July 23, 2025

‘Samudrayaan’ is a project under the Deep Ocean Mission of the Ministry of Earth Sciences (MoES) which envisages the development of MATSYA-6000, a submersible spherical vessel to carry humans into the sea up to a depth of 6km. Towards development of this Human Occupied Vehicle (HOV), National Institute of Ocean Technology (NIOT), MoES signed a Memorandum of Understanding with Vikram Sarabhai Space Centre (VSSC), ISRO for realizing the spherical vessel.

Design of the personnel sphere along with development of the material for realisation was carried out by VSSC. MATSYA-6000 is a sphere of 2260mm diameter with a wall thickness of 80mm, made out of Titanium alloy (Ti6Al4V - ELI grade) and is expected to withstand an external pressure up to 600bar under low temperature conditions of -3°C. This has the capability to carry a three-member crew into the deep ocean.

Major challenge in realizing the spherical vessel is the development of reliable, high penetration (80-102mm thick) Electron Beam Welding (EBW) process and the high-energy (7.5MeV) X-ray radiography facility for the Non-Destructive Evaluation (NDE), which is essential for the certification of the human-rated product. Certification of the facilities, process and the product are planned to be carried out by a third party.

Liquid Propulsion Systems Centre (LPSC) was responsible for developing the process and infrastructure for the welding process and NDE. LPSC-Bengaluru had the facility and expertise to carry out welding up to 20mm thick. To meet the high power demand for welding, the EBW machine was augmented from 15kW to 40kW rating along with additional facilities for chemical cleaning and handling equipment for the higher size and mass. For Non-Destructive Evaluation, the existing X-ray facility in kV range was augmented to 7.5MeV range. Multiple NDE techniques were employed which complement each other in ascertaining weld quality, including Time of Flight Diffraction (TOFD) and Dual Linear Array (DLA) Phased Array Ultrasonic Testing (PAUT).

LPSC developed the welding process through extensive weld trials (nearly 700 trials) for optimizing the process parameters. NDE techniques were established through inspecting artificially created defects and calibration standards were created. The welding procedure specification and weld qualification protocols are getting approved by a third party.

Subsequent to the process development and process optimization, the first welding on the actual hardware and detailed evaluation have been successfully completed. High penetration welding of this scale, i.e. 80mm weld thickness over 7100mm length with 32 minutes of weld duration, was carried out for the first time in the country.