CRYOGENIC PIPING SYSTEMS
Nicholas P. Theophilos, Ph.D., P.E.
Standards and Quality Assurance
Cryogenics (from the Greek ‘‘kryo-genikos,’’ meaning cold generation) is the science
and technology associated with very low temperatures. Depending on one’s point
of view, any temperature below 20F can be set to establish such a demarcation.
Here the 20F point has been selected because it normally represents the onset
of embrittlement for ordinary carbon steels in typical structural applications.
Cryogenics is not a separate branch of physics, since it obeys all laws of ordinary
physics. In fact, cryogenics is low-temperature physics. The reasons for its special
treatment, therefore, are not because of its uniqueness as a science but rather
because of the very special problems it creates as a technology. These problems
relate to embrittlement of materials, large displacements (expansion and contrac-
tion), rapid change of phase due to large heat fluxes (big delta T), and small latent
heats of the fluids involved.
In order to obtain a better appreciation of the special considerations involved
in cryogenic piping system applications, it was felt that it would be necessary to
review the behavior of materials at cryogenic temperatures and the physical and
thermodynamic properties of cryogenic fluids. These considerations are covered in
the sections ‘‘Properties of Cryogenic Fluids’’ and ‘‘Materials Used in Cryogenic
Piping Systems.’’ Additionally, cryogenic piping system design is discussed in the
sections ‘‘Piping Systems Design—Fluids’’ and ‘‘Piping Systems Design—
From the strictly heuristic point of view of fundamental applications of scientific
principles there are hardly any differences between cold box piping and all other
types. Nevertheless, we are making a special topic of cold box piping because of
the confined spaces involved and the conceptual arrangements required to satisfy
logistically workable and economically feasible process considerations. Su