Proceedings of the 2014 Energy Materials Conference: Xi'an, Shaanxi Province, China, November 4 - 6, 2014

By The Minerals, Metals & Materials Society (TMS)

This DVD contains a collection of papers presented at Energy Materials 2014, a conference organized jointly by The Chinese Society for Metals (CSM) and The Minerals, Metals & Materials Society (TMS), and held November 4-6, 2014, in Xi’an, Shaanxi Province, China. With the rapid growth of the world’s energy production and consumption, the important role of energy materials has achieved worldwide acknowledgement. Material producers and consumers constantly seek the possibility of increasing strength, improving fabrication and service performance, simplifying processes, and reducing costs. Energy Materials 2014 has provided a forum for academics, researchers, and engineers around the world to exchange state-of-the-art development and information on issues related to energy materials. 

The papers on the DVD are organized around the following topics:

• Materials for Coal-Based Systems
• Materials for Gas Turbine Systems
• Materials for Nuclear Systems
• Materials for Oil and Gas
• Materials for Pressure Vessels

• Language: English
• Publisher: Wiley
• Release date: Apr 6, 2015
• ISBN: 9781119027997

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The State-of-the-Art of Materials Technology Used for Fossil and Nuclear Power Plants in China

Yuqing WENG

The Chinese Society for Metals 46 Dongsi Xidajie, Beijing, China, 100711

Keywords: Ultra-super-critical; Nuclear power plant; Materials technology; Development

Abstract

Combined with the development of energy in China during the past 30 years, this paper clarified that high steam parameters ultra-supercritical (USC) coal-fired power plants and 1000MW nuclear power plants are the most important method to optimize energy structure and achieve national goals of energy saving and CO2 emission in China. Additionally, requirement of materials technology in high steam parameters USC coal-fired power plants and 1000MW nuclear power plants, current research and major development of relevant materials technology in China were briefly described in this paper.

1. Energy requirement and development strategy in China

Energy is the basis of economic development and social progress. In the past 30 years, China’s economy has been in a period of rapid development, resulting in the increasingly urgent demand for energy. The structure and its evolution of electric power since 2000 in China were listed in Table 1. From 2000 to 2012, the total installed capacity of power in China had a triple increase from 3.19×10⁸ kW to 1.145×10⁹ kW. Coal-fired power and hydro-power took up 71% and 21%, respectively, which were the majority in the Chinese electric power. The proportion of nuclear power kept nearly stable. From the view point of natural resources, China is relatively rich in coal- poor in oil- short in gas, resulting in the fact that coal-fired power is still the major electric power by now and in the future for a long time in China. Available hydro-power resources are nearly exhausted in our country, although they are a kind of clean energy. Wind power is in a rapid development in the past years, but there are still many problems in the collection, storage and synchronization. The proportions of other novel energy resources are too small and there are also many problems. Therefore, the only way to optimize energy structure and achieve national goals of energy saving and CO2 emission in China is to develop high steam parameters ultra-supercritical (USC) coal-fired power plants and 1000MW nuclear power plants.

Table 1 Structure and its evolution of electric power since 2000 in China

2. Development of USC coal-fired power technology and challenges of materials technology in China

The relationship among steam parameters, thermal efficiency and coal consumption of coal-fired power plants was listed in Table 2. Clearly, the higher the steam parameters of power plants, the higher the thermal efficiency, the lower the coal consumption, and the lower the emissions of environmentally damaging gases. The evolution and prediction of steam parameters of coal-fired power plants in China from 1950 to 2020 [1] were shown in Fig. 1. Steam parameters of power plants have been very low for a long time in our country before the year of 2006. It is 2006 when was a brilliant moment in Chinese electricity history, the first 600°C USC coal-fired power generator was operated, which was a milestone in the development of China’s power industry. From then on, the design, manufacturing, and installation of 600°C USC coal-fired power generator developed very fast. By the end of 2012, the total capacity of 600°C USC power generators in our country has reached 110 GW, which took up more than 70% of the total capacity of 600°C USC power generators in the world.

Table 2 Relationship among steam parameters, thermal efficiency and coal consumption of coal-fired power plants

Fig. 1 Evolution of steam parameters of coal-fired power plants in China

To improve the technical level of coal-fired power plants and form independent intellectual property rights from materials research to complete power plant technology, on July 23, 2010, the National Energy Administration set up National innovative consortium for 700°C A-USC coal-fired power technology at the Great Hall of the People. The members of the national consortium includes: China Power Engineering Consulting Group Corporation, China Iron & Steel Research Institute Group (Central Iron & Steel Research Institute), Xi’an Thermal Power Research Institute, Shanghai Power Equipment Research Institute, Institute of Metal Research of Chinese Academy of Sciences, five power providing groups, three electrical equipment manufacturing groups, China First Heavy Industries, China Second Heavy Industries, BaoSteel and Dongbei Special Steel Group Company. Through the innovation of 700°C A-USC coal-fired power technology, the aim of the consortium is to integrate resources effectively, to solve technical problems together, and to realize the research and development of 700°C A-USC coal-fired power generator independently in the near future, promoting the development of relevant industries and opening up a new path for energy conservation and emission reduction in the power industry. For 700°C A-USC coal-fired power generator, heat resistant materials are the bottleneck. If the research on heat resistant materials goes smoothly, China will begin to build demo 700°C A-USC coal-fired power generator around the year of 2020.

3. Development of heat resistant materials used in 700°C A-USC coal-fired power in China

Coal-fired power plants include mainly boiler and turbine. The boiler pipes/tubes and heat resistant components in turbine are the bottleneck for the making of fossil power plants. Whether they can be successfully developed is mainly attributed to the heat resistant materials and equipment manufacturing capacity. The process of developing heat resistant materials mainly includes composition design, processing property, component manufacturing and evaluation of component performance. After long-time careful discussions, the technical committee of National innovative consortium of 700°C A-USC coal-fired power technology has determined the preliminary scheme on 700°C USC boiler pipes/tubes candidate materials, which was shown in Fig. 2[2].

Fig. 2 Heat resistant candidate materials for boilers of 700°C power plants in China

3.1 Water cooling wall materials

T23 steel is used as water cooling wall material in 600°C USC coal-fired power generators. The reason why T23 steel was chosen can be attributed to that the tubes needn’t to be heat treated before or after welding. However, from the industrial experiences, there are many problems on the water cooling walls made by T23 steel without pre-weld or post weld heat treatments. Since the temperature of water cooling walls in 700°C USC coal-fired power generators can reach around 500°C, it is necessary to choose a new kind of material with higher heat resistance. Currently, T23, T91 and G115T are candidate materials to water cooling walls according to the operating temperature from low to high. One of the advantages of this choice is that the diameter and thickness of water cooling wall tubes at different positions can be nearly the same, ensuring excellent heat transfer performance as well as easier and better weldability.

