Accelerated Curing

Accelerated Curing

To speed up the curing of a CIPP lateral liner, the most viable options are a hot water heater or steam unit. If you’ve been lining pipe using the CIPP process, you’ve concluded that waiting for a liner to ambient or air cure at the surrounding temperature takes a long time. So how can you speed up the cure? Heat or UV light both works, however, for small diameter liners with relatively short runs, water or steam appear to be the popular choice. So, what are the considerations that you need to know before you choose the type of heat source you will want to pick?

CIPP liners go through a process where liquid resin forms chemical chains that cause it to harden. This process is called “exothermic” and during the formation of these chains, heat is generated. The temperature that the resin is exposed to accelerates or retards the process, so the colder the temperature, the slower the chemical chains are formed. They are formed giving off the same quantities of heat but over a longer timeline and at lower observed exothermic temperatures due to the heat sink from ambient lower temperatures. During this curing process, the heat we introduce to the resin accelerates the formation of these chains. It can appear as though the more heat you provide, the faster the chains form. Here’s where the trouble starts. More isn’t always better, and in fact can be a detriment to the forming of the chains or hardening. When you make the chains form too quickly, the chains “bump” into each other in the accelerated rate. If they “bump” into each other too fast, they form stress cracks, and these stress cracks will allow water and roots to eventually pass through them. The best example of this if you leave a large amount of mixed resin in a bucket on a hot day you will see the excessive heating and resulting stress cracking.

 

The alternative choices:

Water: This method applies the simple physics of heating water, circulating it inside the tube at a constant temperature between 52C and 82C to accelerate the curing process. The advantages of this method are many. Equipment costs are relatively low compared to UV equipment, and there’s no special training or licenses required to run the equipment. Setting up cure and tear down times are faster for lines under 100 linear metres and 150mm diameter pipe. However, the disadvantages of this method include the large dependable supply required, the time it takes to introduce the water and heat it to get the curing of the liner started and disposing of the water after the cure.

Steam: This method replaces water with steam heat. The steam produced must be coupled to an air compressor to drive the steam from one end of the pipe to the other end. Steam is exhausted to the air, preferably at the opposite end from the introduction of the steam. Pressure coupled with steam can produce steam temperatures over 125C. The advantages of steam include fast generation of heat as soon as the unit is turned on – there’s no heating of cold water or air to contend with. It’s ideal for lines with large hydrostatic head, especially 2m vertical difference or more. Disadvantages of steam pertain to the ability to control the exothermic temperature. When heating the cold resin with steam and exotherm begins, the temperature generated by the chemical process adds to the steam heat. Monitoring of the temperature throughout the curing is mandatory so as not to allow any parts of the liner to exceed 82C because temperatures exceeding this are subject to the stress cracking as noted above. To overcome the increase in temperature, more air needs to be mixed with the steam to keep the temperatures in the range of 82C or less. There are steam generation systems available that have very good heat control built in.

Simply, your situation and operation will most likely dictate which is best for you and for some, ambient cure works just fine. If you’re a contractor who does lining and needs another tool in his toolbox as well as wanting to perform more jobs in a shorter time, hot water or steam may work best for you.

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