Read about START-PROF pipe stress analysis software
As a rule, with decreasing temperature, the strength characteristics increase (the tensile strength, yield stress, fatigue limit, etc.), as well as the modulus of elasticity and decreasing plasticity (relative elongation, impact strength). Also, the coefficient of linear thermal expansion is reduced.
The property of some materials to pass with a decrease in temperature to Brittle fracture without noticeable plastic deformation is called cold brittle.
The nature of the change in mechanical properties with decreasing temperature is different for different materials. The most widely used materials for operating temperature below -70°C is steels from 300 series in the USA and chromium-nickel austenitic steels 12X18H10T in Russia, containing 16-22% chromium and 8-14% nickel. The distinctive features of such steels are corrosion resistance and good viscosity and ductility at low temperatures. When temperature is lowering, the plastic properties of such steels occurs to a much lesser extent than carbon and low-alloy steels. Thermoplastic properties remain good enough to ensure reliable piping operation up to the lowest temperatures (-269°C).
Also, in equipment operating at low and ultra-low temperatures, widely used the non-ferrous metals and alloys due to their ability of preserving ductility at low temperatures.
Cryogenic piping analysis can be done using ASME B31.3, EN 13480 and GOST 32388 codes. ASME B31.3, EN 13480 has no any special methods of analysis of cryogenic piping, but GOST 32388 codes has a special chapter for cryogenic piping stress analysis.
The procedure for stress analysis of cryogenic piping in accordance with GOST 32388-2013 differs from normal temperature piping. In addition to using steel characteristics at low temperatures (allowable stress, modulus of elasticity, linear expansion), the formula for calculating stresses also changes. It is depending on the value of the plasticity factor, and simultaneously used the conditions of the first and fourth theory of strength (Von Mises):
And also the strength conditions are different in various operating modes.