3.2 Materials for superheaters and reheaters

S30432 and S31042, two kinds of austenitic tubes in small diameter, are mainly used in Superheaters (SHs) and reheaters (RHs) in 600°C USC coal-fired power generators. But the temperature range of SHs and RHs in 700°C A-USC coal-fired power generators is from 600°C to 700°C, therefore, a series of tubes are needed to match the requirement of SHs and RHs at different temperature regions. Considering the cost of power plants construction, the maximum operating temperature of advanced austenitic heat resistant steels should be expanded, and the use of expensive nickel-based heat resistant alloys should be lowered. With increasing steam temperature from 600°C to 700°C, the candidate materials are NF709R, Sanicro25/GH2984G and Inconel740H according to the operating temperature. The key issue is to increase the comprehensive performance of the three candidate materials above by optimizing the compositions and the processing, finally, to satisfy the requirement of 700°C demo power plant in China.

3.3 Material for boiler pipes and headers

P92 and P122 ferritic pipes are candidate materials for boiler pipes and headers in 600°C USC power plants. The maximum operating temperature of P92 steel is around 600°C. P122 steel has been eliminated since its allowable stress at 600°C was sharply lowered in recent years. With increasing steam temperature from 600°C to 700°C, the candidate materials are P92, G115P and CCA617 according to the operating temperature. The welding issues between ferritic pipes and nickel-based pipes should also be carefully considered.

3.4 The development of materials for 700°C USC boilers in China

3.4.1 The development of G115 pipe

G115 ferritic heat resistant steel developed by CISRI for 650°C USC power plants has undergone three times trial-manufacturing in BaoSteel. The manufactured boiler pipe in large section is under comprehensive property evaluation. The size of the second trial-manufactured boiler pipe by hot extrusion was Φ254mm×25mm×3500mm. The creep rupture property and corrosion resistance property of manufactured G115 pipes are shown in Fig. 3. So far, G115 possesses the best combination of creep rupture strength and corrosion resistance among all the candidate materials for 650°C USC pipes. If the currently used P92 pipes for 600-620°C USC power plants are replaced by G115 pipes, the thickness of the pipes can be largely reduced, thereby reducing the weigh as well as the difficulty in welding. (Fig. 4)

Fig.3 The properties of industrially made G115 pipes

Fig.4 Comparison between G115 and P92 pipes

3.4.2 The manufacturing of CN617 pipe

CN617 is one of the main candidate materials for 700°C A-USC pipes. The smelting of CN617 alloy with the weight of 6 tons has been successfully finished with the combined efforts of CISRI and Fushun Special Steel Company from January to April in 2013, as shown in Fig.5. The first 6-ton hot extrusion of nickel-base super-alloy pipe with the dimension ofΦ460×80×4000mm has been successfully conducted by CISRI and Inner Mongolia North Heavy Industries Group Corp. Ltd. in October 2013 in China, as shown in Fig.6.

Fig. 5 6-ton CN617 ingot made by FuShun Special Steel Company (VIM+VAR, Ingot size Φ660×1940mm)

Fig. 6 Hot-extrusion of CN617 pipe at Inner Mongolia North Heavy Industries Group

3.4.3 The manufacturing of C-HRA-1 tube

Inconel740H is one of the main candidate materials for superheater and reheater (tube) of 700°C USC power plants. Heat resistant alloy C-HRA-1 was developed by CISRI and Baosteel with independent property right. C-HRA-1 tube with the size of Φ51×8mm was successfully manufactured in the production line of 4.5 ton special smelting and 6000 ton extrusion in BaoSteel Special Metals (Fig. 7). C-HRA-1 heat resistant alloy has equal comprehensive properties with Inconel740H, but simpler chemical composition and superior microstructure stability.

Fig. 7 C-HRA-1 alloy tubes industrially made by BaoSteel and CISRI

3.4.4 The manufacturing of GH2984G tubes

Much effort has been made in the chemical modification of alloy GH984 developed by Institute of Metal Research. By adding B and P, the creep rupture life and high temperature ductility of the alloy were been significantly improved. The formation of detrimental σ phase was prohibited by adjusting the contents of Fe and Ni. By modifying the Ti/Al ratio, the formation of needle-like η phase was prohibited, overcoming the problem of detrimental η phase precipitation as early as 500h at 750°C. Seamless tube was successfully manufactured by Institute of Metal Research of Chinese Academy of Sciences and BaoSteel Special Metals in 2013.

3.5 Heat resistant materials for turbine rotor, casing and blade

Considering the current tonnage limitation of smelting and forging for heat resistant alloys, most turbine rotors for the advanced USC coal-fired power plants are designed and manufactured by dissimilar welding. 12%Cr heat resistant steels were used for the lower temperature regime and nickel base heat resistant alloys were used for the upper temperature regime. To meet the design and manufacturing demands of turbine rotors for 700°C A-USC power plants, the current research is focused on the development of CCA617 and Inconel740H heat resistant alloys of 10 tons without macro-segregation, which also show good weldability with 12% heat resistant steels. Inconel625 is the main candidate material for turbine casing. At present, the difficulty lies in the equipment of vacuum smelting and casting with large tonnage for the cylinder, which can hardly be met by the current smelting and casting equipment in China. The same problem is also faced in Europe and Japan. There are two solutions to this dilemma. The first is to design and build smelting and casting equipment with larger tonnage. The second is to manufacturing Inconel625 castings with large tonnage following the routine of EAF + AOD/LF/VD + ESR.

4. The development of nuclear power plants and challenge for materials in China

Having started rather late, the nuclear power plants in China has generally undergone three stages. (1) Initial stage: 1970s-1993, (2) Moderate development stage: 1994-2005, (3) Active development stage: 2006-present. At present, 17 units with the capacity of 1.47 million kW are in operation in mainland. 28 units with the capacity of 3.057 million kW are under construction (accounting for 40% of the current building units). In China, since the technical route of pressurized water reactor (PWR) was chosen in 1983, all nuclear plants are PWR except the heavy water reactor in Qinshan III. The milestones of the PWR power plant development in China are shown in Tab. 3.

