Place the collars on the pipe 40" in both directions of the repair area where you'll be soldering.
Yes by putting a heat absorbing paste on the pipe (such as The La-Co MFG. companies paste) called Bloc-IT. You spread the paste around the outside of the pipe between the freeze collars and the solder point. Freeze tool users say they can get as close as 12" from the ice plug with the brazing torch using this method spreading heat absorbing paste as a barrier.
The point of least resistance in the pipe is the water not the pipe. In other words the plug will grow lengthwise in the pipe as long as there is water in the pipe and the two freeze collars are not too close to each other the pipe will not burst. The collars should be placed at least 2' apart (1' in each direction of the solder point) from one another even if using the heat absorbing past method described above. If only making one freeze plug the two collars may be placed butted up one against another but do not leave any space between the two collars creating an air pocket and possibly causing a rupture of the pipe. A tee fitting is included to cap off one side of the tee for using only one freeze collar to make one ice plug.
We are incorporated as Flanges and Fittings Inc. but have always done business as M&S Valves & Fittings Company since the day we incorporated over 18 years ago in November of 1983. We are a Master Distributor of Plumbing Specialty Items including pipe freezing and isolation equipment, REMS Piping Tools and Equipment, drinking water sterilization equipment, emergency leak detection equipment and repair kits, as well as a variety of carbon, stainless, and brass siphons. We also have the largest inventory in the country of Cast Steel Flanged Fittings.
Our definition is a company that stocks and has an in-depth knowledge to support a niche line of items for resale using a two step distribution of wholesale dealers selling to contractors in North America. We stock and advertise products others don't or won't for whatever reason.