Alternate Welding Processes for In-service Welding

Overview

Main Objective

Project is to support efforts towards the development and application of procedures for welding on in-service pipelines using alternate welding processes.

Public Abstract

Conducting weld repairs and attaching hot tap tees onto pressurized pipes has the advantage of avoiding loss of service and revenue. However, the risks involved with in-service welding need to be managed by ensuring that welding is performed in a reproducible and consistent manner within an optimal heat input window. The optimal heat input window avoids burn-through (upper limit of heat input) and weld faults or hydrogen induced cold cracking (lower limit of heat input). Welding on live pipelines has been successfully performed for years, using mainly the shielded metal arc welding (SMAW) process. Over the past 25 years, failures have occurred in welds deposited on in-service pipelines, and these failures have been attributed to weldment hydrogen cracking, and inconsistent bead size or penetration profile. Numerous investigations have been completed to address the most significant in-service welding hazards, namely burn-through and hydrogen-induced cracking. Weld procedures designed to avoid burn-through and hydrogen cracking consider primarily the thermal cycle, while pipe chemistry and internal pressure are additional influencing parameters for delayed cracking and burn-through, respectively. The thermal cycle itself depends on the welding heat energy input, heat sink capacity of the pipeline (pipe wall thickness, fluid type and flow rate), and any preheat or post heat applied.

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