NOREM is a
hardfacing Hardfacing is a metalworking process where harder or tougher material is applied to a base metal. It is welded to the base material, and generally takes the form of specialized electrodes for arc welding or filler rod for oxyacetylene and gas tung ...
material developed by the
Electric Power Research Institute
EPRI, is an American independent, nonprofit organization that conducts research and development related to the generation, delivery, and use of electricity to help address challenges in the energy industry, including reliability, efficiency, affo ...
to deal with radiation safety issues associated with the use of
cobalt
Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, p ...
alloys in
nuclear power station
A nuclear power plant (NPP) is a thermal power station in which the heat source is a nuclear reactor. As is typical of thermal power stations, heat is used to generate steam that drives a steam turbine connected to a generator that produces ele ...
coolant systems (see
stellite for a discussion of the problem). It is a
solid-solution strengthened austenitic
Austenite, also known as gamma-phase iron (γ-Fe), is a metallic, non-magnetic allotrope of iron or a solid solution of iron with an alloying element. In plain-carbon steel, austenite exists above the critical eutectoid temperature of 1000 ...
matrix with a continuous network of
eutectic and non-eutectic
carbide
In chemistry, a carbide usually describes a compound composed of carbon and a metal. In metallurgy, carbiding or carburizing is the process for producing carbide coatings on a metal piece.
Interstitial / Metallic carbides
The carbides of th ...
s at the
grain boundaries. It is intended to be deposited by various
welding
Welding is a fabrication process that joins materials, usually metals or thermoplastics, by using high heat to melt the parts together and allowing them to cool, causing fusion. Welding is distinct from lower temperature techniques such as bra ...
processes.
Characteristics
There are eight variants of NOREM currently available, depending on application and designated 02, 02A, 03A, 03B, 04A, 04B, 05A, 05B. A typical elemental composition is 60% iron, 25% chromium, 4.5% manganese, 4.0% nickel, 3.3% silicon, 2.0% molybdenum, 1.2% carbon. Earlier compositions included either significantly more manganese (12% in alloy 04) or significantly more nickel (8% in alloy M2).
These are extremely
hard
Hard may refer to:
* Hardness, resistance of physical materials to deformation or fracture
* Hard water, water with high mineral content
Arts and entertainment
* ''Hard'' (TV series), a French TV series
* Hard (band), a Hungarian hard rock supe ...
alloys. NOREM 02 is ten times as resistant as 308 stainless steel to
cavitation erosion. They are essentially
corrosion
Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engi ...
-immune under the conditions inside
CANDU reactor
The CANDU (Canada Deuterium Uranium) is a Canadian pressurized heavy-water reactor design used to generate electric power. The acronym refers to its deuterium oxide ( heavy water) moderator and its use of (originally, natural) uranium fuel. C ...
s and erode at about 200 micrograms per square centimetre per year under
pressurized water reactor
A pressurized water reactor (PWR) is a type of light-water nuclear reactor. PWRs constitute the large majority of the world's nuclear power plants (with notable exceptions being the UK, Japan and Canada). In a PWR, the primary coolant (water) i ...
conditions. Due to the high hardness, the strength is relatively low: approximately {{convert, 120, ksi, abbr=on yield strength and it fails at 0.6% elongation.
Use in power plants
The first use of NOREM was as replacement discs in three Chemical Volume Control System isolation valves at
Consolidated Edison's
Indian Point unit 2. It is now used in about 800 valves installed by about 30 utility companies. There has been one case of a NOREM valve disc being found damaged, at the
Callaway Nuclear Generating Station
The Callaway Plant is a nuclear power plant located on a site in Callaway County, Missouri, near Fulton, Missouri. It began operating on December 19, 1984. The plant, which is the state's only commercial nuclear unit, has one 1,190-megawa ...
, though it seems the valve was not being used in an appropriate application.
Given the high cavitation resistance, NOREM has been tested for hydroelectric applications; it seems not to be as impressively cavitation-resistant in the field as in the lab, though only one layer of the material was used in the test, and the Electric Power Research Institute recommends at least two.
References
Performance of NOREM Hardfacing Alloys
Further reading
Stainless steels By Joseph R. Davis
Welding