Power Plant Material Insights

				Power Plant Material Insights No. 1 June, 2011

Coal

Ambitious materials development program outlined by Phillips of EPRI at McIlvaine webinar

Jeffrey Phillips, a Senior Program Manager at the Electric Power Research Institute (EPRI), provided an overview of the U.S. Dept. of Energy's and Ohio Coal Development Office's Advanced Ultrasupercritical Boiler ( A-USC) and Steam Turbine Materials Development Program in a recent McIlvaine hot topic webinar . This is a $50 million, 9-year effort aimed at increasing steam temperatures by more than 250°F above the current state-of-the-art. This remarkable effort has now resulted in a code case submission to the ASME Boiler Code committee for a new material which can operate at the targeted conditions. Approval of this material will open the door to the most significant improvement in the thermodynamic performance of coal-fired power plants in 50 years.

The focus on the materials technology portion of the program is nickel based alloys and the development of fabrication and joining technology for the new alloys. Unique considerations are higher temperatures than the European program (760C vs. 700 C), corrosion resistance for U.S. codes, data for ASME code acceptance of new materials, and the inclusion of oxycombustion.

Successes so far include welding technology improvements. Original Inconel 740 Welds showed liquation cracking heat affected zones. Today repeatable 3” (75 mm) think Inconel 740 welds resist cracking under the A- USC conditions.

Alloy 740 allows reasonable thickness while meeting stress requirements for 750 C and 380 bar

Doosan Babcock is active in advancing the ultrasupercritical designs. In a power point presentation in 2009, David Smith made a good comparison showing the advantages of alloy 740. He compared 48 mm tubing operating at 700 C with a design pressure of 380 bar.

Alloy 740 can be welded with gas tungsten or pulsed gas metal arc welding

Inconel alloy 740 was originally found to be susceptible to heat affected zone microfissuring in sections greater than 1 inch in thickness. Now according to J.M Sanders and J.A Siefert of B&W the microfissuring can be eliminated through modification of the base and weld filler metal chemistries. B&W has found that gas tungsten arc welding and pulsed gas metal arc welding are the two most favorable processes. The full paper is found on the B&W website http://www.babcock.com/library/pdf/BR-1827.pdf

Industeel has joined Cresta to develop a lower cost heat resistant steel for USC

There is a strong incentive to reduce investment costs of the "700°C" power plant. One way to achieve this is to develop heat resistant steels capable of operating at higher steam conditions than 300 bar and 600-650°C, which could replace part of the expensive Nickel alloys.

A consortium has been formed to pursue Project Cresta (Creep Resistant Stable). CRMC the research arm of Industeel, Alstom, Dong Energy and others are part of the consortium.

Based on the knowledge about microstructure stability a new alloy and a weld consumable will be designed to produce a compromise between high creep strength (between T91 and T92), high oxidation/corrosion resistance and good weldability. The alloy development should be based on a new concept of alloy design and tools based on thermodynamic and kinetic modeling. The possible application in welded water wall tube-fin constructions without the Post Weld Heat Treatment (PWHT), as well as, in thick pipes manufacture and welded joints with PWHT have to be demonstrated together with the relevant mechanical and oxidation/corrosion testing.

Alloys for A-USC steam turbine rotors, discs, and blades evaluated

A DOE sponsored program is examining the long-term strength, stability, and cyclic behavior of potential turbine materials for A-USC. Patricia Rawls of DOE, Bob Purgert of Energy Industries of Ohio, and John Shingledecker of EPRI say that a breakthrough in steam cycle efficiency can be achieved by using new materials in the boiler and steam turbine. Their analysis appears in the April issue of Turbomachinery International ( www.turbomachinerymag.com)

Three potential alloys for steam turbine, rotors, discs, and blades were selected based on tensile, creep, fatigue, microstructure and thermodynamic stability. Nimonic 105 is the leading candidate for blades and bolting due to its higher creep strength. Haynes 282 is the leading candidate for rotors and discs due to its insensitivity to heat-treatment and microstructural stability. Research to define the processing windor for a larger disc forging is also ongoing.

