THE EFFECT OF MINING SUBSIDENCE AND SEMI ELLIPTICAL CRACK ON THE RELIABILITY OF GIRTH WELDED API X52 GAS PIPELINE USING FINITE ELEMENT METHOD

• Main Author: Rasyid Hanifa, Luthfi
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/66097
• Institution: Institut Teknologi Bandung

Pipelines are a technology in the process of transporting fluids such as oil, gas or water in large quantities and long distances, both onshore and offshore. Steel pipe is currently the main choice in its application because it has a high strength to weight ratio value so that it can reduce material costs. In buried condition, the pipeline will receive additional stress from the ground, one of which is the ground subsidence phenomenon which if it occurs in a mining area is called mining subsidence. These events can cause lateral bending of the pipe so that it can threaten its reliability. In this study, simulations were carried out using the finite element method to determine the reliability of the pipe, especially the welds due to mining subsidence. The presence of defects is also reviewed for potential failure, stress intensity factor through fracture mechanics analysis, and residual strength of the pipe. The simulation was carried out on API 5L X52 PSL 2 pipe which was girth welded with a diameter of 16 inches, 0.5 inches thick, 15 meters long, and an internal pressure of 5.3 MPa using the ANSYS Multiphysics R3 2019 software. Land subsidence due to mining subsidence It is assumed that through the point mass the load comes from the weight of the pipe and the methane gas fluid in it. In the simulation, semi-elliptical defects are presented with various types of defect consisting of external weld, root weld, weld toe, and root near HAZ. Variations in the location of defects are carried out on crown, springline, and inverts in the outer and inner weld areas. Dimensional variations are carried out with an aspect ratio (a/c) of 0.2; 0.4; 1 and relative crack depth (a/t) were 0.2; 0.5; 0.8, respectively. The simulation results show that the pipe with defects in the weld toe and root near HAZ exceeds the safety limit based on the failure criteria. Defects located in the invert have the highest von Mises values followed by springline and crown because of the distribution of stresses when maximum bending occurs. The smaller the aspect ratio value and the greater the relative crack depth can increase the value of von Mises effective stress and stress intensity factor (SIF). At a high aspect ratio value (a/c = 1) the maximum SIF value is at the crack tip, while at a lower aspect ratio (a/c = 0.2 and 0.4) the maximum SIF value is at the crack depth, so when If the SIF value exceeds the KIC threshold value, then the crack can propagate towards the maximum SIF value. The dimension of the defect has a significant effect on the residual strength of the pipe. Increasing the depth of the defect has a more significant effect on the reduction of residual strength than the length of the defect.