Table 3 Historical evolution of Chinese pressed water reactors

The nuclear island of PWR power plant is comprised of reactor pressure vessel (RPV), steam generator, main steam pipe and other components. There are several trends for the design of the main equipment for PWR nuclear island. (1) Larger scale and integration: the unit capacity as well as the weight and size of the single forging is increasing. In the meanwhile, integrated design makes manufacturing more complex. (2) Longer service time: the design life has increased from 40 years to 60 years. (3) More emphasis on safety. The above-mentioned trends put more stringent requirements on the properties of the candidate materials. Forgings for the RPV, steam generator, main pipe, reactor internals and the heat transfer tube for steam generator are the raw materials for building the main equipment inside the nuclear island. Without changing the material (SA508Gr3C11), the service life for the RPV forging has been significantly increased. The maximum weight for the ingot has also increased from 300 ton to 600 ton. SA508Gr3C12 (508-3-2) used for AP1000 steam generator forging is new material developed by China, with superior comprehensive properties. They are both the first attempts in the world to build main steam pipe by solid forging of 316LN with 100 ton and build internal retainer spring forging using F6NM. It is the first time in China to conduct industrial trial and production of heat transfer tube for steam generator using alloy 690. All the above-mentioned technical problems are the bottleneck for developing the nuclear power plants with 1000MW.

5. The development of materials for 1000MW nuclear power plants in China

With the joint efforts of CISRI, China first heavy industries, Baosteel special metals, China second heavy industries, Shanghai heavy industries, and Yantai manor nuclear equipment manufacturing company, breakthroughs have been made in manufacturing whole set of RPV and steam generator forgings for PWR power plants with 1000MW such as CPR1000, AP1000 and EPR. At the same time, alloy 690 used as heat exchange tube for steam generator has been mass-produced for PWR power plants of CPR1000, AP1000 and CAP1400. It should be noted that, it is for the first time in the whole to build AP1000 integrated forging using 316LN as main steam pipe. All the above-mentioned techniques have been successfully applied in the 1000MW nuclear power plants in China.

6. Summary and future trends

Developing 700°C A-USC coal-fired power plants as well as 1000MW advanced nuclear power plants are the critical measures for the energy structure optimization, energy saving and emission reduction in China. The more strict requirements on the materials can promote the development of advanced energy material as well as the manufacturing of its production with high added value. The innovation consortium for China 700°C A-USC coal-fired power plants was founded in 2010 and the national research and development programs associated with 700°C A-USC power plants were launched. Hopefully, the first demo 700°C A-USC coal-fired power plant will be built within 10-15 years. Meanwhile, It is also expected that China can export innovated 1000MW nuclear power plants in the near future.

Acknowledgements

The research was partly and financially supported by the National Basic Research Program of China (973 Program, No. 2010CB630804), and the National High Technology Research & Development Program of China (863 Program, No. 2012AA03A501).

References

1. Z.D.Liu, The research and development of heat resistant steels and alloys used for 700°C AUSC-PP in China, Advanced ultra-super-critical coal-fired power plants, IEA-Vienna Workshop-2012, Vienna, Austria, Sept., 19-20,2012

2. Z.D.Liu, H.S.Bao, G.Yang, S.Q.Xu, Q.J.Wang, Material advancement used for 700°C AUSC-PP in China, Seventh International Conference on Advances in Materials Technology for Fossil Power Plants, October 22-25, 2013, Hilton Waikoloa Village, Hawaii, USA

ENERGY EFFICIENT MATERIALS MANUFACTURING FROM SECONDARY RESOURCES

Diran Apelian¹ and Brajendra Mishra²

¹Alcoa-Howmet Professor of Engineering Director NSF Center for Resource, Recovery & Recycling Metals Processing Institute, Worcester Polytechnic Institute, Worcester, MA, USA

²Professor & Co-Director, NSF Center for Resource, Recovery & Recycling Metallurgical & Materials Engineering Colorado School of Mines, Golden, CO, USA

Keywords: Rare-earth metals; REE; Recycling; Lighting; Magnets.

Abstract

Rare earths metals, including yttrium and scandium, are being increasingly used in clean energy technologies, colored phosphors, lasers and high intensity magnets. There are important defense applications such as fighter jet engines, missile guidance systems and space based satellite and communication systems, based on these metals. The commitment to clean energy technologies by various governments, as well as the projected growth in power and transportation sectors across the globe will certainly escalate the demand for rare earth metals and compounds. This demand implies that to ensure unhindered technological innovation, it is essential to possess secure supply chains for rare earth elements. The United States continues to be one of the largest consumers and importer of rare earths and the trend is expected to continue as the demand increases. In order to ensure secure rare earth supply and attenuate supply-demand imbalances post 2014, it is not only necessary to encourage and support exploration of newer reserves, build a rare earth stockpile, but it is also of utmost importance to look at opportunities to recycle and reuse Rare Earth Elements (REE) from secondary sources, such as post-consumer and manufacturing process wastes. This research describes the technological developments made to convert these valuable resources into functional manufactured materials for lighting industry, automotive and petroleum refining catalysts, and high density permanent magnets. In addition, production of rhenium from advanced aerospace alloys is also discussed from the perspective that it can be recovered for introduction in turbine alloys.

Context

Sustainable development in the 21st century is perhaps the most pressing issue we face. At the same time, it is also a time for remarkable opportunities for materials scientists and engineers (MSE) as many of the solution pathways to these challenges are materials centric.

To put things in context, it is important for us to understand the magnitude of the issues we face. Since 1700’s the volume of goods traded Increased 800 fold. Between 1910-2010 the World’s industrial production Increased 100+ fold. And between 1900-2000 global consumption of fossil fuel Increased by 50 fold. These are highlighted below.

World population is estimated to rise to over 9 billion in the next 3-4 decades. Between the period 1960-1975, a billion people were added, and another billion between the period 1975-1987. Keep in mind that we entered the 20th century with only 1.6 billion people, and exited the same century with 6.1 billion! Furthermore, the population growth is not evenly distributed throughout the world; the growth is occurring more in less developed countries.

More people equates to more consumption and more energy usage. Our hunger for energy is huge. Though population is growing at an average of 1.4% a year, our need for energy is growing at an average rate of 1.7%; certainly not a tenable scenario. Average energy consumption per capita throughout the world is about 57 gigajoules, and for USA it is 230 gigajoules, and 119 for Europe. Such consumption of energy is not sustainable.

Associated with energy usage is the production of greenhouse gases, which have adverse effects on our climate and the environment. There are many debates on the assumptions used in the various models that predict global warming and the levels of CO2 production. One thing that is not debatable is that we need to reduce generation of greenhouse gases.

Food and water, basic human needs is also being taxed. 18% of the world population lacks access to safe drinking water. 20% of the world population is living in absolute poverty (defined as living on less than one Dollar per day); about 1.4 billion people! To exacerbate the situation, 40% of the world population has no access to sanitation.

Urbanization is a phenomenon that has major ramifications. Sustainable mobility – transportation needs- is a significant issue for two reasons. The infrastructure that was built for a world of 5 billion cannot sustain 7 billion plus people. We have major infrastructural gaps. The other reason is that transportation systems are lacking, except in a few countries and major cities, which have become a benchmark for the rest.

