Quality Assurance of Steel Liner works of Pressure Shafts of Teesta-III Project

The Teesta-III HE project (1200 MW) is located in the Himalayan state of Sikkim, in the North-Eastern part of India. The project involved the construction of two nos. steel lined pressure shaft of 1.4 km long including 650 m vertical shaft each. More than 12000 MT of high strength steel plates were used for this work. The adoption of innovative erection methodology by way of doing various erection activities like, welding, NDT and backfill concrete concurrently to compress the completion schedule has been the unique feature of the steel liner erection works. The use of Flux Core Arc Welding (FCAW) for the field joints proved an added advantage on speed and quality of weld. The welding process control and its quality assurance for such high strength steel plates with thickness up to 48 mm in such deep shaft was a big challenge as various problems were encountered during the work. Even Indonesian welders were deployed initially for welding mainly for erection joints in the vertical shafts minimizing the welding defect to less than 2% in harsh conditions. The project stands commissioned in February 17. This paper summarizes various aspects of welding processes and quality control measures practiced for fabrication and erection of steel liners in this project.