Performance Analysis of Dissimilar Metal Welded Pipe Joints

Performance Analysis of Dissimilar Metal Welded Pipe Joints

Okachi, I. I

Department of Mechanical Engineering, Rivers State University,

Nkpolu Oworowurokwo, Port Harcourt, Rivers State.

Adiuku, Udochukwu

Department of Mechanical Engineering, Rivers State University,

Nkpolu Oworowurokwo, Port Harcourt, Rivers State.

Abstract – This study investigates the performance of dissimilar metal welded (DMW) joints between carbon steel (ASTM A106) and austenitic stainless steel (AISI 304) using ER309L filler metal, focusing on their mechanical integrity, microstructural stability, and reliability under high- temperature and high-pressure conditions. DMW joints combine the strength of carbon steel with the corrosion and thermal resistance of stainless steel but are prone to challenges such as residual stress, carbon migration, and intermetallic phase formation. Experimental testingincluding tensile, hardness, impact, and corrosion assessmentswas combined with finite element analysis (FEA) in ANSYS to evaluate residual stress, thermal distribution, and fatigue life. Results show that the carbon steel heat-affected zone (HAZ) is the weakest region due to grain coarsening and carbide precipitation. Microstructural analysis confirmed carbon migration across the fusion interface, forming brittle carbides and delta ferrite phases. The fusion zone displayed higher hardness (225 HV) than both base metals, while the carbon steel HAZ exhibited localized softening (~180 HV). FEA results correlated with experimental observations, identifying maximum residual stresses near the carbon steel HAZ (315 MPa). Weibull reliability analysis indicated accelerated failure rates above 450 °C due to creep and thermal fatigue. Compared with other dissimilar joints (CuCS, AlCS, BrAl), CSASS welds demonstrated superior tensile strength (~490 MPa), toughness, and fatigue resistance. Optimized welding parameters, low heat input, nickel-based fillers, and post-weld heat treatment (PWHT) significantly enhanced reliability. These findings support the adoption of ER309L-based CSASS joints in critical piping systems requiring high mechanical performance and corrosion resistance.

Keywords: Dissimilar metal welding, carbon steel, stainless steel, ER309L, residual stress, finite element analysis, fatigue, reliability.

1. INTRODUCTION

   Dissimilar metal welded (DMW) joints are widely used in industries such as power generation, petrochemical processing, and oil and gas where materials experience combined effects of high temperature, pressure, and corrosion (Sharma et al., 2021). Welding carbon steel (CS) to austenitic stainless steel (ASS) enables cost optimization and performance enhancement, combining mechanical strength with corrosion resistance. However, mismatched thermal expansion coefficients and carbon migration across the fusion interface create metallurgical incompatibilities that lead to

   residual stress accumulation and microstructural embrittlement (Kumar & Sharma, 2021).

   The study aims to analyze the performance and failure mechanisms of CSASS joints fabricated using ER309L filler metal, assessing their mechanical, metallurgical, and reliability characteristics, and comparing them with other dissimilar welded joints to determine optimized joining parameters for critical piping systems.

2. MATERIALS AND METHODS

   1. Materials

      The base materials selected were ASTM A106 Grade B carbon steel and AISI 304 austenitic stainless steel, joined using ER309L filler metal through the Gas Tungsten Arc Welding (GTAW) process. The composition of ER309L (22 24% Cr, 1214% Ni, 0.03% C) provides an austenitic microstructure with excellent corrosion resistance and reduced carbide precipitation (Sridhar et al., 2006).

   2. Experimental Methods

      Mechanical testing included tensile strength, Vickers micro- hardness, and Charpy Impact testing per ASTM E8 and ASTM E23 standards. Metallographic samples were examined using optical microscopy and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS) to identify microstructural transitions and elemental migration.

   3. Simulation and Reliability Modeling

      Finite Element Analysis (FEA) using ANSYS was performed to simulate thermal and residual stress distributions. A double ellipsoidal heat source model was applied to simulate arc energy input during welding. Reliability modeling employed the Weibull distribution to quantify temperature-dependent failure rates, with shape parameters () indicating failure modes.

      Low-cycle fatigue testing revealed crack initiation along the fusion line within fewer cycles compared to homogeneous joints. The fatigue life decreased by ~40% under cyclic thermal loading conditions, consistent with the FEA predictions.

      Figure 4.5 Finite Element Analysis (FEA) Simulation Diagram of Residual Stress Distribution for a DMWJ

3. RESULTS AND DISCUSSION

   1. Mechanical and Microstructural Analysis

      Tensile testing showed that all failures occurred in the carbon steel heat-affected zone (HAZ), confirming it as the weakest region. The ultimate tensile strength ranged between 475 and 498 MPa, slightly below that of the stainless steel base metal (600 MPa). The Vickers micro-hardness profile revealed significant gradients across the weldment: fusion zone (225 HV), stainless steel base (210 HV), and carbon steel HAZ (180 HV).

