ETAM Performance Research on Large Diameter P91 produced by Hot expanding process

Transcription

1 Proceedings of the ASME Symposium on Elevated Temperature Application of Materials for Fossil, Nuclear, and Petrochemical Industries March 25-27, 2014 ETAM Performance Research on Large Diameter P91 produced by Hot expanding process Lijun Yin China Special Equipment Inspection and Research Institute Beijing, China Guang Wu Dexin Steel Pipe (China) Co., Ltd. Wuxi, Jiangsu, China Tong Xu China Special Equipment Inspection and Research Institute Beijing, China Binan Shou China Special Equipment Inspection and Research Institute Beijing, China delivery times and unlimited order quantity, MFLHEDP has become an important supplement to the traditional production processing of steel pipes. ABSTRACT Abstract: The Medium Frequency Local-Heating Expanding Diameter Process (MFLHEDP), also called the hot-expanding process, can produce large diameter thin-wall steel pipes. Because of its advantages, such as low cost, short delivery time etc., MFLHEDP becomes an important supplement for the traditional processes of seamless steel pipe manufacturing. In the presented study, the short-term mechanical properties and the high-temperature long-term rupture strength of a P91 pipe the diameter of which was expanded using MFLHEDP, were tested. The experimental result shows that the performances of the P91 pipe produced by MFLHEDP can meet the requirements of the applicable standards. 2. MAIN PRODUCTION PROCESS A qualified finished P91 was selected as the mother pipe, and this pipe was expanded by using MFLHEDP from Ø to Ø (mm). After heat treatment, its mechanical properties were tested. Next, the pipe was straightened, and ground and both the inside and outside surfaces were polished. Finally, UT, ET, hydrostatic testing, and dimensional checks were carried out (Refer to the following process chart). 2.1 Process Chart Key words MFLHEDP Large diameter hot expanding pipe P91 performance research Mother Pipe 1. INTRODUCTION With the rapid development of the petroleum, chemical and electric power industries, the demand for large diameter thin-walled, extra thin-walled, and irregular dimension seamless steel pipes increases substantially. Because pipes with a Diameter/Wall-thickness ratio greater than 50 are not easy to produce, the development of the Medium Frequency Local-Heating Expanding Diameter Process (MFLHEDP) has been promoted in recent years. MFLHEDP supplements traditional hot rolling processes. Similar production processes have been widely applied in the manufacture of pressure pipe fittings. MFHPEDP is good at the manufacture of large diameter thin-wall steel pipes, extra thin-walled steel pipes, and specially sized steel pipes, and due to its low cost, short Diameter expansion Marking inspectio Lubricant Select mandrel Mechanical testing Heat treatmen UT ET or Hydro End Straightening Inside and Outside Surface Treatment; Dimensional Waste product Storage Fig.1. Process Chart 1 Published with permission.

2 2.2 Hot expanding Equipment used in the hot expanding process includes a special expanding machine, a cone mandrel and an automatic constant temperature heating device. A pipe is expanded by pushing forward the mother pipe over a cone-shaped mandrel inserted inside the pipe. First, debris and oxide scales must be removed from the inside and outside surfaces, and then a coating of lubricant should be applied. The lubricant is a mixture of graphite, scales and water with the moderate proportion. The cone-shaped mandrel used for expanding the pipe must have a smooth surface, with no scratches or irregularities allowed; in general, the mandrel is made from stainless heat resistant steel1cr25ni20. The schema of a cone-shaped mandrel is shown in Figure 2. Fig.2. Schema of a Cone -Shaped Mandrel A1 import area A2 deformation area A3 sizing area A4 flat area A5 Straightening area D1 Import area diameter D2 Sizing area diameter D3 diameter of Straightening area α Angle deformation area L1 Import area length L2 Deformation area length L3 Sizing zone length L4 Flat area length L5 Straightening area length Fig.3. Controlling system of Medium Frequency Heating 1 Heating coil and heating pipe 2 Medium frequency heating device 3 Far infrared thermometer 4 Temperature, the electrical signal (V, I) converter 5 DCR intelligent control center 6 Data display, storage, printing, transfer and other peripheral equipment The measured data of the three parameters, including heating temperature, pushing system pressure, and pushing speed, can be stored in the form of curves or historical data in the industrial personal computer (IPC) as the original record of hot expanding pipe, and it can be exported by the form of database or print. 2.3 Heat treatment The hot expanded pipe was normalized and tempered. The heat treatment curve is shown in Figure 4. Heat treatment parameters are shown in Table 1. The heating method for the hot expanding is medium frequency induction heating. The temperature range of deformation is 750 ± 10. The mother pipe is heated by the medium frequency induction coils. The medium frequency heating system is operated through the automatic numerical control, i.e. the DCR intelligent temperature closed-loop induction heating system (see Figure 3). Whenever the heating temperature is set, this system maintains the temperature stably during the process, no matter how the voltage, current, or other outside factors change. The temperatures of the inner and outer surfaces of the steel pipes are almost the same. Fig.4. Heat treatment curve 2 Published with permission.

