Ellett goes to great lengths in building Monsanto equipment

In 1921 when master coppersmith Sydney J. Ellett opened a small shop to fabricate kettles for hotel kitchens, he probably never dreamed that his company would one day be building sophisticated heat exchangers out of space-age metals like titanium and zirconium for processing plants around the world. To put things in perspective, the company used tools like hand shears and soldering irons to make its first products.

Twenty years and a few facility upgrades later, the bigger picture started to come into focus as Ellett and Company began designing and fabricating heat exchangers for pulp and paper and chemical applications --a hint of things to come.

Flash forward to 1997. Today Ellett's grandson, John Ellett, runs a growing company that fabricates a variety of equipment (including very large heat exchangers) for a variety of industries, using materials ranging from stainless steels to titanium to one of the ultimates in corrosion resistant materials, Zircadyne® zirconium. Some of these units are indeed bigger and more complex than Sydney J. Ellett could have ever imagined.

Ellett Industries Ltd. was chosen to fabricate such a heat exchanger for Monsanto's nitric acid plant in Gonzalez, Florida. Monsanto chose Ellett as its fabricator based on the company's long history and proven track record building equipment for nitric acid applications.

Ellett personnel carefully fit the zirconium-stainless steel tubesheet onto the shell

Monsanto decided on zirconium based on the metal's success record at a similar plant, First Mississippi Chemical, which specified it for a heat exchanger over 12 years ago. Engineers from Monsanto first considered zirconium after reading an article about installation of the First Mississippi unit in this publication (Outlook, Vol.6, No.4) and later, were convinced that the metal was their answer after hearing that it had performed well in this severe service for many years.

Materials Engineer William W. Paden says that Monsanto is anxiously awaiting delivery of the heat exchanger, looking forward to, as he puts it, "fewer headaches and more production." "We're anticipating a 20-year life for the equipment," he said. "With our previous equipment, the best we could hope for was six years."

A Very Big Job

According to David Clift, Manager of Production and Engineering at Ellett, the Monsanto heat exchanger weighs 28 tons, is 29 feet long (T.S to T.S), 5 feet 5 inches in diameter and contains 1,965 Zircadyne^® zirconium tubes. Ellett has a wide range of equipment and facilities that enable it to fabricate units such as this in-house.

Successful manufacture of a zirconium tubed heat exchanger requires establishment of direct lines of communication between the end user, designer, builder, and material suppliers, according to Clift. "Specifications are very demanding. Considerable attention to detail is required when dealing with a product that is expected to last 20 years," said Clift. "Skill and communication are the keys to ensuring on-time delivery of conforming components."

The Monsanto project consisted of four phases: Design; Materials Procurement; Fabrication; and Assembly. After the initial design of the heat exchanger was complete and materials were checked to ensure that they met specifications, Ellett ordered 1,965 Zircadyne zirconium tubes from Wah Chang and tubesheets (clad zirconium on stainless steel) from an explosive fabricator. Ellett rolled and welded the carbon steel shell in-house, then radiography inspected, sandblasted and painted the shell before moving it to the company's clean room.

Working on a fast-track schedule, stainless steel baffles were cut, drilled, and deburred. When the 5-in. thick clad tubesheets arrived, Ellett drilled, reamed, and ring grooved the tube holes. "TEMA" special close fit hole tolerances were maintained.

In the assembly phase, personnel thoroughly cleaned all of the components. Tubesheets and baffles were first power steam cleaned then chemically cleaned to ensure that contaminants were not present. The tubesheet was then fit onto the shell and the baffle skeleton assembled in the shell.

The zirconium tubes were chemically cleaned as they were inserted into the shell and baffle assembly. (All items have to be absolutely clean to ensure 100% defect-free tube-to-tubesheet welds.) All zirconium welds were subjected to dye penetrant and helium leak testing.

Throughout the fabrication process, Ellett performed visual and nondestructive testing inspection of the heat exchanger to ensure quality of fabrication and compliance with Monsanto specifications.

For more information, call Ellett Industries Ltd. at 604-941-8211.

Wah Chang supplied Ellett with 1,965 Zr-702 tubes for the heat exchanger

This heat exchanger, built by Ellett for Monsanto, is 29ft. long and 5 ft., 5 in. diam.

