Modeling Slow Crack Growth Under Thermal and Chemical Effects and Accurate NDT of Cracks for Fitness Predictions of Polyethylene Pipes

Overview

Main Objective

Develop a slow crack growth model for polyethylene pipe failure under chemical and thermal environments and a method for accurate crack size measurements for reliable fitness for service assessment.

Public Abstract

Polyethylene (PE) is a preferred material for water and gas transport and distribution pipelines. PE can undergo brittle type creep rupture through slow crack growth (SCG) without warning. The SCG leading to eventual failure occurs under low stresses well below the yield of the material. Additionally, chemicals inside the transporting fluid and variations in operating temperatures can further accelerate the slow crack growth phenomenon. Safe operation of PE pipes requires accurate monitoring and robust failure models to assess fitness for service. To meet this need, here we aim to develop a physically motivated model for SCG and brittle type fracture in high density PE (HDPE) incorporating both changes due to chemical exposure and thermal effects. We will conduct SCG failure tests at various stress levels, temperatures, and chemical exposure levels on HDPE to elucidate the coupled effects for the new environmental SCG failure model. We will also develop finite element simulations representing ultrasonic nondestructive tests (NDTs) in PE and utilize our simulation data to train a neural network algorithm for accurate NDT measurements of small crack dimensions. Accurate crack size and crack opening measurements along with a robust environmental SCG model developed through this research will allow reliable fitness for service assessments of vintage and in-service PE pipes.

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