PSI - Issue 60

Cyril Reuben Raj et al. / Procedia Structural Integrity 60 (2024) 709–722 Cyril Reuben Raj / Structural Integrity Procedia 00 (2024) 000 – 000

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in ultimate tensile strength for the thermally aged specimens as compared with the as-welded specimens and experiences less tensile strength in the weld zone in comparison to the base metal. Chen et al. (2020) predicted the corrosion behavior in the austenitic stainless steel with the influence of thermal aging and concluded the duplex oxide film formation and formations of Fe and Ni concentrations in the oxide particles, which leads to higher point densities and reduced EIS resistances. Ferrite hardness increases with thermal aging hours, but austenite hardness remains constant. Upon microstructural revelations, higher stress concentrations on the phase boundaries causes the phase boundary separation and the austenite phase splitting off [Li et al. (2013), Kumar and Shahi (2016)]. From the above literatures, it is clearly evident that the nature of embrittlement may vary according to the thermal aging temperatures, period and material properties. Higher ferrite content weldments leads to degrade faster upon accelerated thermal aging. Hence, it is solely dependent on the quantity of ferrite content in the weldments. Our research focuses on the similar austenitic stainless steel 304LN material, where very few researches has been done on thermal aging aspects. In this paper, pipe weld joint of 304LN material prepared with ER308L/E308L consumables has been thermally aged for 10,000 and 20, 000 hours at constant temperature 400℃. The specimens were fabricated from various locations of the pipe weld joint for tensile, hardness and metallurgical examinations. The specimens removed from specific locations i.e. weld zone and heat affected zone of both SMAW and GTAW sections, depicts its unique characteristics concerning test outcomes which was detailed in this research. The observations of the test results obtained from the thermal aged specimens were compared to the as-welded specimen to understand the after effects of thermal aging. This research observation on the effect of thermal aging in the similar stainless steel weld 304LN material would help in long-term operation of light water based nuclear power plants. 2. Materials and methods Austenitic stainless steel pipes were welded with Gas Tungsten Arc Welding (GTAW) upto thickness 6 mm and further proceeded with Shielded Metal Arc Welding (SMAW). The chemical composition obtained from Energy Dispersive X-ray Spectroscopy (EDS) are given in the Table 1 and the welding parameters are provided in the Table 2. Before welding, two similar pipes of dimensions 300 mm in length, 324 mm in diameter and 24.5 mm in thickness were machined accurately to make a conventional v-groove. The pipes were properly cleaned mechanically by using emery paper and chemically using ethanol to restrict dust accumulation or other foreign particles. Initially a full penetration weld was achieved in the root pass with GTAW and subsequent two passes with the use of tungsten filler wire. The filling passes were carried out with SMAW. Filler wire ER308L was used for GTAW and electrode E308L for SMAW. After welding, the welded joint was inspected by Radiographic testing and was found to be free from defects. Table 1. Chemical composition of Austenitic Stainless steel 304LN pipe materials [Dubey (2006)]. Elements in Wt% C Cr Ni Mn Mo Cu Si Al P S Fe SS 304LN 0.023 18.13 8.17 0.82 0.26 1.07 0.46 0.027 0.024 0.001 71.015 ER 308L 0.03 20.1 10.3 1.8 0.1 0.03 0.5 - 0.01 0.01 - E 308L 0.024 16.29 10.18 0.89 2.04 - 0.44 - 0.031 0.03 -

Table 2. Welding parameters used in the present work. Process Joint Design No. of pass Inter-pass temperature

Flux

Filler Wire Diameter

Current

Voltage

Travel Speed

GTAW

Single compound-V Single compound-V Single compound-V

Root-2 pass Root-2 pass 3-8 pass

15 0 ℃

Argon

3.2 mm

110-130 A

15-20 V

30-50 mm/min 30-50 mm/min 60-80 mm/min

GTAW

15 0 ℃

Argon

1.6 mm

90-120 A

15-20 V

SMAW

110 ℃

Basic coated

3.14 mm

100-140 A

20-25 V

2.1. Thermal aging of Austenitic Stainless Steel pipes