Inside this issue

Zircadyne: an alternative to corrosion maintenance

Q&A: Pre-oxidizing zirconium for corrosion control

Vanadium for DIII-D fusion device

Joining Nb₃Sn wire

A changing of the guard at TWC
Riesen to retire later this year

On April 29, Teledyne, Inc. announced that Albert E. Riesen, a Teledyne Wah Chang executive for 20 years, stepped down from his position as TWC president. Riesen, agreed to serve as TWC's president emeritus during the transition period. He plans to retire later this year.

"Through Al's guidance, TWC became a leader in the field of refractory and reactive metals," said Hudson B. Drake, Teledyne, Inc. senior vice president. "His 36-year-long history of achievements at Wah Chang is a record to be proud of, and we thank him for it."

Riesen joined TWC in 1960 as a research and development metallurgist. First named a vice president in 1976, he was appointed to successively more responsible positions until becoming president in 1986.

A1 Riesen led TWC for a decade

Nauman steps in as president of metals/chemicals producer

Ralph Nauman brings broad industrial management experience to Teledyne Wah Chang

On April 29, Teledyne Inc. announced that Ralph A. Nauman, an executive with broad industrial management experience, had been named to succeed A1 Riesen as president of Teledyne Wah Chang.

"Ralph Nauman brings a enviable track record of accomplishment in a wide range of highly responsible managerial assignments to Wah Chang, and we are confident the company will prosper under his leadership," said Hudson B. Drake, Teledyne, Inc. senior vice president.

Nauman comes to TWC from the presidency of Livingston, Inc., an Auburn, Washington manufacturer of composite truck parts. Before that, he was General Manager of the Aerospace Composites Division of BP Chemicals, Inc., a maker of missile launchers, engine nacelle components, and a wide variety of structural aircraft parts. In that role, he steered the company away from low margin build-to-print work to high value, technology-based proprietary products.

Previously, Nauman was director of Thiokol Corporation's work on rocket motors for the Air Force's Peacekeeper ICBM system.

Nauman received his Bachelor of Science degree in metallurgy and material science from the Massachusetts Institute of Technology. He also holds an MBA from the University of Utah.

"Teledyne Wah Chang has the technology and people to provide significant value to our customers," said Nauman. "That's why I am optimistic about our prospects going forward."

Zircadyne Zr an alternative to costly corrosion maintenance

- by Ken Bird, Chemical Engineer

Several studies place the cost of corrosion in industrialized countries at 3% to 4% of their Gross National Product (GNP). These costs are direct costs or losses. What one does not see are the indirect costs. Examples of indirect costs are: loss of production, loss of efficiency, product contamination, environmental impact, etc. For large plants running at capacity, indirect costs could amount to much higher losses than the direct cost of replacing a corroded piece of equipment. Consequently, using a more corrosion resistant, higher priced material could be a very important factor in determining whether a plant is producing profitably or not.

Zirconium is one answer to combat profit-damaging costs associated with corrosion maintenance. Zirconium is a transition element located along with sister elements titanium and hafnium in Group IVb of the periodic table. It is a grayish-white metal, with a density somewhat less than carbon steel. Zirconium is the ninth most common metallic element in the earth's crust and is more abundant than zinc, lead, nickel, or even copper.

The use of zirconium in the Chemical Processing Industries (CPI) is a direct result of the studies carried out on behalf of the nuclear industry by the United States Bureau of Mines and others in the 1940's and 1950's. These studies led to the development of specific alloys that enhanced corrosion resistance in a nuclear environment. Furthermore, upon defining the corrosion resistant properties of zirconium, researchers recognized its possible use as a containment material for the chemical industry.

