Liquid carbon dioxide forms only at pressures above 5.1 atm; the triple point of carbon dioxide is about 518 kPa at -56.6 °C. The critical point is 7.38 MPa at 31.1 °C.
Plumbers use equipment that forces pressurised liquid CO2 into a jacket around a pipe; the dry ice formed causes the water to freeze, forming an ice plug, allowing them to perform repairs without turning off the water mains. This technique can be used on pipes up to 4 in (100 mm) in diameter
-wikipedia