Semi-Automated System for Welding on Live Pipelines and Pressure Vessels

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Sponsor: Shell Global Solutions

Date: Fall 2007

Requirements:
In order for the welding system to perform correctly, several requirements and constraints were imposed on the design. First the system had to be light and maneuverable. The total weight of the system needed to stay under 150 pounds. In addition the system needed to be operated from a safe distance so that if a mistake were made, the user would not be at risk. We required that the system be operated 50 yards from the user. This project was constrained by the previously designed prototype. The team reacquired and assembled the components of the previous prototype and used it as our test setup.

Problem:
Pipelines in service require routine maintenance. To perform this maintenance the process of hot-tapping is used. Perfoming this process requires welding on the pipeline while it is still active. To eliminate the risk of human life Shell wanted to develop and test a semi-automated system for welding on live pipelines. This project’s goal was to assemble and test a prototype system.

Solution:
To complete the project we first reassembled the prototype. To do this we made contact with all the manufacturers and had the welder and bug-O system loaned to us. We then focused on designing the experiments used to validate the performance of the welding system. These tests included welding sample fittings and then tension testing sections that had been welded to see if they would stand up to the loads imposed by the internal pressure of the pipeline or pressure vessel. Once the welding system produced strong consistent welds we planned to pressurize a pipeline and perform a sample weld. We also looked at the control methods. We had to research the welding process and quantify the heat input. The biggest risk in welding on a live pipeline is too much heat input that could cause a hole in the pipe. To control the heat input we found the heat input in terms of the voltage and current through the weld arc and also the travel speed of the torch. Once we had this equation we put in a control loop that would check and regulate the welding parameters to insure that there would not be a failure in the pipeline. Since the system is run solely by the computer, we needed to test the response time of the controller. This was to be done with a software simulation. Future work in this project will yield a more convenient setup and easier operation.

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