Zirconium is exceptionally resistant to corrosion by many common acids and alkalis. Because of this ability to withstand corrosive attack by many industrial solutions, it has found application in major areas of the CPI. The corrosion resistance of zirconium is due to the formation of a dense, tenaciously adherent, chemically inert oxide film on the metal surface. This oxide film protects the base metal from both chemical and mechanical attack at temperatures up to about 400°C. Zirconium has a high resistance to localized forms of corrosion-pitting, crevice corrosion, and stress-corrosion cracking. It is resistant in most organic acids (e.g. formic, acetic, lactic, oxalic). Resistance in the mineral acids (e.g. hydrochloric, nitric, sulfuric, phosphoric) is exceptional as well. Very few materials exhibit resistance to strong alkalis (e.g. sodium hydroxide, potassium hydroxide, and ammonium hydroxide) as well as zirconium. Zirconium is quite unique in this regard and can be used interchangeably between acid and alkali conditions.

Comparative Corrosion Rates of Zirconium in Organic Acids

Corrosive Media	Concentration w/o	Temperature °C	Corrosion Rate mm/y
Acetic Acid	0-99.5%	RT to BP	<0.025
Acetic Acid	100%	160	<0.025
Acetic Anhydride	99%	RT to BP	<0.025
Formic Acid	0-99%	RT to BP	<0.025
Urea Reactor Mixture	---	193	<0.025

(Above) Corrosion resistance of materials to HCl. Materials in this chart exhibit a corrosion rate of less than 0.5 mm/y except for zirconium and tantalum, which have corrosion rates of less than 0.127 mm/y.

(Above) Corrosion resistance of materials to H₂SO₄. Materials in this chart exhibit a corrosion rate of less than 0.5 mm/y, except for zirconium and tantalum, which have corrosion rates of less than 0.127 mm/y.

Above: Iso corrosion curves for various metals in HNO₃.

Note: Zirconium 702 and tantalum exhibit strong corrosion resistance in a variety of conditions. The two metals are particularly well suited to high temperature nitric acid applications.

Comparative Corrosion Rates of Zirconium in Alkaline Materials

Corrosive Media	Concentration w/o	Temperature °C	Corrosion Rate mm/y
NH4OH	0-28%	RT to BP	<0.025
Ca(OH)2	0-28%	RT to BP	<0.025
KOH	0-50%	RT to BP	<0.025
NaOH	0-40%	RT to BP	<0.025

Since the early 1960's, zirconium has been used in the manufacture of urea. Carbamate reactions do not occur with zirconium. Consequently, the life of this metal is essentially unlimited in urea service. Inspection of equipment after 30 years of service has shown no appreciable corrosive attack. Zirconium has been used in acetic acid manufacturing since the early 1970's.

Monsanto (now BP Chemicals) pioneered the use of zirconium in its Texas City, Texas facility. Today, zirconium is specified for all new acetic acid facilities and for replacement of Hastelloy equipment. Acetic acid manufacturing is the number one commercial market for zirconium worldwide. Zirconium is also widely used in the manufacture of formic acid. Methyl methacrylate manufacturing has also relied on zirconium for the production of a quality product.

In the early 1970's, Rohm & Haas began using zirconium in its Deer Park, Texas facility. The company continues to specify zirconium for its process equipment that is exposed to sulfuric acid at temperatures to 130°C. Since the early 1980's, zirconium has been specified for heat exchanger use in nitric acid production facilities. Cooler/condensers, tail gas preheaters and reboilers are specific areas where zirconium offers a distinct advantage over other materials. Nitric acid is the second largest consumer of zirconium in the CPI.

Zirconium is ductile and workable; it is accepted by the ASME for unfired pressure vessels. It can be fabricated using standard shop equipment with a few modifications and special techniques.

Sheet product can be bent on conventional press brake or roll forming equipment to a 5T bend radius at room temperature and to a 3T radius at approximately 200°C. Of primary concern when heating a reactive metal like zirconium is the tendency to react with the atmospheric gases or impurities on or in contact with the metallic surface. Cleanliness is, therefore, a very important consideration. Prior to any heat treatment or welding procedure, the material must be thoroughly cleaned of all traces of lubricants or foreign matter.

Zirconium has been fabricated into all types of chemical equipment, including heat exchangers, reactor vessels, condensers, columns, pipe pumps, valves, etc. It can be clad on carbon and stainless steel backer materials using proprietary resistance welding or explosive cladding techniques.

