Double pipes can be used in certain circumstances to reduce the likelihood of external leaks and increase
the likelihood of detection by monitoring the space between the two pipes. Vacuum jacketed piping is
double walled and is used in liquid hydrogen service to provide insulation. While not equipped with gas
detection in the annular space, loss of vacuum is used to indicate an internal leak. If the outside pipe is
not designed to withstand the pressure of the fluid within the inside pipe, it must be equipped with a
vent to prevent buildup of annular pressure.