Q&A: zirconium in nitric acid

Dr. Te-Lin Yau, Wah Chang's Chief Corrosion Engineer, contributed the following questions and answers discussing the pros and cons of using stainless steels and zirconium in nitric acid service.

Question:

How does zirconium compare to stainless steels in nitric acid service?

Answer:

The addition of chromium dramatically improves the corrosion resistance of iron in nitric acid. Iron corrodes in boiling 65% nitric acid at a rate exceeding 10,000 mm/yr for example. Under the same conditions, corrosion rates for iron with 4.5, 8.0, 17.0, 18.0, and 25.0% chromium are 4,000, 40, 3.0, 0.8, and 0.2 mm/y, respectively. High-chromium iron, 15% Cr, would be useful in nitric acid. The addition of nickel further improves the corrosion resistance; for example, the corrosion rate of the iron-18% Cr-8% Ni alloy in boiling 65% acid is about 0.3 mm/y.

Consequently, stainless steels have established themselves as the workhorse of nitric acid plants for decades. They will continue to be dominant, suitable structural materials for various nitric acid services. However, these alloys have several limitations:

1. Certain types of stainless steels are highly susceptible to sensitization resulting from heating at 650 to 675°C or welding. In fact, boiling 65% nitric acid is powerful in detecting tile sensitization of stainless steels.

2. Most stainless steels, except certain high-chromium types, are only adequate in hot nitric acid. Their corrosion rates in boiling 65% acid exceed 0.13 mm/y.

Even at 0.13 mm/y, each day for every 1000m², about 2.5 kg of metal will be dissolved from the equipment. This level of corrosion would be too high for applications that emphasize product purity and environmental protection.

3. Above the boiling curve of nitric acid, all stainless steels corrode at increasingly rapid rates with increasing temperatures. Stainless steels rely on chromium for their corrosion resistance in nitric acid. Even chromium is not corrosion resistant in nitric acid at elevated temperature. Stainless equipment gives nitric acid producers little room to push the envelope of operating conditions, possibly costing them improved efficiency and productivity.

4. The corrosion resistance of stainless steels decreases in nitric acid when impurities like Cr⁶⁺, Cr³⁺, and Fe³⁺ are also present. That is, stainless steels could autocatalytically corrode in nitric acid.

Zirconium's corrosion resistance to nitric acid is outstanding. In certain conditions, zirconium is even more resistant than the noble metals to the acid. Zirconium's temperature limit is somewhat higher than that of noble metals. Traces of chloride may lead to rapid attack on noble metals, but not on zirconium.

The excellent corrosion resistance of zirconium in nitric acid has been recognized for more than 30 years. Below the boiling point and in 98% nitric acid, and up to 250°C and in 70% nitric acid, a typical corrosion rate for zirconium is less than 0.025 mm/y. Zirconium's corrosion rates are still less than 0.025 mm/y in boiling nitric acid containing dissolved 1% ferric chloride, 1% sodium chloride, 1% seawater, 1% iron, or 1.45% type 304 stainless steel. The presence of heavy-metal ions and chlorides has little effect on the corrosion resistance of zirconium in nitric acid. Normally, zirconium is susceptible to localized corrosion in oxidizing chloride solutions; however, the nitrate ion is an effective inhibitor for the localized corrosion of zirconium in chloride-containing solutions.

Commercially pure zirconium (UNS R60702 or Zr702) is the predominant grade for nitric acid service. It has a much simpler structure than stainless steels. There is little concern for detrimental effects, such as aging embrittlement and sensitization, resulting from heating and welding. Contamination is the major concern in zirconium welding.

Test results show that various products of Zr702, such as plate, sheet, pipe, tube, wire, welds, and forgings, have similar corrosion resistance in nitric acid. The graph below compares Zr with many stainless steels in 65% nitric acid at temperatures above the atmospheric boiling point.

Zirconium is very corrosion resistant in 65% HNO₃ above the boiling point

Q&A: zirconium cost effective

Question:

What are the concerns in applying zirconium for nitric acid service?

Answer:

Zirconium is not totally worry-free for nitric acid service. Like all passive metals and alloys, zirconium exhibits passive-to-transpassive behavior in nitric acid; however, because of its high affinity for oxygen, zirconium does not have an active region in most acids, including nitric acid. Consequently, zirconium has a very noble corrosion potential in nitric acid because of the oxidizing nature of the acid. The corrosion potential and the transpassive potential move toward each other as the acid concentration increases.

