Copper and Copper Alloys

DOE-HDBK-1129-99

employed for the SRS Building 232-H Extraction Furnace retorts. Type 310 stainless steel has

good oxidation resistance and can be considered for elevated temperature applications if oxidation

is a concern. Type 316 stainless has superior creep resistance but inferior oxidation resistance to

Type 310.

Some types of higher-strength austenitic stainless steels not generally employed for tritium service

may be required for fasteners (such as nuts and bolts) in mechanical joints in high-temperature

regions. This may be acceptable if the bolts are exposed to only residual amounts of tritium.

These materials also may be used to contact 3XX stainless steels to avoid galling of mating screw

contact surfaces. Typical materials used in these applications include Nitronic 60, Nitronic 50 (also

called 21-13-9) and Nitronic 40 (also called 21-6-9); these are all nitrogen-strengthened austenitic

stainless steels.

5.1.2.b Copper and Copper Alloys

In principle, copper should be a suitable material in tritium systems. Copper has several tritium-

compatible properties. Tritium has a low permeability in copper, and copper is a ductile, stable,

face-centered-cubic metal and so is resistant to hydrogen embrittlement. The high thermal

conductivity of copper is a desirable property for process vessels requiring heat flow or constant

temperature. Copper can be easily joined in a number of ways (e.g. soldering, brazing, welding).

In spite of these advantageous properties, copper and copper alloys are not commonly used in

tritium systems. Several factors may account for this. The ASME allowable design strength of

copper falls rapidly at temperatures above 200 C, making it difficult to use copper for process

beds that operate at elevated temperature. Also, hydrogen isotopes can react at elevated

temperature with oxygen in copper, whether the oxygen is in solid solution or in copper oxide

precipitates. In either case, water is formed, and over time water vapor agglomerates at grain

boundaries, which eventually results in intergranular cavitation, cracking, and failure. This failure

mechanism is sometimes termed "steam embrittlement." Also, a transition junction (normally

nickel) is required to join copper and the stainless steel components of the remainder of the

system.

5.1.2.c Aluminum and Aluminum Alloys

Aluminum has properties making it potentially desirable for tritium systems. It has a low density

and a high thermal conductivity. Hydrogen isotope permeability is very low in aluminum compared

to stainless steel. Aluminum is used in applications where light weight is important, such as in

containers that must be lifted by personnel in gloveboxes. However, aluminum is not commonly

used in tritium systems. Stainless steel has much higher strength, at room and elevated

temperature. Welding aluminum requires more precautions because aluminum reacts with

atmospheric water vapor, which can cause porosity due to hydrogen in the weld fusion zone.

5.1.2.d Materials to Avoid

Plain carbon steels and alloy steels must not be used for tritium service. These steels have high

strength and (normally) a body-centered-cubic crystal structure, both of which make the material

less ductile and much more susceptible to hydrogen embrittlement. Ferritic stainless steels (such

as Type 430), martensitic stainless steels (both quench-and-tempered (such as Type 410) and

precipitation hardening (such as 17-4 PH and PH 13-8 MO)) and precipitation hardened austenitic

stainless steels (such as AM-350) should not be used for general tritium service; they are all more