Statistical analysis of weld repair length in aerospace pressure vessels

Welding is a governing process in realization of aerospace pressure vessels. In defence and aerospace industry, ultrahigh strength materials viz maragingsteel is being used for realization to meet the mission requirements. The fracture based design is adopted for pressure vessels. The quality of welding is ensured by qualifying the welding process, through procedure qualification, use of qualified welders and Non-destructive testing. Weld joints are inspected using Non destructive testing such as Radiography testing, Ultrasonic testing, Die penetrant testing etc. The weld repairs are carried out when a defects is noticed in Non-destructive testing. The percentage Weld repair length for each weld joint is one of the quality control parameter. Excess weld repair length affects the Factor of Safety of hardware there by performance over a period of time. This necessitates close monitoring of process efficiency and reliability by monitoring weld repair length. Practicing codes, standards, the welding process and personnel qualification are established. The Weld repair length is satisfactorily analyzed to evaluate the process variation and efficiency of process. Use of quality control tools such as control charts help in continuous monitoring and to take necessary corrective actions. This paper uses data from Non-Destructive Testing and quality control tools to predict the trends and process behavior of GTAW welding of Maraging steel Grade 250.