Eventually, under the influence of stress, a critical balance among dissolution rate, film breakdown rate, and film repassivation rate can lead to stress corrosion cracking (SCC). Using the powerful slow strain-rate technique, this SCC susceptibility can be detected even in dilute nitric acid solutions. However, under most conditions, when zirconium has a little time to repair mechanical damage, the concern for SCC is not great until the acid strength exceeds 70%. To prevent SCC, cleaned zirconium equipment can be stress-relieved in air at 500°C for 30 min.

Other concerns include the accumulation of chlorine gas, the formation of strong sulfuric acid resulting from sulfur in feedstocks, and the presence of fluorides in the acid. Chlorine gas may be generated by the oxidation of chlorides in nitric acid. Zirconium is susceptible to pitting in wet chlorine unless it has a cleaned surface. The formation of strong sulfuric acid should be avoided by modifying equipment or process conditions. The corrosion of zirconium in fluoride-containing acids can be controlled by adding an inhibitor, such as zirconium sponge and its compounds.

Question:

Isn't zirconium too expensive?

Answer:

Materials specifiers often bypass zirconium because of its persistent exotic image. They do not consider zirconium as an affordable material. Certainly zirconium was exotic many years ago.

In the 1940s, groups of scientists and engineers were investigating zirconium and other metals for nuclear applications. In 1945, only a few hundred kilograms of zirconium were produced in the U.S. The cost of zirconium was more than $650 U.S./ kg! Today, the price of zirconium is much lower. Zirconium is no longer exotic and is competitive with other corrosion resistant materials.

For example, compare a zirconium cooler condenser to a type 304L cooler condenser. There is no question that the material cost of zirconium is higher than that of type 304L. According to the unit weight prices, the difference can be around 10 times. It should be noted that there is a premium for the nitric acid grade 304L. The difference in price is considerably smaller when zirconium is compared to a highly alloyed stainless steel; however, zirconium is about 20% lighter than type 304L. After adding the fabrication costs for similar cooler condensers, the cost difference between zirconium and stainless alloys can be cut in half (i.e. zirconium is about 5 times more expensive initially). In addition, for the same job, a zirconium unit would be much more compact than a stainless unit.

Without having to factor in a corrosion allowance, a typical zirconium cooler condenser uses zirconium tubes of 19 mm diameter by 1.25 mm wall thickness; with zirconium-clad carbon steel tubesheets and a carbon steel shell. For a low-pressure system, fabricators sometimes use tubes of 0.90 mm wall thickness.

For a stainless cooler condenser, the acid can be condensed on the tube side or the shell side. When the acid is condensed on the tube side, the shell can be carbon steel with stainless tubesheets. However, when the acid is condensed on the shell side, the whole unit needs to be stainless. Either way, to add corrosion allowance is mandatory for a stainless unit. The wall thickness of stainless tubes has to be 1.90 mm or more. Since type 304L is about 35% poorer than zirconium in thermal conductivity, the stainless unit needs more tubes too. Consequently, a zirconium unit may cost less than twice that of a 304L unit.

Today, it is essential to consider all costs, which include materials, fabrication, installation, energy, maintenance, repair, downtime, replacement, and fines. When all costs are considered, it often makes sense to have a zirconium unit.

For questions concerning this article, contact Dr. Te-Lin Yau by phone at 541-917-6777, by fax at 541-967-6989, or by e-mail at tyau@twca.com. For information on ordering zirconium for chemical processing applications, contact Wah Chang by phone at 541-967-6977 or by fax at 541-967-6994.

Register now for Zr in Organics Conference!

Wah Chang is pleased to announce that it will host an International Conference on the Use of Zirconium in Organic Environments. The event will take place September 8-10, 1997 at the Salishan Resort in Gleneden Beach, Oregon.

The 2 1/2-day conference will bring together chemical producers, equipment designers, and fabricators to address all issues concerning the use of zirconium in organic environments. Although the conference focuses on organics, inorganic chemicals will be covered as well since they are present in many organic environments.

