Selection of stainless steels for cryogenic applications_toughness

Selection of stainless steels

Affect of steel structure on toughness

The toughness of the austenitics relies on their fcc atomic structure. The presence of either ferrite or martensite can limit the cryogenic usefulness of the austenitic stainless steels.
The small levels of ferrite usually present in wrought austenitics is not usually detrimental.

Cold working of austenitic stainless steels can also affect their cryogenic toughness.
This is due to the progressive formation of martensite from the ‘meta-stable‘ austenite. In effect this is similar to the presence of ferrite and can be controlled in the same way through compositional changes that stabilise the austenite.
In addition the effects of cold work can be removed by heat treatment. Solution annealing (softening) by heating to around 1050 / 1100 °C and cooling in air, depending on section size, will completely stress relieve the structure and transform the structure back the naturally tough austenitic one.

Welded areas may be at risk of brittle failure at very low temperatures, as ferrite levels in welds are higher than the surrounding wrought steel (to avoid hot cracking on solidification).
Special low ferrite level welding consumables are available for cryogenic applications and should be considered for very low, safety critical, temperature applications.

Castings compositions for austenitic stainless steel also have ferrite levels higher than the corresponding wrought grades BS3100 – Steel Castings for General Engineering Purposes, requires special impact tests at -196°C for the cryogenic application grades such as 304C12LT196. Although there are no major restrictions on composition, this grade is required to meet an additional Charpy impact test requirement of 41 Joules minimum at -196°C

Impact toughness of austenitic stainless steels

When austenitic stainless steels are Charpy tested at -196°C the test piece is usually ductile enough not to fracture (which actually invalidates the test).

Data available however quotes impact energies of over 130J for the 304 (1.4301) type. This is well within the 60-Joule minimum required in BS EN 10028-7 pressure vessel standard for 304 (1.4301) at -196°C.
Any of the austenitic stainless steels should be suitable for applications at these temperatures. The best choices of grades for very low temperatures are those with austenite stabilising additions such as nitrogen e.g. asi n grade 304LN (1.4311). (Higher alloy grades such as 310 (1.4845) or 904L (1.4539) which derive their austenite stability from higher nickel levels could also be considered)

Wrought grades with ferrite stabilising additions such as 321 (1.4541) or 347 (1.4550) may not be suitable at very low temperatures e.g. at the liquid helium boiling point of -269°C.

Impact toughness of other stainless steels

The ferritic, martensitic and duplex stainless steels cannot be considered as cryogenic steels.
Their impact characteristics change at sub-zero temperatures in a similar way to low alloy steels. The transition temperatures will depend on composition and heat treatment.

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Steel Flower – Jungwoo ENE co-developed Cryogenic special industrial equipments

DSME

STEEL FLOWER will acquire cryogenic industrial equipment technology and will start the LNG ship fuel supply business.

  STEEL FLOWER and JUNGWOO ENE have signed an agreement to jointly develop cryogenic special industrial equipments.

  Cryogenic industrial equipment is used in offshore plants and industrial plants using cryogenic refrigerants below -60 ° C. Especially, LNG plant equipments are capable of handling ultra-low temperatures of minus 162 ° C.

  At the agreement, representatives of Steel Flower Byeong-Kwon Kim, President Kim Kook-Jin, Researcher Jeongwoo ene and CEO Lee Sun Ha and Vice President Park Joon-Hyung attended and developed high-pressure natural gas fuel supply system (FGSS) for natural gas fuel vessels, And sharing technology contents for the development of cryogenic industrial equipments, supporting technology development expenses, and planning commercialization.

  In the meantime, Steel Flower has signed a contract to transfer the patent technology of ‘High Pressure Natural Gas Fuel Supply System (HiVAR FGSS)’, a core technology of DSME and next generation LNG fuels, I came. In addition, Jungwoo ENE, which has entered into this technology agreement, has developed technologies related to FGSS such as HP pumps, heat exchangers and cryogenic valves, followed by development of LNG compressors with large shipyards, submersible centrifugal pumps for LNG transportation, LNG cryogenic valves and control valves’ and ‘Vacuum insulation piping for cryogenic liquids’, which are expected to generate synergies through the establishment of a cooperation system.

  STEEL FLOWER Kim Byung-kwon said, “With these two companies’ technical cooperation, we will develop high-priced core parts that are dependent on imports for the time being, and will lead the development and commercialization of low-pressure high-pressure natural gas fuel supply equipment. We will actively respond to the demand for LNG-fueled vessels that are expected to be built and concentrate on preempting the world market. “

  Meanwhile, FGSS is the world’s first proprietary high pressure liquefied natural gas fuel supply system for DSME, which is the core technology of natural gas fuel vessels, which is regarded as the next generation ship.

 Sourced by : ekomeri.com

 

Liquefied Natural Gas

LNG-carrier

Natural gas is the most climate friendly of the fossil fuels releasing less CO2 than oil based products such as diesel.

Natural gas is the world’s third most important energy source after oil and coal. It occurs naturally deep underneath the earth’s crust in many places around the world. Natural gas currently represents a quarter of the global energy supply.

Natural gas is used in industry, in power plants, in district heating and in sea and overland transport. Throughout Europe, natural gas has traditionally been regarded as a form of green energy.

There are many reasons to take an interest in natural gas. It has major advantages over other fossil-based energy sources – not least the fact that natural gas gives off fewer undesirable emissions. But also because natural gas is more efficient and kinder to the environment than the other fossil fuels which are currently used in industry, shipping and overland transport.

Natural gas is converted to LNG by harnessing innovative cryogenic technologies that make it available both for worldwide transport as well as for local markets. This conversion can also contribute to increased use of biogas. The conversion of natural gas into liquid is achieved through refrigeration by cooling natural gas to -162°C.

The resulting condensate is known as Liquefied Natural Gas (LNG). Liquefaction reduces the volume by about 600 times, making it more economical to transport between continents in specially designed LNG carriers. Liquefied natural gas, or LNG, is natural gas in its liquid form. It is the cleanest burning fossil fuel as it produces less emissions and pollutants than either coal or oil.

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