The metal can be machined, drilled and milled by conventional methods. Three basic parameters should be used for all machining operations: slow speeds, heavy feeds, and a flood coolant. Zirconium does exhibit a marked tendency to gall and work harden. Satisfactory results, however, can be obtained with both cemented and high-speed tools. The same techniques and equipment used to cold form stainless steels can also be used on zirconium pipe and tubing. Due to work hardening behavior, spring back may be encountered and provisions for this should be made for any bending operation.

Zirconium can be welded using the same technology and techniques that are commonly used in stainless steel welding with some additional considerations. Because zirconium is more reactive than stainless steel, it demands greater attention to cleanliness and in the use of inert gas shielding. Because of its low modulus of elasticity and thermal expansion coefficient, zirconium has less distortion than stainless steel during welding.

The cost of zirconium is a point of concern for some materials specifiers. Any capital expenditure request must reveal more information than price of material for such a request to be seen favorably by those controlling the budget.

Zircadyne ^® reduces downtime

Several figures must be factored into the equation that reflect the worthiness of a project. Total cost includes the price of the operational unit under consideration plus maintenance, operating condition limitations, product quality, environmental impact, production downtime, safety, etc. All of these items can adversely affect product cost and lower profitability. In addition to profits, implementing capital projects with high returns on investment can help companies maintain their competitive edge. Like all companies, chemical processing firms must constantly be looking for ways to cut costs, reduce downtime and maintenance, ease environmental impact, and improve production and product quality. Maybe zirconium can have a role in your quest for excellence.

For more information, call TWC's Customer Service Department at 541-967-6977.

Q&A: Pre-oxidizing Zr for corrosion control

Te-Lin Yau, who heads TWC's Corrosion Lab, contributed this issue's question and answer. Dr. Yau has studied materials for use in a wide variety of CPI applications for over 16 years and is considered an expert on the subject.

Question:

Should I Pre-oxidize zirconium equipment to improve corrosion resistance?

Answer:

Zirconium is a highly reactive metal. It is normally covered with a layer of oxide film resulting from the spontaneous oxidation reaction in air or water at ambient temperatures or below. This film will form on the fresh surfaces of zirconium created by operations like cutting, machining, and pickling. It is very thin, ranging from < 100 Å to > 1000 Å, but is still more protective than most oxide films in a broad range of corrosive media. This thin film will suppress the reactivity of zirconium and grow to a steady state when zirconium equipment is ex

posed to a compatible environment.

Zirconium is one of very few metals that can take oxygen from water to form a protective oxide film even in highly reducing acids, such as hydrochloric acid. In an incompatible medium, such as hydrofluoric acid, concentrated sulfuric acid and aqua regia, zirconium equipment with a thick, pre-oxidized oxide film will still corrode. Consequently, for most chemical applications, it is unnecessary to pre-oxidize zirconium equipment just for the purpose of improving corrosion resistance.

On the other hand, up to 5µ thick film may form on zirconium equipment resulting from operations like annealing and welding. This film is protective and will not induce galvanic corrosion in its surrounding areas. There is no need to remove this film either.

However, zirconium equipment covered with a thin layer of oxide film is inadequate in preventing mechanical damages, such as galling. It would be advantageous to form a thick layer of oxide film on zirconium equipment or components for mechanically demanding conditions, such as pump shafts, nuts and bolts, and media with abrasive particles. Since it is difficult to wet zirconium with a thick oxide film, the fouling tendency may be reduced.

To get the full benefit of thick oxide films, properly preparing zirconium equipment or components before the oxidation treatment is important. Smooth, uniform and adherent film can only form on zirconium with a smooth, clean surface. Common oxide film formation methods include autoclaving in hot water (360°C for 14 days) or steam (400°C for one to three days), heating in air or oxygen (560°C for four to six hours), and immersing in molten salts (600°C to 800°C for six or more hours). Thick oxide films of high quality should be shiny, dark blue to black, with approximately 20µm in thickness. Zirconium with a rough or contaminated surface may prematurely get into the breakaway oxidation stage and form white oxide films spottily or extensively. The white oxide film is thicker than the black film and may be porous. It is only adequate for non-demanding services.