Housing and shelter needs of the world are also increasing, and on the human side, the need for community which is so vital for a quality life.

Material consumption is at all time high. Many consumer goods are packaged, and the amount of waste that is created per capita is growing. If one considers the amount of material that is recovered and recycled in the overall system, it is pitiful. The average per capita consumption is about 50Kg per person. In the US, only about 50% of beverage cans are recycled, and only ~30% of glass bottles. More recently, if we look at the price of rare earths, we can see the dramatic increases in price. Inorganic materials are not renewable, and they need to be recovered and recycled.

Lastly, health is perhaps the most critical human need, and life expectancy around the world has increased significantly (in US alone it has gone from 70 yrs in the mid 1950’s to close to 80 years old at present), with the exception being Africa. Health care needs around the world have increased, and the cost of health care delivery has also skyrocketed.

PRESENT SCENARIO

Increasingly, the U.S. government, academia, domestic industry, and the public acknowledge the imperative that we need to conserve energy and natural resources while exercising judicious stewardship of the environment. The issue of sustainability is and should be paramount in how we design, manufacture, use, and retire the many products we consume throughout the world. Inorganic materials are not renewable; the need exists for the development of technologies to address materials recovery and recycling. Research supporting materials recovery and recyclability is inherently multidisciplinary and must respond to the needs of a multiplicity of commercial stakeholders from throughout the materials supply chain.

Despite growing efforts to recycle metals, we fail to recover half of the domestic post-consumer metal scrap reclaimable from retired products, and we continue to rely on primary metals production to fulfill two thirds of our manufacturing needs. Use of primary metals, in lieu of scrap, increases global energy consumption as well as the production of greenhouse gases. In order to augment recycling rates the materials community needs to upgrade recovery and recycling processing technologies to maximize the capture of post-consumer scrap and minimize the quantity of manufacturing scrap.

Rare earth elements are a group of 17 elements, which include 15 Lanthanides, Scandium and Yttrium. In spite of what the name suggests these elements are not rare. However, in recent years rare earth elements have become strategically critical for developed and developing economies around the world which is primarily due to the shortage of discovered minable resources [1]. Before 1948, the placer deposits of Brazil and India were the chief sources of rare earth metals for the rest of the world. With increasing demand newer supply sources were needed and for a while the monazite deposits in South Africa played an important role before the production was dominated by Bastnasite reserves in Mountain Pass and China [2].

According to a forecast done by IMCOA, the world rare earth demand is projected to rise to 200,000 tons by 2014 and the Chinese production is expected to be around 160,000 tons [3]. In addition, the demand of rare earths in China itself has increased by 380% between 2000 and 2009, which is believed to be the primary reason behind the export cuts on rare earth [4]. These developments have made rare earth elements a strategically important material as evident by the Rare Earths and Critical Material Revitalization Act of 2010 approved on September 29, 2010 which aims to establish an R&D program within the DOE to assure long term supply of rare earth materials [5]. The US Department of Energy published an analysis of the criticality of selected rare metals, the most critical elements were identified to be Dysprosium, Neodymium, Terbium, Yttrium and Europium - what are also known as the heavy rare earth elements [6]. Based on the demand and supply position of common rare-earths, the prices of common metals like Ce, Nd, Sm, La and Y, went up by 150% to 700% in a short period of six months between January and August 2010 (Table 1).

Table 1: Price Variation of Prominent Rare-earth Metals

According to a survey conducted by IMCOA in 2008 and reported by Kingsnorth, the chief users of rare earth metal by weight, are catalysts (68%), ceramics (7%), metal alloys (7%), polishing (5%), glass (5%), magnets (4%) and phosphors (3%). By 2014 it is projected that the major users of rare earth metals by weight would be metal alloys (25%), magnets (23%), catalysts (16%), polishing (11%), phosphors (7%) and glass (7%). These applications of rare earth metals provide opportunities for recycling through strategic end of life management. Many of the applications could provide efficient sources for heavy rare earth elements which are scarce and, at the same time, critical for development of new technologies. For example, recycling of compact and linear fluorescent lamps can prove to be a useful source of Yttrium, Europium and Terbium whereas recycling of permanent RE magnets used in wind and hydro power generation can become an important secondary source of Neodymium, Praseodymium, Dysprosium and Terbium. The elemental content of rare earths in appropriately sized phosphor dust that is generated from spent lamps exceeds fifteen percent.

Till now, recycling of rare earth has not been implemented on a large industrial scale. Ellis, Schmidt and Jones [7] have reported that recycling of rare earth based materials would have a stabilizing effect on price, supply, and quality. In addition, an infrastructure does not exist for the recycling of rare earth based materials. Higher volume application of rare earth based materials seems eminent, and therefore, the time is right to develop both the technology and infrastructure. Researchers have shown that aqueous processes, as well as molten slag electrorefining techniques are viable methods for returning high purity metals, but have limitations in their ability to be selective and cannot handle all kinds of wastes, such as swarf. Liquid-liquid extraction using metallic solvents presents interesting opportunities that overcome the shortcomings of the other methods. However, more research is required to develop technologies for commercial use [7].

Several constraints on recycling of rare earth were reported in an analysis by Okie-Institute AV [8], such as - need for an efficient collection system, need for sufficiently high prices for primary and secondary rare earth compounds, losses of post-consumer goods by exports to developing countries and the long life time of products such as electric motors and wind turbines. Zhong et. al. suggested that 20-30 % REE magnets are scrapped during manufacturing stage [9]. Other researchers have suggested various pyrometallurgical and hydrometallurgical routes to recover REE from these scrapped magnets [10]. Efforts have also been made to recover REE from used Ni-MH batteries. During pyrometallurgical treatment of these batteries the REEs report to the slag. Various hydrometallurgical routes have been investigated to recover these elements [11,12,13]. Recycling of rare earths from phosphors, as discussed above, provides an efficient way to recover high value heavy rare earth elements. Mei et. al. has provided an overview of various possible recycling methods for recovery of rare earths from fluorescent powder [14]. Not much work has been done on recycling of rare earths from catalysts. Catalysts primarily contain low value light rare earths like lanthanum and cerium which might be one of the reasons why not much effort has been put in this direction. However, once the economics of recycling of REE from spent catalysts becomes favorable, one would expect to recover the light rare earths feasibly and return them back to manufacturing.

A number of extraction processes have been successfully evaluated for application but not many have been commercially developed. However, the impending problem of supply shortage and the soaring prices of rare earths have made the environment conducive to build a recycling economy of these metals to address the problems. Such a strategy, if successfully implemented, would encourage research and development of green technologies and other critical areas by minimizing dependence on unpredictable nature of Chinese rare earth supply. This change in supply scenario, of course, will depend on the specific type of metal and material and its demand. In addition, some of the ‘exotic’ metals, such as rare-earths, molybdenum, rhenium, ruthenium, tungsten, PGMs, etc, for which demand is predicted to stay high and the indigenous resources low, recycling and recovery from spent secondary resources will be only viable option for sustainable growth.

