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The brief survey of steels and nickel base alloys that we just plowed through covers the lion's share of materials that we use in our equipment. There are, however, many other types of metals not included in these two alloy families that are used for special applications. In this section we'll give a quick look at some of these specialized metals that tonnage-wise make only a minuscule part of our products, but without which many of our products could not be made.

1. Elgiloy® (UNS R30003) - 39.0-41.0% Co, 19.0-21.0% Cr, 15.0-16.0% Ni, 1.0% max. Be, 0.15% max. C, 1.5-2.5% Mn, 6.0-8.0% Mo, Balance Fe

Elgiloy® is a cobalt base alloy that is strengthened by a combination of cold work and precipitation hardening. It is frequently specified as a spring material in the Oil Patch because it is corrosion resistant and is capable of developing extremely high strength levels. It is typically annealed around 2150(F and then cold worked until roughly a 50% reduction in area is obtained. If it is going to be used for a spring, it is next coiled, stamped, or otherwise fabricated. Next comes the aging process at about 850-950(F to develop the desired strength. NACE MR0175 allows the use of Elgiloy® springs up to 60 HRC in the cold worked and age hardened condition. Small diameter spring wire can easily have yield strengths over 225 ksi. NACE also allows the use of Elgiloy® bar in any condition up to 35 HRC.

2. MP35N® (UNS R30035) - 0.025% max. C, 19.0-21.0% Cr, 1.00% max. Fe, 0.15% max. Mn, 9.00-10.50% Mo, 33.0-37.00% Ni, 0.15% max. Si, 1.00% max. Ti, Balance Co

Like Elgiloy®, MP35N® finds its greatest use as spring material. It is also used for high strength bolting, tie-down screws, and the like. MP35N® can attain yield strengths over 200 ksi in small diameter wire that has been cold worked and aged. NACE permits MP35N® springs to have a hardness up to 55 HRC in the cold worked and aged

condition. NACE allows the use of MP35N® for other components in sour service at a maximum hardness of 51 HRC and in one of the following cold worked and aged conditions.

B. Aged at 1350(F for at least 4 hours C. Aged at 1425(F for at least 6 hours D. Aged at 1450(F for at least 4 hours E. Aged at 1475(F for at least 2 hours F. Aged at 1500(F for at least 1 hour

MP35N's® high nickel, cobalt, chromium, and molybdenum contents gives it outstanding corrosion resistance. MP35N® and Elgiloy® can usually be substituted for another: an important point to remember because the availability of either one of them in a given product form is often limited. MP35N® springs are generally limited to applications that see temperatures below 400(F because of embrittlement problems at higher temperatures.

3. Titanium Alloys - Titanium alloys are becoming more and more common in the Oil Patch because of their high strength, low weight, and excellent corrosion resistance. Titanium has a hexagonal close packed (HCP) structure (see Figure 1) at room temperature, but

transforms into body centered cubic at 1625(F. Titanium alloys may be divided into alpha, beta, and alpha-beta groups. Alpha alloys have a HCP structure that has been stabilized by tin, aluminum, zirconium, or a combination of any of the three. Oxygen, nitrogen, and carbon also help to stabilize the alpha structure (note the alpha structure in titanium is HCP not BCC as in steels). Beta alloys have a body centered cubic structure (BCC) that has been stabilized with cobalt, columbium, vanadium, iron, manganese, chromium as well as some of the other transition elements. A combination of alpha and beta

stabilizing elements are used in the alpha-beta alloys where both phases may be present.

Alpha alloys cannot be hardened by heat treatment. Their stable alpha structure makes them easy to weld in comparison to the other types. They have excellent corrosion resistance and find frequent use in the chemical industry because of it. Alpha alloys are typically used in the annealed condition. Yield strengths are typically 100 ksi and above. Alpha-beta alloys are precipitation hardenable. They are typically solution annealed high in the alpha-beta region. Depending on a variety of factors, the beta phase that was present during solutionizing will either be retained or undergo a martensite type of transformation after quenching. Aging is typically done somewhere between 900- 1200(F. During aging a fine precipitate of alpha comes out of solution within the retained or transformed beta phase. The final microstructure is typically a mixture of primary alpha (untransformed alpha) and a fine

Figure 1: Hexagonal Close

Packed (HCP)

mixture of alpha precipitates within the beta phase. Aging can increase the strength by 50% over the annealed condition. The more beta stabilizers in the alloy, the greater the hardenability. Alpha-beta alloys are the most widely used titanium alloys.