TWC producing vanadium alloy for fusion device component

Tests indicate V alloys have minimal environmental impact
General Atomics to use V-4Cr-4Ti in DIII-D divertor upgrade

Three energy sources hold the most promise for reducing the world's dependence on fossil fuels: solar energy; fission; and fusion. Solar energy and fission have already taken a step toward this end -both have been alternative methods for producing electricity for many years now (fission on a much larger scale). Fusion, which releases about four times more energy for a given mass of fuel than does fission, is still under development.

Whereas fission involves splitting heavy elements, such as uranium, to form lighter elements and release heat energy, fusion involves fusing light elements, such as hydrogen, to form heavier elements and release energy. On the sun, where fusion occurs naturally, the fuel is hydrogen.

On earth, La Jolla, California-based General Atomics (GA) is using a form of hydrogen (found in ordinary water) called deuterium to fuel its experimental fusion reactor, DIII-D. At temperatures >100,000,000°C, these gaseous elements become ionized (the electrons separate from the nuclei) and turn into what is called plasma. These high temperatures are necessary to overcome the repulsion of the positively charged nuclei.

If the plasma can be kept at these temperatures, under sufficient pressure, for a long enough time, continuous, self-sustained fusion will occur. In the sun, the intense gravitational pressure forces the nuclei together. On earth, we use strong magnetic fields, advanced heating systems, as well as advanced materials to achieve the necessary conditions to create fusion energy.

Teledyne Wah Chang (TWC) is working with GA to meet some of its critical advanced materials needs.

A superior structural material

To fully exploit its environmental attractiveness, fusion energy systems will require the use of low-activation structural materials. Accordingly, careful study has gone into the selection and testing of a number of structural materials in order to find candidate alloys with low induced radioactivity, acceptable physical and mechanical properties, as well as resistance to irradiation induced embrittlement and swelling.

Vanadium alloys are under consideration as a structural material for fusion power plants because they have minimal environmental impact in addition to exhibiting favorable material properties for design -superior to steels and other candidate materials. Over the past few years, studies by scientists at Argonne, Oak Ridge, and Pacific Northwest National Laboratories have concluded that V-4Cr-4Ti is best suited for fusion applications based on the following characteristics:

• Low long-term activation
• Low nuclear decay heat
• High heat flux capability
• High operating temperature capability
• Resistance to irradiation induced swelling and embrittlement
• Low helium and hydrogen generation rate in fusion spectrum
• Compatibility with liquid lithium

In addition to having favorable engineering properties, V-4Cr-4Ti exhibits favorable activation vs. time characteristics. Low long-term activation is a property of vanadium, chromium, and titanium. In a fusion power plant, under a high flux of energetic neutrons, radioisotopes of vanadium, chromium, and titanium are formed in the alloy. These radioisotopes have short half lives, which results in rapid radioactive decay to safe levels. Over time, V-4Cr-4Ti's activity continues to fall, while the activities of other candidate alloys tends to level off.

Control of a fusion power plant is also simplified by lower decay heating in the vanadium alloy as compared to austenitic or ferritic steels. The short decay time allows for both short- and long-term disposal, in contrast to the long-term radiation hazards associated with alloys that contain elements with longer-lived radioisotopes. Impurities that form radioisotopes with long half-lives are clearly undesirable.

Aside from its induced radioactivity advantage, this alloy also has high strength at high temperatures, excellent resistance to neutron-induced embrittlement, a low ductile-to-brittle transition temperature, and ductility that allows it to be formed into sheet, plate, and other mill product forms using standard techniques.

GA experimenting with V alloy

As fusion is increasingly examined in public forums, it is important that visible and meaningful steps be taken to develop the use of low activation materials, according to John Smith, Divertor Project Manager at GA. Accordingly, the purpose of using vanadium in DIII-D is to make such a meaningful step by (1) beginning the process of gaining materials processing "know-how" on the fabrication of full-scale vanadium alloy components as a necessary preliminary step to developing engineering design criteria and (2) demonstrating the in-service behavior of a vanadium alloy in a fusion system.