For Oxy-firing corrosion resistance and cost increase with Cr content

NETL is evaluating materials requirements for oxy firing as applied to existing coal fired plants. Laboratory tests comparing air-firing to oxy-firing conditions were conducted at temperatures expected to result in the highest fireside corrosion rates (675-700 °C). Depending on the CO2 circulation path, sulfur levels will be elevated in both the gas and ash phases. Higher sulfur levels are expected to increase corrosion rates and thus may require more corrosion resistant alloys or coatings in an oxy-fired boiler than in an air-fired boiler. The figure below shows elemental map microstructures for a boiler steel alloy (T92) exposed to various environments (without coal ash, and with two levels of sulfate within a coal ash cover) for 250 hours. In general, corrosion resistance (and cost) increases with increasing Cr in the alloy.

Color-enhanced elemental maps of a boiler steel (grade T92), which contains a moderate level (9%) of chromium, exposed in oxy- and air- firing environments, with and without a covering ash. The original metal surface is indicated by the dotted line. Outer scales are pure Fe oxide (with embedded ash when ash was present). Inner scales are mixtures of layered Fe and Cr oxides and sulfides. Increased sulfur in the coal ash proved to be more important to fireside corrosion than increased sulfur in the gas phase.

For the exposures shown in, thicker scales (meaning more corrosion) are associated with more sulfur in the ash rather than in the gas phase. The layering within the inner scale shows successive instances where a somewhat protective chromia-rich oxide layer has become less protective and broken away from the metal. http://www.netl.doe.gov/newsroom/labnotes/2011/05-2011.html

Linings are a solution to repairing corroded scrubber shells

There have been some major corrosion problems with 2205 stainless used in scrubber vessels at some of the recent installations in the U.S.

This photo of Andy Bernard of Blome taken at Electric Power 2011 shows the solution which many of the plants have taken. Vitrified tile linings are installed over the prepared surfaces.

The issue was first brought to EPRI’s attention before its October 2010 Generation Sector advisory meeting. In early November, EPRI convened a meeting of key stakeholders. In less than two months, EPRI programs 87 (Fossil Materials and Repair) and 75 (Integrated Environmental Control) jointly launched a supplemental project to address the issue. “Once we saw the seriousness of the attacks and their prevalence throughout the industry, we knew we had to act quickly,” said John Shingledecker, EPRI senior project manager. The project aims to identify the root cause, compile guidelines for inspection and fabrication, and develop repair and other mitigation strategies.

First, the project team is surveying U.S. utility FGD systems experiencing corrosion. The survey is collecting information on corrosion in FGD absorber vessels, piping, and spray

headers/nozzles, along with detailed data on materials, fabrication techniques, construction quality assurance/ quality control, operating environments (basic water chemistry, scaling, etc.), and corrosion levels and locations. With the survey results, the EPRI team will document all FGD system designs, chemistries, and materials susceptible to accelerated corrosion. Early indications point to chemistry issues––evidenced by the presence of hard, tenacious scales and deposits on walls and floors––and/or a factor associated with the fabrication of the metallic vessels.

Prior to the early 2000s, FGD absorbers were designed using Type 317L stainless steel or a variation, such as Type 317 LMN. The LMN grade is fully austenitic and has controlled increased additions of nitrogen and molybdenum. The combination of molybdenum and nitrogen enhances resistance to pitting and crevice corrosion, especially in process streams containing acids, chlorides, and sulfur compounds at elevated temperatures. Nearly a decade ago, in seeking higher SO2 removal and different chloride concentrations during operations, a fundamental shift occurred in the way FGD systems were designed and operated. The price of nickel-based alloys spiked, rising by four to seven times. Manufacturers sought other metals, such as duplex stainless steels. Duplex stainless steels have a two-phase microstructure consisting of roughly 50% austenitic stainless steel and 50% ferritic stainless steel, making them about twice as strong as regular austenitic or ferritic stainless steels. Depending on their content, duplex alloys have a range of corrosion resistance. With less nickel and molybdenum, these alloys can cost significantly less than austenitic stainless steels, and because of their increased strength, they can be manufactured with reduced section thickness. Initial evidence indicates many affected FGD systems are fabricated with one of the most common duplex stainless steels, Alloy 2205, a 22% chromium, 3% molybdenum, 5%–6% nickel, nitrogen-alloyed stainless steel. Some affected systems are made of a similar duplex alloy, 255, with a slightly different composition. Concern is mounting that earlier-generation absorber vessels fabricated with austenitic stainless steels may be subject to corrosion as well, but that the attack has gone undetected.