3 Normalizing Table 1 Heat treatment parameter 1050 holding 40min air-cooling Tempering 760 holding 80 min air -cooling Heating rate <300 /h Heating rate <300 /h Temperature variance during holding time ±5 Temperature variance during holding time ±5 3. Testing and inspection results 3.1 Chemical composition The chemical composition of the hot-expanded pipe relative to the requirements of ASTM SA335 [1] is shown in Table 2. As shown, the chemical composition meets the requirements of ASTM SA335. A and B represent both ends of the pipe. SA335 Table 2 Chemical composition C Mn P S Si Cr Mo ~ 0.25~ 8.00~ 0.85~ ~ A B V N Ni Al Nb Ti Zr SA ~ ~ A B Mechanical properties Tensile properties at room temperature Tensile test samples were cut from the half thickness location of the pipe to represent both the longitudinal and transverse directions. Tensile tests were conducted at room temperature, and the results are shown in Table 3. Table 3 Tensile Properties at room temperature Sampling Sampling R p0.2 R m direction location (MPa) (MPa) A(%) Z(%) Longitudinal A B Transverse A B SA ( longitudinal) 13( transvers) / As can be seen, the tensile properties at room temperature meet the requirements of ASME SA335. The location and direction of the sampling has no effect on the pipe s tensile properties. It shows that the tensile properties of the pipe are quite uniform Impact test at room temperature The evaluations were performed according to the Chinese standard GB [2,3] ( 10Cr9Mo1VNbN listed in the GB is equivalent to ASME SA335 P91). The dimensions of the Charpy V-notch specimens are 10mm 10mm 55mm, and the results are shown in Table 4. Table 4 Impact test at room temperature Sampling Sampling location Impact energy AK V (J) direction A 189 A 197 A 220 Longitudinal B 221 B 229 B 215 A 185 A 174 A 198 Transverse B 208 B 214 B (longitudinal) GB Cr9Mo1VNbN (P91) 27(transverse) The data shows that the impact energy at normal temperature is much higher than the requirements of Chinese standard GB Tensile test at elevated temperature Tensile tests at elevated temperature were conducted with longitudinal samples cut from the half thickness location.. The results have been tabulated in Table 5. Table 5 High temperature tensile test sampling temperature( ) Rp 0.2 (MPa) R m (MPa) A(%) Z(%) positions A B A B A B ASME Sec Ⅱ,Part D / / / / ASME Sec Ⅱ, Part D contains no information pertaining to the high temperature tensile properties of P91 above 600.Table 5 shows that the location and direction of the samples have no effect on the tensile properties, indicating that the hot-expanded pipe has uniform tensile properties. 3 Published with permission.