The component that GA is currently developing from vanadium, a portion of the divertor upgrade, consists of a water-cooled ring structure covered with graphite tiles, located inside the base of the device's vacuum vessel. Heat and particle flows are guided along the magnetic field and diverted away from the main plasma. This separation of the plasma to the divertor provides for improved plasma confinement and impurity control.

TWC produces largest ingot

Teledyne Wah Chang began processing the V-4Cr-4Ti for the project in September 1995. Since then, working with a team that included experts from GA as well as Argonne and Oak Ridge National Laboratories, TWC carefully processed the material.

Production involved producing two vanadium ingots, testing the material, consolidating the ingots and alloying them with high purity chromium and titanium (double vacuum melted).

(Above) The DIII-D divertor consists of a graphite tile bolted to a ring baffle structure located inside the base of the vacuum vessel. Heat and particle flows are guided along the magnetic field and diverted away from the main plasma. This separation of the plasma to the divertor provides for improved plasma confinement and impurity control.

(Above) Inside General Atomics DIII-D fusion device. The divertor section, which GA plans to upgrade using a vanadium alloy, encircles the base of the device, sandwiched between the inner and outer walls.

In March 1996, TWC finished work on a 1159-kg. V-4Cr-4Ti ingot the largest ingot of this vanadium alloy ever produced.

At the time this article was written the V-4Cr-4Ti was a few steps closer to being ready for DIII=D, having been extruded into sheet bar. The final steps in the fabrication process involve reducing and forming the material into plate and rod. GA and its subcontractors plan to build the component from the plate and rod an install the new diverter in December 1998.

"The success to date on this project demonstrates how industry (GA and TWC) and national labs can work together," said Smith. "We look forward to our continued collaboration with TWC."

References

1. D.E. Baldwin "Fusion Research at General Atomics" GA Document #084-95.

2. W.R. Johnson, J.P. Smith, and R.D. Stambaugh (General Atomics) "Production and Fabrication of Vanadium Alloys for the Radiative Divertor Program of DIII-D" GA Report GA-A22306.

3. J.R. Peterson "Progress on the Production of Vanadium Metal" Second International Conference on Fusion Reactor Materials, Chicago (1986)

4. J.P. Smith "Technology Development for Vanadium Alloys" GA Document # 048-96.

TWC produced this V-4Cr-4Ti ingot (the largest of its type ever made), which it will form into plate and rod for use in GA's DIII-D fusion experimental divertor.

Nb₃Sn wire-joining effort successful

The Houston Advanced Research Center (HARC), located in The Woodlands, Texas, has developed a very reliable Nb₃Sn superconducting joint technology for Teledyne Wah Chang. High critical current-density (high-J) modified jelly roll (MJR) multi-filamentary wires were spliced with relative ease. The research focused on increasing the use of TWC's high J_c Nb₃Sn wire in a variety of applications, particularly in high field (>600 MHz) NMR spectrometers.

For persistent mode high-field NMR magnets involving several Nb3Sn coils, joints with extremely small resistance are required to maintain an acceptable field-decay rate. For a field decay rate of 0.01 PPM, each joint in a 600 MHz NMR spectrometer should be < 10^-11 Ohms. According to Dr. Gan Liang, HARC's principal investigator, "The 10^-15 to 10^-14 Ohm resistance range of our Nb₃Sn superconducting joints developed for splicing TWC high J_c wires is three to four order of magnitude smaller than that required for persistent mode operation of a high-field NMR magnet."

The range of electric resistance of the joints is about 10^-14 Ohms for currents up to 500 Amp and less than 6x10^-14 Ohms for currents up to 1000 Amp at a background field of 300 Gauss. HARC has tested four joints with a success rate of 100%.

"The extremely low resistance of the joints and the excellent reliability]simplicity of this technology ensures the full scale application of the TWC high J_c Nb₃Sn wires to high-field NMR spectrometer magnets, which require Nb₃Sn-Nb₃Sn superconducting splicing," said Dr. Liang.

For more information on Nb₃Sn, see TWC's web site at http://www.twca.com or call us at 541-967-6977.