Root cause analysis and reliability improvement methods for orbital TIG welding process for propulsion feed system of satellites

Abstract

The orbital tungsten inert gas welding is extensively used in space application such as welding of propellant feed lines and components of the propulsion sub system of satellite, space recovery module and crew module etc. The feed lines are made up of 6 or 10 mm diameter stainless steel tubes of 0.7 mm thickness which are very critical for the successful operation of propulsion system of the satellite. This paper focuses on the root cause analysis and reliability improvement of the orbital TIG welding process. Procedures such as failure modes effects and criticality analysis, cause and effect diagram, fault tree analysis (FTA) and Pareto analysis (PA) are applied to analyze the basic problems encountered with orbital TIG welding to find out critical process failure modes, their causes and remedial actions that can be suggested for process improvement. Cause effect diagram of the welding process is drawn to understand the important parameters such as current, Revolution per minute (RPM), shield gas flow, gap between electrode and tube, gap between tubes, cleanliness etc. causing weld failures. Root cause analysis is carried out using FTA for identification of basic events and their combination effect leading to the weld failure. Further, PA helps to find out which are all the most affecting factors of the process. By implementing these reliability analysis techniques, it is possible to improve the reliability of orbital TIG welding process for propellant feed systems for satellites.