Recycling of metals in the US has shown a growing trend over the past five decades (Fig.1). Recycling provides energy conservation, better environmental control and improved economic process viability for most metals and materials. Many industrially significant metals do indicate higher demand than supply and must find ways to recover these from spent sources, as shown in Table 2. Terbium, dysprosium and yttrium are used in fluorescent light fixtures while neodymium and samarium are used in permanent magnet production.

Fig 1: The Consumption of Primary Metals in the US indicates a steady trend from 1960-95, but the recycled metals consumption shows a growth of over 200 percent. (Matos & Wagner, 1996) [15].

Table 2: Yttrium, Terbium and Dysprosium show a shortfall in supply compared with other rare-earth metals.

TECHNOLOGICAL OPTIONS

Comprehensive reports are available that detail the technological options for rare earth metals recovery from spent phosphor dust [8]. A US patent is also found on the process [16]. A major initiative for resource recovery and recycling was initiated by funding from the National Science Foundation in USA. The Center for Resource Recovery and Recycling (CR³) is a multi-university Center with WPI, CSM and KU Leuven. See www.wpi.edu/+mpi. Within the Center a major portion of the research portfolio is devoted to the recovery of valuable elements. One project is devoted to the recovery of REE from magnets, another from phosphors, and bauxite etc. The matrix given below - Figure 2 - can best describe the research portfolio of CR³.

Fig 2: Matrix describing the research portfolio of the Center for Resource Recovery and Recycling (CR³).

The research group at CSM using the process flow-sheet given below has developed the recovery of rare-earth metals from the spent phosphor dust - see Figure 3. This flow sheet allows the recovery of Eu & Y separately from La, Ce and Tb with over 90% recovery of each of the metals. The RE metal oxide mixtures are over 99% pure. The first step separates most of the glass from the phosphor dust. The easily soluble oxides of Eu and Y are taken into solution and precipitated out as an oxalate. The residue is roasted at high temperature to break down the phosphates, which allows the dissolution and recovery of the difficult RE oxides of La, Ce and Tb. The optimized process includes two pyrometallurgical steps following the two acid digestion and precipitation steps, and results in the recovery of all the five RE metals contained.

Fig 3: Flow sheet for the recovery of rare-earth metals from spent phosphor dust.

The advances made in recovering an ‘exotic’ metal such as rhenium, is described here, which will allow its return to the manufacture of superalloys. Driven by the superalloy sector, which accounts for 80 percent use of Rhenium metal, an annual growth in demand of an average of 5 percent is predicted over the next five years. The current global production is estimated at 50 mT. This demand growth is triggered by an expansion in primary production capacity, greater recycling of rhenium-bearing superalloy scrap and increased use of superalloy ‘revert’. Rhenium is used as an additive to tungsten and molybdenum-based alloys, filaments for mass spectrographs and ion gauges, Rhenium-molybdenum alloys in super-conductors at 10K, electrical contact material due to high wear and arc-corrosion resistance and thermocouples of Re-W for high temperatures. In addition to being produced as a byproduct of molybdenum, it is possible to recycle rhenium during processing and after its use.

Recovery and Refining of Rhenium, Tungsten, and Molybdenum from W-Re, Mo-Re, and other Superalloy Scraps have been carried out via an oxidative pyrometallurgical roast technique. Initially, the scrap is roasted at 1000°C under an oxidizing atmosphere to convert the contained rhenium to water-soluble rhenium pentoxide (Re2O7). The volatile rhenium pentoxide is condensed in the cooler part of the tube furnace. This condensed material is then sent for digestion in water. The aqueous rhenium (ReO4-) is subsequently precipitated as potassium perrhenate upon the addition of potassium chloride via the following reaction:

(1) equation

The potassium perrhenate is filtered and further purified via continued dissolution and recrystallization. After purification, the salt is dried and sent for reduction under a hydrogen atmosphere at approximately 350°C via the following reaction.

(2)

equation

The metallic rhenium is first washed with distilled water, and then 95% ethanol to remove any residual alkali salts. (Heshmatpour, 1982)[17].

The process of Rhenium Recovery from Spent Platinum Rhenium Catalyst relies on the use of sulfuric acid for the dissolution of alumina, rhenium, and to some extent platinum. The rhenium rich solution is separated from the platinum-containing residue and separated from the aqueous aluminum using ion exchange. Rhenium is subsequently eluted from the organic amine resin by way of hydrochloric acid addition. After elution, the rhenium rich eluate is neutralized using ammonium hydroxide. This solution is then evaporated to form a supersaturated solution, and cooled to allow for crystallization of ammonium perrhenate. After continued re-dissolution and recrystallization, a high purity ammonium perrhenate precipitate is obtained (El Guindy, 1997)[18].

A process for the electrolytic decomposition of rhenium superalloys has shown favorable results (US Patent # 0110767). The developers describe a process where titanium baskets, which act as the electrodes, containing superalloy scrap are fed to a polypropylene electrolysis cell containing an 18% HCl solution. The electrolytic dissolution is carried out for 25 hours at a frequency of 0.5Hz, current of 50 amps, voltage of 3-4V, and a temperature of 70°C. The remaining scrap is then filtered from the pregnant solution and sent for further dissolution in sodium hydroxide/peroxide solution. These processes that have shown technical viability on a lab-scale have to be further optimized for commercialization.

SUMMARY

Recycling of these critical and other strategic metals will become a necessity, as demand will outstrip the supply in the future, particularly in US due to import fluctuations. Controlled and reliable source for spent secondary resources will be required. Technologies will have to be developed that are optimized not only economically but also energetically and environmentally. Better separation and scrap-sortation schemes have to be adopted followed by adequate beneficiation and chemical/metallurgical recovery processes. Just as steel and aluminum, these strategic metals primary production will have to be supplemented by secondary recovery for sustainability.

ACKNOWLEDGMENT

We thank Mr. P. Eduafo and C. Anderson, graduate research assistants at CSM, for generating the research data included in this paper. Thanks are also due to the members of the industrial research consortium of CR3- center for resource, recovery and recycling at WPI, CSM and KU Leuven.

REFERENCES

[1] United States Congressional Research Service, Rare earth elements: The Global Supply Chain, March Humphries, 2010.

[2] Sandlow, David, Keynote Address- Technology and Rare Earth Metals Conference 2010, Washington D.C., 17 March, 2010.

