METALLIC PIPE PATCH

The metallic pipe and general-purpose damage control kit is used to make metallic pipe patches, also referred to as a plastic patch. The kit is part of the required repair locker equipment inventory and contains the materials needed to repair various piping-system lines. Most of these repairs can be made and the system restored to service within 60 minutes.

Kit Contents

The complete kit contains the materials listed below. These materials may be ordered individually whenever a need arises to replace them in the kit.

Assembly I

. Four cans liquid resin, 400 grams each

. Four cans liquid hardener, 100 grams each . One piece woven roving cloth, 24 by 40

inches . One piece void cover, 8 by 36 inches . One piece polyvinyl chloride (PVC) film,

48 by 60 inches

. One chalk line, one-eighth of a pound . Four pairs of gloves . Two eyeshields . Four wooden spatulas l One sheet of abrasive cloth, 9 by 11 inches . One pair of scissors l One instruction manual

Assembly II

. Four cans paste resin, 300 grams each

. Four cans paste hardener, 75 grams each . Four tongue depressors

Before you can have a good understanding of the kit and its uses, you will need to know more about plastics in general. The following paragraphs will give you the basics on the materials in the kit.

RESINS AND HARDENERS.- The liquid and paste resins are of the epoxy type. The liquid and paste hardeners are chemical compounds used to harden the resins. These resins and hardeners are packaged in premeasured amounts. For proper mixture and better results, mix all of the hardener in the smaller can with all of the resin in the larger can.

CAUTION: DO NOT MIX HARDENER

WITH RESIN UNTIL ALL PREPARATIONS HAVE BEEN COMPLETED. DO NOT INTER-MIX LIQUID RESIN AND PASTE HARD-ENER OR PASTE RESIN AND LIQUID HARDENER.

When the resins and the hardeners are mixed together, a chemical reaction begins. This reaction is exothermic, which means that heat is given off. For approximately 12 to 17 minutes, the temperature increases gradually until it reaches 120F to 135F. At this temperature a sudden, sharp increase in the temperature occurs until it reaches its peak at about 350F. This sudden, sharp rise in temperature is known as kick-over. At this peak temperature, the resin-hardener mixture begins to solidify and change color from gray to light brown.

The mixture cools slowly because of the poor thermal conductivity of the materials. After kickover, the mixture continues to harden and increase in strength. This process is known as curing. Approximately 30 minutes after kick-over, the patch is strong, hard, and cool enough to use. Do not restore pressure to the system until the patch has cured or when you can place your bare hand on it without discomfort from heat.

Several factors contribute to the control of kick-over. The most important is temperature. Both the initial temperature of the activated resin mixture and the temperature of the atmosphere affect the kick-over time. The initial temperature has the greater effect. When the temperature of the resin and the hardener before mixing is increased, the kick-over time decreases. Also, when

those temperatures are decreased the kick-over time increases.

You should be able to predict the time of kick-over. The kick-over time can decontrolled only within certain limits. Therefore, the patch needs to be completely applied before kick-over occurs.

Figure7-24 shows the relationship of kick-over time to the resin temperature. If you know the resin temperature at the time of mixing, you can determine the amount of time available to apply the patch before kick-over occurs. Look at point A in figure 7-24 where the resin temperature is 800. The kick-over will occur in less time than if the resin temperature was 600 (point 13). The difference in resin temperatures means that you have 9 minutes versus 18 minutes to apply your patch.

NOTE: If the initial resin temperature exceeds 80F, the temperature before mixing should be reduced by artificial means to 73F. This allows for additional working time.

VOID COVERS.- The void cover is a resintreated glass cloth that can be cut and formed to cover the damaged area and is rigid enough to give support to the patch.

WOVEN ROVING CLOTH.- The woven roving cloth is made of a short staple glass fiber woven into a thick, fluffy cloth. This cloth will be 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 a means of applying the resin-hardener mixture.

FILM (PVC).- The plastic film is a thin, transparent polyvinyl chloride material (PVC). It is used as a separating film for the flat patch. Its purpose is 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 keep the activated resin around the patch. Kraft wrapping paper may be used as a substitute if necessary.