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

Md. Tawfiqur Rahman

ทฤษฎี:

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.
Applying a combination of heat treatment processes and fillers for different tested maintenance repairs it is possible to then use a combination of mechanical testing to assess the results.

Methodology:

HEAT-TREATMENT PROCESS SELECTION FOR TYPE-1 REPAIR MAINTENANCE WORK:
A three-stage heat treatment will be prescribed before repair welding. It is 1160°C/4 h + FC/ to 920°C (rate 2°C min−1 ) + AC. This treatment provides good ductility which is helpful for repair welding. [19]. Besides, A four-stage heat treatment will be prescribed after repair welding. It is 11600°C/4 h/AC + 1000°C/6 h/FAC + 900°C/24 h/AC + 700°C/16 h/AC. This treatment provides stress relief after welding. [17]

HEAT-TREATMENT PROCESS SELECTION FOR TYPE-2 REPAIR MAINTENANCE WORK:
A three-stage heat treatment will be prescribed before repair welding. It is 1160°C/4 h + FC/ to 920°C (rate 2°C min−1) + AC. This treatment provides good ductility [19]. For this type of filler and base, metal selection post-weld heat treatment is prohibited. [9]

FILLER FOR TYPE-1 REPAIR MAINTENANCE WORK:
In this type of maintenance work, the high strength of this welding is required because we will deal with components that will operate under high stress. This similar type of filler metal will be chosen with a relatively low modulus of elasticity. Because of residual stress development dependent upon this physical property of the material. [11]

FILLER FOR TYPE-2 REPAIR MAINTENANCE WORK:
In this process filer metal IN-617 and base metal are different, but it is chosen for these two below mentioned reasons.
Firstly, the base material is a precipitation-hardened alloy, and filler metal is solution hardened superalloy which is relatively softer than the base material. We know that nickel base, precipitation hardened superalloy is possessed a tendency to form solidification cracking during welding if we use matching filler during welding. But if we use soft filler like IN 617, the chance of formation of solidification cracking will be minimized. [9]

Secondly, the nozzles are subjected to lower stress levels in-service conditions and its thickness is also thin. So, a dissimilar filler like this can be used for this repair welding purpose. [10]

HEAT INPUT FOR BOTH TYPES OF MAINTENANCE WORK:
Filler metal thickness is an important factor to achieve sound weld and depends on the base material thickness. Because by varying filler metal diameter we can control heat input. A table is presented below for different welding parameters associated with base metal thickness. The data will be used for the repair welding purpose of IN 939. Depending on the practical conditions necessary adjustments will be made. [6]

Heat input is an important parameter for this repair welding. [8] If it is higher than requirements cracks can occur during welding. So, to control this parameter diameter of filler metal can be taken into account.

The available filler metal in the market may not be suitable for this task. For this reason, a bench grinder will be used to reduce the thickness of filler and make it conform to the required task.


Note: From “Superalloy: A Technical Guide,” by Mathew J. Donachie, Stephen J.Donachie, 2002, 2nd ASM International, p.164.

Table 3: Welding Parameters

Furthermore, a finite element-based model in ANSYS with a moving heat source will be developed to estimate the residual stress which may produce in welding for a cross-checking purpose.

MECHANICAL TESTING:

Mechanical testing is very important in this research work. The success of the research depends on the results obtained through these tastings. We know that to conduct the testing phase successfully there is a need for physical properties data such as young's modulus of elasticity, density, etc. are required. These data will be collected from the Total Materia [17] database. Especially the data for young's modulus of elasticity is very sensitive because residual stress formation depends upon this parameter. [11]

The CT specimen will be extracted from the components based on ASTM E1820-15.[18]. Fracture toughness test will be performed according to ASTM E1820-15, with the aid of this testing result remaining life of the weld repair component will be calculated.


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

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