These are just a few of the many scheduled papers:

•The use of zirconium and titanium for flow instruments in the process industry under special considerations or organic environments
•Issues around the use of zirconium in MMA production
•Design and fabrication details for zirconium pressure vessel equipment
•Issues around the use of zirconium in alcohols production
•Characterization of zirconium and titanium by metallography
•Efficiency improvement of distillation columns
•Influence old, welding and heat treatment on the corrosion behavior of zirconium
•Managing a zirconium project: How to succeed
•Surface finish improvement of zirconium in organic solutions

Join us at the Salishan Resort this fall

Registration is $395 per person if paid prior to June 1 and $495 per person thereafter. For more information on the "International Conference on the Use of Zirconium in Organic Environments, contact Wah Chang at 541-926-4211 ext: 6280.

Conference Information

Location:

Salishan Lodge
Gleneden Beach, Oregon 1-800-452-2300
(90 miles southwest of Portland International Airport)

Receptions:
Sunday, September 7, 1997 7PM-9PM
Monday, September 8, 1997 6:30PM-10:00PM (banquet etc.)

Luncheons:
Monday, September 8, 1997 12PM- 1 PM
Tuesday, September 9, 1997 12:45PM-1:45PM

Exhibitor Information

A limited number of booth spaces/ event sponsorships at $500 per company were still available at the time this Outlook was printed. If you would like to participate, contact Mr. Doug Brenizer as soon as possible at 541-967-6906.

Wah Chang/friends to co-host Nitric Acid Show events

Wah Chang, Allegheny Ludlum, and some of the world's best fabricators and suppliers to the Chemical Processing Industry will co-host two lunches and two hospitality suites at the Nitric Acid Producers Meeting, May 19-21, in Biloxi, MS.

Wah Chang and friends are sponsoring two conference lunches, which are tentatively scheduled for noon Tuesday, May 20 and Wednesday, May 21.

Hospitality suites will take place from 5-7:30 PM in Grand Ballrooms B and C. These events will include food and beverages, and a prize drawing every half-hour. In addition, the events will culminate in a truly grand prize drawing on Tuesday, May 20 at 7:15 PM. As in the past, exhibitors will be available to answer materials and equipment questions at all events.

We look forward to seeing you in Biloxi!

Welding Seminar

Wah Chang's fifteenth annual welding seminar will take place this summer, July 15-17, in Albany, OR. Sessions will include classroom and hands-on instruction in welding a variety of reactive and refractory metals and alloys. Classes familiarize TWC's customers with welding and repair techniques for equipment used in the Chemical Processing and other industries. Past seminars have focused on zirconium and titanium alloys. For additional information or to register, please call (541) 967-6924 or (541) 967-6977. Registrants must be experienced in stainless steel or titanium welding. Space is limited, so register soon.

Developments in the CPI

Industrial Alloy Fabricators celebrates 25th

Industrial Alloy Fabricators, Inc. OAF) is celebrating its 25th Anniversary. The Forest Grove, Oregon-based company fabricates equipment for the chemical, petrochemical, food processing, power, mining, pulp & paper, and nuclear industries.

IAF provides custom design and fabrication of heat exchangers (National Board Registration #2000 is shown in picture below), pressure vessels, tanks, pipes, and fittings.

According to José 0livas, VP Sales, "We have an extensive list of equipment fabricated from a wide range of corrosion resistant alloys. Customers have come to rely on IAF's expertise with stainless steel, nickel alloys, titanium and zirconium for their demanding applications. This is accomplished by a team with unmatched dedication to service."

For more information on IAF, call 503-359-0793 (fax: 503-359-9292).

Service Center adds metallurgical engineer to staff

Wah Chang is pleased to announce that Jack Tosdale has joined its Service Center as a CPI Applications Engineer. Tosdale will handle technical service and will be involved in marketing and inside sales in his new position, according to Parry Walborn, who manages Wah Chang's Chemical and Mineral Processing Industries businesses. "In his role as the company's technical services contact, Tosdale will be available to answer customers' technical questions," Walborn said. "He will also be looking for chemical processing applications where Zr may be the answer."

Tosdale is well qualified for this critical position, with 31 years' experience working with refractory metals and ceramics. Since 1979, he has held the positions of Process Control Manager, Process Analysis Manager, Government Sales Representative, and Principal Engineer. Before coming to Wah Chang, he worked in a variety of engineering and quality engineering positions.

Tosdale is currently Chairman of ASTM's B10.02 Committee on zirconium/hafnium and is a member of the titanium and niobium/tantalum committees. He is also a member of the American Society of Metals.