This data is intended for an introduction to the metals used for cryogenic pressure vessels.

WELDING, NINE PERCENT NICKEL CRYOGENIC APPLICATIONS.

A common application in which austenitic stainless and 9% nickel steels is in the construction of cryogenic, liquefied natural gas (LNG) containers. These containers can carry liquid argon, natural gas, helium, oxygen, nitrogen etc. These liquid gases are usually in an approximate temp range of -300 to -450F. Carbon steels and alloy steels have poor toughness and ductility at low temperatures. The alloy steels with nickel, austenitic steels typically 304 - 304L 316 - 316L - 347 and aluminum alloys all have excellent low temperature toughness.

Strict welding regulations are applied to welding cryogenic applications. The weld metal properties should contain low nitrogen, low ferrite, low carbon and high nickel. Filler metals such as Nickel Chrome Molybdenum, Nickel Chrome Iron or high alloy austenitic electrodes.

The Nickel alloy consumables have a coefficient of thermal expansion that is close to the 9% nickel this reduces the risk of thermal fatigue in applications subject to thermal cycling. Typically the mechanical properties of nine percent nickel will be higher than those of the weld consumables utilized. This requires special consideration to weld qualification tests. Note that with the 30X in centrast to the 30XL (low carbon grades). The higher the carbon the lower the impact toughness.

Shop built stainless steel cryo vessels in the USA are built to ASME Boiler Pressure Vessel Code Section V111. Field erected vessels may use the API 620 Q. Austenitic stainless accounts for the majority of metals used for cryo applications. The rest of the applications use 5 to 9% nickel or aluminum. Where high strength is required nine nickel may be chosen instead of an austenitic steel. Its important to remember that nine percent nickel is an alloy that can rust.

 

WELDING AFFECTS ON STAINLESS AND NINE PERCENT NICKEL

• Keep the carbon in the rage <0.03%. Low carbon superior toughness.
• With SMAW, Lime electrodes provide higher low temp toughness than the titania electrodes.
• Weld Inclusions. Slag inclusion can lower low temp toughness. Keep this in mind when comparing weld processes. The two best processes for toughness are GTAW and GMAW.
• As porosity or inclusions are a result of an oxide reaction its logical when MIG welding to use a low reactive gas mix.
  For stainless applications forget that argon 2% oxygen mix recommended by the gas companies, use argon with 2 to 3% CO2. The argon CO2 mix is much less oxidizing and does not have enough CO2 to add to the carbon content of the weld.
• Nitrogen pick up will increase the strength of the stainless welds however it decrease the low temperature toughness.
• If using SAW for stainless, its difficult to meet the weld impact requirements on applications below - 300 F, consider MIG.
• If the stainless pipe ID root weld finish is important, automated TIG systems use low (none pulsed) current for the root.The fill passes can then if required be made with the MIG process. Argon and argon hydrogen mixes are used for the TIG welds.
• Nine percent nickel is often used for economic reasons for large plate, cryo pressure vessel applications down to -320 As mentioned this metal can rust, so this alloy cannot be used on applications where contamination is a concern.
• Nine percent nickel cryo vessels are built to ASME Boiler Pressure Vessel code SectionV111.
• Two material specs are used for the common nickel plates.
  [1] ASTM SA 553/SA 553M Spec for pressure vessel plates. Alloy steels Quenched and tempered 8-9% Nickel.
  [2] ASTM SA 353/SA-353M Spec for pressure vessel plates. Alloy Steels Doubled Normalized and tempered.
• ASTM. AS 553 and SA 353 have the same chemistry 8.5-9.5 nickel the yield strength of 353 is 75 ksi to 85 ksi
  for the 553.
• Most pressure vessel plates are QT 553.
• Weld procedure qualifications for 9% nickel according to section 1X of the boiler code requires impact test made
  at -320F or the lower operating temp. The impact test covers the weld d HAZ. Transverse tensile and bend tests are also req.
• I believe for the nine nickel, you will get great weld data from both Sandvik and Inco Alloy Intentional, consumables such as Ni CR/ Ni Cr Fe/ Ni-Cr-Mo and Sandvik 16.13 CMnW ( 16.5 Cr - 12.6 Ni - 6.9 Mn - W 3.3 bal Fe)
  
  
  
  Note: A good portion of this data is from an article "Welding Stainless and 9% Nickel Steel Cryogenic Vessels" by Avery and Parsons, the Weld Journal Nov 95. For more data on Nickel Steels, visit the web site of the Nickel Development Institute.