature is 80° (point A), the kick over will occur in less time than if the resin temperature were 60° (point B). The difference in resin temperatures represents an application working time of 9 minutes versus 18 minutes.
  Note: If the initial resin temperature exceeds 80° F the temperature should be reduced by artificial means to 73° F prior to mixing. This lowering of the temperature allows for additional application working time.
  22-49. Table 22-2 shows approximate quantities of materials required for pipe patches. The top figure in the boxes shows quantities in the amount of resin and hardener mixture in grams. The second group of figures, immediately below, are the dimensions in inches of woven roving cloth.
  22-50. From the damage control viewpoint, the main advantages of the plastic patch are versatility, simplicity, effectiveness, speed of application, and durability. The plastic patch can be successfully applied to a variety of damaged surfaces (such as smooth edges or jagged protruding edges). Since the plastic has excellent adhesive qualities it can be readily applied to steel, cast iron, copper, copper-nickle, brass, bronze, and galvanized metals.

Figure 22-21. Resin Temperature Versus Kick Over Time Graph

  22-51. The plastic materials and the plastic patch may be readily prepared and applied. By following the instructions outlined in the instruction manual included in the kit, a person with little or no experience can readily prepare the materials and apply a plastic patch. Applying a plastic patch is comparable to applying a battle dressing used in first aid. If the materials are properly prepared and the application procedures are duly followed, the plastic patch will be 100 percent effective. If leakage occurs through a plastic patch, it is likely that proper preparation and application procedures have not been followed.
  22-52. The speed of application will vary somewhat with the size and type of rupture and also with local working conditions. When proper preparation procedures are followed, an inexperienced crew, who have had a minimum amount of teaching and training, can apply a simple patch to a 4-inch pipe in 10 minutes or less. The type and size of the structure to which the patch is applied do not materially affect the time involved in patching. However, some types of damage may require more initial preparation.

Table 22-2. Table of Approximate Quantities of Materials Required for Pipe Patches

  22-53. When applying a plastic patch, you will see that as the individual patch materials are applied, the patch becomes progressively wider. Figure 22-22 shows the relative positions of the patch materials to one another.
  22-54. The buildup in the patch length during application must be considered initially when determining the length of the patch to be applied. Where suitable, allow the patch to extend at least 4 to 5 inches on either side of the rupture.
  22-55. In addition to the size of the rupture, the width of the patch may also depend on the location of the rupture in the pipe system. For example, an elbow rupture may require a wider patch than the same size rupture would require in a straight section of pipe.

Figure 22-22. Relative Positions of Patch Materials

  22-56. Certain specific preparations must be made prior to the actual application of the plastic patch. These are as follows:
  • Secure or isolate the rupture area in the piping system.
  • Remove all lagging.
  • 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 ethyl chloroform. If this solvent is not available, scrape and wipe the surface until it is clean. When a clean surface is obtained, the surface may be further abraded for better adhesion. An abrasive cloth is furnished with the kit.
  • Make sure that the entire pipe surface is dry.
  • Where practical, simplify the rupture by bending or removing irregular projections. This may be accomplished by cutting or burning.
  CAUTION: It is of the utmost importance that no explosive conditions exist prior to using spark-producing tools or burning equipment.
  Determine the materials that will be required, such as the amount of woven roving cloth and the amount of resins and hardeners. For example, a 2-inch rupture in a 2-inch diameter pipe will require 500 grams of activated resin and a piece of woven roving cloth that is at least 25 inches long. Cut the woven roving cloth wide enough to extend at least 3 to 4 inches on either side of the rupture.
  22-57. The following are step-by-step procedures for applying the simple pipe patch.
  • Put on eyeshields and gloves. Then open the liquid resin can and the liquid hardener can.
  • Add hardener to the resin and mix thoroughly for approximately 2 minutes or until a uniform gray color is observed. (Note that the entire contents of the liquid hardener in the smaller can, is the correct proportion for mixing with the entire contents of the larger can of liquid resin.)
  • Coat both sides of the void cover with the resin-hardener mixture and tie the void cover over the rupture with chalk line as shown in Figure 22-23, step A.
  • Lay the woven roving cloth on a clean flat surface. Starting at one end of the cloth, pour on resin-hardener mixture and spread evenly over the entire surface of the cloth using the spatula provided in the kit. Only one side of the woven roving cloth needs to be impregnated. Be sure that the edges are well impregnated with the resin-hardener mixture.
  • Center the woven roving cloth over the void cover with the impregnated side toward the pipe. Wrap it around the pipe not less than three turns and preferably not more than four turns (see Figure 22-23, step B).
  • Wrap the PVC film around the entire patch making at least two complete turns. Tie the PVC film with the chalk line, starting from the center of the patch and working toward one end, making 1/2-inch spacing between spirals (see Figure 22-23, step C). 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, form the center of the patch. Make 1 1/2-inch spacing 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 that for best results the temperature of the liquid resin and the liquid hardener should be approximately 70° F before mixing. The patch will cure in approximately one hour from the initial mixing time. After an hour, pressure may be restored to the piping system. In emergencies, if the temperature of the resins and the hardeners is below 50° F, applying external heat with hot-air heaters may accelerate kick over. However, the external heat must be applied gradually because excessive application of heat will cause the plastic patch to be extremely porous.

Figure 22-23. Simple Pipe Patch


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