As a result, the EPRI study will investigate duplex stainless steels, stainless steels, and alloys prevalent in today’s FGD fleet.

Localized corrosion in the immersion zone along welds and beneath deposits of the WFGD absorber will need a special solution under certain conditions

DNV Columbus Inc. was retained by a utility to investigate the cause of internal corrosion in its wet FGD absorbers. The absorber shells were fabricated by welding together UNS S32205/S31803 duplex stainless steel (2205) plates. The vertical seams in the tank shells were prepared using flux-core arc welding. The horizontal seams used submerged arc welding. The plate thicknesses range from 0.5 inches to 0.1875 inches.

The absorbers were in service for approximately 12 to 18 months before through-wall pinhole leaks were found during regular external visual inspections of the shell. The bulk solution in the immersion zone had an approximate chloride concentration near 5000 ppm, temperature was near 125^oF and the pH range near 5.

The internal surfaces of the absorber shells were covered with tenacious scale. Areas of the absorber were scaled with a black product containing manganese, fluoride, silicon, aluminum, calcium, sulfur, oxygen and iron. Some of the scale was tan to brown (same composition without the manganese) with thickness ranges from less than 0.125 inches to greater than three inches. In areas where the tank wall was not scaled, attack was not evident.

Metal loss was observed near horizontal seam welds, near vertical seam welds, and in the base metal shell plate. The heat-affected zones were preferentially attacked in some instances, but base metal attack was also evident in the same absorber. The pit morphology was characteristic of severe undercutting where the pit mouth can be small and the subsurface metal loss is deep and wide.

Field repair was done. The patch plates were constructed of Hastelloy C-276 and the weld repairs were performed using NiCoMo-4 filler metal.

Brett Tossey of DNV wrote in Power Engineering January 2011 that the conclusions from the investigation are 2205 duplex stainless steel was not able to resist localized corrosion in the immersion zone of the WFGD absorber. Leaks occurred as a result of rapid localized corrosion in Duplex 2205 near the weld. The attack occurred along welds and in the base metal exclusively beneath deposits, leading to crevice corrosion. The attack selectively dissolved the austenitic phase in the duplex stainless steel. The austenite phase was preferentially attacked due to its lower molybdenum and chromium contents when compared to the ferrite phase. There was no evidence that microbial activity played a role.

Nuclear

EPRI programs focus on materials degradation as well as development of advanced materials

Materials research can maximize efficiency and minimize component degradation says David Gandy, program manager in EPRI’s office of Technology Innovation (TI). His remarks are published in the Spring 2011EPRI Journal.

TI programs address both materials degradation and the development of advanced materials. To address materials degradation the program seeks a fundamental understanding of microstructural degradation, corrosion, and erosion in order to predict and extend the life of critical components. In the nuclear segment the focus is on degradation associated with aging, embrittlement, and corrosion.

EPRI is involved with many joint projects. One with Japans Centeral Research Institute of the Electric Power Industry (CRIEPI) is focused on developing lifing criteria for components manufactured of grade 92 ferritic steel. Lifing criteria require information on microstructure, long –term creep fatigue and other factors which that can indicate when a component is nearing the end of its life. “Grade 91, used around the world, has created a lot of headaches due to improper fabrication and heat –treatment practices said Gandy.

“Over the last decade the industry has begun to look at Grade 92 for piping and header applications and we are trying to develop the lifing criteria before many plants install the alloy” concludes Gandy.

Alloy 600 nozzles for reactor vessel closure heads supplied by B&W

Nuclear power plants around the world are in need of a technical, cost-effective and permanent solution to the cracking of Alloy 600 nozzles on reactor vessel closure heads.

Babcock & Wilcox Canada has a solution. It is not only the first company to win a US contract to manufacture a replacement reactor vessel closure head, but also the first to receive contracts to produce replacement heads for every type of nuclear reactor.

The Babcock & Wilcox Technical Services Group, Inc. (B&W TSG) Failure Analysis Laboratory (FAL) is equipped with a wide range of digital photography and metallurgical instruments used to support failure analysis investigations. The laboratory is operated by an experienced staff of engineers and technicians trained in failure analysis techniques including microstructural characterization of metals and deposits, fractography, corrosion processes, welding metallurgy, and mechanical testing.

