We found a possibly helpful article titled “At What Temperature Should You Winterize a Sprinkler System”. Here is the link:
Here is one excerpt from the article:
Effects of Frozen Sprinklers
Water can also freeze inside sprinkler heads themselves. As the frozen water expands, the pressure from the ice can pop off sprinkler heads. Another possible effect is that the water will expand inside the plastic body of the sprinkler, cracking the sprinkler down the side. Water can also freeze inside the small supply tube that pushes the nozzle above ground. Any of these problems requires you to replace the entire sprinkler head with a new unit.