Beta alloys are heat treatable and have much better hardenability than the alpha-beta alloys. Beta alloys are typically aged from 850-1200(F. Aging causes a partial decomposition of the beta phase into alpha. The alpha precipitates out as finely dispersed particles within the retained beta and thus greatly strengthens the material. Cold work or holding at a slightly elevated temperature may result in the formation of additional alpha.

Let's look at a couple of titanium alloys that are used in the Oil Patch. A. Titanium, Grade 12 (UNS R53400) - 0.08% max. C, 0.30% max.

Fe, 0.015% max. H, 0.2-0.4% Mo, 0.03% max. N, 0.6-0.9% Ni, 0.25% max. O, Balance Ti

This commercially pure titanium is not hardenable through heat treatment. It is often used for ring gaskets in highly corrosive environments because of its outstanding corrosion resistance and its relatively low hardness. NACE allows its use in sour

environments when annealed at 1400-1450(F for two hours followed by air cooling and at a maximum hardness of 92 HRB. B. Beta-C® (UNS R586401) - 0.05% max. C, 0.03% max. N, 0.03%

Fe, 0.14% max. O, 3.0-4.0% Al, 7.5-8.5% V, 5.5-6.5% Cr, 3.5-4.5% Mo, 3.5-4.5% Zr, Balance Ti

This heat treatable beta-alloy is finding increasing use in the Oil Patch for highly stressed parts in corrosive environments. It is often

companies are specifying Beta-C® tubulars. Beta-C® is solution annealed at 1500-1700(F. Aging is done at 850-1000(F. Yield strengths over 170 ksi are obtainable in bar that has been aged. Spring wire may have yield strengths in excess of 200 ksi in the cold drawn and aged condition. NACE allows the use of Beta-C® at hardnesses up to 42 HRC. It is used in the annealed or the solution annealed and aged conditions.

C. Ti-6Al-2Sn-4Zr-6Mo (UNS R56260) - 0.04% max. C, 0.04% max. N, 0.15% max. Fe, 0.15% max. O, 5.5-6.5% Al, 1.75-2.25% Sn, 3.5-4.5% Zr, 5.5-6.5% Mo, 0.0125% max. H, Balance Ti

This alpha-beta alloy is capable of being strengthened though heat treatment. It is solution annealed at 1550-1650(F and aged around 1100(F. Yield strengths over 150 ksi can be obtained in bar. NACE allows its use in sour service at 45 HRC maximum in one of the following conditions:

A. annealed

B. solution annealed

C. solution annealed and aged

It is sometimes used for gaskets in the annealed condition and load rings, etc. in the aged.

4. Cemented Tungsten Carbides - A cemented tungsten carbide is a composite material consisting of hard, brittle tungsten carbide (WC) particles in a soft, ductile metal matrix. Cobalt is the binder most commonly used to "cement" the tungsten carbide particles together and is the binder for all of our cemented tungsten carbides. We use cemented tungsten carbides for choke needle tips and seats because of the outstanding erosion and wear resistance afforded by the

tungsten carbide particles. As with all composite materials, the overall properties of cemented tungsten carbides are very dependent on the properties and relative amounts of matrix element (cobalt) and the reinforcing element (tungsten carbide). The higher the tungsten carbide content, the higher the hardness, compressive strength, and abrasion resistance of the overall composite. A price is paid, however, in lower transverse strength and toughness. As the percentage of soft, ductile cobalt binder is increased, the opposite is true. Small amounts of tantalum and titanium carbides may be added to refine the grain size thus increasing the toughness. The cemented tungsten carbides are fabricated into shapes through a powder metallurgy process (see the chapter on Forging, Casting, and Powder Metallurgy).

We use several different grades of cemented tungsten carbide in our products including 94% WC-6% Co and 87% WC-13% Co. Hardness of the 94% WC-6% Co grade is typically about 92 HRA while that of

the 87% WC-13% Co is about 89 HRA. The cemented tungsten carbide is brazed into choke bean or onto the end of the needle. NACE allows the use of these alloys at any hardness.

