to 17 minutes the temperature increases gradually until it reaches 120° to 135°F. Then a sudden, sharp increase in temperature occurs until it reaches its peak at or about 350°F. This sudden, sharp rise in tempera- ture is known as kick-over. At this temperature, 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. The  resin-hardener  mixture  begins  to  cool  slowly because the materials conduct heat poorly. After kick- over, the mixture continues to harden and increase in strength.  This  process  is  called  curing.  Approximately 30 minutes after kick-over (the sharp rise in tempera- ture), 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. 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. Of these two temperatures, the initial  temperature  of  the  activated  resin  has  the greater effect. When the temperature of the resin and the  hardener  before  mixing  is  increased,  the  kickover time  decreases.  Conversely,  when  the  temperature  of the resin and hardener before mixing decreases, the kick-over  time  increases. A knowledge of the control of kick-over is neces- sary since it corresponds to the application of working time. This means, for example, that when the initial temperature  of  the  mixture  is  73°F,  the  patching  ma- terial must be placed over the rupture within 12 min- utes.  Once  the  resin  and  the  hardener  are  mixed,  the chemical reaction cannot be stopped. Therefore, the patch should be completely applied before kick-over occurs. Figure 2-24 shows the relationship of the kick- over time to the resin temperature. If you know the resin temperature at the time of mixing, you are able to determine the amount of time available to apply the patch before kick-over occurs. You can see in figure 2-24 that if the resin temperature is 80°F (point A), the kick-over  will  occur  in  less  time  than  if  the  resin temperature were 60°F (point B). The difference in resin  temperatures  represents  an  application  working time of 9 minutes instead of 18 minutes. NOTE If the initial resin temperature exceeds 80°F, the temperature should be reduced by artificial means to 73°F before mixing. This lowering of the temperature allows for addi- tional application working time. Advantages of the Plastic Patch From  the  damage  control  viewpoint,  the  main advantages  of  the  plastic  patch  are  (1)  versatility,  (2) simplicity, (3) effectiveness, (4) speed of application, and  (5)  durability. The  plastic  patch  can  be  successfully  applied  to  a variety of damaged surfaces, whether with smooth edges or jagged protruding edges. Since the plastic has  excellent  adhesive  qualities,  it  can  be  readily  ap- plied to steel, cast iron, copper, copper-nickel, brass, bronze,  and  galvanized  metals. It is easy to prepare the plastic materials and to apply  the  plastic  patch.  By  following  the  instructions outlined in the instruction manual that is included in the kit, anyone with little or no experience can readily prepare the materials and apply a plastic patch. A plastic patch is applied in much the same way as a battle dressing is used in first aid. If the materials are properly prepared and the application  procedures  are  followed,  the  plastic  patch will   be   100   percent   effective.   If   leakage   occurs through a plastic patch, it is likely that propr prepa- ration and application procedures have not been fol- lowed. The speed of application varies somewhat with the size and type of rupture, and with local working conditions. When proper preparation procedures are followed, a simple patch can be applied to a 4-inch pipe  by  an  inexperienced  crew  who  have  had  the minimum amount of training and indoctrination in 10 minutes or less. The type and the size of the rupture or the shape and the size of the structure to which the patch  is  applied  do  not  materially  affect  the  time involved in patching, but some types of damage may require more initial preparation. The  maximum  period  of  effectiveness  of  a  plastic patch  is  not  known,  but  all  indications  are  that  a properly  applied  patch  can  last  indefinitely  or  cer- tainly until permanent repairs can be made. The patch is  relatively  inert,  being  seriously  affected  only  by excessive  heat  and  concentrated  acids. 2-16