Zhuojin Pipe Fitting Co., LtdCFD Simulation of Erosion Wear in Asymmetric Tee Pipes
Literature Overview
This paper by Mo Li, Liu Qi, and Xu Xianyu from Southwest Petroleum University, published in Lubrication Engineering (2022, Vol. 47, No. 8, pp. 41-46), investigates the erosion wear behavior of asymmetric tee pipes under solid particle-laden flow conditions using a CFD-DPM (Computational Fluid Dynamics - Discrete Phase Model) approach. Funded by the National Key R&D Program (2019YFC031230), the study addresses a critical failure mode in oil and gas production systems where sand-laden fluids cause progressive wall thinning and eventual rupture at tee junctions.
Core Technical Findings
The research examines four key variables: flow velocity (2-10 m/s), particle diameter (0.1-0.5 mm), sand volume fraction (1%-9%), and asymmetric tee branch angle (90°-150°). The following table summarizes the principal findings.
| Parameter | Range | Effect on Maximum Erosion Rate | Relationship Type |
|---|---|---|---|
| Flow velocity | 2-10 m/s | Increases significantly | Exponential growth |
| Sand volume fraction | 1%-9% | Weak at low velocity; linear increase at high velocity | Velocity-dependent |
| Branch angle | 90°-150° | Decreases with increasing angle | Linear negative |
| Particle diameter | 0.1-0.5 mm | Gradual increase | Gentle positive trend |
The most severely eroded region is consistently located at the outer bend wall of the horizontal branch tubes near the three-pipe junction. This finding aligns with classical erosion mechanics: particles following inertial trajectories impact the concave surface of the bend at high angles, causing maximum material removal.
Process and Standards Interpretation
In engineering practice, asymmetric tees are commonly encountered in wellhead flow control systems, separator inlet/outlet configurations, and multiphase flow lines where the branch pipe diameter differs from the run pipe. The study confirms that the erosion rate follows an exponential relationship with velocity, which has direct implications for design velocity limits specified in standards such as API 14E (Erosion Corrosion in Petroleum Industry) and NORSOK M-503.
According to API 14E, the maximum allowable flow velocity for continuous operation in carbon steel piping is calculated as:
V_max = C / sqrt(ρ_m)
where C is a material constant (typically 100-125 for carbon steel in clean service) and ρ_m is the mixture density in lb/ft³. The CFD results from this study validate the conservative nature of these empirical correlations at higher velocities, where erosion rates accelerate non-linearly.
The finding that larger branch angles (150° vs. 90°) reduce erosion is practically significant. In field applications, designers should consider using long-radius tees or swept-branch configurations rather than sharp-angle tees whenever flow geometry permits. This recommendation is consistent with ASME B31.3 Section 331.1.2, which encourages the use of long-radius bends to minimize erosion in high-velocity service.
Engineering Practice Integration
In my experience with offshore platform piping design, asymmetric tees in subsea production manifolds frequently fail within 12-24 months of operation when handling multiphase flows with sand content exceeding 1% by volume. The erosion pattern described in this study—concentrated thinning at the outer bend wall of the smaller branch—matches the failure signatures observed in post-mortem inspections of such components.
Key design countermeasures derived from this research include:
- Limiting flow velocity to below 5 m/s for sand-laden service in carbon steel tees
- Using erosion-resistant alloy overlays (e.g., 13Cr, duplex 2205, or tungsten carbide hardfacing) at the identified high-erosion zones
- Selecting branch angles of 120° or greater to reduce particle impact concentration
- Implementing periodic ultrasonic thickness monitoring (UTM) at the outer bend wall, with inspection intervals shortened as velocity increases
Key Reflections and Study Insights
The exponential velocity dependence of erosion rate underscores why empirical design correlations based on linear velocity assumptions tend to underestimate damage at higher flow rates. The transition from weak to strong dependence of erosion on sand fraction at higher velocities suggests a threshold effect where particle-particle interactions begin to amplify impact energy. Engineers should not treat erosion as a simple linear function of any single parameter but rather as a coupled, non-linear phenomenon requiring comprehensive analysis.
This study provides a valuable simulation-based methodology that can complement traditional empirical approaches, particularly for non-standard geometries where no empirical correlations exist. The CFD-DPM framework offers a path toward component-specific erosion predictions, reducing reliance on generic safety factors that may be overly conservative for some geometries and dangerously optimistic for others.