why don't Pigtail Steam Siphons freeze

[Kcroto]

We are adding to a steam system that is outside. Where we have gauges/transmitters we are installing the traditional pigtail steam siphons.

while reviewing the design I became aware that the siphon was subject to freezing when the system was off line. I called for freeze prevention.

In reviewing the other portions of our system we noted that none of the other siphons were heat traced.

Does anyone have experience with the freezing of siphons? Is it not a problem due to their shape?

Thanks,

Keith