Development of Repair Mechanism and Life Estimation of IN-939 Based Powerplant Components: Part Three

by Md. Tawfiqur Rahman

To help meet the ever increasing demands of fossil fuel powerplants and the associated stringent efficiency requirements, all aspects of material selection are critical to ensuring an overall increased material lifecycle within the plant.
During this investigation two distinct repair methodologies were used; pre- and post-weld heat treatment and TIG welding using suitable filler metals for turbine blades and TIG welding repair using suitable filler metal followed by a post-weld Heat treatment for turbine vanes.

APPROACH AND METHODOLOGY:

IN 939 falls into the group of the nickel-based precipitation hardened superalloy. Gas turbine manufacturing companies like Alstom, Siemens, Simens-Westing house use this superalloy as their nozzle material. Besides, it is also used as a material for retaining ring, diffuser, and other structural members of the gas turbine. [4][5] By reducing the maintenance cost of the power plant, the cost of electricity can be minimized. For this reason, the author studied the microstructural degradation mechanism of IN 939 and will develop a repair mechanism for them by using TIG welding and heat treatment. This enables gas turbine users to repair cracked IN 939 based nozzles and use them further. And as a result, the extra replacement cost can be avoided.

Study of the microstructure of IN 939 shows the following observations:

 



Table 1: Major changes in phases of IN 939 microstructure before and after service: Note. (1) From “ASM Specialty Handbook: Heat-Resistant Materials,” by Joseph R. Davis,1st ASM International, p. 224-233. and (5) Delargy, K. M., & Smith, G. D. (1983). The phase composition and phase stability of a high-chromium nickel-based superalloy, IN939. Metallurgical Transactions A.

 

Due to the detrimental effects of microstructural degradation, IN939 based gas turbine components are fractured. IN939 is a nickel-based superalloy. So, the fractures in it can be repaired by TIG welding. [6] In the preceding paragraph a proposed mechanism of the repair welding process of IN939 based gas turbine components will be described.

Repair of IN 939 Based Gas Turbine components:

The repair process will be of two types and service dependent. In the first group where the components operate under higher stresses like turbine blades the process consisting of both pre- and post-weld heat treatment and TIG welding using suitable filler metal. On the other hand, in the second group where the components operate under lower stresses like the turbine vanes the process consisting of TIG welding repair using suitable filler metal followed by a post-weld Heat treatment.

 



Figure 1: WORKFLOW OF TYPE-1 REPAIR MAINTENANCE WORK

 

 



Figure 2: WORKFLOW OF TYPE-2 REPAIR MAINTENANCE WORK

 

 



Table 2: WELDING SPECIFICATIONS FOR TYPE-1 and TYPE-2 REPAIR MAINTENANCE WORK

 

 

References

1. Davis, J. (1999). Heat-resistant materials. 1st ed. Materials Park, Ohio: ASM Internat.
2. Geddes, B., Huang, X. and Leon, H. (2010). Superalloys. 1st ed. Materials Park, Ohio: ASM International.
3. Davis, J. (2007). Nickel, cobalt, and their alloys. Materials Park, OH: ASM International.
4. Peng, J., Zhang, H., & Li, Y. (2015). Review of Blade Materials for IGT. Procedia Engineering, 130, 668-675. DOI: 10.1016/j.proeng.2015.12.295.
5. Delargy, K. M., & Smith, G. D. (1983). The phase composition and phase stability of a high-chromium nickel-based superalloy, IN939. Metallurgical Transactions A, 14(9), 1771-1783. DOI:10.1007/bf02645547.
6. Donachie, M. J., & Donachie, S. J. (2002). Superalloys a technical guide. MaterialsPark: ASM International.
7. Shaw, S. (1980). The response of IN-939 to Process Variations. Superalloys 1980(Fourth International Symposium).doi:10.7449/1980/superalloys_1980_275_284.
8. Development of repair mechanism of FSX-414 based 1st stage nozzle of the gas turbine. (2017). [online]Available at https://aip.scitation.org/doi/10.1063/1.4984690.
9. Lippold, J., Kiser, S., and DuPont, J. (2013). Welding metallurgy and weldability of nickel-base alloys. Hoboken, N.J.: Wiley.
10. Kitteringham, G. (1987). High-Temperature Alloys for Gas Turbines and Other Applications 1986. High-Temperature Technology, 5(1), 52-54. DOI:10.1080/02619180.1987.11753341.
11. M. Motarri, M.M. Shokrieh, H.Moshayedi.2020, Effect of residual stresses induced by repair welding on the fracture toughness of Ni-based IN939 alloy
12. Dae-Young Kim, Jong-Hyun Hwang, Kwang-Soo Kim, Joong-Geun Youn, A Study on Fusion Repair Process for a Precipitation Hardened IN738 Ni-Based Superalloy
13. R.A. Ainsworth, The treatment of thermal and residual stresses in fracture assessments, Eng. Fract. Mech. 24 (1986) 56–76
14. Y.S. Park, T.K. Kim, D.H. Bae, Assessment of fracture mechanical characteristics including welding residual stress at the weld of Ni-base superalloy 617, 19th European Conference on Fracture, 2012, pp. 163–170.
15. Enhancing power output and profitability through energy-efficiency techniques and advanced materials in today’s industrial gas turbines Zainul Huda, Tuan Zaharinie2and Hany A Al-Ansary
17. Effects of Filler Metals on Heat-Affected Zone Cracking in IN-939 Superalloy Gas-Tungsten-Arc Welds, H. Kazempour-Liasi, M. Tajally, and H. Abdollah-Pour
18. ASTM-E1820-15, Standard test method for measurement of fracture toughness, in, American Society for Testing and Materials, Philadelphia, 2015.
19. Effects of pre- and post-weld heat treatment cycles on the liquation and strain-age cracking of IN939 superalloy To cite this article: H Kazempour-Liasi et al 2019 Eng. Res. Express 1 025026

April, 2021
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