What 12Ni14 Is
12Ni14 is a nickel alloy steel plate for pressurised equipment with a nickel content of about 3.5 percent. It is a European standard grade used for pressurised equipment, boilers and pressure vessels, and it belongs to the group of nickel steels whose whole purpose is to stay tough when the metal temperature falls well below ambient. In the European flat product system for pressure purposes, these nickel steels are covered by the part of EN 10028 that deals with steels with specified low temperature properties, EN 10028-4.
The grade name follows the usual logic: the number refers to the nominal carbon content and the number after Ni gives the nominal nickel content in percent. Dimensions, shape, weight and permissible deviations are ordered in accordance with EN 10028-1.
Mechanical Properties
| Property | Thickness range | Requirement |
|---|---|---|
| Yield strength | up to 30 mm | 355 MPa minimum |
| Yield strength | over 30 to 50 mm | 345 MPa minimum |
| Yield strength | over 50 to 80 mm | 335 MPa minimum |
| Tensile strength | all sizes | 490 to 640 MPa |
| Elongation after fracture | all sizes | 22 % minimum |
The tensile strength band is wider than that of an ordinary structural plate, which reflects the metallurgy of nickel steels: strength is delivered mainly by solid solution and grain refinement rather than by a high carbon content, so the material keeps a high elongation value even at the top of the strength range. The reduction in minimum yield strength with increasing thickness is a normal consequence of slower cooling and lower reduction in heavy plate, and design calculations should use the value that matches the ordered thickness.
How the Nickel Content Works
Nickel dissolved in the ferrite matrix lowers the ductile-to-brittle transition temperature. That single effect is what allows a 3.5 percent nickel steel to be used at service temperatures where a carbon-manganese vessel steel would risk brittle fracture. The carbon level is kept low to protect both toughness and weldability, and the manganese addition provides the strength that the low carbon content would otherwise leave out. The result is a steel with a predictable Charpy energy level at the design temperature, which is what the vessel calculation depends on.
Applications and Fabrication
12Ni14 plate is used for low temperature pressure vessels, boilers and pressurised equipment, including storage and transport equipment for liquefied gases, low temperature heat exchangers and separator vessels in the gas and petrochemical industries. The common requirement is a low design metal temperature combined with internal pressure.
Forming: cold forming within agreed limits, with hot forming followed by a restoring heat treatment where required.
Welding: low hydrogen consumables of matching strength, controlled preheat and interpass temperature, and moderate heat input to protect heat affected zone toughness.
Heat treatment: post-weld heat treatment where thickness or service conditions demand it.
Inspection: ultrasonic testing sheet by sheet and full mechanical testing in the delivery condition, with certificates showing heat number traceability.
Frequently Asked Questions
Q: How much nickel does 12Ni14 contain?
A: About 3.5 percent, which is what gives the steel its low temperature toughness.
Q: What is the tensile strength of the grade?
A: 490 to 640 MPa, with elongation after fracture of at least 22 percent.
Q: What is the minimum yield strength?
A: 355 MPa up to 30 mm, 345 MPa over 30 to 50 mm and 335 MPa over 50 to 80 mm.
Q: Which standard applies to the plate?
A: The European flat product standard for pressure purposes covering steels with specified low temperature properties, EN 10028-4, with dimensions per EN 10028-1.
Q: What is the plate used for?
A: Low temperature pressure vessels and boilers, liquefied gas storage and transport equipment and cryogenic heat exchangers.