[3] Kingsnorth, D., IMCOA, Rare Earths: Facing New Challenges in the New Decade, presented by Clinton Cox SME Annual Meeting 2010, 28 Feb - 03 March 2010, Phoenix, Arizona.

[4] United States Geological Survey, China’s Rare-Earth Industry, Pui-Kwan Tse, 2011.

[5] Rare Earths and Critical Material Revitalization Act of 2010. H.R. 6160. 22 Sep 2010.

[6] U.S. Department of Energy. Critical Materials Strategy. December, 2010.

[7] Ellis, T.W., Schmidt, F.A., and Jones, L.L., Methods and Opportunities in the Recycling of Rare Earth Based Materials, DOE Ames Lab. Report No. IS-M-796, 1994.

[8] Schuler, D., Buchert, M,. Liu, R., Dittrich, S. and Merz, C., Study on Rare Earths and Their Recycling. Report for the Greens/EFA Group in European Parliament, Jan 2011.

[9] Zhong Xialon, Song Ning and Gong Bi., Preparation of Mn-Zn Ferrites Powder by Waste from recycling the NdFeB Magnet Scrap, Journal of Mianyang Normal University, Vol 5, 2010.

[10] Oakdene Hollins Research and Consulting, Lanthanide Resources and Alternatives, Report for Department of Transport and Department of Business, Innovation and Skills. March 2010.

[11] Linyan Li, Shengming Xu, Zhongjun Ju and Fang Wu. Recovery of Ni, Co and Rare Earths from spent Ni-metal hydride batteries and preparation of spherical Ni(OH)2, Hydrometallurgy Volume 100, Issues 1-2, Page 41-46. Dec. 2009.

[12] Bertuol, B. A., Bernardes, A.M., and Tenorio, J.A.S., Spent NiMH batteries - The Role of Selective Precipitation in the Recovery of Valuable Metals, Journal of Power Sources, Volume 193, Issue 2, Pages 914-923, Sep. 2009.

[13] Zhang, P., Yokoyama, T., Itabashi, O., Wakul, Y., Suzuki, T.M. and Inoue, K., Recovery of Metal Values from Spent Nickel-Metal Hydride Rechargeable batteries, Journal of Power Sources, Volume 77, Issue 2, Pages 116-122, Feb 1999.

[14] Mei Guangjun, Xie Kefeng and Li Gang, Progress in Study of Spent Fluorescent Lamps’ harmless disposal and resource utilization, College of Resources and Environmental Engineering, Wuhan University of Technology, China, 2007.

[15] G. Matos & L. Wagner, Consumption of Materials in the United States, 1900–1995, USGS Report, pubs.usgs.gov/annrev/ar-23-107/aerdocnew.pdf, 1998.

[16] R. Otto and A. Wojtalewicz-Kasprzak, "Method for Recovery of Rare Earths from Fluorescent Lamps, US Patent # 2009-0162267, June 2009.

[17] B. Heshmatpour, Recovery and Refining of Rhenium, Tungsten and Molybdenum from W-Re, Mo-Re and other Alloy Scraps, J. of the Less-Common Metals, vol. 86, 121-128 (1982).

[18] M.I. ElGuindy, Processing of Spent Platinum Rhenium Catalyst for Rhenium Recovery, Proc. Rhenium and Rhenium Alloys; Bryskin, B. D., Ed.; The Minerals, Metals & Materials Society Publication, Warrendale, PA, pp 89-97, (1997).

DEVELOPMENT AND APPLICATIONS OF PIPELINE STEEL IN LONG-DISTANCE GAS PIPELINE OF CHINA

Huo Chunyong, Li Yang, Ji Lingkang

CNPC Tubular Goods Research Institute, No. 89 Jinyeer Road, Xi’an, 710077, China

Keywords: Pipeline steel, oil & gas pipeline, microstructure, mechanical performance

Abstract

In past decades, with widely utilizing of Microalloying and Thermal Mechanical Control Processing (TMCP) technology, the good matching of strength, toughness, plasticity and weldability on pipeline steel has been reached so that oil and gas pipeline has been greatly developed in China to meet the demand of strong domestic consumption of energy. In this paper, development history of pipeline steel and gas pipeline in china is briefly reviewed. The microstructure characteristic and mechanical performance of pipeline steel used in some representative gas pipelines of china built in different stage are summarized. Through the analysis on the evolution of pipeline service environment, some prospective development trend of application of pipeline steel in China is also presented.

Demand of Natural Gas and Development of Pipeline in China

Natural gas, a kind of high quality, high efficiency and clean low carbon energy, plays an important role in energy structure of the world increasingly. Therefore, the application of natural gas has been paid much attention in industry and daily life. Since China has much richer natural gas resources, for example, the amount of conventional natural gas resources is 52×10¹² m³ [1], the potential of natural gas industry of China is very huge. With the increase of exploration and development, the annually production of natural gas rapidly increases, and it reaches 1.1×10¹¹ m³ in 2012, the annually increment speed is 13.3%. Although it is predicted that the consumption of natural gas in 2015 will be 2.3×10¹¹ m³ and the proportion of natural gas in primary energy consumption value will be raised to 7.5%, there still is a deep gap comparing with international average level 23.8% [2]. Consequently, there will be a great demand of natural gas consumption in China in the future.

Natural gas pipeline, the most economic way of gas transmission, has been greatly improved in China whether on construction scale or technology level after 50 years development. Low carbon steel, Q235 and 16 Mn, had been utilized in early stage of gas pipeline with low pressure and small outside diameter. The API pipeline steel had been introduced in the natural gas of China, however the steel grade basically did not exceed X65, the outside diameter was not larger than 660mm and pressure was not higher than 6.4 MPa until 2000. This stage was called the first generation of natural gas pipeline of China. In order to meet the requirement of 12 billion annual throughputs, since the 1st West East Gas Pipeline project, outside diameter 1016mm, designed operation pressure 10 Mpa and X70 pipeline steels began to be used in china [3-4]. Based on the success of application of X70 higher diameter linepipe in the 1st WEGP, the X80 pipeline steel had been used in 2nd WEGP whose designed operation pressure is 12 MPa and outside diameter reaches to 1219mm [5-6], this stage was called the second generation of pipeline of China. In terms of further improving throughput and decreasing the cost of construction, development and application of the 3rd generation of gas pipeline using much higher strength X90/X100 and much larger diameter 1422mm line pipe is being carried out by CNPC in present.