      SEMEDS analysis indicated carbon migration from the carbon steel side into the stainless steel, forming carbides along the fusion boundary. The fusion zone exhibited delta ferrite networks embedded within an austenitic matrix, while prolonged thermal exposure encouraged sigma-phase precipitation (Chen et al., 2018).

      Figure 4.1 Carbon Steel/Stainless Steel Welded Joint Microstructure using Scanning Electron Microscope (SEM).

   2. Residual Stress and Fatigue Analysis

      Figure 4.11 FEA-Based Fatigue and Creep Analysis under simulated temperature and pressure variations V-Groove Butt Welded Joint between Carbon Steel, ASTM A106 Gr. B using ER309L Filler Electrode

   3. Reliability Assessment

      Failure rate () increased sharply beyond 450 °C. The Weibull shape parameter () rose from 1.1 at 300 °C to 2.3 at 500 °C, indicating a transition from random to wear-out failure behavior. Elevated pressures (1540 MPa) amplified stress intensities in the fusion zone, accelerating creep and thermal fatigue

      Temperature (°C) Mean Time to Failure (MTTF, h) (Weibull)

      300	26,000	1.1
      400	19,000	1.6
      500	12,500	2.3

   4. Comparative Performance of Dissimilar Joints

      A comparative evaluation was performed between CSASS, CuCS, AlCS, and BrAl welded joints. The CSASS configuration exhibited superior mechanical and corrosion performance (Table 2), validating its suitability for high- stress piping applications.

      Table 2. Comparative performance of dissimilar metal welded joints.

      FEA simulations identified maximum residual stress

      Joint

      Type

      Tensile

      Corrosion

      Weldability Structural

      Strength (MPa) Resistance

      Integrity

      concentrations (~315 MPa) in the carbo steel HAZ due to

      the thermal expansion mismatch between CS (12×10 /°C)

      CS ASS

      480500 ModerateHigh Good Excellent

      and ASS (17×10 /°C). These stresses correlated with observed crack initiation sites under cyclic loading (Shin & Lee, 2017).

      CuCS 270300 Low Poor Moderate AlCS 110160 Low Very Poor Low

      BrAl ~130 LowModerate Poor Low

   5. Mitigation Strategies

      1. Filler Selection: Nickel-based filler (ER309L) reduces carbon diffusion and enhances corrosion resistance.

      2. Low Heat Input Welding: Techniques like GTAW and laser beam welding (LBW) minimize residual stress and intermetallic formation.

      3. Post-Weld Heat Treatment (PWHT): Controlled PWHT (~650 °C, 1 h) reduced residual stress by 4060%.

      4. Corrosion Control: Protective coatings and cathodic protection decreased pitting depth by

         ~65%.

      5. Design Optimization: Smooth joint transitions and buttering layers improved fatigue life by >30%.

4. CONCLUSIONS

   The performance of dissimilar welded joints between carbon steel (ASTM A106) and stainless steel (AISI 304) using ER309L filler metal demonstrates superior strength, reliability, and metallurgical compatibility compared to other dissimilar combinations.

   Key conclusions include:

   • The carbon steel HAZ remains the critical failure region due to residual stress and carbon migration.

   • Residual stress peaks (~315 MPa) correlate with localized cracking and reduced fatigue life.

   • Failure rates rise exponentially beyond 450 °C, transitioning to wear-out failure behavior.

   • Nickel-based fillers, low heat input, and PWHT

     effectively improve durability and performance.

   • Compared with CuCS, AlCS, and BrAl joints, the CSASS configuration offers the best balance of mechanical strength, weldability, and corrosion resistance for high-pressure applications.

5. REFERENCES

1. Chen, S., Wang, Y., Xu, J., & Wang, C. (2018). Microstructure and mechanical properties of dissimilar weld joints between carbon steel and stainless steel using different filler materials. Materials Science and Engineering: A, 711, 612620.

2. Kumar, A., & Sharma, P. (2021). Advancements in dissimilar metal welds for high-temperature steam turbines. Welding Journal, 100(5), 185193.

3. Sharma, P., Verma, A., & Singh, R. (2021). Reliability-based design of dissimilar metal welds in piping systems. International Journal of Pressure Vessels and Piping, 191, 104322.

4. Shin, Y., & Lee, J. (2017). Residual stress and failure analysis of carbon steelstainless steel dissimilar welded joints. Welding Journal, 96(3), 77S86S.

5. Sridhar, N., Kolts, J., & Siewert, T. A. (2006). Dissimilar metal welds and weld overlay: Corrosion aspects. In ASM Handbook, Vol. 13C: Corrosion: Environments and Industries (pp. 179193). ASM International.