5. Stellites® 3 and 4 - Stellites® are cobalt based alloys used for their high wear and galling resistance. We use Stellite® 3 and Stellite® 4 for seat rings in gate valves. In addition to cobalt, both of these alloys contain approximately 30% Cr, 11-14% W, and small amounts of Si, Fe, Ni, and Mo. The big difference is in carbon content. Stellite® 4 contains up to 1% C while the Stellite® 3 may contain up to 2.7% C. The carbon combines with the chromium to form M C type carbides_{7 3} and with the tungsten to form M C-type carbides. It is these carbides6

that give the Stellites® their outstanding wear resistance. The higher carbon content of Stellite® 3 gives it a higher hardness and better wear resistance than the Stellite® 4. Stellite® 4, on the other hand, has better corrosion resistance. Our Stellite® seat rings are made from centrifugal castings (see the chapter on Forging, Casting, and Powder Metallurgy). The only heat treatment they undergo is a stress relief at 1650(F followed by furnace cooling. The stress relieved Rockwell C hardness of Stellite® 3 is typically in the mid to high fifties while that of the Stellite® 4 is in the high forties to low fifties.

6. Tribaloy® T-800 - This is another cobalt based wear-resistant alloy. It has a nominal composition of 3.0% max. Ni and Fe, 28.5% Mo, 17.5% Cr, 3.4% Si, 0.08% max. C, with the balance being cobalt. Instead of relying on hard carbides, this alloy gets its wear resistance from the formation of a hard, intermetallic (Laves) phase that is dispersed throughout a softer matrix. We use this alloy as a hardfacing for gates in gate valves. It is applied by either plasma transferred arc spray (see the chapter on Special Processes) or through HIP’ing powder directing to the gate (see the chapter on Forging, Casting, and Powder

Metallurgy). The overall hardness of the alloy is 54-62 HRC.

7. Union Carbide LW-45® - This is a hard facing coating that we use on gate valve gates. Its nominal composition is 78% W, 12% Co, 5% Cr, and 4% C. It gets its wear resistance from various carbides (such as tungsten carbide, M C) that are dispersed throughout a cobalt-6

chromium matrix. LW-45® is applied using the Union Carbide D-Gun Process®. We will discuss this in detail in the chapter on Special Processes. The bonding of the LW-45® coating to the base metal is through the mechanical interlocking of the particles with the substrate. 8. Colmonoy® #5 - This is a hard facing material that we use to provide

wear resistance on gates, stab pins, and BOP operating pistons. It is nickel based with approximately 10-14% Cr, 2-3% B, 3-4.5% Si, 3-5% Fe, 0.4-0.8% C, and 0.25% maximum Co. It can be applied by several different methods, but we typically use an oxy-acetylene weld process

method, the hardfaced part must undergo a full heat treatment. This causes the hardfacing particles to fuse together and to the base metal thus forming a true metallurgical bond. Colmonoy® #5 has a hardness of 45-50 HRC.

9. Ultimet® (UNS R31233) -Nominal composition 9% Ni, 3% Fe, 26% Cr, 5% Mo, 2% W, 0.06% C, 0.08% N, 0.3% Si, 0.8% Mn, Balance Co.

Ultimet® is a cobalt base alloy that has excellent corrosion resistance and excellent galling resistance. We use it for parts that must come into

moving contact with nickel base alloys (that are exceptionally prone to galling). It can also be used as a weld overlay. Ultimet® is nonheat treatable, but can be cold worked to high strength levels. In the annealed condition it has a yield strength of about 75 ksi. NACE allows its use in sour service in the annealed condition at 22 HRC maximum.

10. Unobtainium (UNS XXXXXX) - This remarkable alloy has half the specific gravity of steel, is immune to environmental cracking and general corrosion, is easily welded, and is capable of developing a high yield strength while maintaining excellent notch toughness down to cryogenic temperatures. It is easy to cast, forge, and machine. It can be used in sour service at any hardness. Galling has never been known to occur. It is not subject to any form of embrittlement. Post weld heat treating is not required. Bars up to 36" O.D. through harden. Chemistry varies. It is made by mills world-wide and costs only pennies per pound. This material is frequently specified by our larger customers.