Above: Proof machining of a super duplex component. Most solid round bars will be converted into components by machining on a CNC lathe.

Alloys distributor looks to foster, and service, North American demand for super duplex grades

July 2019 - There are numerous reasons why manufacturers whose products must meet stringent performance requirements would consider running trials on materials they haven’t specified in the past. It is Rodney Rice’s job, as business development director for Langley Alloys, to work with manufacturers to explore the myriad ways they can qualify super duplex stainless steels for new or existing applications.

So what are super duplex stainless steels? There are the widely used standard austenitic stainless steel grades, 304 and 316, and ferritic grades 410 and 420. Super duplex grades, explains Rice, have almost a 50/50 mix of austenite and ferrite. “It’s a hybrid microstructure combining the benefits of both, namely toughness and high strength, resistance to stress corrosion cracking, excellent corrosion resistance and competitive pricing.”

There are four common grades of super duplex, one of which (Ferralium 255) was invented by Langley Alloys. Each is alloyed with chromium, molybdenum and nickel, which makes them more expensive than common stainless grades. However, they are three to four times stronger than 304 and 316 and offer at least twice the corrosion resistance, says Rice.

Langley owns a deep-hole boring machine for creating a central bore. Langley can bore a solid bar up to 10 feet long and 8 inches in diameter in about an hour. This saves money for machine shops that would have otherwise have to perform that step themselves.

Super duplex grades are suited for industrial applications in highly corrosive conditions: oil and gas exploration and handling; mining; chemical processing; pulp and paper manufacturing; flue gas desulfurization; marine equipment, particularly in seawater; water treatment of any kind, including contaminated water; acids; and mixing rough and abrasive substances.

The ability to withstand high loads, abrasive substances and corrosive substances is vital. “Super duplex grades are robust,” says Rice.

Super duplex makes up less than 5 percent of total stainless steel consumption. “It’s a specialist product. It’s not widely used in more general applications, like cutlery, sinks, automotive exhausts or construction.”

European manufacturers seem more likely to specify super duplex than North American companies are. “We are therefore keen to speak with U.S. customers to understand how these alloys might be considered for their applications. We regularly visit and speak with OEMs, and we are aware of applications where they could be making better use of super duplex in place of more expensive stainless steel or nickel alloys. An increasing demand for their products would certainly help to justify any development work needed to support that switch.”

Metamorphosis

Langley Alloys was founded in 1938 in the United Kingdom as a foundry for copper alloys used in naval and aerospace applications. Many years later, the company divested its forge and rolling mill and became a focused stockist.

The company entered the U.S. market directly about 10 years ago by purchasing a customer that distributed Langley’s products and had previously worked with its longstanding patented products when they were produced by Haynes International under license. The company specializes in super duplex plate at its Vancouver, Washington, service center, which offers waterjet cutting of shaped components.

Five years ago, Langley opened a Houston warehouse in order to service sizable customers based in the UK and Singapore. Langley supplies oilfield services equipment builders such as Baker Hughes, Weatherford International, National Oilwell Varco (NOV) and Schlumberger Ltd., both directly and indirectly, in the United States, Europe and Southeast Asia.

“Our company is tightly focused on super duplex. We aim to excel in this specialist market rather than be another general stockist,” says Rice. Because it’s a small niche, U.S. production of super duplex is limited so Langley Alloys imports from European mills.

Pre-bored billets await dispatch to Langley Alloys’ customers.

Conversion efforts

“I see a lot of products manufactured in regular stainless grades, and then in nickel alloys, but we think there are more opportunities to convert products and customers to super duplex. We work to make them aware of sizes, grades and applications, how to machine and weld it to be used successfully,” Rice says.

In Vancouver and Houston, Langley stocks solid round bar, from 1⁄2-inch to 18-inch diameters. “In between, we have 30 to 40 increments in that range. If our customer is machining a component, there may be a 10 to 15 percent difference in material cost for each 1⁄4 inch used. So we carry a lot of incremental sizes to make sure it is as cost effective as possible. For bar, it is about offering the closest diameter you can machine the finished component from.”

Langley carries many sizes of bar and plate and “a significant volume in each size,” Rice says. “If someone needs X thousands of pounds, we have it available on the floor.”

Langley Alloys has the expertise that is required to advise customers, according to Rice. “We developed a lot of know-how over the years. Our metallurgists are helping customers directly. Even our chairman is a metallurgist.”

Process trends

As customers become busier, Langley has noticed an increased interest in near net shape products that reduce the amount of machining that manufacturers must perform. “We can offer different solutions depending upon the alloy and item size, including hollow bars (in a wide range of external diameter/internal diameter combinations) or bored bars,” Rice says. “As well as saving time, these approaches can save cost and reduce supply chain complexity.”

If the final part has a large hole through the middle, processors will take some time to perform this initial machining step on their lathe. This is particularly true for super duplex grades, which are more challenging to machine. So instead of using solid bar, starting with a hollow bar can save a substantial amount of both time and money.

The problem with hollow bar, however, is that a distributor would have to stock 100-plus sizes in each alloy to serve the market’s requirements, according to Rice. So how do you find a cost-effective way to create a hole? Increasingly, the method is to use a deep-hole borer or drilling machine. “Rather than our customers drilling the hole on individual components, we can use a deep-hole borer to quickly and effectively generate it on a much longer bar in a fraction of the time.”

Langley installed a 40-foot-long boring machine recently. “We use a larger, more powerful machine than our customers have to pre-bore that bar,” so some have begun to turn to Langley to perform “the simple stuff like pre-boring,” he says.

“The tolerance requirement for bored bars is such that the machine has to be big and heavy in order to achieve a straight bore. Otherwise, the other end of the bar would just be junk,” Rice says. It is one thing to bore through carbon or standard stainless but the strength of super duplex grades makes them more difficult to work. “For those used to processing grade 316, super duplex would take several times longer. We see the same issues with our saws,” he adds. “These grades are difficult to cut and machine quickly. We understand how to do that properly, with the correct equipment, blades and tooling.”

Form fitting

Langley has observed another longer-term trend in certain market segments. Select clients are now more likely to specify forgings or machine components from larger diameter forged bars in place of castings, says Rice.

“For smaller production runs or part sizes, casting may not be so attractive anyway, but the improvement in CNC machining centers and the greater consistency of forged components helps to limit any impact of rejections upon the delivery date.”

In response to this trend, Langley has increased its stock range of super duplex alloys from 12- to 14-inch diameters up to 18 inches.

Customers are making the switch because they cannot be certain about the consistency of castings until they start machining the material. And if there is a problem, “you have to reorder the casting, which may take weeks or months. So, although it may be more expensive to machine from a solid bar, it can be quicker, and some customers prefer this route to reduce the risk of rejections or delays,” Rice explains.

“Our stock of super duplex grades combined with the capability of modern CNC machining centers makes this an attractive option.” MM