Numerical Investigation of the Influence of Geometric Features and Weld Metal Properties on Stress and Strain States in X80 Girth Welds
Abstract
1. Introduction
2. Materials
2.1. X80 Girth Welding
2.2. Mechanical Properties of the X80 Girth Welds
2.3. Metallographic Characteristics of the X80 Girth Welds
3. Finite Element Analysis Models
3.1. Geometric Parameters
- (1).
- The pipe geometries on both sides of the girth weld were represented as uniform circular shapes with aligned centerlines. Misalignment was characterized by differences in the outer diameters of the pipes, excluding the impacts of axial deviations and pipe ovality variations.
- (2).
- In each girth weld joint model, all geometric features, such as uneven wall thickness, misalignment, transition angles, and weld reinforcement, exhibited total circumferential uniformity.
- (3).
- This study primarily investigated the condition in which the outer diameter of the thicker pipe exceeded that of the thinner pipe. This construction resulted in a root notch formed by the combination of root weld reinforcement and the transition slope of unequal wall thickness, which presented significant geometric discontinuity and represents the highest risk to pipeline safety.
3.2. Material Properties
3.3. Finite Element Modeling
4. Finite Element Analysis Results and Discussion
4.1. Stress and Strain States of the Girth Welds Without Misalignment
4.2. Stress and Strain States of the Girth Welds with 2 mm Misalignment
4.3. Stress and Strain States of the Girth Welds with Internal Pressure
4.3.1. The Influence of Internal Pressure on the Stress States of the Girth Welds
4.3.2. The Influence of Internal Pressure on the Strain States of the Girth Welds
5. Conclusions
- (1)
- Experimental characterization reveals that weld metal strength variations (M = 0.97–1.11) primarily result from differences in Mn and Ni content in the welding materials. These two elements provide significant solid solution strengthening effects and adjust phase transformation temperatures to promote the formation of fine acicular ferrite, improving the microstructure and enhancing the strength of the weld metals.
- (2)
- Finite element analysis indicates that unequal wall thickness critically influences the stress and strain states at the weld root location. Stress triaxiality η and hot spot strain εH increase as the wall thickness ratio increases. In the girth welds with λw = 0.85, M = 0.9, and no misalignment, as t2/t1 increased from 1.0 to 1.4, the increments in η and εH were 0.238 and 1.24%, respectively.
- (3)
- Numerical analysis reveals that misalignment significantly exacerbates the stress and strain states of girth welds. With 2 mm misalignment, η increased by 0.2–0.4, while the increment in εH from t2/t1 variations reached 5.89%, far exceeding the welds without misalignment. The combination of unequal wall thickness and misalignment exacerbates geometric discontinuity, causing severe stress–strain concentration at the weld root.
- (4)
- Weld metal properties significantly affect girth weld stress–strain states. Calculation results indicate that increasing M reduces stress–strain concentration, but its effectiveness diminishes with geometric discontinuity. For m = 0 and t2/t1 = 1.0, raising M from 0.9 to 1.2 reduced η by 0.180; however, for m = 2 mm and t2/t1 = 1.4, the reduction was only 0.097. Higher λw reduces η and increases εH, particularly in undermatched welds with misalignment.
- (5)
- Numerical simulation demonstrates that internal pressure significantly increases stress triaxiality η and hot spot strain εH at the weld root. The effects of t2/t1, m and λw on stress and strain states are more pronounced under internal pressure-loaded conditions. Higher M intensifies the stress triaxiality response to internal pressure while effectively reducing strain concentration sensitivity.
- (6)
- Based on the analysis results, the design of unequal wall thickness girth welds should limit the wall thickness ratio to ≤1.2 with strict misalignment control, employ counterbore-taper design for larger wall thickness ratios, maintain a high strength matching coefficient with adequate toughness, and select weld metals with low yield-to-tensile ratios to mitigate stress and strain concentration.
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
References
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Materials | C | Mn | Si | Ni | Mo | Fe |
---|---|---|---|---|---|---|
X80 Base metal | 0.063 | 1.83 | 0.28 | 0.03 | 0.22 | Bal. |
Weld material E101T1 | 0.06 | 1.54 | 0.40 | 0.97 | 0.15 | Bal. |
Weld material E91T1 | 0.05 | 1.25 | 0.37 | 0.93 | 0.12 | Bal. |
Weld material E71T1 | 0.05 | 1.25 | 0.36 | 0.22 | 0.003 | Bal. |
Material | Base Metal | Weld Metal E101T1 | Weld Metal E91T1 | Weld Metal E71T1 |
---|---|---|---|---|
Yield strength σy/[MPa] | 587 | 657 | 644 | 570 |
Tensile strength σm/[MPa] | 673 | 719 | 701 | 642 |
Yield tensile ratio λ | 0.872 | 0.914 | 0.919 | 0.887 |
Geometric Parameters/Unit | Value |
---|---|
Wall thickness of the thinner side t1/[mm] | 18.4 |
Wall thickness ratio t2/t1 | 1.0, 1.1, 1.2, 1.3, 1.4 |
Misalignment m/[mm] | 0, 2 |
Cap weld height h1/[mm] | 5 |
Root weld height h2/[mm] | 2 |
Root weld width w/[mm] | 5 |
Weld groove angle α/[°] | 65 |
Thickness transition angle γ/[°] | 45 |
Material Property Parameters/Units | Value |
---|---|
Base metal yield strength σyb/[MPa] | 587 |
Base metal tensile strength σtb/[MPa] | 673 |
Base metal yield-to-tensile ratio λb | 0.872 |
Weld strength matching coefficients M | 0.9, 1.0, 1.1, 1.2 |
Weld metal yield strength σyw/[MPa] | 528.3, 587, 645.7, 704.4 |
Weld metal yield-to-tensile ratio λw | 0.85, 0.95 |
Parameters/Unit | Value |
---|---|
Wall thickness ratio t2/t1 | 1.0, 1.1, 1.2, 1.3, 1.4 |
Misalignment m/[mm] | 0, 2 |
Weld strength matching coefficients M | 0.9, 1.0, 1.1, 1.2 |
Weld metal yield-to-tensile ratio λw | 0.85, 0.95 |
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Guo, B.; Deng, C.; Gong, B.; Liu, Y.; Ning, J.; Zhang, K. Numerical Investigation of the Influence of Geometric Features and Weld Metal Properties on Stress and Strain States in X80 Girth Welds. Metals 2025, 15, 986. https://doi.org/10.3390/met15090986
Guo B, Deng C, Gong B, Liu Y, Ning J, Zhang K. Numerical Investigation of the Influence of Geometric Features and Weld Metal Properties on Stress and Strain States in X80 Girth Welds. Metals. 2025; 15(9):986. https://doi.org/10.3390/met15090986
Chicago/Turabian StyleGuo, Baichen, Caiyan Deng, Baoming Gong, Yong Liu, Jiaao Ning, and Ke Zhang. 2025. "Numerical Investigation of the Influence of Geometric Features and Weld Metal Properties on Stress and Strain States in X80 Girth Welds" Metals 15, no. 9: 986. https://doi.org/10.3390/met15090986
APA StyleGuo, B., Deng, C., Gong, B., Liu, Y., Ning, J., & Zhang, K. (2025). Numerical Investigation of the Influence of Geometric Features and Weld Metal Properties on Stress and Strain States in X80 Girth Welds. Metals, 15(9), 986. https://doi.org/10.3390/met15090986