Till now, the total length of gas trunk-line has reached to 58 000 kilometers by the end of 2013. The net of trunk line has been preliminarily formed, including the 1st WEGP, the 2nd WEGP, the Sichuan-east gas pipeline, the 1st Shaanxi-Beijing gas pipeline, the 2nd Shaanxi-Beijing gas pipeline, the 3rd Shaanxi-Beijing gas pipeline and China-Myanmar gas pipeline, and the national backbone system has been also constructed by several tie lines which includes the Lanzhou-Yinchuan gas pipeline, the Huaiyang-Wuhan gas pipeline, the Jining gas pipeline and Zhongwei-Guiyang gas pipeline. In the Meantime, , three main importing channel of natural gas including the middle Asia pipeline, China-Myanmar pipeline and China-Russia pipeline is being established by CNPC, in which significant progress has been obtained in the northwestern and southwestern of on-shore strategically importing channel of natural gas in China. Up to now, the framework of gas supply of West-east gas pipeline, off-shore gas landing and close-by supply in china has been formed [2].

Development and application of line pipe in natural gas pipeline

The 1st generation of line pipe

A series of pipeline steel and line pipe, such as X52, X60 and X65, had been developed in china since 1990s. Due to the absence of the facility of producing longitudinal submerged-arc welding (LSAW) pipe in that period in China, productions mainly were hot rolled coil and spiral submerged-arc welding (SSAW) pipe. Pipes had been successfully applied in Tarim desert pipeline (X52, OD 426mm), JingXi pipeline (X52, OD 457mm), ShaanJing pipeline (X52, OD660mm), Shanwu pipeline (X52, OD 457mm) and Seninglan pipeline (X60, OD 660mm). Supplementary technical specifications for these projects had been set up based on API 5 L, in which much strict requirementS of chemical content and mechanical properties were proposed, particularly, toughness requirement to ensure the crack arrestability of pipe was stipulated. TMCP technology for coil production was required to achieve a good match of strength and toughness and a good weldability as well. The microstructure of pipe material consists of ferrite and little pearlite as shown in figure 1. Considering the lose of strength caused by Bauschinger effect and to ensure the strength of pipe could meet the specification, a much higher requirement for the strength of coil had been put forward. Figure 2 shows the change of yield strength of steel with ferrite and pearlite microstructure during the process of pie making (SSAW pipe). It can be concluded that the yield strength drops much more obviously for the coil has much higher yield strength. To ensure the yield strength of X65 pipe, the yield strength of coil shall not lower than 480 MPa [7].

Figure 1. Ferrite-pearlite microstructure of X60 pipeline steel.

Figure 2. Change of yield strength of ferrite and pearlite pipeline steel before and after pipe making

The 2nd generation of line pipe

To meet the demand of the annual throughput of 1.2×10¹⁰ m³ in the end of 1990s, the 1st WEGP was designed to use pipe with an outside diameter 1016mm and an operation pressure 10 MPa. To decrease the construction cost of pipeline, X70 line pie with much higher strength was firstly proposed in China for this project. The application technology and development of X70 steel and pipe had been performed by CNPC.

Selection of pipe type. There had been a controversy for a long time in the world on the fact whether spiral pipe can be used in high pressure gas pipeline. At the beginning of 1st WEGP, it was considered that comparing with LSAW pipe, SSAW pipe had many defect, such as long weld seam, high residual stress, poor dimensional accuracy, poor pipe performance due to large fluctuation of coil’s properties. Since there was only SSAW pipe in China and a very few production line of LSAW pipe in China was on demonstration stage in that period, if LSAW pipe was selected, all pipes used in the 1st WEGP should be imported which would bring great challenges for construction cost and schedule control. A feasibility study on the application of SSAW pipe in gas pipeline had been lunched by CNPC. Through systematic analysis on production and inspection capability of domestic manufactures, the property and quality of X70 high strength coils could meet the requirements of production of SSAW pipe. Controlling capability of pipe forming had been greatly enhanced through upgrading and rebuilding on domestic SSAW pipe forming equipment. Welding defect could be effectively controlled with reliable automatic ultrasonic and X-ray inspection system. For residual stress in SSAW pipe, a forming methodology with low residual stress was adopted and residual stress controlling requirements were proposed as well. It had been shown that domestic large-diameter SSAW pipe after strict quality controlled can comply with the technical specification [8].

Development and application of X70 pipe. In order to promote the large-scale application of X70 pipes in the 1st WEGP, Se-Ning-Lan gas pipeline, an X70 trial, was built with diameter 600mm and wall-thickness 10.3mm pipe, and its total length was 11 kilometers. The feature of X70 pipe’s property was obtained and welding materials and technology were developed, which brought the 1st WEGP a vital support on the application of X70 pipes.

Microstructure controlling of X70 pipes. Except for high strength and good toughness, steel with microstructure of acicular ferrite has continuous yielding behavior and high strain hardening ability due to high density movable dislocation in acicular ferrite lath. This feature can compensate and counteract losing of strength caused by Bauschinger effect. So, the requirement of strength of X70 pipe materials can be reduced and a better homogeneity of microstructure and match of strength and toughness can be obtained by using microstructure design of acicular ferrite. Consequently, the requirement of acicular ferrite in microstructure had been stipulated in specification of X70 pipe for the 1st WEGP. It is presented that the X70 pipeline materials has good match of strength and toughness and uniform and fine structure as shown in figure 3. The statistical analysis on the variation of yield strength during pipe forming shows that the average value of yield strength drops with 9 MPa and 4MPa respectively for mill A and B, see figure 4.

Figure 3. Acicular ferrite microstructure of X70 pipeline steel

Figure 4. Statistical results of yield stress before and after forming process

Arrest toughness of ductile fracture in X70 pipeline. Since cleavage fracture in gas pipeline can be generally avoided for the progress of metallurgical technology, the arrest of long-distance running ductile fracture becomes the key problem in technical specification. In terms of API Spec 5L or ISO 3183, BTC Simplified equation can be used for arrest toughness calculation for the main index of 1st WEGP using designed operation pressure 10MPa, 1016mm outside diameter and lean gas. Meanwile, since that the operation parameter of the 1st WEGP is covered by the full-scale burst test database of X70 pipe, the predicted arrest toughness is valid. Since the predicted value was 83J, lower than 94J, it is no need to correct the calculated arrest toughness based on full-scale burst test database. However, an obvious fracture separation was found on the fracture of X70 plates and coils initially produced by domestic steel makers, the maximum value of CVP/CV100 was even up to 1.7. The arrest toughness in the specification of 1st WEGP was determined by a conservatively correction methodology which is calculated value multiplying fracture separation index 1.7. Additionally, considering that X70 pipe was firstly used in China, the corrected arrest toughness was required for the minimum individual value of Charpy impact energy for the sake of security of the 1st WEGP. Therefore, the arrest toughness of X70 pipe used in the 1st WEGP was stipulated that the minimum individual value is 140J and the minimum average value of three specimens is 190J. When testing temperature is −20°C, charpy energy still maintains 200J and above, the maximum value is even up to 400J as show in figure 5.