Jim Fritz says to consider 2205 for nuclear plant cooling systems

In the May issue of Nuclear Exchange (www.nuclear-exchange.com), Jim Fritz of TMR stainless makes a good case for using 2205 stainless rather than carbon steel piping for cooling systems. He observed that most of the systems simply have used bare metal although cement lining and other coating systems were used for more aggressive cooling waters. Common failures have included excessive corrosion rates, pitting and microbiologically influenced corrosion (MIC).

Where MIC is a concern 304 L and 316L are not viable options.. Jim recommends no less than 6% molybdenum grade. PSEG Nuclear installed 6% Mo piping at their Salem Plant 20 years ago and it has been trouble free. But now says, Jim there is an additional option. Duplex 2205 contains 3.2 % moly and 22 % chromium. It can reduce maintenance costs and improve plant safety compared to 304 L and 316 L. In the article Jim cites recent cases to back up his argument. You can receive an introductory free copy of Nuclear Exchange by contacting e.riethorst@kci-world.com

Titanium is a popular choice for surface condensers in power plant cooling systems

Titanium began to be selected for surface condenser when traditionally-used tube materials were failing at an alarming rate. In many cases, these originally installed materials, such as aluminum bronze (C60800) and copper nickel alloy tubes (90/10 CuNi/C70600 & 70/30 CuNi/C71500) failed prematurely due to high chloride and elevated levels of pollution in the circulating water system. In the current edition of Energy-Tech, Dennis J. Schumerth, director of Business Development for Valtimet Inc., states that after years of in-situ testing, which considered competing materials – including yellow metals, stainless alloys and titanium – Gr. 2, titanium was the only material to remain completely unaffected in these hostile environments. Several condensers were initially retubed, either partially or fully in the early 1970s and continue to provide reliable electric power to the grid. Schumerth says that since that time, “more than 6 million feet of welded titanium tubing has been installed without one reported corrosion event – indeed an unparalleled track record where water quality and proper material selection are as important today as it was 40 years ago.”

Solar

Molten Salt requires special materials

There are some big projects underway to use molten salt to store the heat generated by concentrated solar systems. The toughest environment is the hot salt zone. This includes the receiver, piping and storage tanks. The first experience in the U.S. was at Solar Two. This plant is now shut down but was the basis for the newer designs.

Solar Two operated from 1996-199 with INCONEL alloy 625LCF as the material for the central receiver for a molten salt system from Rocketdyne. 385 tubes were 6.2 meters in length. Two 875,000 liter storage tanks were fabricated on site from stainless steel by Pitt- Des Moines.

Gemasolar in Spain is a 17 MW concentrated solar plant using molten salt. It is scheduled for start up this year. The contract for the fabrication of the largest tank, 23m in diameter and 14m high, went to the Barcelona-based tank fabricator Emypro. 347 H plates will be utilized for the fabrication.

Test your materials at the Sandia Labs Solar thermal Test Facility

Operated by Sandia National Laboratories for the U.S. Department of Energy (DOE), the National Solar Thermal Test Facility (NSTTF) is the only test facility of this type in the United States. The primary goal of the NSTTF is to provide experimental engineering data for the design, construction, and operation of unique components and systems in proposed solar thermal electrical plants planned for large-scale power generation. In addition the facility can provide: high heat flux and temperatures for materials testing or aerodynamic heating simulation; large fields of optics for astronomical observations or satellite calibrations; a solar furnace; a rotating platform for parabolic trough evaluation.

The site was built and instrumented to provide test facilities for a variety of solar and non-solar applications. Several mechanisms are available for users to contract with Sandia for use of the facility. Previous users include other researchers, including government contractors and agencies, research institutes, universities, and private companies.

The (NSTTF) welcomes all users. Several mechanisms are available for contracting with Sandia National Laboratories to use the facility. For more information please contact Cheryl Ghanbari, 505-845-3426 or cghanba@sandia.gov to discuss details of specific tests and other ways to contract with Sandia for this type of work.

Industry News

Baik-Doo Metal Corp. supplies steel for boilers and FGD in Korea and export to China and the Middle East

Baik-Doo Metal Corp. represents Industeel, and Stainless & Steel BV for the Korean market. Products include: Heavy and Clad Plates, Heavy Forgings and Castings, Mold & Tool Steel Plates, Cryogenic Steel Plates and ASME ¥² Nuclear Grade, Nickel base Alloys. Due to the fact that Korean OEMS are active in China and the Middle East the company is supplying steel which ultimately is utilized in locations outside Korea.

