Introduction

Pipelines are critical infrastructures for the transportation of oil, gas, and other essential resources. Among these, API 5L X65 grade steel pipelines are commonly used due to their strength and cost-efficiency. However, pipelines buried in soil are vulnerable to extreme events such as subsurface explosions, which may result from accidental or intentional detonations. These explosions generate high-pressure shock waves that propagate through the soil and impact the pipeline, causing significant deformation or even failure.

In recent years, Carbon Fiber Reinforced Polymer (CFRP) composites have gained attention for their exceptional strength-to-weight ratio, corrosion resistance, and energy-absorbing properties. When used as a blanket reinforcement around pipelines, CFRP can potentially mitigate the structural deformation induced by explosive loads.

This study focuses on the numerical analysis of the effectiveness of CFRP blanket reinforcement in reducing the deformation of buried X65 steel pipelines subjected to a subsurface explosion, using advanced simulation techniques based on Coupled Eulerian-Lagrangian (CEL) methods.

Explanation

1. Subsurface Explosions and Pipeline Vulnerability

• A subsurface explosion creates intense stress waves in the surrounding soil medium.
• These stress waves interact with buried pipelines, inducing large deformations, localized buckling, or rupture, particularly when the pipe is not adequately protected.
• The severity of the damage depends on several factors: burial depth, soil type, explosive energy, and pipeline material and geometry.

2. Role of CFRP Blanket Reinforcement

• CFRP blankets can be externally applied to the pipeline surface.
• They act as an additional energy-absorbing layer, redistributing the blast-induced stresses and reducing peak strain in the steel.
• CFRP’s anisotropic properties allow for design optimization, reinforcing the pipeline in specific stress-prone directions.

3. Coupled Eulerian-Lagrangian (CEL) Numerical Method

• Traditional Lagrangian methods struggle with large deformations, such as those caused by explosions.
• Eulerian methods, on the other hand, are better suited for modeling materials like soil and detonation gases that undergo extreme distortion.
• CEL methods combine both: the Eulerian domain is used to simulate the explosive and soil response, while the Lagrangian domain accurately tracks the deformation of the pipeline and CFRP layers.
• This hybrid approach enables detailed simulation of the explosion-soil-pipeline interaction, capturing both dynamic soil flow and structural deformation.

4. Numerical Modeling Objectives

The main goals of the numerical analysis include:

• Evaluating the deformation patterns of X65 pipelines with and without CFRP reinforcement under blast loads.
• Quantifying the reduction in peak displacement and strain due to the CFRP blanket.
• Investigating the influence of CFRP thickness, layering, and orientation on protective performance.
• Understanding the soil-structure interaction during and after the explosion event.

This numerical study is vital for assessing the feasibility and optimization of CFRP reinforcement systems in pipeline protection applications. By leveraging the Coupled Eulerian-Lagrangian method, researchers can simulate complex, real-world explosive events and improve pipeline resilience, enhancing safety and reducing potential economic and environmental consequences.