Figure 5. Charpy energy and shear area of pipe body and its transition curve

Research and application of X80 line pipe. In order to meet the requirement of much larger throughput and much lower cost for long-distance gas pipeline, the application feasibility of X80 linepipe in the 2nd WEGP was proposed on the basis of successful application of X70 linepipe. Firstly, Jining tieline with length of 7.6 kilometer using X80 linepipe was constructed in china to ensure the application feasibility of X80 linepipe in high pressure gas pipeline of China from which the capability of production and construction was demonstrated and a good foundation for large-scale application of X80 pipe in the 2nd WEGP had been established.

Arrest control of ductile fracture. Challenges for arrest control of ductile fracture in the 2nd WEGP are much higher strength, larger diameter and wall-thickness, particularly approximate rich gas (C1>92.4%, C2>3.55% and C3>1.4%) was used. According to ISO3183:2007, Battelle Two Curve Model (BTCM) should be used for arrest toughness predication instead of Battelle Simplified Equation [9]. In terms of the full-scale burst test database of X80 pipe in the world, a correction factor 1.43 was determined. The prediction of arrest toughness of the 1st class district of the 2nd WEGP was performed as figure 1 shown, in which related parameters are 1219mm diameter, 12MPa pressure and 0.72 design factors. Considering the variation of temperature and pressure among compressor stations and the requirement of toughness for the possible lowest temperature in the condition of shutdown for pipeline, arrest toughness of pipe was finally determined as 220J.

Table 1. Prediction results of arrest toughness for the 2nd WEGP

Till now, all the full-scale burst tests of X80 pipe had been carried out using lean gas or air, and no data of X80 spiral pipes. While, transmission medium of the 2nd WEGP was approximate rich gas, and it is the first time in the world to large-scale use X80 spiral pipes in high pressure gas pipeline. Therefore, the arrestability of X80 LSAW pipe and the reliability of arrest toughness of X80 stipulated in the specification were needed to be verified by full-scale burst tests on X80 pipe so that the security of the 2nd WEPG can be insured.

A full-scale burst tests on X80 pipes were conducted by TGRI in 2011 at the test site of CSM in Sardinia of Italy. The test line adopted 72% SMYS stress factor was designed as one side using X80 spiral pipes and another side using X80 longitudinal pipes with a telescope layout of pipe on both sides [10]. The test line was pressurized with rich gas (88% methane) up to a pressure of 12.04 MPa and the burst was initiated by means of a 500mm long explosive charge located on the upper generatrix of the initiator pipe. The explosion created a through thickness cut on pipe. The pipe wall temperature (~15°C) was high enough to ensure the fully ductile fracture propagation. Fracture was regularly injected and propagated with a very high speed along longitudinal directions. Fracture arrested on first pipe on West side (pipe W1) and on second pipe on East side (E2). It is observed from figure 6 that crack speed increased rapidly along the pipe I up to a peak value of about 300m/s and subsequently decreased down to ~235m/s as it entered pipe W1. Here, a slowdown of the fracture occurred (down to ~100m/s) as arrested. Figure 6 also shows that after initiation, the fracture rapidly speeded up along pipe I up to about 350m/s. As it entered pipe E1, fracture slowed down and propagated in the last part of the pipe with a speed about 150 m/s. As it entered the second pipe (E2) crack speed decreased until arrest occurred.

Figure 6. Full scale burst test Fan diagram and crack speed plot

It can be observed from the figure 6 that the crack propagation in the west side of the line arrests on the spiral pipe W1 with a Charpy energy of 198J and in the east side of the line arrests on the longitudinal pipe E1 with a Charpy energy of 233J. It can be concluded that the arrestability of X80 SSAW pipe is not lower than X80 LSAW pipe. When analyzing the test results combined with full-scale burst test database of X80 pipe, for 72% SMYS design factor, the conservative correction factor 1.29~1.46 can be found. From results, the doubts on arrestability of X80 SSAW pipe can be eliminated, and the security of the 2nd WEGP can be guaranteed.

Requirements of X80 pipe used in strain-based design. The methodology of strain-based design had been applied in seismic fault and possible area of ground movement of the 2nd WEGP. Pipes used in these areas shall have a certain buckling deformation resistance except that comply with the requirements of conventional X80 pipes. The related technical requirements were studied based on the FE analysis on strain capacity and tests of X80 pipe with large diameter. In the same time, thermo coating temperature of X80 pipe used in Strain-based design area were defined on the consideration of change of performance insulted by strain aging.

Strain capacity of pipe is related to the strain hardening ability of materials. It is reported that the line pipe steel which has the round house S-S curve has a better deformation capacity and a higher buckling strain than that which has the Luders elongation S-S curve [11]. So, the shape of S-S curve along longitudinal direction of high strain pipe shall be round-house as figure 7 shown.

Figure 7. Round house S-S curve of X80 high-strain line pipe

Anticorrosive coating on external surface and anti-drag coating to improve transmission efficiency is needed for all pipes in gas pipeline. Temperature on surface of pipe would be up to 250°C during the thermo coating process. Although this temperature can not lead to the obvious change of microstructure in pipe, the S-S curve can be changed frequently which can not only result in the occurrence of yield platform but also improve the yield stress and yield ratio of materials with roundhouse-shaped S-S curve after thermo coated. It is often found that strain capacity declines because pipes’ performance can not comply with the requirement of hardening capacity of material, e.g yield ratio and stress ratio. Fig.8 is the test results of yield strength and tensile strength in different conditions of aging temperatures and aging times for X80 pipe. It can be seen that with the aging temperature increased and aging time extended, tensile strength does not change, but yield strength increase obviously. Actually, the coating time is about 5 minutes. According to the test results of 5 minutes aging, when the coating temperature is below 220 degree (even 220 degree), yield strength has no obvious change. Therefore the coating temperature may recommend as below 200 degree. Table 2 shows the technical requirement of X80 high-strain pipe for the 2nd WEGP [12].

Figure 8. The effect of strain aging on strength of X80 linepipe

Table 2. Technical requirements of X80 high-strain pipe along longitudinal direction

Development Tendency and Challenge of Gas Pipeline

With the growth of Chinese economy, the strong demands of natural gas will last and present supply of natural gas will be far from meeting consumption. Great challenges have emerged in the new gas pipeline for the need of large throughput and economic efficiency. Therefore, much higher strength and much larger diameter becomes the inevitable choice. A research on the application of X90 and X100 pipe has been launched by CNPC on the basis of successful utilization of X80 pipe in the 2nd and 3rd WEGP. Although a lot of works have been performed on X100 pipe by some organization in the world, such as fracture control, strain control and welding materials and technology, there will be a series of problems need to be resolved with the aim of large-scale application of X90/X100 pipe in high pressure gas pipeline.