NOREM is a
hardfacing material developed by the
Electric Power Research Institute to deal with radiation safety issues associated with the use of
cobalt alloys in
nuclear power station coolant systems (see
stellite
Stellite is a range of cobalt-chromium alloys designed for wear resistance. The alloys may also contain tungsten or molybdenum and a small, but important, amount of carbon.
History
Stellite is a trademarked name of Kennametal Inc. Prior to tha ...
for a discussion of the problem). It is a
solid-solution strengthened austenitic matrix with a continuous network of
eutectic and non-eutectic
carbides at the
grain
A grain is a small, hard, dry fruit (caryopsis) – with or without an attached hull layer – harvested for human or animal consumption. A grain crop is a grain-producing plant. The two main types of commercial grain crops are cereals and legum ...
boundaries. It is intended to be deposited by various
welding 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 alloys. NOREM 02 is ten times as resistant as 308 stainless steel to
cavitation erosion
Cavitation is a phenomenon in which the static pressure of a liquid reduces to below the liquid's vapour pressure, leading to the formation of small vapor-filled cavities in the liquid. When subjected to higher pressure, these cavities, c ...
. They are essentially
corrosion-immune under the conditions inside
CANDU reactors and erode at about 200 micrograms per square centimetre per year under
pressurized water reactor 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
Consolidated Edison, Inc., commonly known as Con Edison (stylized as conEdison) or ConEd, is one of the largest investor-owned energy companies in the United States, with approximately $12 billion in annual revenues as of 2017, and over $62 b ...
'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, 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