4 3.2.4 Hardness test The results of hardness test are shown in Table 6. Table 6 Hardness test sampling positions hardness(hb) A B The above data shows that the whole pipe has uniform hardness Flattening test Flattening sample exhibited no crack, and also no visible delaminating, white point, inclusions. 3.3 Macroscopic test No coarse grain area, cracks or others defects were found during the macroscopic test. Longitudinal B Fig.5 Non-metallic inclusion Non-metallic inclusion meets the requirement of GB Non-metallic inclusion The non-metallic inclusion evaluation was carried out according to method A of GB/T10561 [5], and the evaluations were performed according to GB ( 10Cr9Mo1VNbN listed in the GB is equivalent to ASME SA335 P91), the results of test are shown in Table 8, Non-metallic B aluminum D spherical A sulfide C silicate sampling oxide oxide DS single particle position crud spherical class fine crude fine crude Fine crude fine e A B GB requirem ent Sum of fine class A B C D 6.5 Sum of crude class A B C D inclusion of different position are shown in Figure 5. Longitudinal A 4 Published with permission.

5 3.5 Microstructure and grain size The microstructure and grain size were evaluated according to GB ( 10Cr9Mo1VNbN listed in the GB is equivalent to ASME SA335 P91). The grain sizes of longitudinal and transverse samples were at the level and the microstructure is tempered Martensite. There was no evidence of overheated structure (See Figure 6). Transverse B Fig.6. Microstructure Longitudinal A 3.6 High temperature stress rupture test The high temperature stress rupture testing was carried out using rod tensile sample Φ5 at 625. The rupture time under different loads is shown in Table 8. Based on data processing and analysis of creep rupture test results, rupture strength curve(see Figure7) can be obtained which can deduce that the rupture strength for 10 5 h is 80.6MPa at 625, and that is greater than the 68.25MPa which specified in ASME BPVC Section Ⅱ Part:D [4]. Table 8 Rupture time under different loads Longitudinal B No. Force ( Rupture Load ( Rupture No. MPa) time(h) MPa) time(h) h h h h h h h h h h The stress rupture strength curve is obtained by Non-linear fitting of data using Origin with the fitting formula yscale(y)= A+B*xscale(X). Parameters are listed in table Table 9. Table 9. Parameter of fitting formula Name Value Standard Error Adj. R-Square: A B Transverse A 5 Published with permission.

6 [3] EN :2002, Seamless steel tubes for pressure purposes Technical delivery conditions, Part 2: Non-alloy and alloy steel tubes with specified elevated temperature properties. [4] 2007 ASME Boiler&Pressure Vessel Code, Section material s, Part D: Properties, ASME Boiler and Pressure vessels Committee [5]GB/T10561:2005,[3] GB/T10561:2005,Steel. Determination of content of nonmetallic inclusions. Micrographic method using standards diagrams[s]. Standardization Administration of the People s Republic of China Fig.7. Rupture stress curve 3.7 Nondestructive testing All steel pipes have been checked by ultrasonic tests and eddy current tests, and no defects were found. All products satisfied the requirements specified in ASTM A 213 and in ASTM E Surface Inspection Pipe inner and outer surfaces contained no cracks, folds, separation layers, scars, oxide scales, or scratches, therefore, the surface quality is good. 4.Conclusion 1. Results of tests and inspection show that the pipe produced by MFLHEDP can satisfied the requirement of interrelated standards. 2. MFLHEDP can be used to produce pipes which are difficult to produce using traditional forging or hot rolling methods, such as large diameter thin-walled and extra thinwalled pipe. 3. MFLHEDP is feasible, stable, and reliable, and it can meet the requirements of power plant boilers. ACKNOWLEDGMENTS This paper is sponsored by the 12th Five-year China National Key Technology R&D Program, No. 2011BAK06B04. REFERENCES [1] 2007 ASME Boiler & Pressure Vessel Code, SectionⅡ- Materials Part A, SA-335: Seamless Ferritic Alloy-Steel Pipe for High-Temperature Service[S].ASME Boiler and Pressure vessels Committee [2] GB 5310:2008,Seamless steel tubes and pipes for high pressure boiler[s]. Standardization Administration of the People s Republic of China Published with permission.