PSI - Issue 70

T. Ramya et al. / Procedia Structural Integrity 70 (2025) 469–476

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4. Field Installation and Experimental Setup

An experimental study was conducted on an HDPE pipe model with the same geometric and material specifications as the actual cold water pipeline used in desalination plant to measure the performance of the FBG strain sensor. As shown in figure 3. an experimental setup was made to measure strain and temperature variations under an applied load.

The dimensions of the HDPE pipe model used in the experiment were as follows:

• Outer Diameter (D): 710 mm (0.71 m) • Wall Thickness (t): 33 mm (0.033 m) • Pipe Length (L): 2.5 m

4.1 Loading and Sensor Placement

The pipe is loaded with a weight of 1 ton (1000 kg) or 9810 N at one end in order to simulate actual loading conditions. From the load application end at a distance of 1.25 meters (L’) on HDPE pipe two FBG sensors were fixed using clamp to measure strain variation accurately. The clamp made of SS316L was designed to hold two FBG sensors at a distance of 90 degrees apart and fixed on the pipe. Since underwater adhesives and welding methods are not suitable for fixing the sensors on HDPE pipe the clamps are used to fix it. The strain distribution is analysed at two regions using FBG sensors .Based on these measurements the structural integrity and mechanical behaviour of HDPE pipelines subjected to external forces can be analysed .

4.2 Stress and Strain Calculation Methodology

In analyzing the High-Density Polyethylene (HDPE) pipes mechanical behaviour under applied loads, fundamental stress-strain relationships are utilized (Vlase et al.(2020) and Kiass et al.(2025) ). The axial stress (σ) in the pipe is determined using the relationship:

Axial Stress ( σ ) = F / A

(2)

where F represents the applied axial load (in Newton) and A represents the pipe’s cross -sectional area. For a hollow cylindrical pipe, the cross-sectional area is calculated as: Cross-sectional area (A) = π 4 (D 2 −d 2 ) (3) where D is the outer diameter and d is the inner diameter of the pipe. This formula accounts for the annular region of the pipe's cross-section that bears the applied load (Krushelnitzky and Brachman (2009)). (4) where E is the HDPE pipe’s Young’s Modulus which defines the materials stiffness or resistance to elastic deformation under applied stress [18] (Dusunceli and Colak (2006)). This equation assumes that the material behaves elastically within the operating stress range. These fundamental equations help the assessment of structural integrity and design optimization for applications such as fluid transport systems and deep-sea pipelines by providing essential insights into the mechanical response of HDPE pipes. Once the axial stress is determined, the corresponding axial strain (ε) is computed using Hooke’s Law: Axial Strain ( ε) = σ / E