Nickel prices could drop 10%

The 2012 nickel surplus will rise to 60,000 metric tons from 12,000 tons in 2011, making nickel the most oversupplied metal relative to output or use, according to Bank of America Merrill Lynch, the most-accurate forecaster tracked by Bloomberg over two years. New mines will boost supply 11 percent in 2012, the most in 17 years, Macquarie Group Ltd. says. Prices may drop 10 percent to $20,000 a ton by Dec. 31, the median estimate in a Bloomberg survey of 17 analysts and traders shows.

Construction and transport account for 37 percent of nickel demand, with another 18 percent used in machinery and electrical applications. China is the world’s biggest nickel producer. The nation’s least-efficient makers of nickel pig iron, a cheaper alternative to refined nickel, need about $20,000 a ton to break even, according to Societe Generale SA.

While stainless-steel output rose 8.6 percent to 8.39 million tons in the first quarter, a record for the period, the International Stainless Steel Forum said last month that gains won’t be sustained through the year. The Brussels-based group’s members account for about 75 percent of global output. Rising production may also mask a swing toward demand for steels containing less nickel or substitution with other materials.

Tidal/Wind/Wave

Oregon Iron Works and American Bridge have contracts for Reedsport Wave Energy

Ocean Power Technologies has let contracts for the fabrication of the Power Buoy wave generator which will be deployed off the coast of Reedsport, Oregon. American Bridge Manufacturing will build the subsurface floats. Oregon Iron Works will fabricate the steel spar.

Pelamis Wave Power project to primarily use mild steel with some stainless

This project in the UK will use mild steel for the main structure with smaller quantities of copper, stainless steel, rubber, and plastics for other parts. Pelamis is going to be stationary so there is no worry about the drag from marine growth. A marine coating is applied to structural steel surfaces in the atmospheric and splash zone. Cathodic protection is applied to areas of the structural steel components in the submerged zone using sacrificial anodes.

Composites will be considered for many tidal, wind, and wave projects

Angus Fleming is Managing Director of Aviation Enterprises. The company produces rotors for tidal stream generators. He points out that composites have an advantage because fatigue is not a factor even with a 25 year service life. Epoxies are generally selected for underwater applications because they are the most resistant to progressive moisture absorption and hydrolytic attack.

AEL has produced eleven meter diameter rotors for the Marine Current Turbine Seaflow unit and the subsequent 16 meter rotor for the full scale Sea-gen.

Materials at Coal-Gen

Salt River Project replacement scrubber materials will be discussed at Coal-gen

Nelson Rosado is currently the Lead Mechanical Engineer on the Coronado Emissions Control Project (CECP) for Sargent & Lundy. Horizontal wet scrubbers are being replaced. The materials of construction for the new scrubbers will be discussed during his presentation on August 17 at Coal-gen in Columbus, Ohio.

Design of zero liquid discharge systems will be subject of pre conference workshop at Coal-gen

John Schubert of HDR Engineering will provide a 4 hour course on design considerations for zero liquid discharge systems at Coal-Gen. the course will be on Tuesday afternoon at 1PM (August 16). The course will provide an overview of the treatment needs and process unit operations commonly employed to achieve zero liquid discharge (ZLD). The course is based on HDR project experience with ZLD in these and other industries, and provides a sound basis for understanding the technical considerations involved in successfully implementing ZLD.

Producer	Customer	Item	Quantity	Application
Industeel	Wolsung # ¾ KHIC	SA516 GR.70	1000 MT	Steam generator, pressurizer, degasser
Industeel	Jinshan Nuclear KhIC	SA516 Gr.70	1000 MT	Steam generator, Pressurizer, degasser
Industeel	Sequoyas RSGY	SA508 Forging shell	1200 mt	Replacement steam generator
Industeel	HHI, KHIC, Daewoo, Korea Cottrell, Ssangyong Heavey Industries, Jung Il Enc	Super duplex and super ausenitic	4000 tons	FGD for Tae-An, Dang-Jin, Bor-Rung, Yong-Dong, Ulsan, and Yosu
Industeel	Doosan Heavy Industries	SR 50A	450 MT	FGD